Citation
Annual meeting of the Florida State Horticultural Society

Material Information

Title:
Annual meeting of the Florida State Horticultural Society
Cover title:
Proceedings of the Florida State Horticultural Society for ..
Abbreviated Title:
Annu. meet. Fla. State Hort. Soc.
Creator:
Florida State Horticultural Society -- Meeting
Place of Publication:
[Florida?]
Publisher:
The Society
Publication Date:
Frequency:
Annual
regular
Language:
English
Physical Description:
v. : ill., ports. ; 24 cm.

Subjects

Subjects / Keywords:
Horticulture -- Congresses ( lcsh )
Gardening -- Congresses -- Florida ( lcsh )
Gardening -- Congresses ( lcsh )
Genre:
serial ( sobekcm )
conference publication ( marcgt )

Notes

Citation/Reference:
Bibliography of agriculture
Citation/Reference:
Biological abstracts
Citation/Reference:
Chemical abstracts
Citation/Reference:
PESTDOC
Citation/Reference:
RINGDOC
Citation/Reference:
VETDOC
Citation/Reference:
Nuclear science abstracts
Citation/Reference:
Selected water resources abstracts
Dates or Sequential Designation:
64th (Oct. 30, 31, and Nov. 1, 1951)-89th (1976).
Funding:
Florida Historical Agriculture and Rural Life

Record Information

Source Institution:
Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location:
Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
000006221 ( ALEPH )
01387526 ( OCLC )
AAA7465 ( NOTIS )
88647898 ( LCCN )
0097-1219 ( ISSN )

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of the

FLORIDA STATE

HORTICULTURAL SOCIETY




VOLUME 69

1956.


Published by the Society




FLORIDA STATE HORTICULTURAL SOCIETY, 1956


SIXTY-NINTH ANNUAL MEETING
of the

FLORIDA STATE


HORTICULTURAL SOCIETY













held at
ORLANDO, FLORIDA
November 7, 8 and 9
1956







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


FLORIDA STATE

HORTICULTURAL SOCIETY


Executive Committee


1956


PRESIDENT
R. A. CARLTON
West Palm Beach


SECRETARY
Dn. ERNEST L. SPENCER
Bradenton

PUBLICATION SECRETARY
RALPH P. THOMPSON
Winter Haven


TREASURER
R. R. REED
Tampa

EDITING SECRETARY
W. L. TAIT
Winter Haven


SECTIONAL VICE-PRESIDENTS


CITRUS
C. A. ROOT
Winter Garden

KROME MEMORIAL
RoY O. NELSON
South Miami


VEGETABLES
Louis F. RAUTH
Delray Beach

ORNAMENTAL
DR. T. J. SHEEHAN
Gainesville


PROCESSING
DR. R. D. GERWE
Lakeland


MEMBERS-AT-LARGE
HOWARD A. THULLBERY, Lake Wales DR. F. S. JAMISON, Gainesville
FRANK L. HOLLAND, Winter Haven J. ARTHUR LEWIS, Miami
E. S. REASONER, Bradenton






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


FLORIDA STATE

HORTICULTURAL SOCIETY



Executive Committee


1957


PRESIDENT
ROBERT E. NORRIS
Tavares


SECRETARY
DR. ERNEST L. SPENCER
Bradenton

PUBLICATION SECRETARY
RALPH P. THOMPSON
Winter Haven


TREASURER
R. R. REED
Tampa

EDITING SECRETARY
W. L. TAIT
Winter Haven


SECTIONAL VICE-PRESIDENTS


CITRUS
CHARLES D. KIME, JR.
Waverly

KROME MEMORIAL
DR. PAUL L. HARDING
Orlando


VEGETABLES
NORMAN C. HAYSLIP
Ft. Pierce

ORNAMENTAL
S. A. ROSE
Gainesville


PROCESSING
DR. JAMES M. BONNELL
Plant City

MEMBERS-AT-LARGE
R. A. CARLTON, West Palm Beach FRED J. WESEMEYER, Ft. Myers
FRANK L. HOLLAND, Winter Haven DR. GEORGE D. RUEHLE, Homestead
DR. R. D. GERWE, Lakeland







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Constitution


Article I-NAME-This organization shall be
known as the Florida State Horticultural So-
ciety.
Article II-OBJECTIVE-The objective of
this Society shall be the advancement and de-
velopment of horticulture in Florida.
Article III-YEAR-The year shall begin
January 1 and close December 31.
Article IV-CLASSIFICATION OF MEM-
BERSHIP-There shall be three classifications
of membership, all of which carry voting
privileges:
A-Annual
B-Sustaining
C-Patron
Nothing in this article shall be construed as
operating against or cancelling the privileges
of Life Members accepted as Life Members
prior to the adoption of this constitution.
Article V-ELIGIBILITY FOR MEMBER-
SHIP-Any individual, firm or partnership in-
terested in the development and advancement
of horticulture in Florida shall be eligible for
membership.
Article VI-DUES-Dues shall be paid an-
nually according to classification at rate as
prescribed in By-laws.
Article VII-ANNUAL MEETING The
Society shall hold an annual meeting each year
in accordance with the By-laws unless pre-
vented from doing so by causes beyond its
control.
Article VIII SECTIONS The Society
shall be divided into sections representing
various horticultural interests as provided in
the By-laws.
Article IX-OFFICERS-The officers shall
consist of a President, a Vice President from
each section, a Secretary, a Publication Sec-
retary, an Editing Secretary, and a Treasurer,
which officers shall be elected by a majority
vote of the membership present at the annual
meeting and shall assume their respective of-
fices at the beginning of the new year.


Article X-SUCCESSION-In the absence
of the President or his inability to serve tem-
porarily the Vice President of the Citrus See-
ton shall serve instead. If the position of
President is vacated, the Executive Committee
shall designate his successor.

Article XI-EXECUTIVE COMMITTEE -
The Executive Committee shall consist of not
more than 15 persons including the immediate
Past President and all Officers above named,
the others to be elected at same time and
in same manner as prescribed in Article IX.
The President shall be chairman of the Exec-
utive Committee. The Executive Committee
shall have authority to act for the Society be-
tween annual meetings.

Article XII-MEETINGS OF THE EXEC-
UTIVE COMMITTEE-The Executive Com-
mittee shall meet upon call of the Chairman
at such time and place as may be approved by
a majority of the Committee. A majority of
the Committee shall constitute a quorum. The
Committee may be canvassed by mail and
vote by ballot in like manner.

Article XIII COMMITTEES The Presi-
dent shall with the approval of the Executive
Committee appoint all standing or special
committees as provided in the By-laws.

Article XIV-DUTIES OF OFFICERS -
The President shall be the official head of the
Society to preside at all Executive Committee
meetings and at the general session of the
annual meeting. He shall be directly respon-
sible to the Executive Committee and may be
removed from office for cause by an affirma-
tive vote of a majority of the full Executive
Committee.

The Vice Presidents shall be members of the
Executive Committee. The Vice President of
the Citrus Section shall assume the duties of
the President in the temporary absence of the
President. The Vice Presidents of the various
sections shall preside over the particular sec-
tions of which they are representatives at the
annual meeting.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


The Secretary shall record all records of all
meetings of the Executive Committee and shall
be responsible except as may otherwise be
designated in the By-laws for recording and
keeping proceedings of the annual meeting.
He shall likewise issue and mail out statements
of dues to the membership, notices of meetings
and perform such other dutes as ordinarily
accrue to that position.
The Publication Secretary and Editing Sec-
retary shall perform such duties as may be
prescribed and authorized by the Executive
Committee.
The Treasurer shall be responsible for all
funds paid into the Society and shall issue and


countersign all vouchers paying bills or ac-
counts against the Society. The Treasurer
shall be placed under bond in an amount de-
termined by the Executive Committee, pre-
mium on which shall be paid by the Society.
Article XV-AMENDMENTS-This Consti-
tution may be amended at any annual meet-
ing upon the recommendation of a majority of
the Executive Committee when approved by
a majority vote of the membership present.
Article XVI-EFFECTIVE DATE This
Constitution shall become effective immediate-
ly upon approval by a majority vote of the
membership at the annual meeting in October
1951.


iZ3j1 -fa~


1. The Society's year shall begin January
1 and end December 31.

2. Dues-dues shall be paid annually for
the current year and shall be payable to the
Treasurer of the Society. Dues shall be as
follows:


Annual Membership
Sustaining Membership
Patron Membership


$ 4.00
$ 10.00
$100.00


3. Annual Meeting-the Society shall hold
an annual meeting in the fall of each year at
a place and time selected by a majority vote
of the Executive Committee. The order of
business at the annual meeting shall be de-
termined in advance each year by the Execu-
tive Committee.
4. The meetings of the Society shall be
devoted only to horticultural topics, from sci-
entific and practical standpoints, and the pre-
siding officer shall rule out of order all mo-
tions, resolutions, and discussions tending to
commit the Society to partisan politics or mer-
cantile ventures.


5. SECTIONS-The Society shall consist
of the following sections:
Citrus Section
Vegetable Section
Krome Memorial Institute
(Tropical and Sub-Tropical Fruits)
Ornamental and Floriculture Section
Processing Section
Other sections may be added on recommenda-
tion of a majority of the Executive Commit-
tee when approved by a majority vote of the
membership present at an annual meeting.

COMMITTEES
Nominating Committee-The President not
less than thirty days before annual meeting
shall appoint a nominating committee consist-
ing of not less than two persons from each
section, which committee shall make nomina-
tions at the annual meeting of the Officers and
other members of the Executive Committee for
the ensuing year; Provided that the members
representing various sections shall seek advice
of each section in open meeting concerning






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


the nomination of Vice President for that sec-
tion. Such nominations by the committee how-
ever shall not preclude nominations from the
floor.
Program Committee-The Vice Presidents of
the various sections shall constitute a Program
Committee of which the President shall be the
Chairman and the Secretary and Treasurer
shall be ex officio members.
Auditing Committee The President with
the approval of the Executive Committee shall
appoint an auditing committee which commit-
tee shall confer with the Treasurer in prepar-
ing an audit to be presented by the Treasurer
at the annual meeting. The President shall
appoint such other committees as may be
deemed advisable and approved by the Exec-
utive Committee.

DEPOSITORY
The Executive Committee shall have au-
thority to select a depository or establish a
trusteeship for funds of the Society as it may
deem in the best interest of the Society. All
Patron Membership dues and all donations,
unless otherwise specified by donor, shall be
invested by the Treasurer in United States
Government bonds. The earnings from these
bonds shall be left as accrued values or re-
invested in the United States Government


bonds unless it is ordered by the Executive
Committee of the Society that such earnings
can be made available for operating expense.
APPROVAL OF BILLS
All bills before being paid shall be approved
by the President, Secretary or Treasurer, and
vouchers drawn to pay such bills shall be
signed by the President or in his absence the
Vice President of the Citrus Section and coun-
tersigned by the Treasurer.
HONORARY MEMBERS
Any individual who has rendered especially
meritorious service to the Society and to the
advancement of horticulture in Florida may be
designated by a two-thirds vote of the full
Executive Committee and approved by a ma-
jority vote of the Society as an Honorary
Member of the Society. Such honorary mem-
bers shall not be required to pay dues.
AMENDMENTS
These By-laws may be amended at any an-
nual meeting by an affirmative majority vote
of the membership present when such amend-
ments have been approved and recommended
by a majority of the Executive Committee.
These By-laws shall take effect immediately
upon adoption by the membership at the an-
nual meeting in October, 1951.




FLORIDA STATE HORTICULTURAL SOCIETY, 1956


(PIOZEC Cdin23

of the

FLORIDA STATE


9zJi 'tiauLitwaf SocairQ

1956



VOLUME LXIX PRINTED 1957


CONTENTS

Officers for 1956 ---------- ---......... .... .......... ..----- ...--I----------- ---- II
Officers for 1957 ........----------------... -- ---------....-----------..... ...------------- III
Constitution and By-Laws --------------------------....... ---.. ---.__.-...........-------.---------- IV
President's Annual Address, R. A. Carlton, West Palm Beach -.-..----- ____.--- ------------. 1
Plant Research in the Atomic Age, George L. McNew, Boyce Thompson Institute for
Plant Research, Inc., Yonkers, N. Y. --------------- 4
The Mediterranean Fruit Fly Eradication Program in Florida, Ed L. Ayers, Plant
Commissioner, State Plant Board of Florida, Gainesville, and G. G. Rohwer,
Area Supervisor, U. S. Department of Agriculture, Lake Alfred .__......------------ 12
Award of Honorary Memberships -------..-- ----- .. .-----.------- -------.- --- 15


CITRUS SECTION

Injury and Loss of Citrus Trees Due to Tristeza Disease in an Orange County Grove,
Mortimer Cohen, State Plant Board of Florida, Gainesville --- ----------.- -.._-- 19
Effect of Phosphate Fertilization on Root Growth, Soil pH, and Chemical Constitu-
ents at Different Depths in an Acid Sandy Florida Citrus Soil, Paul F. Smith,
U. S. D. A. Horticultural Station, Orlando -- ---------.. ._____ 25
Starting and Maintaining Burrowing Nematode-Infected Citrus Under Greenhouse
Conditions, William A. Feder and Julius Feldmesser, U. S. D. A. Horticultural
Station, Orlando _. ----.. ---... .... --...._-..._- ...... ..........._.. -.. -__---_. _..__.. .... _____ 29












FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Preliminary Investigations on Dieback of Young Transplanted Citrus Trees, Gordon R.
Grimm, U. S. D. A. Horticultural Station, Orlando ------------ 31
The Possibility of Mechanical Transmission of Nematodes in Citrus Groves, A. C.
Tarjan, Florida Citrus Experiment Station, Lake Alfred ------ 34

Transmission of Tristeza Virus by Aphids in Florida, Paul A. Norman and Theodore
J. Grant, U. S. D. A. Horticultural Station, Orlando --...--------------------- 38

Physiologic Races of the Burrowing Nematode in Relation to Citrus Spreading Decline,
E. P. DuCharme, Florida Citrus Experiment Station, Lake Alfred, and W.
Birchfield, State Plant Board of Florida, Gainesville...-- ------------- ----. 42

Citrus Rootstock Selections Tolerant to the Burrowing Nematode, Harry W. Ford,
Florida Citrus Experiment Station, Lake Alfred---- ------- 44

The New 4-H Club Program for Citrus Production Training, Jack T. McCown, Florida
Agricultural Extension Service, Gainesville_. -----_------ _____- ...-----------.. -... 52

Field Observations of Several Methods of Managing Closely-Set Citrus Trees, Fred
P. Lawrence, Florida Agricultural Extension Service, Gainesville, and Robert
E. Norris, Florida Agricultural Extension Service, Tavares .. --- 54

Timing Fertilization of Citrus in the Indian River Area, Herman J. Reitz, Florida
Citrus Experiment Station, Lake Alfred_- --------- 58
Is Stem Pitting of Grapefruit a Threat to the Florida Grower? L. C. Knorr and W. C.
Price, Florida Citrus Experiment Station, Lake Alfred.--------- 65

Seasonal Changes in the Juice Content of Pink and Red Grapefruit During 1955-56,
E. J. Deszyck and S. V. Ting, Florida Citrus Experiment Station, Lake Alfred----- 68

Effectiveness of Different Zinc Fertilizers on Citrus, C. D. Leonard, Ivan Stewart and
George Edwards, Florida Citrus Experiment Station, Lake Alfred ---- 72

Increased Utilization of Grapefruit Through Improvement in Quality of Processed
Products, F. W. Wenzel and E. L. Moore, Florida Citrus Experiment Station,
Lake Alfred ---- --------- -----..----... .... ..------------------ 79

Long Range Relationships Between Weather Factors and Scale Insect Populations,
Robert M. Pratt, Florida Citrus Experiment Station, Lake Alfred ---- 87

Notes on the Use of Systox for Purple Mite Control on Citrus, Roger B. Johnson,
Florida Citrus Experiment Station, Lake Alfred ------ ----- 93

Progress Report on Greasy Spot and Its Control, W. L. Thompson, John R. King and
E. J. Deszyck, Florida Citrus Experiment Station, Lake Alfred ----- 98

Use of 1, 2-Dibromo-3-Chloropropane on Living Citrus Trees Infected with the Bur-
rowing Nematode, Julius Feldmesser and William A. Feder, U. S. D. A.
Horticultural Station, Orlando _. -..-...--------- 105


VIII





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


PROCESSING SECTION
Rapid Determination of Peel Oil in Orange Juice for Infants, R. W. Kilburn and L. W.
Petros, Florida Citrus Canners Cooperative, Lake Wales ------- ___ ____ 107
Effects of Finisher Pressure on Characteristics of Valencia Orange Concentrate, O. W.
Bissett and M. K. Veldhuis, U. S. Citrus Products Station, Winter Haven .........-- 109
A Study of the Degrees Brix and Brix-Acid Ratios of Grapefruit Utilized by Florida
Citrus Processors for the Seasons 1952-53 Through 1955-56, E. C. Stenstrom
and G. F. Westbrook, Citrus and Vegetable Inspection Division, State Depart-
ment of Agriculture, Winter Haven --._____--- ----------.-..--.....-- __ --. 113
Diacetyl Production in Orange Juice by Organisms Grown in a Continuous Culture
System, Lloyd D. Witter, Metal Division, Research and Development Depart-
ment, Continental Can Co., Inc., Chicago, Il1.---------_____-__ -----------.. 120
Standardization of Florida Citrus Products, Arthur R. Pobjecky, Southern Fruit Dis-
tributors, Inc., Orlando ........ ..........___----------------_--...---_._______ 125
Citrus Vitamin P, Boris Sokolcff, Isidor Chamelin, Morton Biskind, William C. Mar-
tin, Clarence Saelhof, Shiro Kato, Hugo Espinal, Taekyung Kim, Maxwell
Simpson, Norman Andree and George Renninger, Southern Bio-Research Lab-
oratory, Florida Southern College,' Lakeland ----- ____ ------------ ------_ 128
Vacuum Cooling of Florida Vegetables, R. K. Showalter and B. D. Thompson,, Florida
Agricultural Experiment Station, Gainesville. --------------..... -----_ 132
The Quality Control of Chilled Orange Juice from the Tree to the Consumer, Leo J.
Lister, Halco Products, Inc., Fairvilla, and Arthur C. Fay, H. P. Hood and
Sons, Boston, Mass. ____.___....... --...----------__--- 136
Hydrocooling Cantaloupes, K. E. Ford, Georgia Experiment Station, Experiment,
Georgia _---... ------- ____--....--- ........------ -------- ... 138
The Sloughing Disease of Grapefruit, W. Grierson and Roger Patrick, Florida Citrus
Experiment Station, Lake Alfred- ------- .. __ 140
Effect of Variety and Fresh Storage Upon the Quality of Frozen Sweet Potatoes,
Maurice W. Hoover and Victor F. Nettles, Florida Agricultural Experiment
Station, Gainesville -...---------- ......._........-------- -- ---- --- 142
Storage Studies on 42 Brix Concentrated Orange Juices Processed from Juices Heated
at Varying Folds. II. Chemical Changes with Particular Reference to Pectin,
A. H. Rouse, C. D. Atkins and E. L. Moore, Florida Citrus Experiment Sta-
tion, Lake Alfred ............ ............. ...........---------------- --------1...--.-- 145
Purification of Naringin, R. Hendrickson and J. W. Kesterson, Florida Citrus Experi-
ment Station, Lake Alfred .---. .-------._____.... ..... ..- 149

Sectionizing Marsh Seedless Grapefruit, Gray Singleton, Shirriff,Horsey Corporation,
Ltd., Plant City .____.. ... ..------ ..... --.----- ---.- .....-- 152
An Effective High Pressure Cleaning System for Citrus Concentrating Plants, D. I.
Murdock and C. H. Brokaw, Minute Maid Corporation, Orlando .----.-..__ 154






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Some Studies on the Use of Sodium Nitrite as a Corrosion Inhibitor in the Canning
Industry, J. R. Marshall, Tampa Laboratory of Research and Technical De-
partment, American Can Co., Tampa... --------------.--------------------- 159
Reducing Losses in Harvesting and Handling Tangerines, W. Grierson, Florida Citrus
Experiment Station, Lake Alfred .-----..... ----------- ..---------------------- 165
Quality of Canned Grapefruit Sections from Plots Fertilized with Varying Amounts
of Potash, F. W. Wenzel, R. L. Huggart, E. L. Moore, J. W. Sites, E. J.
Deszyck, R. W. Barron, R. W. Olsen, A. H. Rouse and C. D. Atkins, Florida
Citrus Experiment Station, Lake Alfred .._... -----------------------------------.- 170
Storage Studies on 42 Brix Concentrated Orange Juices Processed from Juices Heated
at Varying Folds. I. Physical Changes and Retention of Cloud, E. L. Moore,
A. H. Rouse and C. D. Atkins, Florida Citrus Experiment Station, Lake Alfred---- 176
Effect of Thermal Treatment and Concentration on Pectinesterase, Cloud and Pectin
in Citrus Juices Using a Plate Type Heat Exchanger, C. D. Atkins, A. H. Rouse
and E. L. Moore, Florida Citrus Experiment Station, Lake Alfred ------ 181
Distribution and Handling of Frozen Fruits, Vegetables and Juices, George J. Lorant,
Birds Eye Laboratories, Albion, New York------------ 185
Dried-Citrus-Pulp Insect Problem and Its Possible Solution with Insecticide-Coated
Paper Bags, Hamilton Laudani, Dean F. Davis, George R. Swank and A. H.
Yeomans, Stored-Products Insects Laboratory, Savannah, Georgia- --- 191


VEGETABLE SECTION

Progress Report on Cantaloupe Varieties, B. F. Whitner, Jr. Central Florida Experi-
ment Station, Sanford _---_.. -- .-----....------ .-------------- ---------- 195
Phytotoxicity of Fungicides to Cantaloupes, Robert A. Conover, Sub-Tropical Experi-
ment Station, Homestead -------. -......---------------- ------------- 198
Irrigation of Sebago Potatoes at Hastings, Florida, Donald L. Myhre, Florida Agricul-
tural Experiment Station, Potato Investigations Laboratory, Hastings--- 200
Use of Certain Herbicides in Fields of Growing Tomatoes Progress Report, John C.
Noonan, Sub-Tropical Experiment Station, Homestead------- 204
Crop Production in Soil Fumigated with Crag Mylone as Affected by Rates, Applica-
tion Methods and Planting Dates, D. S. Burgis and A. J. Overman, Gulf Coast
Experiment Station, Bradenton -___--.....___.---.....----------..------- 207
Breeding Objectives and the Establishment of New Breeding Lines of Southernpeas,
A. P. Lorz, Florida Agricultural Experiment Station, Gainesville ----- 210
Factors Influencing Consumer Preference of Southern Peas (Cowpeas), Maurice W.
Hoover, Florida Agricultural Experiment Station, Gainesville ------- 213
Outlook for the Production of Southern Field Peas for Freezing, James Montelaro,
Minute Maid Corporation, Plymouth ..---------------- 216






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Insect Problems in the Production of Southern Peas (Cowpeas), John W. Wilson,
Central Florida Experiment Station, Sanford, and W. G. Genung, Everglades
Experiment Station, Belle Glade --.-------....-...-------.------.-_----- 217
Influence of Nitrogen, Phosphorus, Potash and Lime on the Growth and Yield of
Strawberries, R. A. Dennison and C. B. Hall, Florida Agricultural Experiment
Station, Gainesville ..... -------.-.. ---------- .. .-- .....---- _--------__ 224
Lime-Induced Manganese Deficiency of Strawberries, C. B. Hall and R. A. Dennison,
Florida Agricultural Experiment Station, Gainesville -..-------.--_________ ________-- 228
Cucumber Fungicides for the West Coast of Florida, Grover Sowell, Jr., Gulf Coast
Experiment Station, Bradenton ._--__-_..____ .____ .__ ______-------------.-.... ... ------ 230
Notes on Current Developments of Gray Mold, Botrytis Cinerea Fr. of Tomato and Its
Control, R. S. Cox, Everglades Experiment Station, Belle Glade, and N. C.
Hayslip, Indian River Field Laboratory, Ft. Pierce ..--______..- ._____------- 235
Evaluation of Control Methods for Blackheart of Celery and Blossom-End Rot of
Tomatoes, C. M. Geraldson, Gulf Coast Experiment Station, Bradenton -------- 236
Control of Diseases in the Celery Seedbed, R. S. Cox, Everglades Experiment Sta-
tion, Belle Glade -... .. -----------------.- 24........ 242
The Assay of Streptomycin as it Relates to the Control of Bacterial Spot, Grover
Sowell, Jr., Gulf Coast Experiment Station, Bradenton --____._______..-------- 244
Control of Pole Bean Rust with Maneb-Sulfur Dust, Robert A. Conover, Sub-Tropical
Experiment Station, Homestead -_________ .. _----------- .------ 247
Fungicidal, Herbicidal and Nematocidal Effects of Fumigants Applied to Vegetable
Seedbeds on Sandy Soil, A. J. Overman and D. S. Burgis, Gulf Coast Experi-
ment Station, Bradenton ______.------------------ ----- ----- _250
Variety Tests of Commercial Types and New Breeding Lines of Southernpea, L. H.
Halsey, Florida Agricultural Experiment Station, Gainesville ________-- -- __ 255
Results of Different Seeding and Fertilizer Rates for Potatoes at Hastings, E. N.
McCubbin, Florida Agricultural Experiment Station, Potato Investigations
Laboratory, Hastings --___ ________. .----------.- ___ -- ----___-------------______ ....._ 259
Production of Spinach for Processing on Muck Soils of Central Florida, M. M. Hooper,
Vegetable Grower, Apopka ..---_.. _---__-----. _.------_... 261


KROME MEMORIAL SECTION

The Concept, Duties, and Operations of the Florida Avocado and Lime Commission,
C. F. Ivins, Florida Avocado and Lime Commission, Homestead ------- 262
Notes on Tropical Fruits in Central America, Wilson Popenoe, Escuela Agricola
Panamericana, Tegucigalpa, Honduras -.-.-.____-. __ -------- ...__ -- 267
Marketing of Limes and Avocados in Florida, Harold E. Kendall, South Florida
Growers Association, Inc., Goulds... ... --- --...-_----- .-- 270








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


The Sub-Tropical Fruit Program of Dade County, John D. Campbell, County Agri-
cultural Agent, Homestead ._.---------..-------------------.. 272
Some Observations on Lime and Avocado Grove Cultural and Maintenance Practices
in Dade County, Norman E. Sutton, Grove Management, Inc., Goulds..----------- 274
Future of Florida Minor Tropical Fruit Industry in Doubt, Nixon Smiley, Miami
Herald Farm and Garden Editor and Director, Fairchild Tropical Garden,
Miami -_.-_-...-------- .--------------.. ----------------. ------------------ 275
Krome Memorial Avocado Variety Committee Report, F. B. Lincoln, Chairman,
Homestead ..----------.- --........ ...... .......... .------------------------.---- 276
Pollination and Floral Studies of the Minneola Tangelo, Margaret J. Mustard, S. John
Lynch and Roy O. Nelson, Division of Research and Industry, University of
Miami, Coral Gables __.._------....-... ..................----------------- 2277
Changes In Physical Characters and Chemical Constituents of Haden Mangos During
Ripening at 80 F., Mortimer J. Soule, Jr., and Paul L. Harding, U. S. D. A.
Horticultural Station, Orlando -..-.. ..---------------------- --- 282
Further Rooting Trials of Barbados Cherry, Roy O. Nelson and Seymour Goldweber,
Division of Research and Industry, University of Miami, Coral Gables.---.-.. 285

Research on Sub-Tropical Fruits as a Result of Mediterranean Fruit Fly Eradication
Program, Geo. D. Ruehle, Sub-Tropical Experiment Station, Homestead...------ 287

Some Effects of Nitrogen, Phosphorus and Potassium Fertilization on the Yield and
Tree Growth of Avocados, S. John Lynch and Seymour Goldweber, Division
of Research and Industry, University of Miami, Coral Gables.----- 289

A Comparison of Three Clones of Barbados Cherry and the Importance of Improved
Selections for Commercial Plantings, R. Bruce Ledin, Sub-Tropical Experi-
ment Station, Homestead .......----.----------------------- 293
Rare Fruit Council Activities, 1956, William F. Whitman, Salvatore Mauro, Seymour
W. Younghans, Miami Beach --.. ..--.... -----..... -..........--------------- 2.. 297

Some Notes on a Weevil Attacking Mahogany Trees, F. Gray Butcher and Seymour
Goldweber, Division of Research and Industry, University of Miami, Coral
Gables _._.. _... .. .------ -------. -.. .-... .-.... .------------ -------------- ----- 303

Response of Lychees to Girdling, T. W. Young, Sub-Tropical Experiment Station,
Homestead .. ----------- ..... ... ---------.--- ......- ------- ---------... ----- 305

Some Aspects of the Lychee as a Commercial Crop, Gordon Palmer, Florida Lychee
Growers Association, Osprey ....____------ -_......----- .....-------------------.. 309

The Effects of Longtime Avocado Culture on the Composition of Sandy Soil in Dade
County, John L. Malcolm, Sub-Tropical Experiment Station, Homestead ..--- 313

Rooting of Peach Cuttings Under Mist as Affected by Media and Potassium Nutrition,
Mario Jalil, Escuela Agricola Panamericana, Honduras, and Ralph H. Sharpe,
Agricultural Experiment Station, Gainesville ______...- ---- 324






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Some Effects of Nitrogen, Phosphorus and Potassium Fertilization on the Growth,
Yield, and Fruit Quality of Persian Limes, Seymour Goldweber, Manley Boss
and S. John Lynch, Division of Research and Industry, University of Miami,
Coral Gables ...------- ------------------ ...----____________- 328


ORNAMENTAL SECTION

Mist Propagation of Roses, S. E. McFadden, Jr., Department of Ornamental Horti-
culture, University of Florida, Gainesville ..---. --. .... ____-----------_.- --------- 333
Gladiolus Botrytis Control, R. O. Magie, Gulf Coast Experiment Station, Braden-
ton .- --- ----.--------------- --------------..---. ....--..._____------------.... 337
Some Notes on Philodendron Hybrids, Erdman West and H. N. Miller, Florida Agri-
cultural Experiment Station, Gainesville_ ..--.----_____... __...-------------------- 343
Fertilization of Gladiolus, S. S. Woltz, Gulf Coast Experiment Station, Bradenton .-- 347
Studies on the Nutritional Requirements of Chrysanthemums, S. S. Woltz, Gulf Coast
Experiment Station, Bradenton ------------------------- ___-----------------..-- 352
Virus Ring Spot of Peperomia Obtusifolia and Peperomia Obtusifolia var. Variegata,
M. K. Corbett, Florida Agricultural Experiment Station, Gainesville .....----------- 357
How to Landscape Our Outdoor Space for Living, Thomas B. Mack, Florida Southern
College, Lakeland ----------- ------------- --- .. ....-.......-- ------- ------ 360
Regional Performance of Hemerocallis in Florida, Eunice T. Knight, Apopka ---- 363
The Palm Society, Dent Smith, The Palm Society, Daytona Beach... -------- 366
Comparison of Happiness Rose Production on Four Rootstocks, S. E. McFadden, Jr.,
Department of Ornamental Horticulture, University of Florida, Gainesville.------- 368
Florida Nursery Law, Paul E. Frierson, State Plant Board of Florida, Gainesville 370
Research in the Ornamental Field in Control of Mediterranean Fruit Fly, E. W. Mc-
Elwee, Florida Agricultural Experiment Station, Gainesville --__.------......-..- 379
The Florida Flower and Nursery Industry, Cecil N. Smith, Florida Agricultural Ex-
periment Station, Gainesville -._.--..-......---- .--__-------...___--------- 380
The Downward Movement of Phosphorus in Potting Soils as Measured by P", Daniel
O. Spinks and William L. Pritchett, University of Florida, Gainesville------..... 385
Twelve Bauhinias For Florida, R. Bruce Ledin, Sub-Tropical Experiment Station,
Homestead .._.._-----. ..... ------ ...---- ------ __------_..--------.-____ 388
Pesticides and Plant Injury, S. H. Kerr, Florida Agricultural Experiment Station,
Gainesville 3_. ------------ --------- ---... -------- --.-.----- ------- 398

The Effect of Parathion as a Corm and Soil Treatment for Gladiolus, E. G. Kels-
heimer, Gulf Coast Experiment Station, Bradenton _______..----------------- 403
The Genus Solandra in Florida, R. D. Dickey, Florida Agricultural Experiment Sta-
tion, Gainesville ____.-------------- ---.---------------------- -__ -__ -______.... 465








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Studies on Chemical Weed Control in Plumosus Fern, C. C. Helms, Jr., J. M. Crall and
E. O. Burt, Watermelon and Grape Investigations Laboratory, Leesburg-- 407
Fungicides and Plant Injury, Albert P. Martinez, State Plant Board of Florida,
Gainesville ........... ..... ..--------------- ---- -------- ------------------------ ---- 413
The Hunting Billbug a Serious Pest of Zoysia, E. G. Kelsheimer, Gulf Coast Experi-
ment Station, Bradenton -_. ----------- .. ------------------------ ------------------ 415


ANNUAL REPORTS

Necrology -----... -------. ..-------- ---------.----------- ------------------------------- 419
Report of Executive Committee. -------------.-- .-.. --.. ..-- .. ------------------------------ 421
General Business Meeting .-----------......--- .---....... .------- ------- ---------------------- 421
Resolutions ------- ------- -- ----------------------------- 421
Report of Treasurer -----. ..---- -------. ---- ---- ----- ----------- 422
List of Members--- ...... .- ---.... ....- .-.--- --.-------------- ----- ---------------- 423
Index --... .......-.-- .... -------------------- -------------- ---- 433


XIV
















THE PRESIDENT'S ADDRESS


R. A. CARLTON
West Palm Beach
One of the duties imposed upon the Presi-
dent of this Society is an annual address on
the activities of your Society and the general
state of Horticulture in Florida. I am glad to
report that your Society is now the third larg-
est Horticultural Society in the United States
and the seventh oldest society. It is exceeded
in membership by the Wisconsin and Michigan
Horticultural Societies in that order. The oldest
society is in Ohio and was organized in 1847.
The Wisconsin Society which has the largest
membership has received State aid since 1879
which may account in some measure for the
size of its membership.
In the preparation of this address it was
natural to reflect upon the changes that have
occurred in the activities of the Society in the
more than 30 years in which I have been a
member, and more or less active in the So-
ciety's functions. When I became a member,
the horticultural crops of the State were strug-
gling along on an unbalanced program of nu-
trition, and your Society was struggling in
about the same manner.
Colonel Bayard F. Floyd had been Secre-
tary since 1917 and most of the Presidents
and Executive Committeemen of those days
insisted on the Colonel running it as a one
man show, and imposed upon him the com-
plete responsibility for the program, arrange-
ments for the meetings, and everything else
requiring much work and time. I recall that
some of the young upstarts in the Society
about 25 years ago, myself included, became
somewhat critical of some of the Colonel's
best efforts at program and meeting arrange-
ments. As usual, everybody thought something
should be done but nobody wanted to do any
work. This state of mild criticism prevailed
until about 1939 when the speaker and some
others approached the Colonel about forming
a Vegetable Section of the Society. The
Colonel was quite agreeable and cooperative
but flatly declined to accept any responsibility
for a program for such a section. Being brash
and bold, I accepted this responsibility and
during the next five years I learned how easy


it is to talk too much. Anyway, during those
years working with Colonel Floyd I gained a
deep appreciation of the problems he had
faced through the years and sincerely re-
gretted any criticism I ever had of his efforts.
His untimely death in 1945 prevented the
Society from ever awarding him any honorari-
um, if it had been possible for the Society to
accord him anything commensurate with the
services he had rendered.
It affords me great pleasure to report that
during the past year your Society operated
under a new deal compared to the years out-
lined above. This year it was a pleasant ex-
perience to see how all your General Officers -
worked together as a team to develop the pro-
gram and arrangements for this meeting. The
Chairman of each Section readily accepted
the responsibility of developing the program
for his Section, and the Executive Committee-
men from the Society at large were most help-
ful to the General Officers in arranging the
many details of this meeting. I wish to express
my sincere appreciation for the help and co-
operation I have received from one and all.
Some of my foregoing remarks have empha-
sized the fact your Society has been most for-
tunate in the selection of a Secretary. This
good fortune still prevails in Dr. Ernest L.
Spencer. He has all the attributes of other good
secretaries with an additional one of getting
more work out of other people without making
anybody mad.
During the past two years your Society
created a Fellowship in Virology at the Uni-
versity of Florida. This Fellowship was
awarded to Mr. Robert Bozarth, a graduate of
Everglades High School in 1948 and the Col-
lege of Agriculture, University of Florida, in
1952. He is presently directing his study on
the viruses of gladiolus. When these viruses
have been isolated they will be identified by
symptoms, host reaction, cross protection, and
by the use of the Spinco Ultra Centrifuge at-
tempts will be made to purify and crystallize
the viruses. These studies will aid in the de-
veloping of practical and economical control
measures that can be applied by the growers.
Realizing full well the complex field involved
in research on crop viruses, the recipient of






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


this Fellowship expressed his problems well I
thought and I quote, "To use a bit of double
talk, we are experimenting with experiments
to carry on the experiment." This certainly in-
dicates he knows what he is up against.
During April a major outbreak of the Medi-
terranean fruit fly occurred in Dade County,
Florida and since that time this insect has been
found in some 26 counties. The reoccurrence
of this insect in the State had been expected
by many due to the increase in air travel to
the State from all parts of the world, and the
reduced inspection service at ports of entry.
Many of us who remembered the hectic days
of the eradication campaign in 1929 were ap-
palled by prospects of a similar experience.
However, time had wrought many changes in
Techniques of control, insecticides and bait at-
tractants used in eradication of this insect.
No one could fail to be impressed by the fact
that with the discovery of an outbreak of this
insect today, this spot, and many miles of area
surrounding would be thoroughly sprayed
within a matter of hours. Respraying of such
areas would occur almost in the twinkling of
an eye, in opinion of some of us, who were
constantly faced with wash jobs on our cars.
A full report will be made to the Society at
this meeting on the status of the control pro-
gram of this insect. I feel the control agencies
have done a remarkably good job on this prob-
lem and should be congratulated on avoiding
much confusion and hysteria that usually ac-
companies a control and eradication program
of this magnitude.
Your Society has been much concerned in
recent years with the control and eradication
of spreading decline in citrus. I do not have
figures later than June 1st, 1956, but at that
time inspection had been made on 4,421 grove
properties comprising approximately 18,000
acres. Infested groves were 960, comprising
about 7,500 acres. Inspection had been made
of 2,243 nurseries of which 306 were found
to be infested. Beginning July 1st, 1955, the
State Plant Board started its program of pull-
ing trees from infested grove properties and
treating the soil to eradicate spreading decline.
As of June 1, 1956, 200 grove properties com-
prising 1440 acres had been pulled and treated
at a cost per acre of approximately $305.00.
This total cost may be broken down with
$89.00 cost to push and bum trees, and


$150.00 to remove roots and do a thorough
job of treating the soil. The State. Plant Board
expects to complete the removal of all infested
acreage by July 1, 1957, and treat the acreage
from which trees and roots have been re-
moved. This clearly indicates fine progress in
the control and eradication of this production
problem.
Despite the dual threats of fruit fly and
spreading decline and other problems, the
citrus industry continues to set new records
of production with an estimated 138,000,000
boxes of fruit to be harvested in the coming
season. Except for the war years, the citrus
section never had it so good, due in a large
measure to its hand maiden the Processing
Section which utilized 71 percent of last sea-
son's crop. The Processing Section is diligent-
ly making every effort to improve quality and
increase consumer demand for its products.
Much progress is being accomplished as re-
flected in increased consumption of all pro-
cessed citrus products.
In the field of the Krome Memorial Section
of your Society, much progress may be noted.
Nutritional sprays of zinc, manganese and
iron chelates have revolutionized the produc-
tion picture on the limestone soils of Dade
County where much of the commercial acreage
of subtropical fruits are planted. Mechanical
improvements in land preparation and devel-
opment on this unusual soil has also contrib-
uted to increased acreage. Two lime concen-
trate plants in Dade County are contributing
much to stabilizing the market for Persian
limes. Some 6500 acres are now planted to
this fruit crop in Dade County.
New mango varieties are encouraging in-
creased plantings of this fruit. This is one
fruit immigrant that the longer it stays with us
the better it gets. New variety developments
are a far throw from the the first Mulgoba
tree that fruited successfully in West Palm
Beach around the turn of the century. Some
of you have heard the beloved Dr. David
Fairchild tell the Society of his hopes and fears
of the early plantings of mangos in Florida.
The annual Mango Forum and exhibit is a
state-wide organization and I believe is a
fitting example of Dr. Fairchild's fondest hopes
for this fruit in the western world.
Lychees have reached commercial produc-
tion and a growers association was formed in






CARLTON: PRESIDENT'S ADDRESS


1951. This association is actively working on
production and marketing problems.
In the realm of the Vegetable Section,
U.S.D.A. Truck Crop statistics reveal the
Florida growers brought 385,000 acres of
vegetable crops to the point of harvest last
season, with shipments of 155,000 carlot
equivalents. Acreage of vegetable crops has
increased 21 percent and volume of shipments
42 percent in the past five years. In the same
five year period returns on vegetables at the
F.O.B. level have increased 31 percent. To-
matoes continue to be the most important
vegetable crop grown in the State with the
value of last year's crop exceeding the value
of all animal products sold in the State. Last
season 4.6 percent of the State's tomato pro-
duction was shipped as vine-ripened and this
supply resulted in much attention being di-
rected toward this new development from a
marketing standpoint. A study is now being
made by Agricultural Economics Department
of the College of Agriculture on the market
outlook for vine-ripened tomatoes. The Chair-
man of this year's Vegetable Section of your
Society is a successful vine-ripened tomato
grower. I predict that the marketing of vine-
ripened tomatoes is here to stay and that Flori-
da will soon develop this activity into a major
enterprise.
Last season Florida harvested 37,700 acres
of sweet corn, which was a crop not grown
commercially in the State 15 years ago. The
State now furnishes a continuous supply of
this crop to the markets from October until
July.
Notable advances have been made by all
phases of the vegetable industry in mechani-
zation of production and harvesting processes.
One of the newest harvesting machines to
come to my attention is for tomatoes. This
machine has an overall width of 365 feet.
Such developments are resulting in larger
growing operations.
The Ornamental Section of your Society is
a phase of horticulture that has increased
phenomenally in recent years. The gladiolus in-
dustry has expanded since 1940 from 4,500
acres producing 5,000,000 dozen blooms to
11,600 acres producing 20,000,000 dozen
blooms. The growing of chrysanthemums has
jumped from 5 acres in 1950 to 230 acres


with a large part of this enterprise located in
Martin County. Last season 46 growers har-
vested 3,500,000 bunches of pompons and
72,000 dozen standard blooms valued at $3,-
500,000.00. This is a good example of a hot
house enterprise being adapted to production
in the open under Florida's climate.
A sizeable industry has developed on the
woody peat soils of Highlands County in the
production of calladium bulbs. This enter-
prise has meant much to the economy of that
area. The importance of large ornamental
nursery business in the State is well known.
The eternal light of your Society is its pub-
lished proceedings. Volume 68, relating to the
1955 meeting contains 400 pages. In the 69
years of the Society's existence its proceedings
have reported the best history of Florida's
horticulture both practical and technical.
Several years ago an index was published
of volumes 5 through 37 of the proceedings.
Three years ago your Executive Committee de-
cided to compile an index of volumes 38
through 68 and this was completed this sum-
mer and now published and available to mem-
bers. This work of indexing the proceedings
was done with the intent of encouraging mem-
bers to better use their proceedings as refer-
ence material for any phase of horticulture in
which they might be interested.
I realize that I, and possibly many other
members, have not used their proceedings in
the past as we should have, and possibly this
was due in part to a lack of an index which
would permit us to refer quickly and efficient-
ly to any person or subject covered in the pro-
ceedings.
The Society has grown too large and com-
plex for any member to attend the sessions and
hear all the papers which might be of interest
and value to them. Study of the proceedings
is the only way then in which the Society may
be of the most value to you. I would be remiss
in duty if I didn't urge every member here to
use and appreciate the work and knowledge
recorded in your Society's proceedings. I am
not one to sermonize, but if I were, an appro-
priate text might be found in Matthew 5:15:
"Neither do men light a candle and place it
under a bushel, but upon a candlestick; and
it giveth light unto all who are in the house."






FLORIDA STATE HORTICULTURAL SOCIETY, 1956

PLANT RESEARCH IN THE ATOMIC AGE


GEORGE L. McNEW
Boyce I 1i.,"' i Institute
for Plant Research, Inc.
Yonkers, N. Y.

When your fine secretary invited me to ap-
pear on this program last June, I demurred
long enough to prove my modesty and then
hastened to accept before he changed his
mind. As usual, I always enjoy a trip to your
unique state. It is a particular honor and
pleasure to appear before such a venerable
and respected society as yours to discuss cer-
tain new aspects of agricultural research.
At the very outset we should come to an
understanding that nothi. I, .ith;. i c,, .ty
in the next hour ill .,it .'--. F l.oi 's
agriculture. You will probably not find a single
item to help you increase soil fertility, sup-
press insects or alleviate plant diseases. After
all, you have one of the better, if not the best,
agricultural research services in the United
States to provide such information. Since it
would be foolhardy for me to attempt to com-
pete with such talent in your own fine institu-
tions, I will spend this hour discussing selected
items of research behind their research. Per-
haps we can take a stroll behind the scenes to
see what sort of principles of life and living
processes are being investigated in order to
provide a jumping off place for future research
in agriculture.

THE CHALLENGE OF THE MODERN ERA
Our newspapers like to refer to this as the
atomic age. Perhaps this is fitting because it is
an era of change, growth and violent adjust-
ments. To many of our citizens it has become
an era of frustration, uncertainty and worry as
we face a violently explosive international
situation and see our economy shaken and un-
stable on the rapidly shifting sands of techno-
logical change and social unrest.
Athhli.lzh we know that atomic violence
hangs over our heads by day and night, I
would not have us live in fear and trepida-
tion. There is another side to this whole pic-
ture that we should never forget. The same
forces that threaten us can be diverted to our
peacetime use and a 11. ..-1 progress. It is this


story of progress through research in the com-
mon great cause of humanity that we will in-
spect here today.

THE NEW ERA IN RESEARCH
The opportunities in research were never
more promising of glorious success than to-
day. Scientists have behind them a mass of
knowledge to be used as a foundation and
new research tools that were undreamed of
three decades ago. For the first time in the
history of science man can trace the meta-
bolism of a living thing by use of radioactive,
unstable atoms. You can label a part of a tissue
as it grows, a molecule in process of digestion,
or even the parasite or pest that attacks the
crop. The tissue, the molecule, the parasite, or
the insect then becomes so conspicuously
unique that it can be traced wherever it goes
and yet it behaves exactly the same as all of
its less conspicuous brethren.
The physical chemist has given the biologist
a host of other relatively simple tools to help
in manipulating and separating the labelled
molecules. By use of paper partition chroma-
tography one can separate out all the amino
acids, ketones, aldehydes, acids, growth hor-
mones, etc., then identify them and measure
their concentration. Assays that would have
taken many months to perform can now be
done in 48 hours. Best of all, however, the
new techniques reveal related but previously
unknown compounds to whet the curiosity
and initiative of the investigator. No less sig-
nificant is the use of elution column chroma-
tography, ultracentrifuges, electrophoresis
equipment and a host of other devices to sep-
arate and purify components with biological
activity.
If there is any question about the identity
and concentration of any material there are
spectrophotometric devices to substantiate one's
opinions and guide his research. For example,
just think of this fact. One of our scientists
tells me that we can now make a complete
amino acid analysis of a single female house-
fly in two days. If we find an undescribed
amino compound we can elute it and get a
complete fingerprint of its characteristic bonds
within two hours by use of infrared absorp-
tion. You can do all this if the miserable old





ILkNEW: PLANT RESEARCH


fly had as much as a few micrograms of the
chemical in her body.
This example could be multiplied a hun-
dred-fold by choice of other devices and tech-
niques-the physical chemist who pulls two
closely related viruses apart in an electrophore-
sis apparatus by minute differences in their
surface charges or by differences in their mass
or density in an ultracentrifuge, or the X-ray
crystallographer who plots the arrangement
of invisible and active atoms one to another
in a crystal lattice that one barely sees under
the most powerful microscope. This is a great
era in which to live. Every scientist worthy of
the name should thrill to the opportunities be-
fore him to understand the universe.
For many decades the botanist and horti-
culturist have been interested in the outside
of plants. They did a necessary job of describ-
ing the organs and determining the relation
of one plant to another. We learned how to
change these external appearances by breed-
ing, altering their nutrition, or exposing them
to chemicals. However, no one knew exactly
what had been done or why plants reacted the
way they do. Today a new viewpoint is com-
ing into plant research. We are more interested
in what a plant does than what it looks like.
The activities going on inside of millions
of tiny cells in each tissue arouses one's
imagination. There is a beehive of activity in
one of these cells-with a volume of less than
one-billionth of a cubic inch-that would put
the best man-made factory to shame. For ex-
ample, if one provides the leaves of a plant
with labelled C"0s, within five minutes there
may be detected 57 new organic compounds
in the tissue. Within a couple of hours some
of the very complex new molecules are being
secreted from the roots. One must admit that
the dynamics of cell operations are tremend-
ous.
The activities of these cells are of interest
to men because anyone who can control the
cell can change the tissue and thereby regulate
the entire plant to our selfish purposes. One
can make cells grow faster, change their shape,
inactivate them completely, change their
heredity; render them more nutritious or make
them immune to disease by use of the appro-
priate chemicals. Therefore the scientist who
will take the time and effort to understand
cell functions should be able to uncover basic


principles of life which he can exploit in mak-
ing plants more serviceable to man. By the
same token, the man who would control in-
sects, diseases and weeds has an obligation to
study them carefully to determine their
strengths and weaknesses.
By so doing, the biologist can orient the ef-
forts of the chemist in developing new types
of chemicals to solve many problems in plant
culture. The examples we will consider here
today lie in this general area on the frontiers
of science. They are chosen from work of
various scientists at Boyce Thompson Institute,
not because they are the only work in the area
or even superior to that of others but because
of my familiarity with them.
FUNGICIDAL BULLETS
Men have been at war with the fungi since
time eternal. You people here in Florida need
not be reminded that tremendous quantities of
chemicals must be applied to plants to prevent
fungous diseases. You contribute a substantial
share of the 125 million dollars spent each
year in the United States on control of plant
diseases.
In spite of this terrific investment we are
only partially successful in reducing the rav-
ages by fungi. According to our best estimates
they still destroy 7% of our potential agricultur-
al productivity. This amounts to about 2.8
billion dollars a year. To get down to brass
tacks it means that every man, woman and
child in the United States pays $24.20 a year
in tribute to the fungi. Each family would be
horrified if it entered $96 a year in its house-
hold budget as the cost of plant diseases but
such are the facts.
Obviously we need better methods of con-
trolling diseases. Some people may make their
contribution by breeding resistant plants, im-
proving crop rotations etc., but we have elected
to see what can be done in improving fungi-
cides. There are several good fungicides but
we need more and the only way we are going
to get them is invent them. We have decided
to learn all we can about the ones now avail-
able so we can develop better ones. Here are
a few examples of recent developments.
Sulfur operates in a unique fashion. The
particle of sulfur deposited on a leaf or fruit
volatilizes and reaches the spore in the vapor
phase. By use of radioactive sulfur (S") Drs.








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Miller and McCallan have shown that the sul-
fur atom is taken up by the spore and is almost
immediately reduced to hydrogen sulfide. It is
released within a couple of minutes from the
spore and, contrary to previous conceptions,
the HS does not act as a fungicide in destroy-
ing the spore. Please note that facts such as
these could be determined only by using iso-
tope tracer techniques.
Once these facts were out in the open our
scientists began to wonder how sulfur could
destroy a spore without entering into cell re-
actions. Biochemical studies have shown that
the spore suffers irremedial damage when it
gives up two hydrogens to reduce each sulfur.
For each molecule of sulfur reduced, the spore
releases a molecule of carbon dioxide. By the
time the spore has reduced 15,000 to 25,000
parts of sulfur per million units of body weight
it succumbs.
The search in this area goes on to determine
what organic acid in the spore is undergoing
decarboxylation. Insofar as we know, sulfur is
unique among the fungicides in its ability to
destroy a spore solely by robbing it of ma-
terials. All other fungicides enter the spore
and react with vital cell constituents. Sulfur is
a hit and run bullet that bleeds the spore to
death.
The organic fungicides are far more fas-
cinating. They can be designed in a wide
variety of forms with only minor differences
in configuration. By trial and error, chemists
have learned that there is a rigid requirement
of chemical structure to attain effective fun-
gitoxicity. Why does a minor change in chemi-
cal structure affect the fungicidal activity so
drastically? It is becoming increasingly clear
that the changes either influence the ability
to penetrate the fungous body, to enter into
certain vital cell reactions and disrupt them,
to change resistance to the cell's detoxification
mechanisms or to modify the stability and per-
sistence of the molecule.
Most of you know that there are two quin-
one fungicides on the market under the trade-
names of Spergon (chloranil) and Phygon
(dichlone). Many of you may have heard me
say in years past that dichlone was about 20
times as fungicidal as chloranil. This appears
to be true when one measures their effect on
spore germination but it is contrary to what
one would expect from their chemical at-


tributes. Dr. Owens has cast much light in
this area by recent studies on the effect of
several dozen quinones and hydroquinones on
enzyme systems. He found that there was a
very close correlation between fungitoxicity
and ability to inhibit sulfhydryl- and amino-
bearing enzymes. An exception was observed
in comparing benzoquinone and naphthoquin-
one analogues. He was finally able to show
that benzoquinone appeared to be less active
than naphthoquinone because it was detoxi-
fied more readily by entering into extraneous
reactions. Dark-colored spores secrete sub-
stances that inactivate much of the benzo-
quinone before it can penetrate and destroy
the spore.
Most of us have wondered what roles are
played by the halogens on the organic mole-
cules so commonly used as insecticides, fungi-
cides and herbicides. Dr. Burchfield has care-
fully studied the effect of placement of two
types of chlorine in the symmetrical triazines,
a new class of fungicides developed by Dr.
Schuldt in cooperation with chemists of the
Ethyl Corporation. These compounds have the
following structure:


6 (chloroanilino)-2,4-dichloro-!-triazine

The two chlorines on the triazine nucleus
were found to be essential for reaction with
sulfhydryl-bearing enzymes and related com-
pounds. If they are replaced with other groups
the molecule becomes impotent because it can-
not react in the cell environment. The chlorine
on the anilino group serves a multiple function.
When placed ortho to the nitrogen it activates
the chlorine on the triazine nucleus. One
might describe it as a booster charge because
of its effect on electron density at the vital
part of the molecule. Therefore, if the chlorine
is substituted at this point activity may be in-
creased several-fold, depending upon the
species of fungus affected.
This booster effect declines as the chlorine
is pushed farther away into the meta or para






McNEW: PLANT RESEARCH


positions on the phenyl ring. In spite of this
diminishing effect the parachloroanilino com-
pound is much more active than its meta ana-
logue. This has been shown to be due to its
greater ability to penetrate the spore wall of
certain fungi.
The concepts on spore penetration have
changed drastically in the last three years. We
are learning that certain groups such as the
parachlorophenyl, or the long alkyl chain of
14 to 17 carbon atoms alter the lipoid solu-
bility of a molecule enough to regulate com-
pletely the ability to penetrate the waxy and
oily layers in the fungous wall. Merely by
changing the length of the carbon chain in
the 2-position of the imidazoline nucleus it is
possible to render the molecule safer for use
on plants and more destructive for spores at
the same time. Glyodin was developed by Drs.
Wellman and McCallan merely by lengthening
the carbon chain from eleven atoms where it
rendered the molecule violently injurious to
the plant and relatively weak for the fungus to
17 carbon atoms where the reverse situation
held.
In studies employing radioactive molecules,
Dr. Miller has been able to show that fungi-
cides not only penetrate the spore wall at un-
believably fast rates but may also change the
permeability of spore membranes. If spores
are placed in a suspension containing 2 p.p.m.
of glyodin they will accumulate up to 6000
p.p.m. of their own body weight within 2 to 5
minutes. Interestingly enough, such a spore
destroyed by this organic chemical will take
up just as much mercury or silver fungicide
as a normal living one. Likewise, he found
that mercury and silver did not interfere with
each other although it had been assumed that
heavy metals might be expected to occupy
similar reaction sites. The spores actually took
up more mercury after they had been exposed
to silver than comparable untreated spores.
This was traced to a change in the semi-
permeable membranes of the spore. Silver af-
fects the spore so its cell constituents are lost
more readily and external chemicals penetrate
more actively.
By patient studies such as these we are
cataloguing the effects of changes in chemical
structure on the activities of various types of
molecules. The ultimate goal of course is to
define all the characteristics of a fungicide so


we can design one that will penetrate the
fungous body, enter into a vital reaction with
an enzyme or metabolite, but not be detoxi-
fied by extraneous reactions. This is a big
order but it is not an impossible one.

VIlus MULTIPLICATIONS AND PATHOGENESIS
One of the great areas of knowledge to be
developed is the nature of virus infections in
plants. In spite of the monumental strides for-
ward in the past thirty years, the riddle of how
viruses multiply and cause disease remains un-
solved. The presence of virus protein does not
necessarily cause disease symptoms. Investi-
gators have isolated and identified heavy
weight proteins from apparently normal
plants so removal of proteins from normal
pathways of metabolism does not explain the
disease conditions. As a matter of fact nu-
cleic acid may be combined with proteins
without inciting symptoms as witnessed by the
research on recovery of tobacco from ring
spot done by Dr. Price, a former member
of our staff, now with the Citrus Experiment
Station.
On the assumption that there is some physio-
logical disturbance other than the abnormal
use of protein, Dr. Porter has been investi-
gating the biochemical changes in plants dur-
ing the incipient stages of infection before
disease symptoms appear. The first reaction of
a plant to the tobacco mosaic virus appears to
be an abnormal synthesis of amino acids. By
use of paper chromatography he has been
able to demonstrate a net increase in alanine,
threonine, aspartic acid, lysine, gamma amino-
butyric acid, asparagine and serine within 72
to 96 hours. After attaining this peak concen-
tration they began to decrease so they were
present in subnormal concentrations after 192
hours. Glutamine followed the same pattern
except that it attained a much higher peak
and within a shorter period after inoculation
of the virus. Apparently there is some mechan-
ism of nitrogen assimilation triggered by the
virus before it begins to multiply much less
create symptoms. As soon as the virus begins to
multiply, the concentration of amino acids
declines. The mechanism by which these
changes are implemented is imperfectly un-
derstood and obviously justifies much more
investigation if we are to understand the
physiological basis of pathogenesis by viruses.







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Within the past five years the scientific
world has come to understand much more
about the virus particle itself. Dr. Magdoff
has been studying the physical properties of
southern bean mosaic virus by X-ray diffrac-
tion. Interest is being directed primarily to-
ward the spatial relationship of nucleic acid to
the protein and to the packing of subunits of
the virus in crystals. We now know that
viruses may be degraded by removing nucleic
acids and can be restored to activity by re-
combination of these two components, so
studies of this sort become extremely im-
portant.
There is no more exciting area of research
than these on virus proteins. The very basis of
life is involved in the studies on ribonucleic
acid and protein synthesis. In due season, as
techniques are perfected on viruses, one may
expect such studies to be extended to the
mechanisms of heredity. Far in the future the
redesigning of chromosomes by chemical
methods far more advanced than the primitive
use of colchicine today to induce polyploidy.

THE MECHANISM OF ACQUIRED RESISTANCE
OF INSECTS TO INSECTICIDES

One of the serious problems facing the
agriculturist is the tendency of insects to ac-
quire resistance to insecticides. For example,
greenhouse operators have found that red
spider mites develop resistant populations
within a few months to two years after a new
chemical is introduced. In the past decade
they have run through five new chemicals
that were found only by a tremendous invest-
ment in funds and research time. The mites
are so tiny that we have not had the courage
to begin a study of them. There are equally
interesting cases of resistance in houseflies,
mosquitoes, flea beetles, lice, etc., that can be
used. Currently our people are working on
the resistance of houseflies to chlorinated hy-
drocarbons since they present an excellent
subject for study on the comparative biochem-
istry of resistant and susceptible populations.
By use of pure culture techniques to avoid
microbiological contaminants, paper chroma-
tography to separate and measure cellular
components such as amino acids, and use of
Geiger counters to follow the pathway of
metabolism of unstable atoms such as S"' we


are obtaining considerable information on
what happens when an insect becomes resist-
ant.
Dr. Moorefield has continued studies which
he began while he was a student at the Uni-
versity of Illinois. The flies resistant to DDT
have a new type of enzyme known as dehydro-
chlorinase. This material makes it possible for
the insect to detoxify the chemical by remov-
ing HCI from the molecule. The enzyme does
not require a metallic constituent to activate
it and appears to be a specific sulfhydryl type
of material. Within the past year, Dr. Moore-
field has shown that the ability to produce
this enzyme is latent in the larvae of an ordin-
ary population of DDT-susceptible insects but
probably does not occur uniformly in all in-
dividuals. When larvae are exposed to DDT
only those with exceptional ability to generate
this enzyme mature. Because of this, the re-
sistant adults have demonstrable quantities of
dehydrochlorinase while comparable suscepti-
ble insects do not.
It is perfectly obvious that we need to know
more about the metabolic processes of insects
which permit them to detoxify chemicals or
develop alternate metabolic pathways to es-
cape the lethal effects of insecticides. Since
sulfhydryl compounds allegedly play such an
important role, Dr. Cotty and Dr. Hilchey
have been studying sulfur metabolism. Con-
trary to ordinary beliefs that animals must ob-
tain their sulfur from organic materials in
plants, these investigators have demonstrated
that insects can convert sulfates into sulfur
amino acids. By use of paper chromatography
to separate the various acids and measure their
concentrations and by feeding sulfates and
other materials labelled with S' they have
been able to trace the process in aseptically
reared cockroaches and houseflies. The sul-
fates are converted into methionine and the
methionine is changed into cystine through an
intermediate cystathionine. The cystathionine
seems to serve as a unidirectional regulant
since cystine cannot be converted back into
methionine. The cystine may be converted into
taurine and excreted as such.
Preliminary evidence indicates that some re-
sistant houseflies have exceptional ability to
synthesize glutathione but further research
along these lines will be required to establish
the point.





McNEW: PLANT RESEARCH


THE PROCESSES OF ABSCISSION FORMATION
One of the very vital processes in plants is
the ability to shed leaves and blossoms. The
process depends upon the formation of an
abscission layer of cells at the base of the
leaves or blossoms but beyond this knowledge
very little is known. We know that many plant
disease agents produce a biochemical change
that causes diseased leaves to fall so one may
assume that chemical messengers are involved
in abscission cell formation. Since we know so
little about the chemical stimuli we have very
imperfect control over defoliation of cotton to
facilitate picking or removal of leaves from
nursery stock to improve its storage qualities.
Neither do we know how to prevent shatter-
ing of foliage from forage legumes, or loss
of leaves from diseased plants and blossoms
from cut flowers such as the rose.
Sometime ago we set out to design a new
type of heterocyclic sulfur fungicide. We
failed completely insofar as making a fungicide
was concerned but we did notice that some of
the compounds had ability to cause the leaves
to drop from beans. Over a period of two
years we have synthesized a variety of related
compounds and succeeded in developing a
new class of defoliants that can be applied
either through the roots or directly to the
foliage.
The remarkable thing about these new
materials is that thev cause a simple physio-
logical defoliation without burning or distort-
ing the leaves. As a matter of fact they dupli-
cate the natural processes of leaf shedding
almost precisely. A couple of days after the
material is added to soil the innermost leaves
begin to change color. Some members of the
series cause the leaves to take on a red tinge,
then become yellow and finally drop from
the plant. Defoliation proceeds steadily out-
ward and upward until the entire plant is de-
foliated. If the plant is held for several weeks
it completes its dormant period. New buds
break forth and the plants resume normal
growth. These materials offer such a wonder-
ful opportunity to study the biochemistry of
defoliation that we were prompted to organ-
ize a study of defoliation by natural processes,
freezing and chemicals.
Dr. Plaisted has found that within a matter
of a couple of days after a defoliant is applied


to cotton, the number of free amino acids in
the petiole increases from three to about
twelve. A similar phenomenon has been ob-
served in the leaves of deciduous trees in the
fall and Dr. Weinstein found that rose petals
undergo an increase in soluble nitrogen after
cutting. This promising lead suggested that the
first stage in abscission formation is the stim-
ulation of amino acid production and that
these amino acids would facilitate formation of
new cells in the abscission layer.
Unfortunately the story on abscission will
not prove so simple. A careful study of the
total nitrogen balance indicates that the amino
acids are the result of senescence in which
proteolysis occurs rather than the incitants of
a .new process. However, we do have one fas-
cinating lead in Dr. Plaisted's work. He has
found an active principle in shattered blos-
soms that causes abscission of foliage in nor-
mal healthy plants. Studies are underway to
isolate this factor and learn more about its be-
havior. The significance of this research to
date is that we are building up a set of ex-
perimental procedures for regulating and
studying this vital, but very seriously neglected
field.
THE REGULATION OF PLANT GROWTH
If studies such as those described on the
fungicides, viruses, insecticides and foliage
abscission seem far-fetched, unrealistic and not
likely to ever produce significant practical re-
sults, I would like for you to bear with me a
moment while we outline the consequences of
another basic research program. About 25
years ago the Institute assigned Dr. Zimmer-
man and Dr. Hitchcock to a study of how
plants grow. They were free to study any
aspect of plant growth and differentiation that
appealed to them. Their attention was grad-
ually focused on methods of altering the nor-
mal balance of growth hormones or chemical
stimuli in plants by adding chemicals to the
plant.
From this research there came knowledge
on the use of ethylene gas to anaesthetize cells
or regulate maturation processes in cells, and
root-inducing substances that have been use-
ful in plant propagation. Interest in indole and







FLORIDA STATE HORTICULTURAL SOCIETY, '1956


naphthalene compounds led to a study of
other types of acids, especially chlorinated de-
rivatives of benzoic acid and eventually to
aryloxy acids such as 2,4-D. By 1941 they
had described the selective growth regulant
ability of 2,4-D and opened the doors to a
new era in weed control and the development
of specific growth regulants.
There is no need to dwell upon how the
American public grasped the opportunity to
remove broadleafed weeds from lawns, road-
sides, wheatfields, pastures and cornfields.
Within ten years, consumption of 2,4-D ex-
ceeded 25 million pounds a year. Even more
important was the contagious enthusiasm of
dozens of chemical companies to hunt for
other classes of regulants and selective herbi-
cides and of scores of experiment stations to
employ weed specialists to study the chemical
control of weeds. An entire new profession
sprang up within a decade. A national society
and four regional weed control conferences
were organized so thousands of scientists meet
annually to discuss progress and plan for the
future. This probably has been the most pro-
gressive and dynamic branch of agricultural
science in the past two decades.
Peculiarly enough, 2,4-D came into exist-
ence because someone was interested in
growth processes. These men were not as-,
signed to work on weed control. There is good
reason to believe that they might never have
discovered such a material had they been told
that they were to study weed control because
they would have had no background, either
from experience or literature knowledge to
suggest that selective growth regulants should
have been used. If ever there was an example
to show how science makes its big steps for-
ward, this is one.
Science needs depth and breadth of under-
standing. The men of science must dig be-
neath the surface to find more than meets their
eyes. If research projects are defined so speci-
fically that scientists must follow narrow,
rigidly prescribed objectives, their effective-
ness will be minimized because it is these big
steps forward that clear the way for the work-
men of science to build a new house of knowl-
edge. Let us look at four rooms in the 2,4-D
house to see what has happened since 1941.


The 2,4-D molecule has three significant
features. These are the two chlorines on the
benzene ring:
-CH2COOH





Cl

the oxygen linkage between the ring and acid
groups, and the free carboxyl group. Explora-
tory research has indicated that the oxygen
link may be replaced with nitrogen to give a
weaker class of regulant but so far nothing
of practical significance has developed in this
area.
Study soon showed that the halogens played
very dominant roles. The chlorine para to the
oxygen was found to be indispensable but the
ortho chlorine could be eliminated or replaced
by a methyl group to give a compound only
slightly less effective. However, when a third
chlorine was added to one of the free positions
a gamut of effects was obtained. A chlorine
in the 8-position to give the 2,3,4,-trichloro
compound has very little effect on regulant
ability. When added in the 6-position so both
positions ortho to the oxygen are blocked, the
compound is essentially inactive. When the
chlorine is added in the 5-position to give
2,4,5-trichlorophenoxyacetic acid there is a
slight diminution of regulant activity for some
plants and an increase in the caustic or lethal
effect on others. This new compound will
destroy raspberries and woody plants that are
very resistant to 2,4-D. This was the first major
step forward and has been tremendously im-
portant in brush control on ranges and farm
pastures.
The next step came from a study of the car-
boxyl riuphiipii McNew and Hoffman found
in 1946 that the acid group could be converted
,to a salt, amide or ester without d ir, ,\-
ing activity. In other words the 0-C--OH
group could be changed without d. str, .iii,
regulant ability provided a free carbonyl
(C=0) grouping remained. This fact was ex-
ploited fully in the next few years by three
lines of development. The -\,l. tii t of the ma-
terial was reduced so it would be less hazard-





McNEW: PLANT RESEARCH


ous for use around valuable susceptible plants
by converting it to metallic or other salts. The
acid was rendered readily dispersible in water
by converting it to the very soluble triethano-
lamine salts. Finally, it was converted to one
of the esters which were more effective in
the arid western areas than the salts because
of their volatility and lipid solubility proper-
ties.
The third change came from further studies
in the Institute laboratories on 2,4-dichloro-
phenoxyethanol and its sulfate ester. Dr. King
found that these materials were essentially in-
active on plants normally susceptible to 2,4-D.
Thus the replacement of the free carbonyl
group by a hydroxyl group was fatal to the
herbicidal activity. The project might have died
at this point had he not noticed that the ethyl
sulfate ester, since named Crag Herbicide I,
would prevent germination of weed seeds
when it was sprayed on the soil. He showed
that the compound was activated into a herbi-
cide by ordinary soil but not by steam steri-
lized soil. It remained for Dr. Vlitos to show
that Bacillus cereus var. mycoides, a common
soil bacterium, produces a sulfatase enzyme
that removes the sulfate radicle. Other bacteria
in the soil oxidize the resultant ethanol deriva-
tive to 2,4-D acid. Thus soil microorganisms
can generate 2,4-D in the soil in sufficient
quantities to kill weeds. This is a safer, more
selective type of compound than 2,4-D. By
extending this principle to other analogues of
the phenoxy-ethanol series a whole comple-
ment of new compounds is being evolved that
can be used to destroy weeds in fields of such
sensitive crops as tomato.
The fourth development came from study-
ing the effect of increasing the length of the
carbon chain in the acid. Dr. Wain of England
has confirmed earlier observations by Syner-
holm and Zimmerman that 2,4,-dichloroary-
loxy compounds with an even number of car-
bon atoms in the side acid are more toxic than
the compounds with an odd number. This has
been shown to be due to the ability of plants
to metabolize this part of the molecule by re-
moving two carbons at a time to convert the
material back to 2,4-D. Because of this 2,4-
dichlorophenoxybutanol may be converted
into 2,4-D by some plants. Peculiarly enough,
the legumes such as peas and alfalfa do not
have this ability so the butanol derivative does


not hurt them even as it destroys wild mustard
and other weeds growing in pea or alfalfa
fields.
These four developments within the first
decade of the 2,4-D era show what can be
done by the ingenuity, curiosity and alertness
of scientists once they are given a new tool to
work with. Of course these four achievements
stand out like brilliant gems of intellectual at-
tainment but one must remember the tens of
thousands of hours of patient research and
hundreds of ideas that failed. They are the
overhead that must inevitably be paid for
every advance in research.

SUMMARY
We have foraged far afield in our discussion
here today. Some of you may be confused by
the complexity of the details as to chemical
structures or the nature of cell activities. You
have my humble apologies for overburdening
you. However, the details are not too import-
ant. They are nothing more than illustrations
of the basic principles we have been eluci-
dating. If you can leave here with a positive
impression as to the general principles in-
volved we will feel that all the hours spent in
preparation and travelling down here were
well spent. Let us look at these principles.
Principle 1. The scientific agriculturist is
turning his attention from exterior considera-
tions to a study of cell metabolism. This new
trend is absolutely necessary if we are to make
systematic progress in the future. Remember,
the person who can control the operation of
cells can determine the fate of the individual
plant, the disease agent, the insect, etc.
Principle 2. It is possible to design mole-
cules to do almost fantastic things to a cell.
Although our knowledge is in a most primi-
tive state there is a great gleam of light shin-
ing down upon us. It is possible to design mole-
cules that fit like the key in the lock of cell
morphology and physiology. Molecules can be
made to penetrate one type of tissue and not
another, to change cell permeability, to enter
into different metabolic pathways, and even
to differ in their stability and reactiveness. Re-
member that the future will see new kinds of
molecules in the garden. They will take the
place of insects, diseases and weedy plants
and make plants rebel at their own genetics.







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Principle 3. The type of basic research that
must be pursued in this great development
does not come easily. It takes time, patience
and many, many dollars. It is necessary that
every one of us understands this and encour-
ages it. Men must be encouraged to seek basic
principles of life processes so investigators
such as themselves can use intelligence in
creating new processes of farming and new
products. The scientist who operates from a
sound set of basic principles is efficient, ef-
fective and adaptable. Without these principles
he must experiment by blind probing. Even-
tually blind research becomes too expensive to
support because of the low rate of progress.
Principle 4. There never was a time when
biologists had better research tools at their
disposal than today. The things that can be
done in a-most routine fashion simply were
not dreamed of twenty years ago. There is a
certain measure of hazard to the tremendous


technological strides of our lifetime but the
long range view is that more good will come
from it than harm. People will be fed better,
clothed warmer, and housed more satisfactori-
ly because of scientific progress. We are con-
fident that the future is brighter for having
knowledge of the atom even though it may
do great damage in the hands of a moron or
a moronic society.
Before every scientist there is an opportunity
to serve as never before. There are available
new tools, more money, and more challenge
than ever before. If this nation and its demo-
cratic processes are to continue strong, healthy
and progressive its security will come through
skillful use of every mental and physical re-
source at our command. Therefore it is not
only a privilege to be a scientist in such a
great era; it is a moral obligation to serve
skillfully and progressively with the long
range viewpoint uppermost in our minds.


THE MEDITERRANEAN FRUIT FLY

ERADICATION PROGRAM

IN FLORIDA


ED L. AYERS, COMMIISSIONERI
State Plant Board of Florida
Gainesville

G. G. ROWER, AREA SUPERVISOR
U. S. Department of Agriculture
Lake Alfred
Modern warfare against a major agricultural
insect-enemy in Florida has come into its own
in the present Mediterranean Fruit Fly Erad-
ication Program. The combination of aircraft
and improved chemical control procedures,
supported by an intensive inspection program,
has beaten the fly back and should effect com-
plete eradication within a matter of months.
More than 25 years ago this same insect in-
vaded Florida and was eradicated after a long
and expensive fight that exhausted 18 months
in time and $7,500,000 in state and federal
appropriations. That was a campaign that
created a great deal of criticism with its poli-
cy of destroying all host fruits and vegetables.


In addition, the arsenic used in spraying host
plants did much damage to those plants and
trees.
That was modern warfare in those days-
utilization of the best known methods of erad-
icating a fly that had seriously affected fruit
and vegetable production in other parts of the
world. Regardless of procedures followed the
outcome was the successful eradication of the
Medfly, the only time in agricultural history
that this insect had been eradicated from any
country.
The present campaign against the Medfly
began only a few days after a Miami resident
reported to the Dade County Agent's office
that larvae had been found in a backyard
planting of grapefruit. Tentative identification
of the larvae as that of the Medfly was made
by state and federal laboratories, and the posi-
tive identification followed the receipt by these
same laboratories of fly specimens trapped in
the Miami area.
The early weeks of the campaign could not
have been much different from those of the






AYERS: MEDITERRANEAN FRUIT FLY


first fight, for the methods were very similar.
Until research men could formulate an effec-
tive program, the eradication plan moved along
the old lines of destruction of host fruits and
vegetables and the ground spraying of host
plants and trees.
Today, however, the modern idea is the
use of chemical control procedures tested and
approved in other campaigns against the same
fly. In this instance, the testing ground was
Hawaii, where the Medfly is only one of
three major fruit fly threats. The Florida
fight has offered the first complete test for
these chemicals and procedures.
Within two weeks after the initial find a
network of traps had been cast over the state
in an effort to delimit the infestations; and the
malathion spray formula, involving a protein
hydrolysate bait, had been given its first test
in the heavily infested areas of Miami.
When fly catches disclosed that the infes-
tations were more widespread in Florida than
at first thought, spraying took to the air with
the employment of aircraft equipped for this
purpose. These aerial applications marked the
real break with the past and the time-con-
suming procedure of destroying host fruits and
vegetables was discarded.
The spray mixture of malathion, an organic
phosphate, and a protein hydrolysate bait
proved successful under Florida conditions.
Malathion, used in the form of 25 percent
wettable powder, was selected for the pro-
gram because it possesses the lowest mam-
malian toxicity of any effective toxicant avail-
able for Medfly control.
The theory of aerial application of insecti-
cides has been applied to the program and
proved an unqualified success as evidenced by
the fact that the Medfly apparently has been
eradicated from almost half the state's 27 in-
fested counties within the space of six months
and insecticidal treatments discontinued. To
accomplish this malathion bait sprays, through
October, have been applied to 750,000 acres
one or more times. The repeat treatments to
this acreage have accounted for the treatment
of more than 5,000,000 acres. Dieldrin sur-
face treatments have been applied under host
plants to 28,000 acres.
During the early months malathion was
utilized at the rate of one-half pound of toxi-


cant per acre, but this dosage has been cut
to approximately three-tenths of a pound in
recent months.
The attractant first used in the mixture was
an enzymatic protein hydrolysate from brew-
er's yeast or casein, employed at the rate of one
pound per acre. Later a less expensive attract-
ant, an acid hydrolysate of corn protein in
liquid form was used at the rate of one quart
per acre. Only one pint of this liquid attractant
now is used, mixed with three-tenths of a
pound of actual malathion and enough water
to compose one liquid gallon of mixture. This
spray is applied at the rate of one gallon to
an acre.
In the early stages of the campaign the
spray was applied at 10-day intervals in order
to kill each new generation of the fly. This
schedule was set up on the basis of a normal
life cycle of approximately 30 days. In a
breakdown of this cycle, roughly 10 days each
are allotted to the larval and pupal stages, and
the period required before the female fly be-
comes sexually mature enough to lay eggs.
The eggs hatch in one to two days.
The purpose of the 10-day spray schedule
was to kill the immature fly in the pre-ovi-
position period. The use of dieldrin for the
treatment of soil surfaces is designed to kill
the larvae leaving the fruit to enter the ground
to pupate, and also kill adult flies emerging
from the soil. Dieldrin granular 30-40 mesh is
applied at the rate of 50 pounds of 10 percent
material per acre, or approximately five pounds
actual dieldrin per acre. The material is ap-
plied to the soil under host fruits.
When the infestations persisted in some
limited areas after several months of spraying
field inspections disclosed that some adult
flies were appearing in traps after the 30-day
life cycle period. Some of this occurrence was
attributed to heavy showers, but research
proved that the fly larvae were still alive and
active in over-ripe guava drops 19 days after
the first spray. Larval development was de-
layed to approximately 21 days in over-ripe
mango drops and as long as 25 days in some
mummified grapefruit, sour orange, and tan-
gerine shiners. This prolongation of one stage
in the reproduction process meant a greatly
extended life cycle which had to be com-
pensated for through extending the bait spray
treatments.








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Spray applications have been cut to seven-
day intervals in recent months and the possi-
bility of flies escaping the poison spray re-
duced to an infinitesimal point. Effectiveness
of the spray has been attested to by recent
findings which disclose an exceptional drop in
the fly populations in the state. Twelve coun-
ties have been released from the aerial spray
program, and two others are scheduled for
release in the next two weeks. In addition,
four of these counties no longer are subject to
fumigation regulations for fruits and vege-
tables originating in those counties.
The decrease in fly finds is more than en-
couraging in the light of trapping reports.
During the summer months when the fly ap-
parently was making most headway, the field
total never exceeded the August figure of 18,-
000 traps. Finds at that time were numbered
at more than 2,000 flies. That was listed, as
encouraging in the light of 5,000 finds from
4,000 traps in June. But even more progress is
noted in the latest figures which disclose less
than 600 finds from 48,000 traps.
Effectiveness of the trapping operation was
increased by the improvisation of a new type
of trap designed by a research entomologist
with the program. This trap is a horizontal
plastic model open at opposite ends.
The principal attractant used in the trapping
operation is oil of angelica seed, which is
mixed with a poison, three percent DDVP
(Dimethyl Dichloro Vinyl Phosphate). Chlor-
dane or DDT powder is dusted in the dry
traps to kill ants that might remove the flies.
One of the important parts of the program,
the roadblock, has been discontinued as a re-
sult of the sharp drop in fly infestations.
The system of roadblocks was established
in the first weeks of the program and con-
tinued until last month when vehicular in-
spections were considered no longer necessary.
Check points were set up around heavily in-
fested areas to protect other parts of the state
from equally as heavy infestations.
In five months of operation the roadblock
inspectors checked more than 4,000,000 ve-
hicles and confiscated many tons of host fruits,
vegetables and plants. This was of inestimable
value to the eradication program, since it was
established beyond a doubt that the fly moved
to other points in the state along well-traveled
highways. This movement paralleled that of


vehicular traffic. It is impossible to estimate
how far and how fast the insect would have
traveled without roadblocks to halt that pro-
gress.
Complete eradication of the Medfly is the
aim of the program and must be accomplished
in order to protect the agricultural interests of
Florida and of the United States.
The use of dieldrin for soil applications and
of malathion for foliar treatment has per-
mitted Florida to move practically all fruit and
vegetable crops to date. That is in sharp con-
trast to the first eradication program in which
host fruits and vegetables were destroyed.
In short, the present program is eradicating
the fly and permitting the marketing of com-
modities under almost normal circumstances.
In this, fumigation has played an extremely
important role and will continue to play that
role until the Medfly has been completely
eradicated. EDB (ethylene dibromide) is
used to fumigate citrus and other host fruits
and MB (methyl bromide) many host vege-
tables. Both gases are used in specially con-
structed or modified gas-tight fumigation
houses equipped with special air circulation
and gas volitization equipment. At the end of
October more than 175 fumigation chambers
had been approved for use in the Medfly pro-
gram in connection with fumigating material
regulated on account of the Mediterranean
Fruit Fly Quarantine. In addition, 37 fruit
processing plants had so modified their pro-
cessing procedures to permit them to handle
the regulated fruit without endangering fur-
ther spread of the Medfly.
Presence of the Medfly in other countries is
marked by increased cost and reduced pro-
duction. This is especially true in lands around
the Mediterranean Sea where the European
and Mediterranean Plant Protection Organiza-
tion has set up a committee to study the fly
and its control. Last meeting of this body was
held in September of this year at Bonn, Ger-
many. Since no eradication program has been
devised in that part of the world, the emphasis
was on fumigation and physical controls.
Germany, incidentally, is vitally interested
in the fly, since the pest has been prevalent
there since 1954. The Medfly was first dis-
covered there in 1936, but did not appear in
damaging proportions until last year. Imported
fruit is believed to be the cause for the in-






AWARD OF HONORARY MEMBERSHIPS


festations, since the winters in Germany are
considered severe enough to eliminate local
incidences of the fly. Nevertheless, the peach
crop in Germany has been infested in particu-
lar cases to 100 percent, enough to affect the
national economy. Apricots, apples, pears, and
tomatoes also have been infested in that coun-
try.
Peaches grown in Egypt also have been 100
percent infested when no control is applied;
certain parts of Brazil no longer export citrus,
and Spain ships only early varieties of citrus
which must be marketed before ripening prop-
erly.
Reports of this kind emphasize the fact that
the Medfly must be eradicated from Florida.


Although the program is many months away
from that successful conclusion, there is every
reason to believe that eradication will be ac-
complished within the space of one year. The
program is being financed by state and federal
governments, with each appropriating an
equal half of the over-all eradication fund of
$10,000,000. That is a small figure on the
basis of the present day dollar value when
compared with the cost of the first fight.
The cooperation of personnel of the Florida
Department of Agriculture, State Experiment
Stations, other civilian and military govern-
mental agencies and the general public has
been of inestimable value to the eradication
program.


AWARD OF HONORARY MEMBERSHIPS


LLOYD STANLEY TENNY
Lloyd Stanley Tenny was born near Hilton,
N.Y. eighty years ago this month and was
reared on a farm. He received his A.B. Degree
from the University of Rochester in 1902,
served as Assistant Pathologist with the U. S.
Department of Agriculture from 1902 to 1904,
as Assistant Pomologist 1904 to 1907 and as
Pomologist for the U.S.D.A. until 1908 when
he returned to Cornell for further study. From
1911 to 1913 Mr. Tenny was with Cornell's
Agricultural Extension Department, being ad-
vanced to Professor of Extension. He was the
first state leader of county Agricultural Agents
in New York and helped organize the first
Farm Bureaus.
Mr. Tenny was Secretary-Manager of the
Florida Growers & Shippers League from 1913
to 1916, Secretary of Florida East Coast As-
sociates 1916-17, and Secretary-Treasurer of
the Coral Reef Nurseries from 1917 to 1918.
Mr. Tenny was Vice President of the East-
ern Fruit and Produce Exchange of Rochester,
N. Y., and of the North American Fruit Ex-
change of New York City and president of
the Southern States Produce Distributors from
1918 to 1921. The Bureau of Agricultural
Economics called him as Assistant Chief 1921
to 1926 and as Chief in 1928. He was Vice
President of the California Vineyardists As-
sociation in 1928-29; President of the Federal
Fruit Stabilization Corporation of California


1929-30; and General Manager of the Chicago
Mercantile Exchange from 1929 to 1943 when
he retired. He is now living in Henderson-
ville, North Carolina.
Few men have so profoundly influenced
Florida Agriculture in five short years as did
Mr. Tenny. He was one of the BIG FIVE
(consisting of P. H. Rolfs, H. Harold Hume,
W. J. Krome, Wilmon Newell and Lloyd S.
Tenny) who played a tremendous part in
Florida Horticulture. Mr. L. B. Skinner (for
years President of this Society) brought Mr.
Tenny to Florida to organize the Grower's and
Shipper's League in 1913. Soon thereafter Dr.
E. W. Berger took to his office samples of
Citrus Canker because Mr. Tenny had been a
Pathologist. Mr. Tenny recognized it as a very
serious threat and "sold" the Florida authori-
ties on the idea that eradication would be
cheaper in the long run than control. How
right he turned out to be!!!
Soon, the eradication of Citrus Canker was
made the number one objective of the Grow-
er's and Shipper's League because Florida had
no department in its government which could
undertake it, no funds and no law. Just
imagine!!! Mr. Tenny threw himself into the
fight with all of his tremendous energy, skill,
knowledge and resourcefulness. He whipped
together an organization, raised the finances
and together with others of the BIG FIVE
drew up and secured the passage of the
"FLORIDA PLANT ACT OF 1915." Having






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


secured the law that was necessary, he helped
the others select the "PLANT COMMISSION-
ER" Dr. Wilmon Newell; the "State Nursery
Inspector" and the "Port Inspection Depart-
ment," which in cooperation with the U.S.D.A.
was responsible for the inspection of all plants
entering the State from foreign countries.
Having helped make the Plant Board a go-
ing concern, Mr. Tenny turned his attention
to the task for which he had been brought to
Florida, that of getting better rail rate sched-
ules for Florida growers and shippers.
It is not too much to say that but for the
timely arrival of Mr. Tenny the Florida citrus
industry might very easily have been wiped
out by Citrus Canker. Like all other members
of the BIG FIVE, Mr. Tenny was a giant.
The Florida State Horticultural Society takes
pleasure in making Mr. Lloyd Stanley Tenny
an Honorary Member and regrets that the
state of his health requires that it be in ab-
sentia.

ARTHUR FORREST CAMP
Dr. Arthur Forrest Camp came to Florida
from California in 1923, and during the en-
suing thirty-three years has compiled a record
of service to horticulture equalled by few-
surpassed by none.
He graduated from the University of Cali-
fornia with honors in 1920; and was awarded
his Doctor's Degree in 1923 by Washington
University, St. Louis, Missouri, and immedi-
ately started on a career that was to be de-
voted not only to horticultural advancement
in Florida but to advancement on an interna-
tional scale.
From 1923 to 1929 Dr. Camp served in
several important research positions with the
Florida Experiment Station at Cainesville, and
in 1929 was made Horticulturist In Charge,
Department of Horticulture. This same year
he was made an agent of the U.S.D.A., and
played an outstanding part in the eradica-
tion of the Mediterranean fruit fly. In 1930 he
returned to the Experiment Station and served
as head of the Horticulture Department until
1936 when he became Horticulturist In Charge,
Citrus Experiment Station. Since 1944 Dr.
Camp has served as Vice-Director, Agriculture
Experiment Stations, in charge of the Citrus
Experiment Station. He personally carried on
research until 1944, and under his guidance


the Citrus Experiment Station has grown in
both size and stature until it now occupies
and enjoys an outstanding position in the field
of horticultural research.
Dr. Camp has over one-hundred publications
on citrus and other tropical and sub-tropical
crops. Some of these publications, especially
those dealing with the fertilization and nutri-
tion of citrus have been and are being used
as guideposts in production management. His
development of a coordinated system of spray-
ing and fertilizing citrus is in a large measure
responsible for the tremendous per-acre pro-
duction citrus growers now enjoy as com-
pared to the 1930s. The development of such
a program has been worth untold millions to
the citrus industry, as it has enabled growers
to maintain a rather uniform per-box cost over
the last twenty-five years while per-acre costs
have gone steadily upward.
As an agent of the Florida Citrus Commis-
sion, Florida Citrus Mutual and the Florida
State Plant Board, Dr. Camp has been called
upon for fact-finding trips to South and Cen-
tral American countries, Spain, Japan, Cali-
fornia, and Texas. His reports following these
trips enabled the various agencies to formulate
plans to protect and promote citrus in Florida.
He is considered the citrus industry's outstand-
ing spokesman on technical subjects, and has
been called on many times to state the indus-
try's case before legislative committees of both
the State and Federal governments.
Dr. Camp has done consulting work on
Citrus production, marketing and processing
in many foreign countries for governments,
companies, cooperatives, and individuals -
including Cuba, Jamaica, Haiti, Honduras,
Nicaragua, Costa Rica, Guatemala, Argentina,
Brazil, Paraguay, Peru, Surinam, Bermuda,
Mexico, Sweden, Spain, and Japan. He was
made an Honorary Citizen of Argentina in
recognition of assistance given the citrus in-
dustry in that country.
Dr. Camp was instrumental in setting up
and carrying out research into the tristeza
problem, a new disease that posed a threat
to Florida citrus and one that decimated many
groves in South America. Thanks to this work
tristeza no longer poses the threat that it once
did.
Dr. Camp is an honorary member of the
Kiwanis Club and Gamma Sigma Epsilon,





AWARD OF HONORARY MEMBERSHIPS


and a member of the Florida State Horticul-
tural Society, American Society for Horticul-
tural Science, American Association for the
Advancement of Science. He is in American
Men of Science, Who Knows-and What and
Who's Who in American Education. He is a
grove owner, and the president of the Haines
City Citrus Growers Association.
It is with tremendous pleasure that the
Florida State Horticultural Society recognizes
the great service that Dr. Camp has rendered
to the horticulture of the State of Florida and
other countries and his leadership in the field
of citrus research that has been largely re-
sponsible for the enviable position the Florida
Citrus Industry holds today.

HAROLD G. CLAYTON
It is a great privilege to present to the
membership of this Society a distinguished na-
tive Floridian who has, by unanimous vote
of the Executive Committee, been designated
to receive an Honorary Membership in the
Society.
Harold G. Clayton was born February 27,
1892, at Ocala, Fla. He grew up and attended
public schools in Tampa; received B.S. Degree
in agriculture from University of Florida in
1914; received M.S.A. Degree from same in-
stitution in 1916. After a brief period of farm
work he was made County Agent in Manatee
County, in March 1917. He entered military
service in World War I on May 15, 1918 and
served until December 6, 1918. Early in 1919
he returned to county agent work and in
October 1919 he was made District Agent
with the Agricultural Extension Service at
Gainesville. He continued as District Agent
until November 1934, at which time he was
asked by the Director of the Extension Service
to assume administrative direction of the
Agricultural Adjustment Administration, later
the Production and Marketing Administration,
and now Agricultural Stabilization and Con-
servation Committee. He served in this posi-
tion until July 1, 1947. During this period he
continued to hold a cooperative appointment
with Extension Service. On July 1, 1947 he
was made Director of the Florida Agricultural
Extension Service, the position he held until
May 31, 1956 when he retired.
H. G. Clayton married the former Miss
Harriet Ray, of Tampa. The Claytons have


one child, Peggy, who is now Mrs. Peggy
Clayton May, and two grandchildren.
As Secretary to the State Agricultural Ad-
justment Administration Committee, a mem-
ber of the State Defense Council, Chairman
of the State USDA War Board during World
War II, he rendered outstanding service to
Florida agriculture by arranging for the pro-
curement and proper distribution of vital
agricultural supplies and by stimulating farm
people to extraordinary effort in war crop
production, in buying U.S. War Bonds, in
salvage drives, and in other activities con-
nected with the war effort.
Through his knowledge of Florida agricul-
ture, his careful study and understanding of
the functions of all agencies concerned with
agriculture, and his persistent efforts to work
in close harmony with all agencies and groups,
he has been instrumental in bringing about
effective working relationships between these
agencies and groups for the maximum service
to Florida agriculture and the solution of
major agricultural problems.
While serving as district agent, he was ac-
tive in promoting 4-H Club work and in co-
operation with the state 4-H Club agents he
helped to start the state's 4-H camping sys-
tem, which today is outstanding in the Nation.
From 1947 he served as Administrator to
the State Soil Conservation Board. He was
appointed to this position by two different
boards since the State Soil Conservation
Board was completely reorganized by the 1953
Legislature.
He served as Chairman of the State Seed
Certification Advisory Committee.
He was a member of the Farmers Home
Administration State Advisory Committee.
He was a member of the State Agricultural
Stabilization and Conservation Committee.
He collaborated with Florida Forest Serv-
ice and Soil Conservation Service in a weather
modification evaluation study.
During his service as Director of the Flori-
da Agricultural Extension Service the number
of county agents increased from 61 to 66.
(Florida has one county which is not classi-
fied as an agricultural county.) The number
of assistant county agents has increased from
18 to 54; the number of home .demonstration











FLORIDA STATE HORTICULTURAL SOCIETY, 1956


agents from 41 to 52, and the number of as-
sistant home demonstration agents from 9 to
22. The total staff of specialists has been in'-
creased from 14 to 33. Mr. Clayton's wide
knowledge of and service to horticulture in
Florida is reflected again by the fact that this
increase in specialists' services covers every
phase of horticulture in our state.
Mr. Clayton has for many years been a
faithful member of this Society and a regular
attendant and keen observer at its meetings;
learning the needs, problems, views, of people
actually engaged in various horticultural enter-
prises; using his knowledge and his ability to
strengthen and direct the Agricultural Exten-
sion Service for the common good.


Always modest-never once grasping for
spotlight or for front page-devoted to Florida,
her horticulture, her agriculture, her farm
youth-never asking for anything for himself
other than an opportunity to serve others -
always trying to see the other fellow's point of
view. A person whose soundness of judgment
has been recognized by those at the highest
levels in our state government and institutions.
A man who has by both precept and example
rendered outstanding service to this Society
and to Florida horticulture. Always a gentle-
man-a person of highest character-who- has
in every way measured fully to the highest
standards of honorary membership in this dis-
tinguished Society.





COHEN: TRISTEZA DISEASE


CftZL<- Section


INJURY AND LOSS OF CITRUS TREES DUE

TO TRISTEZA DISEASE IN AN

ORANGE COUNTY GROVE'


MORTIMER COHEN
State Plant Board
Gainesville

Soon after the discovery of tristeza in
Florida, it became apparent that careful study
over an extended period of time would be
necessary to assess accurately the amount of
damage done by this disease and to make
predictions regarding future losses. In July
1952, therefore, a large grove near Winter
Garden in which many trees with tristeza had
been found, was mapped tree-by-tree, by a
group of Plant Board inspectors.
In the mapping, trees were rated on the
following scale:
0 -Healthy
1 -Slight decline
2 -Moderate decline
3 -Severe decline
X-Dead or missing
R-Replant tree
Infected trees in this grove are of mature
size and are not stunted. The large size of
the trees and the observable spread of disease
in the planting are taken to indicate that the
disease was brought in by natural means,
probably by aphids, rather than through in-
fected budwood. This is in contrast to the
situation in other parts of the state where
the majority of infected trees apparently had
tristeza virus introduced with the original
bud.

'/The information reported in this paper is not due
to the efforts of a single individual but is the result
of the cooperative work of many individuals now or
formerly on the Plant Board staff. Among the people
whose efforts have materially aided in the collection
and assembly of the data presented in the paper are:
J. N. Busby, K. E. Bragdon, A. C. Crews, L. W.
Holley, Dr. L. C. Knorr, Mrs. Enid Matherly, John
Perry, C. R. Roberts, Mrs. Jean Smith, Howard Van
Pelt.


This grove has been mapped twice a year
since July 1952, the last mapping having
been completed in July 1956. The entire
area included in the study is shown in Figure
1, which also provides a graphic comparison
between the condition of the grove in July
1952 and in July 1956. The entire grove area
consists of about 80 acres. Approximately 20
acres, planted entirely to Temple oranges on
sour orange stock, are not included in our
statistical summary because many trees in
that portion of the grove showed signs of de-
cline from water damage in 1954 and it was
desired to restrict the study, as much as
possible, to the effect of tristeza only. The
remaining 60 acres consists of 4169 trees, of
which 88 per cent are Temples on sour
orange rootstock, mainly 26 to 30 years old.
Also in the grove are 297 Valencia trees on
sour orange stock, about 200 trees on grape-
fruit stock, and a small number for which the
rootstock is undetermined. Properties owned
by 4 different individuals are included in this
60 acre block. It should be stressed that this
is not a neglected planting but that normal
practices of cultivation and fertilization are
being followed.
Figure 1 shows only trees rated 2, 3, X or
R, that is, trees in definite decline, missing or
replanted. Trees rated 1, those in slight de-
cline, are not included, because slight symp-
toms are sometimes due to transient causes
and not to tristeza. This map contrasts trees
affected in July 1952 (shown as O's) with
the large number of additional trees affected
by July 1956 (shown as X's). The many
trees which went into serious decline in the
4-year interval between the 2 mappings can
be clearly seen. All portions of the grove
were not affected equally. Some of the older
areas planted with Temple orange on sour
orange stock were the most severely affected













Fig. 1. Spread of disease in an orange grove near Winter Garden from July 1952 to July 1956. Map shows trees in moderate or severe decline, dead,
missing or replanted. Trees with slight symptoms of decline are not shown. All trees are of the Temple orange variety except for the indicated block of
Valencias.


0 0 000
XO 0
X
(XX XX X0 X
S OX 0 0000
K X X 0
0 X X X XX
XXXX X X
X 0 0
X X
X X X
X XOOXX X
X XX XX 0
X XXOX X X
XXXXXXO
XXX XX OXX
0 X XXOX X
C XXX XXX X
X XXX X
X 0 X
X X


x o
x 0
X 0 0
XX 0
X
XX X 0


X


x x
0 0 X U
0XX XXX O
X X X
0 0 0 0 00 X C
00 0 X
X X X X X X
X 0 0 X X 0


X X X X


X 0 0 X

SXX 0
I X 0 0 XX OX
SX X X
0
X 0 X
SX X 0 K

XX X 0 X
X X XX
XO XX X
X X
K X X


XX X X
X 0 OXX
OXX XXXXOXXX XX 0 0
X XXOXX XXX 00 OX XXX
X 0
( OX XXOOOXXO XXX 0 0
0 X XOXXOXOO X
X I IXXXXXX XOX XXO
XXX X XOXXXXXXX OX XOO
X OXXX X X X 00000

X X XB X XX X 0
X O I X X X 0
So Bar x x o n


X 0


0 X 00
0 0 X liX
0 X
I 0


X x
0 X 0
0 O X X X
K 00 X 0 0 X
XX iXX
1 X
X X X
X X X
X XX XX 0
X OXXX K X
0 00 X
0 000 XX
X X 0 X
OX 0 X00 0
X X XX OX X
X XO X 0
XXX X XX
X X 0
X X
X X X X XO
XX X X XX
X X XX XXO
XX XXX X XOX


0
0


X


XXX
XO X

0
XX




X X
K 0


XX
XXX X
X X X X

XX X XX
X XXX
000 X 0
0 X X


x x
SOX

X X
0 00


x x

XX
X 0
x x


OX 0 0
X XX OX X
xo XXX oX X oox
XXX XOOXO X -00
XX X X 0
OX X X X
XXO X X XXOXX XX O X X
XXX XXX X x
OOXOOX X X X XOXX
OXXO X XXXO XXX XX XXXXX
XX XX XO X XX X XO0
O XXX XX X X XXX X X X 0
XX XOXXXXX XO XXX X
0 XOXXXX 000 XX OX XX
OX XXX X XXX
OXXOOOOX OXXXX 0 XO00
Xox X X XXOX XXO X
XOOO OXXXXX XOX
OOXXX XOOOXX 0 0 X
XOXX XXOOX XXO 0 X X
XXIX XOX0 XXX XXO XX
XOXX X XOO 0 X XX
OXXXXXOX XXXX'OXO X XXXXX
XOXX XXX x Xx
XOX X XX OX XXX XXX
000 OX 0 XXOX


0 X
IX X X 0
0

)X X
X
( XO
0 X0
x

XXX



X X
0
X
X 0 X
X X
X XOX X
O0


3 X
XX

0
X
X
0 0


I0
X


XXX XX
X X


0 X
'00
0000
XX
0 0
X
X
0

XOX

0 0
O XO
OX X


XXXXX
XXOX
XXX
X 0


X 0 X
X
00


X0 X
0 X X
X 0 OX
S0 X X X
XX 0 X X
X 0 XX XX
X X X
X X X
X
X X X 0 X X


X 0 0 OX 0


0 0
X X X X
X 0 X X 0


MAP: 0 Trees in decline, dead, missing or replanted in July, 1952
X Additional trees affected by July, 1956


XX
XX X
0

X


X X

X
X


X 0

0


Cl









COHEN: TRISTEZA DISEASE


but the eastern portion of the area studied
was not as badly affected as the middle por-
tion. Trees in the Valencia .orange block,
which is thoroughly infected with psorosis as
well as tristeza, were not as severely injured,
on the average, as trees in the Temple blocks.
The western-most planting consists of Temple
trees which are approximately 8 years old. A
relatively low proportion of these trees
showed symptoms of decline.
Most striking is the relative absence of
disease in all trees on grapefruit rootstock.
These are located in some of the rows direct-
ly south of the Valencia block. This situation
is discussed below.
The increase in the number of trees in de-
cline from 1952 to 1956 did not come about
abruptly, but was the result of a steady trend,
as is shown diagrammatically in Figure 2
where the number of trees in classes 2, 3, X
and R at each mapping is indicated by a
line graph. Trees in class 1, those in slight
decline, are not included in this graph. The


SFIG. 2


0 I
JULt D.
I1.;2


Tma RTOD 2, 3, X OD R INN *A ORIGE CIWNTY P
rROM JULY X"2 mT JULY P15.


JULY tFE. AUG. IM. AUG. JULY
1953 11% 155 li56


TABLE 1


DISEASED, MISSING, AND REPLANT TREES IN AN

ORANGE GROVE NEAR WINTER GARDEN


NUMBER OF TREES


CLASS OF DECLINE PERCENTAGE
DEAD OR TOTAL OF ALL
DATE SLIGHT MODERATE SEVERE MISSING REPLANTS AFFECTED TREES


July 1952 285 186

Dec. 1952 360 173

July 1953 241 201

Feb. 1954 452 264

Aug. 1954 444 298

Mar. 1955 1540 307

Aug. 1955 393 209

Jan. 1956 433 196

July 1956 385 158


22 19 107


27 100

30 135

37 137


220 137


66 7 346


220 269 479


619

820

874

1125

1312

2266

1321

1382


14.8%

19.6

20.9

26.9

31.4

54.3

31.6

33.1


1511 36.3









FLORIDA STATE HORTICULTURAL SOCIETY, 1956


total number of trees in classes 2, 3, X and R
increased from 334 in July 1952 to 1126 .in
July 1956. Thus 27 per cent of all trees in
the grove were in definite decline or missing,
dead, or replanted by July 1956. If this rate
of increase of diseased trees continues for the
next 4 years, July 1960 will see 46 per cent
of all trees in the grove in this category of
seriously affected trees.
It is interesting also to compare the num-
ber of trees in all classes during the succes-
sive mappings from 1952 to 1956 as shown
in table 1. The major increase in "total trees
affected" during this period is in replant
trees and trees dead or missing, but the num-
ber of trees in intermediate stages of decline
has also remained at a higher level than was
observed during the first two mappings. In
March 1955, a three-and-one-half-fold in-
crease over the previous reading in the num-
ber of trees in slight decline was recorded.
The count occurred after a relatively dry win-
ter. The transient nature of this apparent de-
cline is indicated by the fact that most of
these trees were again rated as healthy in
the subsequent 3 mappings. If one projects
the data in Table 1 to July 1960, and in-
cludes also trees showing slight symptoms of
decline, it will be found that 57.8 per cent
of all trees in this grove will have been af-
fected by the end of 4 more years, provided
the present rate of increase in the number of
trees in decline continues.
What is the evidence that these trees are
suffering from tristeza disease? Numerous
trees have been examined for the presence of
honeycombing-that pattern of tiny holes in
the bark below the bud union which has
proven to be quite reliable in Florida as a
field test for the presence of advanced tris-
teza in trees on sour orange rootstock. A
high proportion of the trees examined have
shown this symptom.
A more specific method for determining if
plants are suffering from tristeza disease is
the histological examination of the bark from
the bud union of suspect trees as described
by Schneider (1). Bark samples collected at
random from 38 trees in decline in the grove
were examined using this method. Of the 33
trees examined, 30 were found to be positive
for tristeza. Six of the histologically tristeza-
positive trees were indexed on key lime
seedlings, and all 6 were found, by the trans-


mission test also, to be carrying the tristeza
virus.
It is interesting to contrast the results of
these histological tests with similar tests made
on trees in the 20-acre area previously men-
tioned as having been excluded from the
study because its trees had suffered from
water damage. Bark samples from 11 trees
in decline in the water-damage area were
examined and 10 of these were found to be
negative for tristeza.
It is quite clear, therefore, that, in the 60
acres under study, tristeza was the major
cause of decline. On the basis of this evi-
dence it can be estimated that upwards of
90 percent of the diseased trees studied were
injured by tristeza disease.
When trees in this grove once begin to
deteriorate, they do not recover, but con-
tinue to decline and eventually die. This can
be seen by observing the fate of trees found
in decline when the grove was first mapped
in July 1952. Figure 3 summarizes the in-
formation on all the trees rated as being in
slight, moderate, or severe decline in July
1952. Of a total of 483 trees in all categories
in 1952, 294 were dead, missing or replanted
by July 1956, and 396 trees or 82 percent
were more seriously in decline than in 1952.
As might have been expected, more of the
trees at first judged to be in slight decline
Fla.
Rtlng in July 1956 of Tres Wtei in Slight, Mocr.te. nd Snever
decline In July 1',52 in a Citrus Grove n.ear Wlrer C ef;.





Improve! Deteriorated
"o y 2 f .. o... ..,.


1952 ; H I- 1! H ,... 19595




- ---^ -- --
I-roved Dt- rriorated

1956 .*
1952 tr e c evere tc1i- n, in 1951




erer-e or oeliaon

Helthy Slight Moderte Severe Dead or R.eplrnted







COHEN: TRISTEZA DISEASE


proved to have been affected by a temporary
condition, and a higher proportion of these
trees showed recovery. If the 203 trees which
were found to be in moderate or severe de-
cline are considered alone, it is seen that 189
trees or 93 percent were more seriously in
decline in 1956 than'in 1952.
The fact that trees in decline generally do
not improve but continue to decline further
is an additional indication that tristeza is
responsible for the condition of the grove. It
is enlightening, in this connection, to com-
pare the fate of trees in that area of, the
grove which was affected by water damage
with trees from an area in which tristeza was
the prime disease factor. In a portion of the
water damage area in August 1954, 274
trees were rated as showing some degree of
decline. Two years later only 22 percent of
these trees showed any deterioration; some
of these, no doubt, were suffering from triste-
za. On the other hand, in a comparable area
in another part of the grove where no water
damage had been noted and where 180 trees
were in decline in August 1954, 52 percent
of the trees had deteriorated by July 1956.
When tristeza was first found in Florida,
most pathologists expected to see a repetition
of the damage done in South America. One
of the warnings issued by pathologists was
to avoid planting citrus on grapefruit root-
stock because it, like sour orange rootstock,
had been found in South America to make
a combination non-tolerant to tristeza. After
extensive examination of Florida citrus groves,
however, State Plant Board inspectors have
not been able to find any trees on grape-
fruit rootstock which were in decline be-
cause of tristeza infection. When the grove in
this study was examined, it was found that
the bud union on about 200 trees had a con-
figuration which indicated that the rootstock
was grapefruit rather than sour orange.
These trees have been watched since 1952
and it is of interest to examine Figure 4
which is a map of the portion of the grove
containing the trees on grapefruit rootstock.
Figure 4 shows both the rootstock and tree
condition in August 1955. Trees on grape-
fruit rootstock are mixed in with trees on sour
orange rootstock thus providing an excellent
comparison of the behavior of trees on these
two rootstocks under identical environmental
conditions. Even a casual examination of


FLO..
CO0DITIO0 OF tio0.S 1N A PLANTING ON NlED SOURI 0RANG
AND CNAP1FRUIT ROOTSTOCKS
AUGUST 1955


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- R"thy
1: Slitt 11-n
R JN..IAN
N Adua.N D~dt,,.
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A D..A NAUun
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Figure 4 will reveal that very few of the trees
on grapefruit rootstock are in decline while
a very high proportion of the adjoining trees
on sour orange rootstock are diseased. Bark
samples were taken from 9 of the grapefruit
trees which did show some sign of decline,
and were examined microscopically. None of
the specimens was found to have histological
indications of tristeza.
These observations do not prove that citrus
trees on grapefruit rootstock cannot be in-
jured by tristeza in Florida, since these trees
may eventually show tristeza injury, but it is
very apparent that grapefruit cannot be con-
sidered to be in the same class as sour orange
insofar as susceptibility to tristeza in Florida
is concerned.
One of the purposes for undertaking the
study of the grove near Winter Garden was
to explore the possibilities for predicting fu-
ture outbreaks of tristeza in Florida. To
carry out this aim, two small plots containing
58 trees in all were set up for special study of
trees on sour orange rootstock. Trees in one
plot had Valencia orange tops, and Temple
orange tops were used in the second plot.
Bark samples have been taken periodically
from trees in these plots and prepared for
microscopic examination. In the course of this
study, 6 previously healthy trees in these
plots have developed histological symptoms
of tristeza. These histological symptoms were
evident from six months to 2 years before
there was any visual indication in the field


" '








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


that these trees were diseased. This confirms
the observations made by Schneider (1) on
trees with quick decline disease in California.
Thus, a tool actually is available for short-
time prediction of future deterioration of
citrus trees from tristeza disease.
Since it is obvious that histological symp-
toms of tristeza must be preceded by en-
trance of the virus into a tree, a number of
healthy-appearing trees were indexed on key
lime seedlings to determine if any of them
were carrying the virus of tristeza. In this
way it was hoped the interval between the
introduction of the virus and the first ap-
pearance of histological symptoms could also
be approximated. This phase of the work has
produced most surprising results. So far, 21
trees in this grove which are histologically
normal have been checked by transmission
test for the presence of tristeza. Of these, 15
trees or 71 percent have been found to be
positive for tristeza. Furthermore, 4 out of 5
trees on grapefruit rootstock which were
similarly indexed proved to be carrying tris-
teza virus although, as previously mentioned,
there is no indication, in Florida, that trees
on grapefruit rootstock are injured by this
disease. If the foregoing sampling of the
trees in this grove can be considered repre-
sentative it must be concluded that about
three quarters of the healthy-appearing trees
in this grove are carrying the virus of tristeza.
The most surprising aspect of this project is
that only one of the trees tested has so far
shown histological signs of tristeza disease,
although a few of these trees are known by
indexing to have been carrying the virus for
almost 3 years, and most of the trees are
known to have been infected for almost 2
years. It should be mentioned that similar
virus-carrying susceptible trees, which appear
healthy and do not show histological signs of


tristeza, have been found elsewhere in
Orange county, and a few have been found
in other counties in the state (2). The signi-
ficance of this finding is not fully under-
stood. It may be that the virus has an ex-
tremely long incubation period before it be-
gins to affect the phloem of the host tree.
(Phloem breakdown is one of the earliest fea-
tures of the histological picture of a tree in
decline with tristeza disease). Another citrus
virus disease with an incubation period of
many years is already known-psorosis disease
-but it has not been suggested previously
that this might also be the case with tristeza.
A second possibility is that an additional fac-
tor as yet unknown, in addition to the virus
indexed, must be present before the disease
can begin to run its course. In any case, this
matter is being studied actively, and con-
tinued observation of these trees certainly
should throw more light upon the problem.
The above considerations should not ob-
scure the central fact that tristeza disease in
Florida has caused serious losses to citrus.
Although this paper describes conditions in
a single grove only, many other groves in
Orange county and elsewhere have been
damaged by tristeza. At present, many of the
factors involved in producing an outbreak of
this disease are not understood and cannot be
predicted. Growers who plant groves on sour
orange rootstock, the only rootstock used in
Florida on which trees are definitely not
tolerant to tristeza, are risking the life of their
planting. Is it wise, therefore, to continue the
use of this dangerous rootstock where other
rootstocks can do the job safely?
LITERATURE CITED
1. Schneider, Henry. 1954. Anatomy of bark of
bud union, trunk, and roots of quick-decline-affected
sweet orange trees on sour orange rootstock. Hil-
gardia 22: 567-581.
2. Cohen, Mortimer. 1956. Incidence of tristeza
virus in Florida in trees not yet showing field
symptoms. Phytopath. 46: 9 (abstract).





SMITH: PHOSPHATE FERTILIZATION


EFFECT OF PHOSPHATE FERTILIZATION ON

ROOT GROWTH, SOIL pH, AND CHEMICAL

CONSTITUENTS AT DIFFERENT DEPTHS

IN AN ACID SANDY FLORIDA CITRUS SOIL


PAUL F. SMITH
Horticultural Crops Research Branch
Agricultural Research Service
United States Department of Agriculture
Orlando

In recent years, certain studies (4, 10)
have been made to explore the relation be-
tween fertilization practices and root devel-
opment of citrus in the sandy soils of Florida.
Those reports were concerned primarily with
the effect of nitrogen sources and rates and
methods of timing on the density of roots in
the top 5 feet of soil, where the changes in
chemical composition were relatively small.
With adequate liming, nitrogen appears to
have little or no permanent effect on soil
composition (10).
The present studies involved deep sampling
in a long-term phosphate experiment in
which there has been a large permanent
change in the phosphorus status of the soil
because of the accumulation of applied phos-
phate. Previous reports (7, 8) describing the
results from this experiment for the first 6
years, failed to show any beneficial response
in tree growth, yield, or fruit quality to ap-
plied phosphate. No additional data on these
factors are presented here, but the results
through the 13th year are still essentially the
same. The present report is concerned with
the density of small roots, soil pH, and cer-
tain chemical constituents in the soil in rela-
tion to the rate of phosphate fertilization.
EXPERIMENTAL METHODS
Pineapple orange trees on Rough lemon
stock were planted on a virgin plot of ground
in a random block experiment in 1942 and
certain plots have never received any phos-
'/This study was made possible by the generous
cooperation of Loren H. Ward of Orlando, Florida, in
whose grove the experiment lies. The technical as-
sistance of G. K. Scudder, Jr., and G. Hrnciar is
gratefully acknowledged.


phate. The soil is a transitional type between
Lakeland and Eustis fine sands, previously
identified as Lakeland (7, 8). The plan fol-
lowed is to apply 0, 1, 3, and 8 units of
P,.0, respectively, to different plots for each
4 units of nitrogen used. There are six 12-
tree plots for each phosphate level. The P0,s
comes from 20 percent superphosphate, and
compensatory amounts of gypsum are given
so that all plots receive the amount of CaSO,
carried by the highest level of superphosphate.
The highest rate of PA0, was the usual com-
mercial rate at the time the experiment was
started, but current recommendations (6) call
for a drastic reduction. The experimental rates
of P,20 described above will be referred to as
none, low, medium, and high in discussing
treatments.
All trees have regularly received 3 applica-
tions a year of a mixed fertilizer containing
little or no organic material and no super-
phosphate. The current mixture is 10-0-10-3
(MgO) 0.5 (Mn0)-0.5 (ZnO)-0.1 (B,0o) ap-
plied at the rate of 24 lb. per tree per year.
Copper also was included for the first 10 years
but omitted since. Zinc was applied in spray
form only once and that was in the spring of
1954. For the first 9 years the appropriate
quantities of superphosphate and gypsum
were also applied 3 times a year and to the
same area as covered by the mixed fertilizer.
From the 10th year on, these materials have
been applied all in one spring application. No
attempt has been made to compensate for the
calcium carried as the phosphate salts, but a
relatively high rate of dolomitic limestone has
been regularly applied to all plots.
In July 1955 eight 2-inch cores of soil were
taken from each plot. The most uniform trees
were selected, and in most cases only one
core was taken per tree. The cores were taken
at the tree-drip line and to a depth of 5 feet.
The samples were taken by depths of 0-6 in.,
6-12 in., 12-24 in., 24-42 in., and 42-60 in.
The 8 cores of soil for the respective depths





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


I LSD 0.05


500.
400.

pp300
P 200.
100


Ill


OLMH OLMH OLMH OLMH OLMH


5.0
I4.0.


02.0-
20
i--
U 1.0
2.0
(3
Ar


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IiI Ii l 11 1111


OLMH OLMH OLMH OLMH OLMH


I LSD 0 0.05


PPL
K ,


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II Ill


80

60

40
PPM
MN20

0 I II111nl.i


illi miii lull


ULrnM ULMH ULM ULMm ULMH OLMH OLMH OLMH OLMH OLMH
0-6 6-2 12-24 24-4242-60 0-6 6-12 12-24 24-42 42-60
Fig. 1-G. Root growth and various soil factors found at different depths (in inches) in an experimental
Pineapple orange grove on acid, sandy soil after 13 years of differential fertilization with superphosphate.
The symbols O L M H represent zero, low, medium,and high rates of application. Fig. 1 (upper left)-
total soil phosphorus; Fig. 2 (upper right) concentrations of small "feeder" roots found; Fig. 3 (center
left) soil pH; Fig. 4 (center right) exchangeable potassium; Fig. 5 (lower left) total copper; Fig. 6
(lower right) total manganese. The L.S.D. bars indicate the required difference for significance at the
5% level between any two treatments or depths.


Ill


6.5
6.0.
5.5
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AA


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SMITH: PHOSPHATE FERTILIZATION


were composite, screened to remove the
fibrous "feeder" roots, and thoroughly mixed
by rolling on a canvas cloth, and portions were
saved for laboratory analyses. Rootlets smaller
than about 1/16 inch in diameter were sorted
out, dried, and weighed. In addition to pH,
total amounts of P, Cu, Mn, and Zn were de-
termined on certain soil samples after total
digestion in sulfuric-nitric acid mixtures. Ex-
changeable K, Ca, and Mg were determined
by neutral ammonium acetate extraction.

RESULTS AND DISCUSSION

Phosphorus status of soil-The values found
for total P are shown in Fig. 1. The data are
very consistent and show that while most of
the applied P is held in the top foot of soil,
there is a gradual accumulation throughout
the top 5 feet. This is in agreement with the
findings of Spencer (11) that superphosphate
gradually distributes itself through the top
few feet of soil. Actually, more total P was
found than was applied to the plots receiving
superphosphate for 13 years. This is doubt-
lessly due primarily to the fact that the low-
hanging foliage interferes somewhat with the
machine spreading of the superphosphate, and
there would be a zone of relatively high P
just outside the foliage line due to the deflec-
tion of particles. Sampling in this area showed
an increase of 1900 lb. of P per acre through
the 5-ft. column, whereas only about 1250 lb.
of P had been applied. Thus, the sampling
method may also exaggerate the other effects
associated with differential phosphate fertili-
zation. It is felt, however, that the trends
would be indicative of the nature of the re-
sponses even though the magnitudes might
differ somewhat from those shown.
Density of feeder roots-The distribution of
feeder roots is shown in Fig. 2. The data are
presented as the weight of roots found in a
square foot of soil 6 inches deep taken from
each depth zone. The total dry weights of
feeder roots expressed as grams of roots per
square foot column 5-ft. deep are as follows:
No phosphate 23.8; low phosphate 21.4;
medium phosphate 21.3; and high phosphate
16.3. It is of interest that Ford (3) also found
16.3 as an average weight of roots in com-
mercial groves of this age category. These
soils too, would have been high in phosphate


because the groves were grown before the
general drop in applied phosphate in com-
mercial groves.
While the data in Fig. 2 are less consistent
than those for the concentration of P in Fig. 1,
they clearly indicate that high-phosphate
fertilization somehow causes a sharp reduc-
tion in the quantity of feeder roots in the top
12 inches of soil. In the 6 to 12-inch zone all
3 levels of applied phosphate significantly re-
duced root growth. It is probable that the
effect on root growth is somewhat exaggerated
in the area sampled because of the uneven dis-
tribution of applied phosphate. Even so, it is
difficult to avoid the conclusion that applied
phosphate has had no beneficial effect on root
growth in this experimental grove. The de-
pression of root growth below 12 inches is not
statistically significant, but the trend is still
present to the 42-inch depth. Even to the 60-
inch depth there is no suggestion of increased
root growth as a compensation for the reduc-
tion in growth at the shallower depths.
Since tree size, appearance, and yield
records do not yet reflect the density of roots
as measured here, it remains to be seen
whether such a reduction is a definite handi-
cap to the tree. No explanation is offered as
to why superphosphate depresses root
growth, but the effect is somewhat similar to
that found with a high rate of ammonium ni-
trate (4).
Soil pH-Increased acidity at all soil depths
was associated with the use of superphosphate.
Fig. 3 shows the pH values found at differ-
ent depths in relation to treatment. In the
two upper sampling depths there is a grad-
uation in pH values corresponding to treat-
ment. At the 3 lower depths, there was little
or no difference among the pH values for the
3 rates of superphosphate, but those for the
plots that received none were appreciably
higher.
Superphosphate is not a simple material as
it contains a mixture of phosphatic salts, gyp-
sum, iron and aluminum oxides, silica, and
trace quantities of several other substances.
It is mildly acidic and gives a pH reading of
about 3 when mixed with water. The acid-
ulating effect of superphosphate on most soils
is of little or no practical significance be-
cause of the buffering action of the soil. How-
ever, with very sandy soils of low exchange








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


capacity and high rates of application, addi-
tional liming apparently is required to offset
the acidifying effect of superphosphate.
The effect of superphosphate in lowering
pH is particularly evident in the top 12 inches
of the soil and corresponds to the area of maxi-
mal phosphate accumulation and maximal de-
pression in root growth. Yet it appears doubt-
ful that there is a simple cause and effect re-
lation between pH and root growth. Previous
studies (10) in which the pH was varied in
this same general range, but without super-
phosphate as a variable, showed no depres-
sion in root growth due to lowered pH. Like-
wise, studies with different levels of phosphate
in solution cultures did not show any adverse
effect of high phosphate on root growth (2).
Thus, while it is not yet established what
causes the depression in root growth, it is ap-
parent that superphosphate does not have a
beneficial effect on soil reaction.
Effect of phosphate level on exchange K,
Mg, and Ca-There was practically no effect
of phosphate treatment on the extractable
quantities of the three base elements (K, Mg
and Ca). The only difference of consequence
was the tendency for more K to be retained
in the upper depths where the greatest amount
of phosphate had accumulated in the soil
(Fig. 4). Mg values were virtually identical
at all depths in all treatments and the respec-
tive total pounds per acre in 5 ft. of soil were
no phosphate 340; low phosphate 321; me-
dium phosphate 349; and high phosphate 330.
Ca showed a slight, but irregular and non-
significant, increase with values of 1176, 1090,
1307, and 1290 lb. per acre for the same
respective treatments. This Ca trend was not
accentuated in the upper soil depths where
the phosphate accumulation was the greatest.
Effect of phosphate level on the total
amounts of Cu, Zn, and Mn-There was no
significant effect of phosphate level on the
total amounts of any of these metals found in
the soil. The concentrations of Cu and Mn are
shown in Fig. 5 and 6. Zn showed a mean
value of 19 p.p.m. in the top soil and about 8
.p.m. in all lower depths regardless of treat-
ment. These results are in harmony with the
results found in a topsoil sampling 5 years pre-
viously (8). Both Zn and Mn show increases
as a result of continued use of these elements


in the fertilizer. No Cu was applied during
the interval, and Cu status of the soil is vir-
tually unchanged.
GENERAL DISCUSSION
Several studies (1, 5, 7, 8, 11, 12) have
shown that phosphate accumulates in Florida
citrus groves. Removal of this element by the
citrus crop is not large, being about 0.5 lb. of
P per ton of fruit (9). Application of super-
phosphate does not markedly increase the ab-
sorption of phosphorus by the tree in ordin-
ary acid, sandy Florida grove soil (7). The
evidence thus far fails to show any beneficial
effect of applied phosphate on citrus in this
State except in a few cases, such as on muck
soil or very light sands where the content of
native phosphate is very low.
Wander (12), studying soil factors in re-
lation to presence or absence of liming, noted
that a phosphate differential existed in the
topsoil and concluded that the greater reten-
tion of Mg and Mn in the limed plots was due
to the absorptive capacity of the accumulated
calcium phosphate. The present results, in ad-
dition to previously published data (8), fail
to show any relation between large phosphate
accumulations and the retention of Ca, Mg,
Mn, Cu, or Zn. Thus, it appears possible that
the effect noted by Wander was not attribu-
table to phosphate but to pH. Liming probably
retarded the losses of phosphate, Mg and Mn
for the same reason rather than through the
indirect method postulated.
It might be expected that phosphate ac-
cumulation would also result in greater Ca
accumulations in the soil, particularly if there
was a reversion to calcium phosphate. How-
ever, neither exchange Ca nor total Ca (7, 8)
is appreciably changed. The work of Spencer
(11) offers an explanation since he found
that most of the phosphate accumulated in
Florida sandy grove soils is in the form of
iron and aluminum phosphates rather than
calcium phosphate.
SUMMARY
Soil samples to a depth of 60 inches were
taken in a Pineapple orange grove on an acid,
sandy soil after 13 years of differential fer-
tilization with superphosphate. Data derived
from these samples showed that (1) the
largest increase in P was in the top 12 inches
of soil, but some increase was noted at all





FEDER AND FELDMESSER: BURROWING NEMATODE


depths, (2) the total weight of "feeder" roots
in the 60 inches was nearly one-third less in
the high phosphate plots than where none
was applied, (3) appreciable acidity was im-
parted to the soil by the superphosphate, par-
ticularly in the top 12 inches, and (4) there
was somewhat more exchangeable K found
as a result of increased phosphate but the ex-
changeable Ca and Mg were unaffected and
there were no differences in the total amount
of Cu, Zn, or Mn regardless of treatment.
None of these findings can be construed as
being highly beneficial to the culture of citrus.
LITERATURE CITED
1. Bryan, O. C. The accumulation and availability of
phosphorus in old citrus grove soils. Soil Sci. 35:
245-259. 1933.
2. Chapman, H. D. and D. S. Rayner. Effect of
various maintained levels of phosphate on the growth,
yield, composition, and quality of Washington navel
oranges. Hilgardia 20: 325-358. 1951.
3. Ford, H. W. The influence of rootstock and tree
age on root distribution of citrus. Proc. Amer. Soc.
Hort. Sci 63: 137-142. 1954.


4. W. Reuther and P. F. Smith. The
effect of nitrogen on root development of Valencia
orange trees. Proc. Amer. Soc. Hort. Sci. (MS sub-
mitted for publication).
5. Peech, M. Chemical studies on soils from Florida
citrus groves. Fla. Agr. Exp. Sta. Tech. Bull. 340.
1939.
6. Reitz, H. J., et al. Recommended fertilizers and
nutritional sprays for citrus. Univ. of Fla. Agr. Exp.
Sta. Bull. 536. 1954.
7. Reuther, W., F. E. Gardner, P. F. Smith and
W. R. Roy. A progress report on phosphate fertilizer
trials with oranges in Florida. Proc. Fla. State Hort.
Soc. 61: 44-60. 1948.
8. Reuther, W., P. F. Smith and A. W. Specht. Ac-
cumulation of the major bases and heavy metals in
Florida citrus soils in relation to phosphate fertiliza-
tion. Soil Sci. 73: 375-381. 1952.
9. Smith, P. F. and W. Reuther. Mineral content of
oranges in relation to fruit age and some fertilization
practices. Proc. Fla. State Hort. Soc. 66: 80-86. 1953.
10. Smith, P. F., and W. Reuther. Preliminary re-
port on the effect of nitrogen source and rate and
lime level on pH, root growth, and soil constituents in
a Marsh grapefruit grove. Proc. Soil Sci. Soc. Fla. 15:
108-116. 1955.
11. Spencer, W. F. Phosphatic complexes in the soil.
Ann. Rpt. Fla. Agr. Exp. Sta. p. 193, 1952; p. 218,
1953.
12. Wander, I. W. The effect of calcium phosphate
accumulation in sandy soil on the retention of
magnesium and manganese and the resultant effect
on the growth and production of grapefruit. Proc.
Amer. Soc. Hort. Sci. 55: 81-91 1950.


STARTING AND MAINTAINING BURROW-

ING NEMATODE-INFECTED CITRUS

UNDER GREENHOUSE CONDITIONS


WILLIAM A. FEDER AND JULIUS FELDMESSER

Fruit and Nut Crops Section and
Nematology Section
Horticultural Crops Research Branch
Agricultural Research Service
United States Department of Agriculture

Orlando

The current nematode research program
requires the use of large numbers of burrow-
ing nematode-infected citrus seedlings as
well as a large and reliable supply of burrow-
ing nematodes. Large numbers of infected
seedlings are needed for the chemical screen-
ing program and for various biological studies
and other fundamental work. Obtaining suf-
ficient burrowing nematodes from naturally
infected grove trees requires a great deal of
time and labor. A method of raising and main-
taining burrowing nematode populations on
citrus in the greenhouse was, therefore, de-
vised.


Studies, which will be reported elsewhere,
indicate that the burrowing nematode will
infect and reproduce readily in citrus seed-
lings growing under normal greenhouse con-
ditions in Florida. It was also found that
grove subsoil, turned up while digging for
nematode-infected roots, contained many
small nematode-bearing root fragments, and
that citrus seedlings planted into this soil in
pots under greenhouse conditions were readily
infected and supported a burrowing nematode
population.

These observations were utilized in guid-
ing the construction of two drained concrete
soil tanks. These concrete block tanks were
constructed on a 4-inch thick, poured con-
crete slab and the soil-bearing portions had
inside dimensions of 10' x 4' x 2' and 16' x 4'
x 2', respectively. The bottom of the soil-
bearing portion of the tank is raised one block
width above the concrete slab and is con-
structed of 9" No. 9 expanded metal resting
on cross bars of 2" x 2" x W" angle iron. The
metal surfaces are all coated with red lead








FLORIDA STATE HORTICULTURAL SOCIETY, 1956


primer and asphalt paint to reduce rusting
and corrosion. The completed tank is shown
in Fig. 1.


Fig. 1. Inside of soil tank showing cross supports,
expanded metal bottom, and a portion of the walls.

In filling the tank with soil a 2-inch layer
of X" lime rock was first poured onto the ex-
panded metal bottom. Sterilized field soil was
then placed on the lime rock layer to a depth
of 4 inches. Finally, the remaining space in
the tank was filled with the required num-
ber of yards of subsoil taken from beneath
trees known to harbor the burrowing nem-
atode in their roots. This soil was brought
from the grove in closed metal garbage cans
to avoid contamination of citrus plantings
enroute. The soil in the tank was wet down
and tamped and allowed to settle for a few
days. Seedlings of Rough lemon and Duncan
grapefruit and seeds of both these varieties
were then planted in the tank in rows, and
the rows were marked with planting date and
type of material planted. These plantings
were watered carefully to avoid water dam-


age and were cultivated and fertilized in a
routine manner. It was found that the small
root fragments, which seemingly contained
the bulk of nematodes found in the subsoil,
did not wash down upon watering, but in-
stead, some worked to the surface of the soil,
if watering was excessive. It was necessary to
push them below the surface when this oc-
curred. Water, which leached through the soil,
was collected in large pans and examined
periodically for the presence of burrowing
nematodes. To date, no burrowing nematodes
have been recovered from the leaching water.
After 6 weeks, burrowing nematode in-
fected seedlings were harvested from the
tank. These seedlings bore few to many lesions
on the roots and all stages of the burrowing
nematode were found within the lesions. The
smaller tank holds about 1,300 growing seed-
lings when loaded to capacity, and the larger
one about 2,100 seedlings. Seedlings usually
are grown 3 months in the tank before they
are harvested. This period is sufficient for
them to overcome the initial shock of trans-
planting and to develop an adequate top
and root system. Damping off occurs infre-
quently and is controlled by applications of
wettable captain to the soil between the rows.
In order to minimize trap-cropping, a few
infected roots are cut up and buried after each
row of seedlings is dug up. In this manner,
an active burrowing nematode population has
been maintained in one tank since January
1956. This population has now survived a
winter and a summer in the tank under normal
greenhouse conditions. Approximately 800 in-
fected seedlings have been harvested since
January 1956.








GRIMM: DIEBACK INVESTIGATIONS


PRELIMINARY INVESTIGATIONS ON

DIEBACK OF YOUNG TRANS-

PLANTED CITRUS TREES'


CORDON R. GRIMM


Horticultural Crops Research Branch
Agricultural Research Service
United States Department of Agriculture

Orlando

INTRODUCTION
Dieback of transplanted citrus trees refers
to a progressive dying of a pruned branch or
trunk from the cut surface toward the root. It
has been recognized in Florida for as long as
groves have been planted. Usually the losses
from this disease have been minor, but within
the past few years they have increased suf-
ficiently to warrant investigation. Large acre-
ages have been planted at all seasons of the
year, and it has become apparent that losses
of young trees from dieback have increased
disproportionately with the increased acreage
planted.
A study of the nature and cause of dieback
was started by reviewing the methods of trans-
planting citrus trees. No general agreement
was found among growers or nurserymen as
to the best method of transplanting. Practices
in top pruning the trees varied considerably.
Methods of handling, watering, and subse-
quent care also varied. A diversity of opinion
prevailed on the importance of fibrous roots
and of the leaves at the time of transplanting.
To determine the role of all of the various
steps involved in transplanting on the inci-
dence of dieback, controlled experiments were
performed under field conditions. In con.
junction with these tests, laboratory isolations
were made to determine the microorganisms
associated with this disease.

1/The author wishes to acknowledge the cooperation
and donation of citrus trees from Mr. C. F. Fawsett,
Jr., of Orlando, Fla. and the following nurseries:Lake
Garfield Nurseries Co., Bartow, Fla.; Glen St. Mary
Nurseries Co.. Winter Haven, Fla.; Grand Island Nur-
series, Eustis, Fla.; and Ward's Nursery, Avon Park,
Fla.


PROCEDURES AND RESULTS
Temple orange and Glen Navel orange on
Cleopatra mandarin rootstock, i and % inch
in diameter, were used in transplanting tests
to determine the effect of top pruning, the ab-
sence of fibrous roots, and defoliation. Trans-
planting experiments were begun in Novem-
ber and March at the U. S. Department of
Agriculture experimental farm 7 miles west of
Orlando, Florida. Each experiment was com-
posed of eight treatments with eight trees
each replicated four times, making 32 trees
per treatment (table 1). Each treatment was
a combination of three separate operations;
e.g., the trees for treatment 1 had branches,
fibrous roots and leaves; those for treatment
8 had their branches, fibrous roots, and leaves
removed. Branched trees were pruned to
leave 4-to-6-inch branches; the trees without
branches were pruned to trunks approximately
16 inches high; all fibrous roots and all leaves
remaining after top pruning were removed
with pruning shears in the groups indicated.
The trees were planted with a 5 x 5 foot
spacing and the entire area was kept free of
weeds.
Excellent, good, fair, and poor were used to
describe the subsequent growth of the tree. An
excellent tree had little or no dieback on the
cut branches or main trunk and vigorous
sprout growth; good and fair trees had rela-
tively increased amounts of dieback and rela-
tively decreased sprout growth; poor trees
either had died back far enough to make re-
placement desirable or were dead. Observa-
tions were continued until no further changes
in growth habit were apparent.
Table 1 shows the numbers of excellent,
good, fair, and poor trees within each treat-
ment for the November and March plantings.
As a group, trees with fibrous roots present
were distinctly better in both the November
and'March plantings than those with fibrous
roots removed. As a group, trees with branches
present were better than trees with branches









FLORIDA STATE HORTICULTURAL SOCIETY, 1956


removed, and trees with leaves present were
better than trees with leaves removed in the
fall planting only. Statistical analyses of both
experiments showed the comparisons dis-
cussed to be highly significant.
A third experiment of 3 x 2 x 2 factorial de-
sign was made to compare entire trees ex-
posed to the sun for 1, and 2!3 hours with
trees that were shaded and had their roots
protected from drying by packing in wet
sphagnum moss from the time they were dug
until transplanted. The influences of leaves and
of no leaves and of a 3-hour delay in watering
after planting in comparison with watering at
planting were measured within each group.
Treatments were made on 2-inch Parson
Brown orange trees on Rough lemon rootstock
pruned to a 16-inch trunk and planted June 7,
1956. Each of the following treatments was


replicated three times with 5 trees each, mak-
ing 180 trees:
1. No sun exposure, leaves on, watered at planting
2. wteng delayed for 3 hours
3. off, watered at planting
4. watering delayed for 3 hours
5. 1-1/4 hour exposure leaves on, watered at planting
6. watering delayed for 3 hours
7. off, watered at planting
8. watering delayed for 3 hour.
9. 2-1/2 hour exposure, leaves on, watered at planting
10. watering delayed for 3 hours
11. off, watered at planting
12. watering delayed for 3 hours
The trees exposed to the sun were laid on
cultivated ground; the air temperature 3
inches above the surface was 93' F. and 112'
on the ground surface. All trees were planted
with a 5 x 5 foot spacing and arranged by
treatment in a definite plot design. All were
watered on the day of planting with 6 gallons
of water at the times designated, and every
4 or 5 days thereafter during the next 6 weeks
as weather conditions required.


Table 1. Distribution of trees by growth classes of Excellent, Good,
Fair, and' Poor following treatments at two planting seasons


November planting- March planting/
Treatments-/ E G F P E G F p

Branches present
Fibrous roots present
1. Leaves present 24 7 0 1 16 5 5 6
2. leaves removed 6 11 7 8 17 4 4 7

Fibrous roots removed
3. Leaves present 1 3 24 4 1 2 8 21
4, Leaves removed 0 3 10 19 Z 2 5 23

Branches removed
Fibrous roots present
5. Leaves present 5 2 10 15 11 2 9 10
6. leaves removed 0 2 7 23 6 6 7 13

Fibrous roots removed
7. Leaves present 1 3 6 22 2 1 7 22
8. Leaves removed 0 0 3 29 5 4 5 18

1/ Each treatment has a total of 32 trees.
2 Temple orange/Cleopatra mandarin 1/2-in. planted 11/9/55. Data taken
2/23/56.
I/ Glen Navel orange/Cleopatra mandarin 5/8-in. planted 3/23/56. Data
taken 6/7/56.




GRIMM: DIEBACK INVESTIGATIONS


Table 2. Mean inches of dieback and new sprout growth 6 weeks after
transplanting Parson Brown orange trees, as influenced by
exposure, defoliation, and delay in initial watering


Treatment Dieback Sprout growth
in. in,
Exposure to the sun
0 hour 1.58 32.53
li 4.25*** 17-02***
21 5.12*** 3.85***

Leaves present 3.02 18.99

Leaves removed 4.28* 16.16

Watering
at planting 3.59 17.63
delayed for 3 hours 3.71 17.97

*Indicate statistical significance at odds of 19:1
***Indicates statistical significance at odds of 999:1


The results are summarized in Table 2 in
terms of average inches of dieback of the
main trunk and average inches of total new
sprout growth per tree for the respective
treatments. Trees exposed to the sun for 131
or 231 hours prior to planting had considerably
more dieback and less sprout growth than
trees that had been protected from drying
with wet sphagnum moss. Statistically the dif-
ferences are very highly significant. It should
also be noted that trees without leaves at the
time of transplanting had significantly more
dieback than trees with leaves at the time of
transplanting. Time of initial watering did
not affect the amount of dieback or sprout
growth of the trees in this experiment.
Preliminary observations on the effective-
ness of various pruning paints for the control
of dieback were made during February,
March, April, and May on sweet orange trees
with various amounts of top pruning and de-
foliation. De-Ka-Go, Carbolineum, and pastes
of Zineb, Orthocide, and neutral copper were
applied to the cut surfaces immediately after
pruning and before the trees were dug at the
nursery. The treated trees were planted at
random with non-treated trees and compari-
sons were made in the same planting. Only


6 percent of the trees showed measurable
dieback, and this seemed to occur regardless
of the presence or absence of wound paint.
Several fungi and an unidentified bacterium
have been isolated from trees affected with
dieback. However, investigations to date have
not shown any one organism to be consistently
associated with dieback. Colletotrichum gloeo-
sporioides was isolated from 60 percent of the
trees; Diplodia natalensis, Phomopsis citri,
Fusarium spp., and bacteria were isolated from
10 to 30 percent of the trees.
DIscussIoN
Field observations and experimental data
indicate that dieback of transplanted citrus
trees is largely a result of mishandling the
trees at some point during transplanting.
Transplanting citrus trees involves many op-
erations such as pruning, digging, transporting,
planting, watering, and fertilizing and any one
or all may be done carelessly enough to injure
the tree. Environmental conditions at the time
of operations, such as temperature, humidity,
wind and water, and soil characteristics may
also have direct influences on the success of
transplanting.
The presence of healthy fibrous roots and
their protection from drying at all times have





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


proved to be important for vigorous tree
growth, which apparently provides the best
defense against dieback of transplanted citrus
trees.
The presence of leaves can have a marked
influence in preventing or checking dieback of
the tree. It is not uncommon for dieback to
proceed down one side of a limb or trunk on
which no leaves are present and to stop on
the other side at the first leaf. Exactly how a
leaf stops dieback is not known; it may be
only by sustaining healthy tissue through the
normal leaf functions. Even though the leaves
are lost shortly after planting, they may be
beneficial to the tree during transplanting. In
the third experiment, trees with leaves during
exposure to the sun lost their leaves 2 or 3
days later, yet they had significantly less die-
back than trees without leaves.
From the data obtained thus far it would
seem advisable to top prune trees only mod-
erately, maintaining 4-to-6-inch branches. This
was particularly true for fall-planted trees,
which were larger and stronger, and had less
dieback 4 months after planting. Incidental
observations have shown that the advance of
dieback down a branch is often checked tem-
porarily and sometimes permanently at the
crotch.
A causal organism of dieback cannot be en-
tirely ruled out. However, the fact that a tree
has less dieback because of the presence of


fibrous roots, leaves, and branches, coupled
with the fact that at present no one organism
has been isolated consistently from all die-
back trees, suggests that good transplanting
methods offer the best control of this disease.
It is evident that during transplanting of citrus
the entire tree, particularly the fibrous roots,
should be protected from drying at all times.
Once the tree has been set in the grove it
should be watered at planting and again the
second or the third day afterward; and, in
Central Florida sandy soils, every 3 to 5 days
thereafter for the first few weeks as weather
conditions require.
SUMMARY
Dieback and new sprout growth of young
transplanted citrus trees were measured in re-
lation to (1) top pruning, (2) defoliation, (3)
root pruning, (4) exposure of the entire tree
to the sun before transplanting, and (5) de-
layed watering after transplanting. The pre-
liminary results indicate that dieback may be
a result of injurious transplanting operations.
Healthy fibrous roots were shown to be very
important for vigorous tree growth and to
constitute one of the best defenses against
dieback. The presence of leaves appeared to
be beneficial in limiting the amount of die-
back, especially in fall-planted trees.
Investigations to date give no definite in-
dications that fungi or bacteria are primary
causal agents of dieback.


THE POSSIBILITY OF MECHANICAL

TRANSMISSION OF NEMATODES

IN CITRUS GROVES


A. C. TARJAN
Florida Citrus Experiment Station
Lake Alfred
The somewhat phenomenal spread of the
burrowing nematode, Radopholus similis
(Cobb) Thorne, in recent years has been at-
tributed to subsoil drainage (3), to the move-
ment of the nematode itself, and to the ac-
tivities of humans (4). This latter means of

Florida Agricultural Experiment Station Journal
Series, No. 529.


dispersal of the organism has been imple-
mented mainly by the widespread dissemina-
tion of infected citrus nursery stock and other
cultivated plants. It generally has been as-
sumed that various implements and mechan-
ical devices also play a role in the spread of
the burrowing nematode as in the case of
certain other plant pathogenic nematodes
(1, 2, 5). Although shovels, cultivators, and
mobile harvesting machinery have been im-
plicated, it was suspected that bulldozers
were mainly responsible. The "pull and treat"
program (6) of the Florida State Plant Board,







TARJAN: TRANSMISSION OF NEMATODES


which is accomplished by the destruction of
burrowing nematode infected citrus and sub-
sequent soil treatment with D-D soil fumi-
gant, uses bulldozers for elimination of desig-
nated trees. The machines enter the groves,
fell the trees and place them in piles for burn-
ing. If infested soil and infected roots were
capable of being picked up and transported,
the bulldozers, with their undesired cargo,
might be assigned on the following day to
either clearing virgin land for future groves
or pushing out old or undesirable trees to
make way for a new planting. In either case
it was assumed that nematode inoculum
might, in this manner, be disseminated to non-
infested land.
With the cooperation of Mr. Charles Pouch-
er, Florida State Plant Board, Lake Alfred,
and the various contractors involved in clear-
ing infested grove sites, a study was under-
taken to determine (1) if bulldozers and cul-
tivators were carrying soil and debris infested
with nematodes, (2) the relative kinds and
frequency of occurrence of these nematodes,
and (3) whether clods of soil and debris in-
fested with burrowing nematodes might be
suitable inoculum for infecting potted citrus
plants. The vast majority of the sites visited
were groves affected by spreading decline, but
in a few cases noninfested groves were also
inspected. Soil, including roots when avail-
able, was scraped off bulldozer tracks and
was obtained also from various locations on
the "dozer" body. Samples thus obtained
were stored in pint jars, returned to the
laboratory, and processed for nematodes.
During the course of this study, 63 samples
were collected from 23 different groves in
Lake, Polk, and Orange Counties. Genera of
nematodes identified are listed in Table 1
while the relative abundance of nematodes in
each of the samples is shown in Table 2.
Nematode genera with saprozoic or preda-
tory feeding habits comprise the longest list
in Table 1. There were additional genera of
this group that were not identified principally
because only spear-bearing nematodes were of
primary interest in this study. The bulb and
stem nematodes, Ditylenchus spp. were the
most numerous among the plant parasites
found. Although many species of this genus
are not parasites of higher plants, it has long


been suspected that other species are capable
of inflicting serious root damage. Likewise, in
the "Suspected Plant Parasite" group, the
genus Dorylaimus probably contains species
that are plant parasites as well as those which
are predatory in feeding habit.
Data in Table 2 shows that most of the
samples obtained yielded from 26 to 75 nema-
todes and that in no case did a sample fail to
yield living nematodes. This is especially signi-
ficant when it is taken into account that the
major part of this survey was conducted in
the winter and spring months of 1956 during
an extended drought. Occasionally a sample
consisted of only a small number of apparent-
ly desiccated roots and soil which was scraped
off the body of the bulldozer, while at other
times the sample was found packed under
pressure in crevices in the tracks and had to
be forcefully pried out. In one case, the
machine operator had finished for the day
and in an attempt at disinfestation had sprayed
the tracks with diesel fuel, a substance which
has been assumed to be nematocidal. The soil
sample, obtained about one hour after the
spraying, yielded numerous active, apparently
healthy nematodes when processed in the
laboratory the next day.
Ironically, the only time that Radopholus
similis was obtained was from a sample taken
from a machine pushing out apparently
healthy grapefruit trees for purposes of re-
planting with orange.
The imposing list of plant parasites shown
in Table 1 disproves the conception that such
nematodes cannot possibly survive in soil
clods or debris exposed to air and sun. Where,
in the case of certain plant parasites, adequate
moisture is needed to prevent desiccation,
matter containing adequate moisture can be
found tightly packed on the bulldozer tracks.
In one case, a bulldozer being transported by
truck was intercepted about two miles from
the grove site in which it had been working.
As expected, numerous nematodes were ob-
tained from the soil samples collected from
the machine.
Although the foregoing data proved that
certain machinery is capable of disseminating
nematodes, the question remained whether
inoculum thus translocated was capable of in-
stituting an infection at a new location. Con-






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


sequently tests were conducted on potted
seedlings simulating actual conditions as
closely as possible.
Thirty 9-month-old grapefruit seedlings
growing in autoclaved soil in 46 oz. cans were
divided into five lots of six plants each. These
were placed evenly in large flats of auto-
claved soil, so that only the upper fifth of the
can projected above the soil. This was done


to maintain as constant a soil temperature as
possible within the cans. Inoculum consisted
of finely cut citrus feeder roots which were
moderately infected with burrowing nema-
todes. In simulating the physical state of po-
tential inoculum as it had been observed on
the bulldozers, various combinations of in-
fected roots, mashed citrus fruit, clay, and
soil were mixed and shaped by hand into


Table 1. Ge

Plant Parasites


Tylenchulus (1) a/

Radopholus (1)

Tylenchorhynchus (2)

Criconemoides (1)

Tylenchus (6)

Ditylenchus (18)

Meloidogyne (1)

Dolichodorus (4)

Hemicycliophora (1)

Pratylenchus (12)

Trichodorus (3)

Hoplolaimus (2)

Rotylenchus (3)

Belonolaimus (1)

Tylenchidae (2) b/


nera of nematodes found in soil collected from bulldozers
Suspected Plant Parasites Saprozoite


Aphelenchoides (31)

Paurodontus (1)

Dorylaimus (11)

Xiphinema (3)

Tylencholaimus (3)

Pseudhalenchus (5) 2/

Belondira (1)

Nothotylenchinae (1)


es and Predators


Rhabditis (17)

Diplogaster (5)

Acrobeles (8)

Cephalobus (2)

Tripylidae (1) b/

Diplogasteroides (2)

Rhabditolaimus (1)

Monhystera (2)

Alalmus (1)

Prismatolalmus (1)

Acrobeloides (2)

Discolaimus (2)

Mononchus (2)

Vilsonema (2)
Eucephalobus (2)

Plectus (1)

Aporcelaimus (1)

Chiloplacus (1)

Cervidellus (1)

Aphelenchus (10)


a/ Numeral indicates frequency of occurrence.

b/ Identified only to family or sub-family.

c/ New genus-technical description currently being prepared.





TARJAN: TRANSMISSION OF NEMATODES


Table 2. Relative number of nematodes recovered
from soil samples.


No. of Nematodes Frequency in Samples
151 or more 12
76-150 13
26-75 22
11-25 8
10 or less 8
none 0


small clods. All of these inoculum combin-
ations were either placed on or partially im-
bedded in the soil contained in the cans, some
of which had been watered immediately prior
to inoculation. This was done to approximate
the condition where infested material had
either fallen from a bulldozer to the ground
or had been pushed into the ground by the
machine tracks. Watering the soil in some of
the cans simulated rainfall prior to inocula-
tion. After the inoculum was introduced,
water was applied to those cans which had
not been pre-wetted. One flat was placed in
a room provided with artificial illumination, a
constant temperature of approximately 78" F.,
and a relative humidity which averaged about
80 percent during hours of illumination and
95 to 100 percent in total darkness. Two flats
were placed outside exposed to sunlight, while
another flat was placed in the partial shade
of a slat house. A control flat containing
plants which had received combinations of
nematode-free citrus roots, citrus pulp, clay
and soil was placed outside exposed to weath-
er conditions.
Plants were harvested and screened for bur-
rowing nematodes by the root incubation
technique (7) approximately 10 weeks after
this experiment was initiated. It was found
that only plants which had been protected
from exposure to direct sunlight, i.e. those
placed in the constant temperature room and
those placed in the slat house, became in-
fected with burrowing nematodes. It did not
appear to make any difference whether the
plants were watered prior to or after inocula-
tion, whether the inoculum rested on or was
inserted in the soil, and whether the inoculum


was combined with clay, crushed citrus fruit,
soil, or any combination of these.
These results, although derived from tests
with potted seedlings, indicate that situations
could arise in the field where nematode-
infected inoculum might be carried into non-
infested land, come into contact with the soil
in a shaded area prior to or following a rain,
and could institute an infection of host plants
growing in the immediate vicinity.

SUMMARY
A survey was undertaken in which soil and
root samples were obtained mainly from the
tracks of bulldozers employed in eradicating
citrus groves afflicted with spreading decline.
This survey was conducted mainly during the
winter and spring months when the citrus area
had received a minimum rainfall. Sixty three
soil and root samples were collected from
twenty-three groves in Polk, Lake, and Orange
Counties. Fourteen different genera of known
plant parasitic nematodes including Radopho-
lus similis, the burrowing nematode, were
identified. Experiments were conducted in
which burrowing nematode infected citrus
roots in combination with clay, crushed citrus
fruit, and soil were introduced into pots con-
taining 9-month-old citrus seedlings. After
inoculation, these plants were either exposed
to sunlight or placed in shaded areas. Only in
the latter case did plants incur burrowing
nematode infections. It is concluded that
mechanical equipment such as bulldozers arc
capable of transmitting nematodes which,
under the proper conditions, can institute in-
fections of citrus.
LITERATURE CITED
1. de Carvalho, J. Cj 1953. Ditylenchus destructor
em Tuberculo-Semente Importado da Holanda. Rev.
Inst. Adolfo Lutz. 13: 67-74.
2. Courtney, W. D. and H. B. Howell. 1952. In-
vestigations on the Bent Grass Nematode, Anguina
Agrostis (Steinbuch. 1799) Filipjev, 1936, U. S. Dept.
Agr., PI. Dis. Rotr. 36 (3): 75-83.
3. DuCharme, E. P. 1955. Subsoil Drainage as a
Factor in the Spread of the Burrowing Nematode. Fla.
State Hort. Soc., Proc. 68: 29-31.
4. Simanton, W. A. 1956. How Has Spreading De-
cline of Citrus Spread? Sunshine State Agr. Res. Rpt.
1 (3): 5, 7.
5. Steiner, G., A. L. Taylor, and Grace S. Cobb.
1951. Cyst-forming Plant Parasitic Nematodes and
their Spread in Commerce. Helm. Soc. Wash., Proc.
18 (1): 13-18.
6. Suit, R. F., E. P. DuCharme, and T. L. Brooks.
1955. Effectiveness of the Pull-and-Treat Method for
Controlling the Burrowing Nematode on Citrus. Fla.
State Hort. Soc., Proc. 68: 36-38.
7. Young, T. W. 1954. An Incubation Method for
Collecting Migratory Endo-parasitic Nematodes. U. S.
Dept. Agr., P1. Dis. Rptr. 38 (11): 794-795.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956

TRANSMISSION OF TRISTEZA VIRUS BY

APHIDS IN FLORIDA


PAUL A. NORMAN
Entomology Research Branch
THEODORE J. GRANT
Horticultural Crops Research Branch
Agricultural Research Service
U. S. Department of Agriculture
Orlando
The mild tristeza virus was transmitted
from Temple orange trees to Key lime test
plants by two species of aphids in preliminary
experimental work (16). The green citrus
aphid (Aphis spiraecola Patch) gave positive
transmissions to 9 of 128 test plants and the
melon aphid (A. gossypii Glover) to 1 of 26
plants. Higher ratios of infection have been
obtained in recent tests with the combined use
of controlled sources of inoculum in several
varieties of citrus seedlings, multiple-branched
Key lime test plants, larger numbers of aphids
per plant, and timely observations to detect
initial symptoms. This report presents results
obtained with this improved technique. It in-
criminates the black citrus aphid (Toxoptera
aurantii (Fonsc.) ) as a vector, and describes
tests with other insects and mites, so far neg-
ative, as vectors. Studies of Meyer lemon trees
as sources of inoculum are also discussed.
METHODS
In order to establish tristeza virus in plants
of different citrus varieties, two Key lime
plants (T, and T,) were selected as standard
sources of the virus inoculum. These plants
had been infected in March 1953 as a result
of aphid transmissions from a stunted Temple
orange tree on a red lime (Rangpur type)
rootstock (16). Green citrus aphids were
transferred to these plants after they had fed
on the Temple orange for 116 hours, 75 to
the T1 plant for a 1-hour transmission feeding
period and 30 to the T, plant for 23 hours'
feeding. Both these Key lime plants have been
used in other pathological investigations (8)
and the reactions on the Key lime are consid-
ered typical of the mild tristeza virus in
Florida.


Leaf pieces from the T, and T. sources were
used to inoculate greenhouse-grown citrus
seedlings. The Valencia and Florida sweet
seedlings were considered to be nucellar, and
the Temple oranges were sexual seedlings
selected for characteristics of the parent varie-
ty. Presence of the tristeza virus in these
plants was confirmed by retransmission with
leaf-piece transfers to Key lime plants. The in-
fected Valencia and Florida sweet seedlings
were transplanted to a field and the infected
Temple orange plants were kept in pots in a
screen-house. Individual plants were re-
checked by leaf-piece inoculations into Key
lime plants for proof of continued presence of
the virus in the young growth at the time of
each acquisition feeding by aphids.
In the previous tests (16), in the present
tests with the black citrus aphid, and in
studies of Meyer lemon as a source of virus,
small Key lime plants 8 to 12 inches high with
single stems and 25 to 150 aphids were em.
played. In the other tests healthy Key limes 18
to 20 inches high were cut back or the tops
bent over to stimulate rebranching, and col-
onies of 300 to 700 aphids were used.
Pathological investigations had indicated
that the optimum time to observe initial symp-
toms of vein clearing associated with the mild
tristeza virus was 20 to 40 days following tis-
sue inoculation. In insect-inoculated Key lime
plants 30 to 60 days following infestation was
found to be the optimum period. Thereafter
the symptoms might diminish, especially under
summer conditions in the greenhouse. Initial
symptoms did not always occur on all
branches. The branches showing symptoms
were tagged so that they could be observed
frequently and used for testing retransmission
by means of leaf inoculations into Key lime
plants.
Isolated aphid colonies of single species
were placed on young, succulent growth of
healthy citrus seedlings and allowed to feed
for 24 hours, since previous tests with other
species (3, 5) had indicated that such feed-
ing would free them of tristeza virus. The
young shoots with the aphids were then trans-






NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION


ferred to the infected seedlings that had been
previously tissue-inoculated and tested, and the
aphids were allowed to move over voluntarily.
After a 25-hour period to acquire the virus,
aphids on shoots from the infected seedlings
were placed on the multiple-branched Key
lime test plants in separate cages at the labor-
atory. Again the aphids were allowed to move
over voluntarily. At the end of 24 hours counts
per unit of leaf area were used as a basis for
estimating the total number of aphids present
on each test plant. Representative aphid spec-
imens were collected for positive identifica-
tion. The test plants were sprayed twice with
0.04 percent nicotine sulfate before they were
transferred to the greenhouse.
TESTS WITH GREEN CITRUS AND
MELON APHIDS
The results given in table 1, from tests
carried out in March and April 1956, show
that the green citrus aphid transmitted the
virus from three varieties of infected citrus
seedlings to Key lime plants. All test plants
infested with melon aphids became infected.
The proportion of successful transmissions by
both species was much higher than in the
previous tests (16).
Table 1.--7Transmiion of tri.tesa virus by aphid. fro. various citrus
seedlings to multiple-branched Key lie. plants.


Source of Inoculum Number of Aphloa per Numobr of Toot Plant
Test Plant Infested Infected
Oreen itrus aphida
V..locia 300 3 1
400 4 2
lorMlda t 300 1 3
Te.pl. 400 2 1
kelop aobids
T..pl. 700 6 6

In these tests initial symptoms of tristeza
were detected on one or more branches of the
test plants 5 to 6 and, in one case, 8 weeks
after inoculation. New young leaves of in-
fested branches showed distinct vein clearing
and a veinlet pattern that frequently faded as
the growth matured. After the initial vein-
clearing symptoms disappeared, some leaf
cupping and deficiency signs remained. Pres-
ence of the virus in all aphid-infected plants
was confirmed by tissue transmissions to ad-
ditional Key lime plants.


TESTS WITH THE BLACK CITRUS APHID
One positive transmission of tristeza virus
was obtained in five tests with the black citrus
aphid. In this test 25 alate adults and nymphs,
all reared from one adult, were given an ac-
quisition feeding period of 48 hours on an
infected Valencia orange scion grown on a
potted Key lime rootstock in the greenhouse.
The transmission feeding period was 4 hours.
Presence of the virus in the aphid-infected Key
lime test plant was confirmed by leaf-tissue
transfers. The identity of the aphid species
was confirmed by Louise M. Russell, pf the
Entomology Research Branch. This is the first
record of positive transmission of tristeza virus
by this species.

MEYER LEMON AS A SOURCE
OF TRISTEZA VIRUS
Meyer lemon trees are present in dooryards
or small plantings in most citrus areas. Some
Meyer lemon trees have been found to carry
tristeza virus (11, 17, 20), but investigations
in Texas (4, 18) indicate that its spread from
this host is not common. Because of the wide
interest in Meyer lemon as a host, tests were
made to transmit the virus from it. Three aphid
species were used as vectors. Colonies of 5 to
50 apterous adults were employed. In 16 tests
with the black citrus aphid and 21 tests with
the melon aphid no transmissions were ob-
tained. In 107 tests where the green citrus
aphid was used, 2 transmissions were secured.
In the first positive transmission a Meyer
lemon tree at Minneola, Fla., was the source
of inoculum. Thirty apterous adult green
citrus aphids fed for 421' hours on this tree
and 42 hours on the test plant. Scattered but
distinct clearing of veins occurred on the
young leaves of the Key lime test plant 5
months later. These symptoms became less
evident as the leaves matured, and subsequent
new growth showed no further symptoms.
While these transmission tests were being car-
ried out, budwood from the Meyer lemon
branch that the aphids had fed on was
brought to the greenhouse and side-grafted
into 5 Key lime plants. All these plants showed
strong vein- and veinlet-clearing symptoms,
which were evident for a longer period and
were more distinct than those observed on the
Key lime plant infected as a result of aphid
inoculation.





40 FLORIDA STATE HORTICULTURAL SOCIETY, 1956


The Meyer lemon scion on one of the graft-
inoculated Key lime plants was allowed to de-
velop, and subsequently green citrus aphids
were fed on it for 24 hours and then trans-
ferred to two Key lime plants for another 24
hours. One plant, on which 75 aphids fed,
showed no symptoms, but the other, on which
50 aphids fed, developed transitory leaf symp-
toms 4 months later. This limited symptom
expression of tristeza suggested that either the
source of inoculum contained only a very mild
tristeza-virus strain or the aphids had sorted
out and transmitted only a portion of the virus
strain" mixture.
In order to obtain further information, leaf-
piece transfers and scion grafts were made.
The Key limes inoculated with tissue from
the Meyer lemon at the end of 2 months
showed striking vein- and veinlet-clearing
symptoms. The Key limes inoculated with tis-
sues from the aphid-transmitted source showed
only slight deficiency symptoms and a tenden-
cy for slight cupping of some leaves. Three
months after the inoculations observations
were made for the presence of stem pits. Two
plants tissue-inoculated from the Meyer lemon
source had averages of 28 and 100 pits per
10 centimeters of stem; two of three plants
tissue-inoculated from the aphid-infected Key
lime source had no pits, and one plant had 1
pit per 10 centimeters of stem. These results
show that a milder form of tristeza virus was
transmitted from the Meyer lemon by the
aphids than was transmitted by tissue grafts
from the same source.

TESTS WITH OTHER INSECTS AND MITES
Tests were also made with other insects
and mites found on citrus in Florida. The
sources of inoculum were tristeza-infected Key
lime seedlings. Thus far there have been no
positive transmissions. The species tested as
vectors, with the number of Key lime plants
infested, were as follows: green peach aphid
(Myzus persicae (Sulz.) ) 4, citrus mealybug
(Pseudococcus citri (Risso) ) 49, leafhopper
Homalodisca triquetra (F.) 35, blue sharp-
shooter leafhopper (Oncometopia undata
(F.) ) 7, big-footed plant bug (Acanthocepha-
la femorata (F.) ) 14, southern green stink
bug (Nezara viridula (L.) ) 29, stink bug
Euschistus obscurus (P. de B.) 7, citrus red
mite (Metatetranychus citri (McG.) ) 8.


TEST PLANTS As A MEASURE
of VIRUS TRANSMISSION
Tristeza of citrus was first recognized as a
disease of sweet orange on sour orange root-
stock. This scion-rootstock combination was
used in initial studies, which showed that the
disease is caused by a virus and can be trans-
mitted by tissue grafts (1, 6) and by Aphis
citricidus (Kirk) (1, 3, 13, 15). As informa-
tion advanced, West Indian, Mexican, and Key
lime plants were employed as means of de-
tecting this virus (9, 10, 14, 19).
The primary symptoms of vein and veinlet
clearing and stem pitting on the Key lime
plants are useful. Improvements in the pro-
duction and detection of symptoms on the
test plants have been sought as means of ob-
taining further information on virus transmis-
sion. In the present investigations the use of
standardized sources of inoculum, multi-
branched Key lime plants, large aphid popula-
tions, and observations at critical periods have
given high ratios of virus transmission under
early-spring conditions. The recovery from
initial symptom expression in the summer sug-
gests that the Key lime plants are not as good
indicators of tristeza virus under high-temper-
ature conditions. Temperatures appear to af-
fect not only the occurrence of vein clearing
on the leaves, but also stem-pitting symptoms,
as noted by Grant and Higgins (8).
The intensity of symptoms on the test plants
also varies with the virus strain. Recent patho-
logical investigations indicate that the mild
tristeza virus in Florida may be a mixture of
strains (8). By use of the aphid-transmitted
mild-virus source plants T, and Ts, and with
leaf-piece transmissions to Key lime plants and
successive selections of leaf pieces and trans-
missions to other Key lime plants, evidence
was obtained of virus strains that cause many
stem pits and some that cause few to no pits.
Apparently the tristeza virus strains could
exist in varying mixture levels in infected
plants. Work in South Africa (12) and Brazil
(7) has shown that aphids have transmitted
a mild form of the virus from trees known to
be carrying the severe form. In the present
study of Meyer lemon as a virus source, the
two transmissions obtained by means of aphids
produced notably milder symptom expression
on Key lime plants than those obtained by
tissue transmission.





NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION


TRANSMISSION OF TRISTEZA VIRUS
IN CITRUS GROVES
The green citrus aphid is the most abundant
aphid on Florida citrus. It usually limits its
feeding to seasonal growth flushes of succu-
lent terminals which vary with the citrus
variety and rainfall conditions, and its feeding
curls the tender foliage. The black citrus aphid,
appearing later in the season, feeds on more
mature leaves. The melon aphid, although less
prevalent on citrus than the green citrus
aphid, is also found on young growth.
Recent studies in California (5) indicate
that in four districts where measurements
were taken the yearly average number of
aphids of all species flying to a single orange
tree ranged from 185,725 in the coastal area
to 956,238 in the area around Covina and
Azusa called the intermediate district. The
respective figures for the melon aphid alone
were 3,200 and 35,600. Since the melon aphid
is the demonstrated vector of tristeza virus in
southern California, it is not surprising that
the disease spread most rapidly in the inter-
mediate district. Green citrus aphids made up
more than 85 percent of the aphids caught
flying to the orange trees, but neither this
species nor the black citrus aphid has been
shown to carry the tristeza virus in California.
We do not have comparable data for aphid
populations in Florida. However, our studies
show that all three species are potential vec-
tors of the tristeza virus.
Each tristeza-infected tree serves as a
reservoir from which the aphids can obtain
the virus. There are two types of reservoirs-
(A) an infected tree on a nontolerant root-
stock, as sour orange, which shows decline
symptoms and produces delayed, weak flushes
of new growth; and (B) a tree on a tolerant
rootstock which has apparently healthy
growth but carries the tristeza virus. The latter
is a more dangerous source of the virus, be-
cause the succulent flushes of new growth are
suitable for aphid feeding and transmission of
the virus at the time other normal, healthy
trees are flushing. The visibly diseased trees
(type A) seem to be less dangerous sources of
inoculum because of their 10-day to 2-week
delay in producing new flushes of growth that
are less vigorous.
In California Dickson et al (5) reported
that the rate of spread of tristeza in the groves


seldom exceeded two new infections each year
from each diseased tree. They noted, how-
ever, that the most rapid spread was generally
in the intermediate area where most orchards
were ruined commercially about five years
after the disease was first reported in them.
This area had the largest number of flying
aphids.
In Florida the visible spread of the disease
has been greatest in a Temple orange grove
where all trees were reported as being on sour
orange rootstock. Actually some were growing
on tristeza-tolerant rootstocks and it is be-
lieved that these trees have served as more
favorable reservoirs of virus for aphid trans-
mission than the visibly diseased trees on sour
orange rootstock.
The more infected trees available, the great-
er is the chance for aphids to acquire the virus
and transmit it to other trees. In Florida the
number of visibly diseased trees is not always
a reliable measure of the number of infected
trees, for frequently there are mixtures of
rootstocks.
Surveys made by the State Plant Board of
Florida (2) show a widely scattered distribu-
tion of tristeza-infected trees. These trees
serve as sources of virus, and as aphid infesta-
tions are not usually controlled by present
spraying practices, the number of infected
trees in the State may be expected to in-
crease.
SUMMARY
The green citrus aphid was found to trans-
mit the tristeza virus from infected Valencia
and Florida sweet seedlings as well as from
the Temple orange variety previously reported.
The black citrus aphid was shown for the first
time to be a vector of the virus. Seven other
insects and one mite species did not transmit
the virus.
Improved techniques have given high
ratios of transmission by the melon and green
citrus aphids. The techniques utilize con-
trolled sources of inoculum in several varieties
of citrus seedlings, multiple-branched Key
lime test plants, 300 to 700 aphids per test,
and timely observations to detect initial symp-
toms.
Transmissions of virus by the green citrus
aphid from Meyer lemon produced notably





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


milder symptom expression on Key limes than
those obtained by tissue transfers to Key
limes from the same Meyer lemon source.
REFERENCES CITED
1. Bennett, C. W., and A. S. Costa. 1949. Tristeza
disease of citrus. Jour. Agr. Res. 78 (8): 207-237.
2. Cohen, M., and L. C. Knorr. 1953. Present status
of tristeza in Florida. Proc. Fla. State Hort. Soc. 66:
20-22.
3. Costa, A. W., and T. J. Grant. 1951. Studies on
transmission of the tristeza virus by the vector
Aphis citricidus. Phytopathology 41 (2) : 105-113.
4. Dean, H. A., and E. O.. Olson. 1956. Preliminary
studies to determine possibility of insect transmission
of tristeza virus in Texas. Jour. Rio Grande Valley
Hort. Soc. 10: 25-30.
5. Dickson, R. C., Metta McD. Johnson, R. A. Flock,
and Edward F. Laird, Jr. 1956. Flying aphid popula-
tions in southern California citrus groves and their
relation to the transmission of the tristeza virus.
Phytopathology 46 (4): 204-209.
6. Fawcett, H. S., and J. M. Wallace. 1946. Evidence
of the virus nature of citrus quick decline. Calif.
Citrogr. 32 (2): 50, 88, 89.
7. Grant. T. J., and A. S. Costa. 1951. A mild strain
of the tristeza virus of citrus. Phytopathology 41(2):
114-122.
8. Grant, T. J., and Richard P. Higgins, 1956. Oc-
currence of mixtures of tristeza virus strains in
citrus. Submitted for publication in Phytopathology.
9. Grant, T. J., A. S. Costa, and S. Moreira. 1951.
Studies of tristeza disease of citrus in Brazil. V.


Further information on the reactions of grapefruits,
limes, lemons, and trifoliate hybrids to tristeza. Calif.
Citrogr. 36: 310, 311, 324-329.
10. Knorr, L. C., and W. C. Price. 1954. Diagnosis
and rapid determinations of tristeza. Fla. Agr. Expt.
Sta. Ann. Rpt., pp. 196-197.
11. McClain, R. L. 1956. Quick decline (tristeza) of
citrus. Calif. Dept. Agr. Bul. 45(2): 177-179.
12. McClean, A. P. D. 1954. Citrus vein-enation vi-
rus. So. African Jour. Sci. 50(6): 147-151
13. McClean, A. P. D. 1950. Virus infections of
citrus in South Africa. Farming in So. Africa 25 (293):
262; 25(294): 289.
14. McClean. A. P. D. 1950. Possible identity of
three citrus diseases. Nature, (London) 165: 767.768.
15. Meneghini, M. 1946. Sobre, a natureza e trans-
missibilidade da doenca "tristeza" dos citrus. Biologico
12: 285-287.
16. Norman, Paul A., and Theodore J. Grant. 1953.
Preliminary studies of aphid transmission of tristeza
virus in Florida. Proc. Fla. State Hort. Soc. 66: 89-92.
17. Olson, Edward O., and Bailey Sleeth. 1954. Tris-
teza virus carried by some Meyer lemon trees in
South Texas. Proc. Rio Grande Hort. Inst. 8: 84-88.
18. Sleeth, Bailey. 1956. Occurrence of tristeza in
two citrus variety plantings. Jour. Rio Grande Valley
Hort. Soc. 10: 31-33.
19. Wallace, J. M., and R. J. Drake. 1951. Newly
discovered symptoms of quick decline and related
diseases. Citrus Leaves 31: 8, 9, 30.
20. Wallace, J. M., P. C. J. Oberholzer, and J. D. J.
Hofmeyer. 1956. Distribution of viruses of tristeza
and other diseases of citrus in propagative material.
TU. S. Dept. of Agr. Plant Disease Rptr. 40(1): 3-10.


PHYSIOLOGIC RACES OF THE BURROWING

NEMATODE IN RELATION TO CITRUS

SPREADING DECLINE


E. P. DuCHARME' AND W. BIRCHFIELD2

The burrowing nematode, Radopholus simi-
lis (Cobb) Thorne, is now known to parasitize
more than 125 different species of plants.
Some species show no evident effects of the
parasite, whereas other species such as rough
lemon suffer severely. Many of the susceptible
species are grown as ornamentals around
homes and, if parasitizedd by burrowing nema-
todes, may be a source of infection for citrus
growing close by. If all the burrowing nema-
todes that parasitize these plants are alike,
then any infected plant could spread the in.
fection to nearby citrus. On the other hand,
should some colonies of burrowing nematodes
be so specialized that they do not feed on
citrus, then their presence on host plants
would not be a threat to adjacent groves. Be-
cause of the extensive host range of the bur-

Florida Agricultural Experiment Station Journal
Series No. 540.
'/Florida Citrus Experiment Station, Lake Alfred.
2/Florida State Plant Board, Gainesville, Florida.


rowing nematode, it is important to know
whether physiologic races of burrowing nema-
todes occur in nature and whether there are
races that do not parasitize citrus. A physiolo-
gic race is generally understood to be identi-
cal with the species in morphological respects
but to differ from it in some aspect of its
physiology, such as parasitism.
In Florida, clumps of banana, Musa nana
and M. sapientum, are often planted in and
about citrus groves bordering lakes, marshes,
irrigation ponds and drainage ditches. The
first evidence indicating the existence of a
physiologic race of burrowing nematodes that
differs from the burrowing nematodes causing
spreading decline came from such a clump of
banana plants. The banana roots were heavily
parasitized with burrowing nematodes whereas
the citrus roots were not. Roots from this loca-
tion were examined four times during the fol-
lowing year. Each time the citrus roots were
free of burrowing nematodes although the
citrus roots were intermingled with the para-





DUCHARME AND BIRCHFIELD: PHYSIOLOGIC RACES


sitized banana roots. Attempts to infect the
roots of sour orange seedlings with burrowing
nematodes from this location were not success-
fiul. The burrowing nematodes from this loca-
tion, although they would not feed on citrus,
could not be distinguished morphologically
from those causing spreading decline. In this
discussion burrowing nematodes that parasit-
ized banana but not citrus will be designated
as the "banana race."
Clumps of banana plants in or next to 39
citrus groves and other clumps in 30 loca-
tions where there was no citrus were examined
for presence of burrowing nematodes. In the
39 locations next to groves, the citrus and
banana plants were close enough for root con-
tact. Among these places examined, burrow-
ing nematodes had parasitized banana but
not citrus in 9 locations, both banana and
citrus in 4, and only citrus roots in 3. No
burrowing nematodes were found in the re-
maining 23 locations. Of the 30 isolated
clumps of banana, 13 were parasitized by bur-
rowing nematodes and 17 were not. None of
the parasitized banana plants appeared to be
diseased, whereas all infected citrus had
symptoms of spreading decline. These ob-
servations indicated the existence of three
physiologic races of burrowing nematodes,
separable by their ability to parasitize either
banana or citrus or both.
Experiments were conducted under con-
trolled conditions to test the hypothesis de-
rived from observations made in the field that
at least three strains of burrowing nematodes
exist. In the first experiment, sour orange seed-
lings planted in sterile soil maintained at
temperatures of 75" to 78' F. did not become
parasitized when inoculated with the banana
race of burrowing nematodes. In another ex-
periment, nematode-free banana plants and
rough lemon seedlings planted side by side in
the same container were inoculated with col-
lections of the banana race and the race
causing citrus spreading decline. The inocu-
lated test plants were grown for six months
with the soil temperature maintained at 75' to
78" F. The burrowing nematodes from banana
infected the banana test plants, but not the
rough lemon seedlings although the roots of
both plants were intermingled. In contrast, the
burrowing nematodes from a grove affected by
spreading decline readily parasitized the rough


lemon roots and attacked the banana roots as
well.
In another study, nematode-free sour orange
seedlings and banana plants growing in steam-
sterilized soil were cross-inoculated with bur-
rowing nematodes from the same sources used
in the preceding experiment. The soil tem-
perature was maintained at 75" to 78' F. The
burrowing nematodes from banana reinfected
banana but not the sour orange seedlings, and
those from a spreading decline affected grove
parasitized both the sour orange and banana
test plants. The results of these experiments
confirmed the existence of two of the three
physiologic races found in the field.
Burrowing nematodes that cause spreading
decline are physically like those of the banana
race. The average length and width of female
nematodes from both races was almost identi-
cal and there was no significant difference in
the physical proportions. No morphologic
character was found that could be used to
distinguish one physiologic race from the
other. The two physiological races of the bur-
rowing nematode (Radopholus similis) that
have been found in nature have been separated
only by differences in parasitic activity on
citrus and banana. The existence of a possible
third race, found in the field on citrus only,
was not studied in the laboratory experiments
undertaken.
It is likely that other physiological races of
this nematode can be detected by using addi-
tional species of host plants. Burrowing nema-
todes collected from several kinds of orna-
mental plants failed to parasitize citrus in ex-
ploratory tests, possibly because they may be
similar to the banana race. On the other hand,
we know that the physiologic race causing
spreading decline will infect Persea americana
Mill., (avocado); Malpighia glabra L., (Bar-
bados cherry); Hedychium coronarium Koen-
ig, (ginger lily); and Musa paradisiaca var.
sapientum Kuntze, (common banana in Flori-
da). At present it is not known how many
physiological races of the burrowing nematode
are involved in the spreading decline disease
of citrus, but the existence of such races could
explain some of the variation that occurs in
the severity of disease expression among af-
fected groves. In the search for resistant citrus
rootstocks, it will be necessary to test prospec-
tive plants against different populations of





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


burrowing nematodes from numerous loca-
tions.
Since one of the physiological races para-
sitized both citrus and banana, it becomes
necessary to determine which race is present
before deciding whether or not infected ban-
ana or other plants should be considered po-
tential reservoirs of infection for citrus. Until


there is some practical way to distinguish these
races, it is necessary for growers to take ut-
most precaution to avoid introducing any bur-
rowing nematodes by planting infested orna-
mentals in or next to citrus groves. The exist-
ence of physiologic races of burrowing nema-
todes does not minimize the gravity of the
spreading decline problem.


CITRUS ROOTSTOCK SELECTIONS TOLERANT

TO THE BURROWING NEMATODE


HARRY W. FORD
Florida Citrus Experiment Station
Lake Alfred
The purpose of this paper is to report the
evaluation of certain rootstock material that
seemed to show resistance to spreading de-
cline. Spreading decline caused by the bur-
rowing nematode Radopholus similis (Cobb)
Thorne (7) generally affects all citrus root-
stocks used commercially in Florida. Between
1951 and 1955, a total of 54 trees were found
that appeared healthy although surrounded by
decline trees. The trees were reported by Ex-
periment Station personnel, extension workers,
production managers, growers, and inspectors
of the Florida State Plant Board. Most trees
were eliminated as possible burrowing nema-
tode resistant candidates after a preliminary
inspection. A few trees showed potentialities
worthy of intensive study for burrowing nema-
tode resistance.
METHODS
The feeder roots of each tree recommended
for study were sampled for the presence of
the burrowing nematode by the root incuba-
tion technique suggested by Young (10). A
feeder root distribution pattern was compiled
for comparison with a representative standard
for healthy trees. The method of root sampling
is described in another papei (4). Trees were
accepted as candidates for the test program if
the root profile compared favorably with that
of a healthy tree even though burrowing
nematodes were found associated with the
roots. Forty-four of the 54 candidates were
eliminated by this test.
Florida Agricultural Experiment Station Journal
Series No. 551.


Ten trees were entered in the test program.
The sweet orange scions of two trees were sus-
pected as the source of the tolerant factor and
were therefore included in the test program
and coded sweet oranges E and F. Two trees
were seedling sweet oranges and were coded
sweet oranges G and H. One tree was a seed-
ling of Cleopatra mandarin and coded Cleo-
patra I. The rootstocks of four of the trees ap-
peared to be rough lemon and were coded
rough lemon. The abbreviated designations
were RL-A, RL-B, RL-C, and RL-D. The
rootstock of the last candidate was unidenti-
fiable as a common citrus species and was
coded Clone X.
In order to obtain test material, roots of
the desired tree were severed and both cut
ends of each root lifted above the surface of
the ground and tied to stakes. Five to 40 per-
cent of the severed roots of rough lemon and
five to 12 percent of sweet orange stocks pro-
duced sprouts. The sprouts were permitted to
grow until eight to 15 expanded leaves were
present. The sprouts were removed and cut
into leaf bud cuttings by severing the stem
above and below the bud with pruning shears.
Henceforth the term cutting will be used in
this report to indicate a rooted leaf bud cutting
in which the bud has developed into a leafy
shoot. The propagating procedure is con-
tained in a separate report by Ford (3).
Root sprouts of promising candidates have
been topworked to older citrus trees to obtain
seed to determine if the nematode tolerant
factor is seed transmitted.
The following tests were performed to eval-
uate the material: I. A candidate rootstock
clone was first evaluated by comparing the
growth of six cuttings planted in sub-soil in-






FORD: CITRUS ROOTSTOCK SELECTIONS


fested with the burrowing nematode and six
cuttings in non-infested citrus grove sub-soil.
Separate 1.25 gallon containers were used for
each cutting. The containers were placed in a
water cooled temperature tank that maintained
the soil temperature at 78 F. The plants in
each container of decline soil were inoculated
three times with burrowing nematodes ob-
tained from different commercial groves. The
cuttings were permitted to grow for three to
six months depending on rate of growth and
time of year.
II. Six Clone X cuttings were planted in
containers filled with steam sterilized soil.
Two hundred hand picked burrowing nema-
todes were placed on the roots of each plant
and permitted to develop for six months.
III. Six months old cuttings of RL-A, RL-B,
and Clone X were budded with Parson Brown,
Valencia, and grapefruit scions by using a
patch bud technique (2). Three to six months
after budding, the plants were tested for
growth and nematode infestation in the tem-
perature tank.
IV. Sweet orange E and sweet orange F
were budded on susceptible rough lemon seed-
lings to determine if nematode tolerance in
the roots could be induced by the scion of a
budded tree.
V. Twelve cuttings of RL-A, RL-B, and


Clone X were grown in decline sub-soil to
determine the influence of N and K on the
population of burrowing nematodes. Two
levels of N and K in factorial combination
were applied as nutrient solutions twice weekly
for four months. The following concentrations
in ppm were used: N, 25 and 200; K, O and
300. Also, 24 cuttings of Clone X were di-
vided into two groups. One group was planted
in burrowing nematode infested soil and the
other in non-infested soil. Each group was
sub-divided into two groups of six plants each
to which two levels of N were applied. Nitro-
gen at 25 and 210 ppm in the nutrient solu-
tion was applied twice weekly.
VI. The ability of the nematode to pene-
trate the feeder root, lay eggs and reproduce
was determined by an aceto-osmic staining
procedure developed by Tarjan and Ford (8).
Rooted leaf-bud cuttings of clones RL-A, RL-
B, and Clone X were planted in sterilized soil
in separate petri dishes with a one half inch
square of No. 41 Whatman filter paper under
the root tip. Twenty-five female burrowing
nematodes in 0.3 ml. of water were placed on
the root tip and covered with a layer of soil.
The inoculated roots were stained and cleared,
after two to 26 days at 78 F. under artificial
light, so that nematodes and eggs could be
seen inside the roots.
VII. The number of eggs in the cortex and


Table 1. Root distribution of the parent tree of selected root-
stock clones as compared to susceptible rough lemon


Rootstock clone Feeder roots in indicated 10 inch depth zones
0-10 10-20 20-30 30-40 40-50 50-60 Total

Clone X 9.2 11.2 16.0 12.6 8.8 5.9 63.7

Rough lemon B 1.9 .9 6.0 6.4 3.6 1.6 20.4

ucgh lemon C 3.0 1.2 1.9 .5 .2 .1 6.9

Rou-h leion P 3.9 2.2 4.4 3.3 .9 .3 15.0
b
Roulh lemon (Check) /-.7 2.1 5.3 4.3 3.7 2.0 22.1



a Mean of 4 samples to a depth of 5 feet expressed as rrams dry weight in a
column one foot square.
b o 10 trs 25 rs old in soil not infested with spreading decline.
!lean of 120 trees 25 years old in soil not infested with spreading decline.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


stele of the feeder root of Clone X as com-
pared to RL-A was determined by comparing
single roots from a cutting of each clone
placed together in a petri dish. Fifty female
burrowing nematodes were placed between
the two roots and incubated for four days after
which the roots were stained and cleared.


VIII. From October 1955 to January 1956,
fruit samples were collected from the Parson
Brown scion of Clone X and compared with
Parson Brown on rough lemon. Measure-
ments were made of internal fruit quality. Ap-
pearance and palatability were evaluated by a
panel.


Table 2. Growth and R. similis population of cuttings from selected root-
stock clones after 3-4 months in temperature tank.


Clone Soil Shoot Growth Fresh wt. Fresh wt. Number
Condition cm. Shoot Roots R. similis
(grams) (grams) per cutting

Rough lemon A Infested 45 28 21 117 ;e81
Non infested 48 30 26

Rou4h lemon B Infested 47 34 25 201 A 113
Non infested 51 37 31

Rourh lemon C Infested 39 32 23 123 + 75
lon infested 44 35 28

Rough lemon D Infested 43 46 61 352 203
Non infested 51 55 66

Sweet Orange Ec Infested 29 9 7 25 11
Non infested 38 12 12

Sweet Orange Fc Infested 29 16 13 37 16
Non infested 35 22 16

Sweet Orange Gd Infested 4 4 4 39 t 21
Non infested 9 7 5

Sweet Orange Ed Infested 5 3 2 41 1S
Non infested 7 4 3

Cleopatra Ic Infested 10 2 1 24 7
seedlinf 7on infested 24 5 3

Clone X Infested 28 45 49 3 3
Kon infested 27 37 3?


a 1:ean of 6 plants froni separate containers.


u Incubated in fruit jars for 48 hours.

SThe scion of a tree being tested as a potential rootrtoc!k.

d Parent plant a seodlin. tree.

e Standard deviation of the mean.





FORD: CITRUS ROOTSTOCK SELECTIONS


Table 3. Growth and R. similis population of Clone X cuttings in steam
sterilized soil inoculated with 200 .R. similis per plant.a


Treatment 3 months 6 months
Shoot growth Shoot tiob Number' Shoot growth ShootratiobNumberv
cm. Root R. similis cm. Root R. similis
__per cutting per cutting

Inoculated 21 .9 2 t 2 49 .9 1 1

Untreated 19 .9 47 .8


a Mean of 6 plants from separate containers.
Fresh weight of shoot divided by fresh weight of roots.

C Plants removed from containers and roots incubated in fruit jars for 48 hours.


RESULTS
In Table 1 feeder root measurements of the
parent trees of four rootstock candidates grow-
ing in decline soil are compared with the root
density of trees on ordinary rough lemon in
non-infested soil. Rough lemon B had a root
density comparable to a healthy tree to a
depth of five feet while Clone X had three
times the root density of ordinary rough lemon.
The growth and burrowing nematode in-
festation of cuttings taken from 10 candidate
rootstock clones is shown in Table 2. Shoot
growth of RL-A and RL-B was reduced seven
percent by the presence of the burrowing
nematode. Both rough lemon clones supported
a population of burrowing nematodes com-
parable to spreading decline susceptible
rough lemon. There was no reduction in shoot
length or root weight of Clone X when grown
in burrowing nematode infested soil and the
population of burrowing nematodes was re-
duced to a very low level in all replicates of
the test.
Nematode survival and plant growth when
200 hand picked burrowing nematodes were
placed on the roots of six individual cuttings
of Clone X in sterilized soil are shown in
Table 3. After six months, the burrowing
nematode population had disappeared from
the roots of 50 per cent of the cuttings and
one to three nematodes were found on the
roots of the remaining plants. There was no


depression of growth by the burrowing ne-
matode.
The effect of a budded scion on nematode
survival and plant growth of RL-A, RL-B, and
Clone X is presented in Table 4. Growth com-
parisons between grafted combinations of the
different clones are not entirely valid because
all of the tests were not performed at the same
time. Growth of grapefruit and Parson Brown
scions on RL-A was reduced 10 and 18 per-
cent respectively. The Valencia bud on RL-B
was taken from the parent tree of RL-B so
that the budded combination was genetically
the same as the original tree in the field. This
combination showed a 10 percent reduction
in growth. The growth of cuttings of Clone X
budded with Parson Brown from the original
parent tree was not reduced in decline soil
and the burrowing nematode population com-
pletely disappeared. Studies of Ruby Red
grapefruit and Temple budded on Clone X
were in progress only two months when this
manuscript was written. The burrowing ne-
matode population consisted of two to four
adult females. No larvae were present indi-
cating that the nematode population was not
increasing. Sweet orange E and sweet orange
F when budded on susceptible rough lemon
were retarded in growth 65 percent by the
nematodes so that the results are not reported.
Unbudded cuttings of sweet orange E and F
were also reduced in growth (Table 2). The
data indicate that the two sweet orange clones






FLORIDA STATE HORTICULTURAL SOCIETY, 1956

Table Growth and similis population of budded rootstock cutting
Table 4 Growth and R. similis population of budded rootstock cuttings.


Graft com- Scion Soil Duration Shoot growth Fresh wt. Number b
bination Condition (months) cm. of plant R. aimilis
Rootstock (grams) per cutting

Rough lemon A Grapefruit. Infested 3 13 21 75 A 47
Non infested 14 28

Rough lemon A Parson Brown Infested 3 35 97 156 81
Non infested 43 124

Rough lemon B Valenciac Infested 3 26 84 23
Non infested 29 -

Clone X + Parson Brownc Infested 4 29 112 0
Non infested 30 103

Clone X Ruby Red Infested 2 2 1
Clone X Temple Infested 2 4 1


a Mean of 6 plants from separate containers.

b Incubated in fruit jar for 48 hours.

c Combination genetically the same as original tree found in the field.


do not have nematode tolerant characteristics
that originate in the top of the trees as orig-
inally suspected.
The effect of N and K nutrition on nema-
tode infestation of the host has attracted the
attention of several workers (1, 5, 6). Oteifa
(5) found that nutrition was of considerable
importance in determining the development
timne of root knot nematodes Meloidogyne in-
cognita.
Nitrogen and K levels had no significant ef-
fect on the burrowing nematode population of
RL-A, RL-B, and Clone X so that the results
are not reported. The growth of Clone X cut-
tings was modified, by increased N and K,
from that reported for citrus in sand culture
(9). Additional studies are in progress to
evaluate the effect of nutrition on growth of
Clone X cuttings.
The effect of N level on growth of Clone X
in infested as compared to non-infested citrus
grove sub-soil is shown in Table 5. Shoot
growth was not affected by the burrowing ne-
matode infested soil condition at either of the
two N levels.


Studies of burrowing nematode activity by
staining in situ indicated that reproduction of
burrowing nematodes was depressed in the
cortex of the feeder roots of Clone X cuttings
as compared with the cortex of RL-A, RL-B
or ordinary rough lemon cuttings. Oc-
casionally nematodes penetrated the stele
of Clone X and after 21 days there was an in-
crease in the nematode population. There was
no indication of an exit of nematodes from the
stele. No burrowing nematodes penetrated the
stele of RL-A, RL-B or rough lemon under the
conditions of this experiment. Eighty-five tests
were made on the rough lemon clones. Ap-
parently there is a difference between species
from the standpoint of burrowing nematodes
entering the stele. Nematodes were found in
the stele of pummelo, for example.
A detailed comparison was made between
Clone X and RL-A by placing female burrow-
ing nematodes between single roots from each
clone. The results of this test are shown in
Table 6. There were 60 times more eggs in
the cortex of RL-A than in the cortex of Clone
X. In the cortex of RL-A eggs were scattered





FORD: CITRUS ROOT;


throughout the tissues while in the cortex of
Clone X all eggs that could be found were
close to the body of the nematode. When ne-
matodes penetrated the stele of Clone X, a
condition that occurred in 11 percent of the
samples, considerably more eggs were found
per nematode.
A panel of Experiment Station personnel
preferred the external fruit appearance of Par-
son Brown on rough lemon to that of Parson
Brown on Clone X. However the panel pre-
ferred Parson Brown on Clone X for eating
quality. Juice characteristics of Parson Brown
on Clone X and rough lemon are shown in
Table 7.
DISCUSSION
RL-A was secured from the rootstock of a
Valencia orange tree in Lake Alfred that had
been in spreading decline infested soil for four
years prior to 1951. Dense foliage covered the
tree with leaves of normal size which was in
marked contrast to adjacent trees with symp-
toms of spreading decline. The grove was
pulled before the burrowing nematode was

Table 5. Effect of N on gro, th
cuttings in infested ax
temperature tanka


STOCK SELECTIONS 49

identified as the cause of spreading decline.
RL-B, the rootstock of an 18 year Valencia
tree from a grove in southern Polk County
was transplanted into spreading decline soil
in 1941. Thus the feeder roots have been in-
fested with the burrowing nematode for at
least 14 years. The tree was considerably
larger than surrounding decline trees even
though some feeder root damage was detected.
Below five feet the root- density fluctuated
considerably during a one year period.
The results of growing plants of RL-A and
RL-B under controlled conditions in infested
soil and inoculation of individual roots in
petri dishes indicate that the two rough lemon
clones are reasonably tolerant to the damage
of the burrowing nematode. The number of
burrowing nematodes and the damage within
the root cortex of the two tolerant clones are
comparable to susceptible rough lemon. The
nature of the tolerance of these rough lemon
clones is not understood; however, the rapid
rate of shoot growth and development of new
feeder roots is probably an important factor.

mad R. sinilis population of Clone A
id non infested soil after 3 months in


Treatment Soil Shoot growth Sho2 atioc Number
Condition cm. Root R. similis
per cutting
Low N Infested 26 1.3 6 + 3

Non infested 23 1.3


High N Infested 29 1.0 3 2

Non infested 27 .8

Significance N.S. N.S. N.S.


a Mean of 6 plants from separate containers.

b 25 ppm and 210 ppm of N respectively applied twice weekly.

c Fresh weight of shoots divided by fresh weight of roots.
dRoots incubated in fruit jars for 48 hours.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Table 6. Number of R. similis and eggs found in feeder roots of Clone X a
and Rough lemon A cuttings four days after nematode inoculation.



Rootstock Corte Stele
R. simil1s Eggs smiles Eggs

Rough lemon A 10.1 97.2 -

Clone X 5.2 1.6 3 9

Significance **

L.S.D. at .05 3.1 21.2


Fifty female burrowing nematodes placed between a feeder root of Clone X
and a feeder root of Rough lemon A in a petri dish.

b Mean of 35 replicates in which the nematodes invaded the cortex.

c The mean of 4 replicates in which the nematodes invaded the stele.

* Statistical significance at 5 percent level.
** Statistical significance at 1 percent level.


It is conceivable that the burrowing nematode
could damage RL-A and RL-B under poor
grove management practices. This possibility
will have to be evaluated under field condi-
tions. At the present time RL-A and RL-B are
propagated by cuttings although an evalu-
ation of seed propagation is in progress. It is
essential that the seed produce a very high
percentage of nucellar plants as assurance that
the rootstock will be genetically the same as
the original parent. Tests for susceptibility to
tristeza and xyloporosis are in progress.
Clone X, a rootstock that has not been iden-
tified, is resistant to the burrowing nematode
found in citrus groves. The clone is not com-
pletely immune because nematodes penetrated
the feeder roots and in 50 percent of the
plants one to four nematodes survived three
to six months. In every test conducted with
cuttings of Clone X, the rate of growth in ne-
matode infested soil was equal to or better
than in non-infested soil. Laboratory studies
indicated that the resistant factor was con-
fined to the root cortex and had a detrimental
effect on the eggs laid by the nematode.
The 25-year-old parent tree of Clone X
was discovered in a grove near Davenport,


Florida in 1954. The tree was 16 feet high and
yielded six boxes. Root samples taken at the
periphery of the tree over an 18 month period
were devoid of burrowing nematodes. Feeder
roots from the four adjacent trees were al-
ways found to harbor the nematode. With the
exception of an area nine feet square near the
southeast corner of the tree, feeder roots of
adjacent rough lemon trees did not penetrate
the dense root system of Clone X. The re-
sistance of the feeder roots to the burrowing
nematode and the dense nature of the root
system suggests that the stock may also be
of value as a biological barrier against the
spread of the burrowing nematode.
Fruit of Clone X are not available at the
present time so that all progeny have been
obtained from leaf bud cuttings. The clone is
more difficult to propagate and grows slower
than rough lemon. The leaves appear to be
resistant to anthracnose caused by Colletotri-
chum gloeosporioides Penz but susceptible to
sour orange scab caused by Elsinoe Fawcetti
Bitancourt and Jenkins. In containers, the roots
were more frequently damaged by excess
water than roots of rough lemon.
The reaction of Clone X to other diseases






FORD: CITRUS ROOTSTOCK SELECTIONS


such as tristeza and xyloporosis is unknown
at present. The stock should be evaluated in
the field for general horticultural characteris-
tics before being recommended for use in
Florida citrus groves.
SUMMARY
Between 1951 and 1955 a total of 54 trees
were found that appeared healthy although
surrounded by decline trees. Most trees were
eliminated as potential burrowing nematode
resistant candidates after a preliminary in-
spection. Ten trees were entered in the test
program.
The results of growing cuttings of candi-
date clones in spreading decline infested soil
and inoculation of individual roots in petri
dishes indicated that two rough lemon clones
were tolerant to the burrowing nematode
even though a high population of burrowing
nematodes was found on the roots. Growth
of plants was reduced 10 to 18 percent.
A third rootstock, that has not been identi-
fied, was found to be resistant to the burrow-
ing nematode infecting citrus groves. Plant
growth was not reduced in infested soil and
the population of burrowing nematodes al-
ways decreased and frequently disappeared.
The resistant factor was found to be confined


to the root cortex and had a detrimental ef-
fect on the eggs laid by the nematode. The
absence of information on general horticultural
characteristics, mineral nutrition, tristeza and
xyloporosis, indicate that field tests must be
evaluated before this clone can be recom-
mended for planting in Florida citrus groves.
LITERATURE CITED
1. Chitwood B. G. and B. A. Oteifa. 1952. Nem-
atodes parasitic on plants. Ann. Rev. Microbiol.
6:151-184.
2. Ford. Harry W. 1956. Unpublished data.
3. Ford, Harry W. 1957. A method of propagating
'citrus rootstock clones by leaf bud cuttings. Proc.i
Amer. Soc. Hort. Sci. (In press).
4. Ford, Harry W., Walter Reuther, and Paul F.
Smith. 1957. Effect of Nitrogen on root development
of Valencia orange trees. Proc. Amer. Soc. Hort.
Sci. (In press).
5. Oteifa, B. A. 1953. Development of the root
knot nematode Meloidogyne incognita as effected by
potassium nutrition of the host. Phytopath. 43:
171-174.
6. Oteifa, Bakir A. 1955. Nitrogen source of the
host nutrition in relation to infection by a root-knot
nematode Meloidogyne incognita. Plant Disease Re-
porter 39 (12): 902-903.
7. Suit, R. F., and E. P. DuCharme. 1953. The
burrowing nematode and other parasitic nematodes
in relation to spreading decline of citrus. Plant
Disease Reporter 37(7). 379-383.
8. Tarjan, A. C. and H. W. Ford. 1957. A modified
aceto-osmium staining method for demonstration of
nematodes in citrus root tissues. Phytopath. (In
press).
9. Webber, J. H., and Batchelor, L. D. 1948. The
Citrus Industry. Vol. I. Univ. of Calif. Press. Berke-
ley, Calif.
10. Young. T. W. 1954. An incubation method for
collecting migratory endo-parasitic nematodes. Plant
Disease Reporter. 38(11): 794-795.


Table 7. Juice characteristics of Parson Brown on Clone X compared to
Parson Brown on rough lemon, 1955-56.



Rootstock Date Juice by Soluble Acid Soluble Mgs. Vitamin
Weight Solids Solids to C/10010Ls.
% f Acid
Ratio

Clone X Oct. 7 52.0 9.2 1.10 8.3 69.2

Rough lemon Cot. 7 50.7 9.4 1.21 7.7 58.4

Clone X :ov. 8 54.6 10.3 1.05 9.8 55.0

Rough lemon Eov. 8 50.9 10.1 1.27 7.9 55.0

Clone X Dec. 13 50.0 11.4 .97 11.7 63.1

Rough lemon Dec. 13 54.7 10.7 .94 11.4 60.0

Clone X Jan. 3 53.8 11.8 .81 14.6 66.1

Rough lemon Jan. 3 58.8 11.4 .88 13.0 64.6





FLORIDA STATE HORTICULTURAL SOCIETY, 1956

THE NEW 4-H CLUB PROGRAM FOR CITRUS

PRODUCTION TRAINING


JACK T. MCCOWN
Florida Agricultural Extension Service
Gainesville
Agricultural progress in America during re-
cent decades has been astounding. Looking
at agricultural history it can be seen that this
progress is closely associated with the em-
phasis agriculture has placed on developing
its youth. Major agricultural enterprises have
had specific programs to inspire youth. This
is a part of the citrus industry that is lacking
today. Realizing that many boys do not have
the opportunity to study citrus the Agricul-
tural Extension Service is expanding its citrus
youth program to meet this need. This paper
will outline the Extension- Service's citrus
youth program in order that you may become
better acquainted with its aims and objec-
tives. The Extension Citrus Advisory Com-
mittee which plays an important part in de-
veloping this program, has outlined a 5-year
project for 4-H Club boys wishing to become
more intimately acquainted with the industry.
The 5-year program as outlined below will
meet all requirements for a 4-H Club project.
Upon completing each year's requirements,
the youth may continue his work toward the
following year's requirements without wait-
ing for an end of a calendar year.
The requirements for the first year are:
1. Map a 10-acre bearing grove showing
the location of (1) healthy trees, (2) missing
trees, (3) dead trees, (4) diseased trees, (5)
young resets.
2. When the map is completed, it should
show the total number of trees in the blocks,
the number of healthy trees, and the number
of diseased, dead and missing trees.
3. Be able to identify citrus fruits that
have been injured by (1) rust mites, (2) scale,
(3) melanose.
4. Plant a citrus seedbed either as an
individual home project, or in a cooperative
club project. Discuss size and location of
your seedbed with your local leader, or Ex-
tension Agent. (Minimum size of seedbed
to be determined.)


5. Keep neat and accurate records in a
record book, showing the work that has been
done, and write a story about your citrus ac-
tivity.
SECOND YEAR'S REQUIREMENTS
1. At least 6 months after completion of
the first year map, make another map show-
ing the location of (1) healthy trees, (2)
missing trees, (3) dead trees, (4) diseased
trees, (5) young resets.
2. When the map is completed, it should
show the total number of trees in the block,
the number of healthy trees and number of
diseased, dead and missing trees. Refer to
your first year map and copy the comparable
figures and set them down below the first
year's figures. Note whether the general con-
dition in the grove is (1) improved, (2)
worse, (3) the same. Mention the progress
of the grove in the story at the end of the
year.
3. Be able to identify early, midseason and
late oranges, two kinds of grapefruit and one
kind of tangerines. It is not necessary to iden-
tify by variety, but the club member should
be able to examine the fruit and determine
whether it is early, midseason or late.
4. When the seedbed is between 12 and 18
months old, line out the seedlings. Discuss
location of nursery and its size with the local
leader or Extension Agent.
5. Be able to identify 5 pests of citrus (may
be insects, diseases or both).
6. Keep neat and accurate records and
write a story on the second year's citrus ac-
tivity.
THIRD YEAR'S REQUIREMENTS
1. About 9 months after making the second
map, make a third one the same way.
2. Determine the number of skips in the
10-acre plot due to missing, dead, or diseased
trees. From this figure, calculate the per-
centage of trees missing. The percentage of
crop loss in the grove would be about the
same. Knowing what price per box the fruit
brought, calculate the financial loss to the
grower.





McCOWN: CITRUS PRODUCTION TRAINING


3. Bud the nursery. The 4-H Club mem-
ber should demonstrate to the local leader or
the Extension agent his ability to bud and
properly care for the nursery. The budded
trees should be properly labeled. Certified
budwood should be secured if possible. If
certified budwood is used, the buds should
be selected and the budding done under direct
supervision of the leader and the State Plant
Board representative.
4. Be able to identify and know the ap-
proximate harvest season-whether early, mid-
season or late-of the following citrus fruits:
Oranges-Parson Brown, Hamlin, Navel, Pine-
apple, Jaffa, Valencia, Lue Gim Gong. Grape-
fruit-Duncan, Marsh Seedless, Foster Pink,
Thompson Pink, Red; Tangelos Orlando,
Minneola, Thornton; Miscellaneous, one
variety of lemon, Persian (Tahiti) lime, Mer-
cott.
5. Be able to identify four insects and
three diseases that are of economic import-
ance in citrus production.
6. Keep neat and accurate records and
write a story of the year's activities.
FOURTH YEAR'S REQUIREMENTS
1. Be able to identify leaf symptoms of the
following mineral deficiencies in citrus: nitro-
gen, magnesium, zinc, manganese and iron.
2. The club member should be able to
demonstrate his ability to stake out a grove
for planting.
3. Sell or plant out the nursery trees. Learn
to plant nursery trees in the grove by plant-
ing under the supervision of the club leader
or Extension agent. Keep a record of how
these trees are cared for the first year. In-
clude dates for each operation, including
amount of water per tree, banking, planting
cover crop, analysis and amount of fertilizer,
insect and disease control.
4. Be able to identify five citrus insects and
four diseases and tell how they can be con-
trolled.
5. Explain what is meant by the "on tree"
price growers get for citrus. Keep a record of
"on tree" prices for one season from October 1
to June 15 for oranges and grapefruit. (Con-
tact the same grower, grove caretaker, or cash
buyer once each week and ask him the "on
tree" price. Record this information, in table
form in the record book, showing if it is early,
midseason or late fruit prices.)


FIFTH YEAR'S REQUIREMENTS
1. Keep the following record on a bearing
grove from September 1 to August 31. Fertili-
zation: date, analysis, number of pounds per
tree, method of application. Actually be on
hand and watch the entire operation for at
least one application. Know how to correct
or prevent nitrogen, magnesium, manganese,
zinc and iron deficiencies.
Spraying: Date, what is being sprayed for,
materials used in the spray, approximate gal-
lonage or pounds of dust per tree.
Cultivation: Date, kind (disc, plow, acme).
Cover crop: Date planted, kind and seed-
ing rate per acre (if not volunteer). Know
why cover crops are needed in Florida citrus
groves. Observe harvesting operations and
spend at least half a day with a picking crew.
2. Know what "top working" means and
how it is done.
3. Draw a floor plan of a fresh fruit pack-
ing house, single strength, sectionizing plant
or concentrate plant and know the funda-
mentals of their operation.
4. Keep neat and accurate records and
write a story of the year's activity.
By providing this type of program we
should achieve many objectives. First of all,
the youth, through his association as a 4-H
Club member would develop his leadership
abilities. (2) Such a program would inspire the
boy's interest in citrus through a closer 'associa-
tion with many segments of the industry. (3)
Provide the citrus industry with better trained
personnel upon completion of this project. (4)
Prepare some of these young men to achieve
a better job by becoming better skilled. (5)
Inspire a desire in some to further their educa-
tional training by attending college.
Now comes the question of what course of
action must be taken in order that we may
achieve these aims and objectives. A 4-H Club
member who enrolls in a citrus project will
through his local leader or county agent's
leadership be made aware of the require-
ments necessary to carry on a project for 5
years. He will also be instructed in the pro-
cedure of keeping records, as a project record
book will be provided outlining each year's
work. Upon completion of a year's project,
several boys will be selected from each county
to attend the annual Junior Citrus Institute.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


This Institute is held at 4-H Camp Cloverleaf
for the purpose of putting a final touch to the
citrus project work for the year. Attending
the Institute will be an award for the boy do-
ing the best project work in his county. The
Junior Citrus Institute this past year was
jointly sponsored by the Chilean Nitrate Edu-
cational Bureau of Orlando and Dolomite
Products Inc., of Ocala. In addition to the
Junior Citrus Institute, we are preparing to
promote additional interest among the club
members in citrus by providing fruit judging
contests and similar activities at the various
county fairs throughout the state. At this
time the boy will also be given the oppor-
tunity to participate in insect, disease and
other identification contests.
It is important that the citrus industry take
part in developing this program. Men in the
industry can be of help by showing an interest


and taking an active part in local project
work. We may also inspire the youngsters
through encouragement and recognizing a job
well done. In some instances financial aid may
be necessary for clubs to develop local proj-
ects. Examples would include: nursery
projects, small groves for demonstration pur-
poses, tours and training schools. Organiza-
tions and individuals may help by making
available funds for this purpose. We feel that
the program outlined will be successful. How-
ever, greater goals may be achieved if we rea-
lize the importance of such a youth program
and show an interest by putting forth a con-
certed effort to insure success. The young
people of Florida are a part of the citrus in-
dustry. Let us prepare them to accept its fu-
ture responsibilities in order that our industry
may continue to be a leader among the various
American agricultural enterprises.


FIELD OBSERVATIONS OF SEVERAL

METHODS OF MANAGING CLOSELY

SET CITRUS TREES


FRED P. LAWRENCE
Florida Agricultural Extension Service
Gainesville
ROBERT E. NORRIS
Florida Agricultural Extension Service
Tavares
You will note from your program that the
title of this presentation is "Field Observa-
tions of Several Methods of Managing Closely-
Set Citrus Trees." That title sounded simple
enough when it was submitted to the program
chairman but now that we have had more
time to contemplate we are not so sure. For
instance, how close is close? To help answer
this question we turned to Webster's Colle-
giate dictionary only to find more confusion
than enlightenment. We were reminded first
of all that it depends how you pronounce the
word. If you put a "z" in the pronunciation-
cloze-it means to "shut up" and considering
the small amount of actual data we have, that
might not be a bad idea. There are many
other meanings, of course, but Definition No.


25, having the parts near together, is the one
that seems most appropriate for our use.
Applying this definition, consider first the
citrus tree spacings of the various producing
areas of the world. In Italy and other Medi-
terranean countries citrus trees are usually
spaced 10'x10' or 10'x12' which results in 300
to 450 trees per acre. The Japanese orchards
average 240 to 300 trees per acre. Egypt's
predominant spacing is 12'x18'; Peru 18'x18';
Brazil 21'x24'; California 22'x22' and Florida
25'x25'.
The planting distance in a given area de-
pends upon such things as variety, species of
rootstock used, type and fertility of the soil,
the length of the growing season, and, to a
large extent, upon the attitude of the indi-
vidual doing the planting. To illustrate the
latter point it might be well to point out that
quite a number of California growers, accord-
ing to an article in the October '55 issue of
Citrograph, are turning to what they call
hedgerow plantings and some groves are
planted as closely as 8x10 which gives some
490 trees per acre.




LAWRENCE AND NORRIS: FIELD OBSERVATIONS


All of these plantings, or at least a major
portion of them soon reach a point where the
limbs and branches of the various trees inter-
lock and overlap and unless special man-
agement practices of pruning are applied the
bearing surface of such trees diminishes and
naturally the production declines in propor-
tion.
According to the best estimates available
Florida has 497,400 acres of bearing trees,
333,690 acres or 67% of which are 16 years of
age or older. A great many of these groves are
planted on spacings of 15x30, 20x24, 25x25
and similar distances and if we apply defini-
tion No. 25 to the word close we will find
that most of these trees have their parts near
together; hence we can apply the term close-
ly planted and in need of some form of prun-
ing.
Time will not permit our discussing the
varied and many methods of pruning em-
ployed in the various citrus producing areas
of the world-or even all of those practiced in
Florida-so we will confine our remarks to
some field observations of several methods of
managing closely-set citrus trees; to narrow
it down even more we propose to discuss
briefly the following practices:
1. Hedging
2. Heading back
3. Thinning by tree removal
4. Topping-a form of rejuvenation prun-
ing
In fairness to those who may read this
paper in the printed proceedings we should
state that from this point on our talk will be
illustrated with color slides and we shall at-
tempt to present, as clearly as possible, a
word picture of these various methods of
pruning.
Despite the difficulties associated with
crowded groves, very little pruning of any
nature has been undertaken in Florida either
to prevent or to correct the situation. This has
probably been due to the fact that earlier ex-
periments suggested that pruning was an op-
eration that contributed very little to over-all
fruit production. In instances of moderate to
severe pruning, a loss of fruit was noted with-
out any apparent compensating effect on
quality or fruit size.
On the basis of these earlier experiments,
recommendations were made that pruning


should be confined to the removal of dead
wood and occasional broken limbs. This
recommendation, plus the fact that pruning
is an expensive operation, has also brought
about the situation that pruning in Florida
until comparatively recently has been con-
fined to the inside of the tree and to the re-
moval of dead wood.
Insofar as the records show, no effort has
been made to limit the size of citrus trees in
Florida or to control crowding by judicious
pruning of the periphery of the tree until some
growers began to hedge the periphery of their
trees in the late 40's.
1. Hedging of citrus is a form of pruning
designed to facilitate grove management prac-
tices and to improve the quality of fruit pro-
-duced. It is a practice that is becoming in-
creasingly popular among Florida citrus grow-
ers as a way to alleviate the problem of over-
crowding which ultimately results in a loss of
production.
Hedging provides a means by which the
bearing surface of trees is reduced in area
without greatly reducing their bearing ability.
Indeed, in the case of some varieties, especial-
ly tangerines, hedging actually increases the
per cent pack-out of fresh fruit in the first
crop following the pruning operation by in-
creasing fruit size. Fruit color and textures
also are often improved because of increased
sunlight and more effective insect and disease
control.
One of the most valuable advantages of
hedging, and the primary reason for its use
in the first place, is to open the tree middles
by removing interlocking branches. This al-
lows for the movement of tractors, discs, spray
and dust equipment and trucks through the
grove without damage to the trees and fruit
or to the equipment and operator. It speeds
up grove operations generally, thereby reduc-
ing cultural costs.
If you would like additional information on
hedging or plans for a hedging machine we
suggest you obtain Experiment Station Bulle-
tin 519 by D. S. Prosser and Extension Serv-
ice Circular 115 by R. E. Norris.
2. Heading Back-This term and the type
operation it implies is seldom used in Florida
citrus; however, it is used rather extensively
in the California lemon industry as well as
throughout most of the other citrus producing






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


areas of the world. It consists of removing a
portion of the tree at regular intervals in order
to retain a rather constant size of the tree.
There are certain advantages and disadvan-
tages to this method of pruning but since it
appears to be of little value under present
Florida conditions we will pass over it.
3. Thinning by tree removal-This is a prac-
tice that has long been contemplated by
Florida growers but one that has seldom been
practiced. Numerous Florida groves planted
during the last 80 years were spaced 15x30,
or a similar distance, with the idea of re-
moving every other tree. Few growers, how-
ever, have actually removed these trees and
many have practiced little or no heading back
or pruning of any kind.
Only in recent years have some few grow-
ers actually thinned their groves by removing
trees in the closely-spaced rows. We regret
that we do, not have more yield and cost data
to present on these operations but the prac-
tice is not general and accurate data is scarce.
We do have slides of one complete operation
to show and some yield and cost data on the
one operation:
The grove, consisting of a 10 acre block of
Hamlins budded on rough lemon root, was
planted in 1939 with a tree spacing of 15x25.
The soil type is deep phase Lakeland fine
sand. The trees were never headed back or
hedged and as a result the limbs were inter-
locked badly and many of the lower branches
were dying as a result of shading. During the
last 5 years production decreased, very mark-
edly so during the past two seasons, which,
as you know, were dry. During January and
February 1956 every other row was removed
by sawing the limbs off with a power saw and
running all wood under 4 inches in diameter
through a chipping machine. The stumps
were treated with a tree killer (without suc-
cess) on two occasions and as a final effort
the stumps were sawed level with the ground
and a chopper run down the row to remove
all suckers.
The crop has not yet been harvested but the
owner estimates his crop loss at 25% over the
previous year's yield.
Some figures on the operation:
The rows were 21 trees long-2 men cut 2
rows per day. Two men could trim the large
limbs and stack the brush on 5 rows per day.


It required 3 men 5 days to run all brush
from the 10 acres through the chipping ma-
chine. It took 4 men 3 days to haul out all
limbs above 4 inches in diameter. It should
be pointed out that this grove had a problem
of no place to haul and burn the brush so it
had to be disposed of in place.
To dispose of the trees in the manner
described the owner figured the total cost of
the operation at $1.50 per tree.
Of particular interest in the group of slides
shown on this operation is the one showing
how rapidly the remaining trees are filling in.
Based on the progress the trees have made
this year, it is believed that the grove will be
back to normal production next year.
Some comments on similar operations:
Block B-Red grapefruit on rough lemon
stock 10 years old was planted 1232x30 on
Lakeland fine sand. Every fourth tree on the
diagonal was sawed off flush with the ground
with a pulpwood saw, dragged out and
burned. The following year there was no
noticeable reduction in crop. At 12 years of
age (next year) the grower plans to remove
every other tree on the diagonal-thus reducing
the spacing to 25x30 at which time he will
begin a program of hedging. Based on pre-
vious experience the grower feels there will
be very little per acre loss in production-if
any.
Block C-Twenty-five year old Valencias
on rough lemon stock were planted 15x30 on
Eustis fine sand. The trees were very crowded
so every other tree was "buckhorned," bull-
dozed and replanted. The year before moving
the production on the block was 4400 boxes.
Fifty trees were removed and the following
year the production dropped to 3960 boxes.
The plan is to move 50 trees per year until
the operation is completed. After the third
year it is anticipated that the loss of 50 trees
per year will not result in any loss of total
crop produced.
Some figures on this operation:
It took 2 men 3i day to saw and re-saw 20
trees; one man ,2 to whitewash (by hand) 20
trees; one man one day to remove (by drag)
the brush from 20 trees; four men, a bull-
dozer, a flat truck and a water wagon one
day to push, haul li mile and re-plant 20 trees.
The total cost of labor for this operation ex-
clusive of equipment was $2.60 per tree.





LAWRENCE AND NORRIS: FIELD OBSERVATIONS


The re-set trees began bearing the second
year at the rate of about box per tree aver-
age and in the third year they were yielding
a box average. The fourth year's yield will
probably be between three and four boxes.
And now the last practice to consider-
4. Topping, a form of rejuvenation pruning:
Rejuvenation pruning is a term used by hor-
ticulturists to describe the objective of re-
invigorating trees by stimulating more and
better shoot growth and fruitfulness. This
pruning must be severe enough to remove suf-
ficient foliage to stimulate new growth over
much of the tree.
When enough of the top is cut off, a
growth response usually occurs throughout
the woody framework. In order to produce,
from pruning, an invigorating effect in a large
old tree, it is necessary to make many small
cuts or remove some of the large branches.
The method we have chosen to report on
is that of removing the complete top of old
seedling trees at varying heights from ground
level to eighteen feet. This, too, is a new
practice in Florida and although again, facts
and figures are not abundant, we have some
slides that are at least interesting. This prac-
tice might well be described as an act of
desperation brought on in many groves by in-
creased overlapping of limbs which resulted
in a marked increase of pest and disease and
a gradual dying of lower limbs. In some old
seedling groves it is 10 to 15 feet from the
ground to the first limb. The tops are sparse,
the foliage is small, production is down and the
cost of picking (usually from a 40 foot ladder)
is such that it makes the operation very ex-
pensive.
During the last ten years many growers
have been experimenting with various meth-
ods of pruning to try to alleviate this condi-
tion. From these various methods of pruning
we will discuss only the one wherein the en-
tire top of the tree is removed. The data pre-
sented is from two different blocks of old
seedling trees owned by two different grow-
ers. Both growers topped only a few trees in
1947. Grower A started by topping trees in
every other row at a relatively constant height
of roughly 5 feet from the ground. Grower B
topped about 20 trees in a block. These trees
were topped from 1 foot to 15 feet in height.


Grove A-Cut back every other row in
January 1947 just after the fruit was picked.
The trees were whitewashed immediately.
They started to sprout out in about six weeks
and grew very vigorously the first year. The
second year they put on only a few scattered
fruit. The third year the growth was very
dense and possibly because of the large trees
on two sides, tended to grow upright but pro-
duced better than a box average of fruit. By
the fourth year it was obvious that although
the trees had good big broad leaves and were
growing vigorously, they would soon be back
like the old trees so it was decided to cut
back the trees on both sides of the row. Some
trees bore as much as 8 boxes of fruit the
fourth year. These trees (as you can see by
the slides) now have the characteristic ap-
pearance of budded trees and are yielding 10
boxes per tree. The new wood is quite thorny
and some pruning to thin and shape is neces-
sary.
Grove B-The initial operation was begun
in February 1947. In this block it was noted
that trees cut below 5 feet did not appear to
come back as rapidly as did ones cut at a
greater distance from the ground. Those trees
topped above 5 feet were more difficult and
expensive to handle in the original operation
and did not respond any faster. It now appears
that the trees cut 10 feet and higher will
never "head-out" low and will ultimately be
right back like they were originally; whereas
the trees cut at 5 to -10 feet take on the char-
acteristics of budded trees and will apparent-
ly remain relatively "low-headed" provided
they are hedged to prevent inter-locking. Of
special interest in Grove B was one particular
tree that yielded 16 boxes the fifth year. All
trees in Grove B are currently producing an
average of 10 to 12 boxes of fruit.
In summary we again wish to point out that
the contents of this paper are purely the re-
sults of field observations with no thought of
making recommendations at this time. How-
ever, it seems logical that in many instances
of closely-spaced trees high production can
be maintained or regained through one of the
forms of pruning outlined in this paper:
1. Hedging:
A comparatively new method of prun-
ing which is rapidly being adopted by
Florida growers to relieve the adverse ef-





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


fects of crowding and shading found in
most Florida groves 15 years old and older.
Advantages:
a. Increased effectiveness of pest control.
b. Decreased damage to trees and equip-
ment.
c. Faster more economical grove opera-
tions.
d. Decreased dead wood.
e. Increased "pack-out" of fresh fruit.
f. Better sizes and better color of fruit.
g. More attractive appearance of grove.
Disadvantages:
a. Usually a reduced yield for at least
one year .
b. A fairly costly operation (varies from
7,'c to 78c per tree)'/
2. Heading back:
We have not observed enough of this
type of pruning in Florida to offer any
comments.
3. Thinning by tree removal:
As we have pointed out there are now
quite a number of growers who have re-
cently turned to this method of relieving
a crowded condition but very few have
adequate records (because of length of
1/Agricultural Extension Service Circular 115.


time) to prove or disprove the value of
the operation. It would appear from the
limited operations we have observed that
if a grower has access to additional land
and in instances of healthy trees a new
grove that will bear heavily in 4 to 5
years can be established at an economic
figure.
4. Topping, a form ot rejuvenation pruning.
It is too early to make positive state-
ments relative to this operation; how-
ever, it appears that by topping two or
more rows per year (beginning on the
outside row) this could raise production
and reduce cost of harvesting in old
canopied groves.
Advantages:
a. Reduces height of tree.
b. Greatly improves tree vigor.
c. Increases yield and size of fruit.
d. Produces increased cover crop growth.
Disadvantages:
a. Complete loss of crop for two years.
b. An expensive operation.
c. New trees quite thorny.
d. If trees are not whitewashed and cuts
coated with water repelling paints the
trees will be weak and soon rot away.


TIMING FERTILIZATION OF CITRUS IN

THE INDIAN RIVER AREA


HERMAN J. REITZ
Florida Citrus Experiment Station
Lake Alfred

Several years ago, considerable interest was
expressed in the relative value of various sys-
tems of timing fertilizers. Partly as a result of
this interest, several experiments were in-
itiated to resolve this question. Some of the
experiments conducted in Central Florida have
been reported recently (3, 4). This paper
presents the results of an experiment con-
ducted at the Indian River Field Laboratory
near Fort Pierce. The results agree with the
other Florida data cited above in indicating
that time of application of fertilizer is a
relatively minor consideration, if the appli-

Fla. Agri. Expt. Sta. Journal Series No. 546.


cations are made during the drier part of the
year.
EXPERIMENTAL METHODS
The experiment to be described was begun
in January, 1949, and was terminated with
the 1955-56 crop. The trees used were Val-
encia oranges on sour orange rootstock planted
on single beds in 1940. The soil in the ex-
perimental area was classified Parkwood loamy
fine sand with pH ranging from 6.8 to 8.3 in
the surface and with pH values above 6.8 in
all depths to 42 inches. The surface samples
contained carbonates equivalent to about 14
percent calcium carbonate and organic matter
of approximately 3 percent. The soil also con-
tained 12 to 30 percent clay plus silt (parti-
cles less than 0.05 mm. in diameter) in various
layers, thus being much finer in texture than
soils used for citrus in Central Florida. In





REITZ: TIMING FERTILIZATION


this soil, the trees were known through
measurement to have 75 percent of their fine
root system in the upper 19 inches from the
crown of the hed.
The seven experimental treatments con-
sisted only of variations in the time of appli-
cation of mixed fertilizers during the year. Dur-
ing each calendar year, every tree in the ex-
periment received the same amount and
analysis of fertilizer. The yearly total rates
and analysis used were changed several times
during the course of the experiment, as shown
in Table 1. Rates were increased up to 1953
to achieve a greener, more dense foliage, and
increased further after 1953 to achieve greater


Table 1. Amounts and analyses of fertilizer used
in the experiment

Year Analysis(a) Annual Rate,
per tree
Pounds
1949 3-6-8-3-0-1 16
1950 3-6-8-3-0-1 20
1951 4-6-8-5-0-i 20
1952 5-6-8-5-0-. 30
1953 6-6-8-5-0-0 30
1954 8-4-10-7-0-0 24
1955 8-4-10-7-0-0 24
(a)N-P205-K20-MgO-MnO-CuO respectively.


yield, as was indicated might be possible by
an adjacent experiment involving different
rates of fertilization. The changes in analysis
were influenced by trends in Central Florida
fertilizer practice during the period. The tim-
ing treatments were as follows:
Treatment 1:
All fertilizer applied February 15th.
Treatment 2:
One-half total fertilizer applied Febru-
ary 15th and one-half June 15th.
Treatment 3:
All fertilizer applied May 1st.
Treatment 4:
One-half fertilizer applied May 1st and
one-half October 15th.
Treatment 5:
All fertilizer applied October 15th.


Treatment 6:
One-half fertilizer applied June 15th and
one-half applied December 15th.
Treatment 7:
One-third fertilizer applied February 15th,
one-third June 1st, and one-third November
1st.
The schedule was adhered to within prac-
tical limits. All the treatments were replicated
four times, at first using six trees per plot. Later
it became recognized that several of the trees
were affected by crinkle scurf and that addi-
tional trees were non-typical of the Valencia
variety. These trees were then discarded and
the results quoted are based upon the typical
trees remaining in the plots insofar as this
was permitted by the records.
RESULTS
Plot Observations-At the beginning of the
experiment in January, 1949, the trees were
somewhat small for trees nine years of age
and also were showing the symptoms of low
fertilization level. In August, 1949, a severe
hurricane struck the grove and caused about
90 percent defoliation on all trees and almost
complete loss of the fruit crop. Throughout
1950 and 1951, the foliage on all trees was
light green and sparse, but this condition im-
proved slowly throughout the period and was
fairly satisfactory by the end of 1952.
Through 1953 to the end of the experiment,
all trees had satisfactory foliage conditions ex-
cept when modified by treatments as noted
below.
The most conspicuous changes in tree ap-
pearance were brought about by application
of all fertilizer in October. In the last four
years of the experiment, all trees so treated
were notably earlier in blooming and coming
into growth in the spring than other trees. The
extreme example of this was observed Janu-
ary 7, 1954, when approximately one-third of
all trees so treated were in full bloom from
leafless inflorescenses while the trees in other
treatments were completely without bloom.
Twig growth on these trees was also early
in development, and the twigs were long and
had many leaves per twig. These leaves in
most years did not become dark green as did
leaves from other treatments, and in some
years the trees became conspicuously nitrogen-
deficient and sparse of foliage during the post-





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


bloom and early summer season. In late sum-
mer, some greening of foliage occurred even
before fertilization, presumably due to break-
down of organic matter in the soil. Trees given
one-half the fertilizer in May and one-half in
October were similarly but less conspicuously
affected.
Trees given all fertilizer in May were at
the opposite extreme in appearance com-
pared with trees fertilized only in October.
These trees had limited spring growth, in num-
ber of twigs or length of twigs, and this spring
growth became dark green slowly. The bloom
was sometimes very late, not reaching a peak
in 1954 until about April 9, and not then be-
ing profuse or conspicuous. The general leaf
color in the post-bloom period was fairly dark
green due to the color of the old leaves and
the absence of new flush. In the early sum-
mer period, the characteristic appearance of
these trees was dull grayish green, the foliage
was thin, and there were numerous dead twigs
in the trees. During the late summer and fall
the trees were of average foliage appearance,
but this was generally the case with nearly all
of the trees except possibly those fertilized
only in October.
The general appearance of trees in all of
the other treatments was not outstanding in
any respect and the trees were fairly green
throughout the year.
Tree Size-The circumference of the trunks
of the trees in the experiment was measured
first in August, 1950, and again in January,
1956. The averages showed that the increase
in trunk circumference was smaller for the
trees receiving all the fertilizer in October
than for any other treatment. However, dif-
ferences in neither the actual trunk circum-
ferences nor in the increases during the period
were large enough to be of statistical signi-
ficance, indicating that the timing of fertiliza-
tion had doubtful effect on tree size.
Leaf Analysis-Leaf samples were taken for
mineral analysis on a number of occasions dur-
ing the course of the experiment, beginning in
1952. In one series, samples of leaves from
fruit-bearing twigs were collected from four
of the treatments at approximately monthly in-
tervals from March, 1953, to May, 1954. This
less commonly used type of sample was select-
ed because it was desired to study the nutri-
tional status of leaves most closely associated


with the fruit. It was coincidental that the
severity of the leaf symptoms observed was
greatest in the year that was picked for this
study, so the differences found are doubtless
greater than would have been found in other
years.
The analytical results for nitrogen are pre-
sented in Fig. 1. These results correlate with
the appearance of the trees. For example, the
trees fertilized only in January and those
fertilized three times per year maintained a
reasonably good green color of leaves and
relatively high nitrogen level throughout the
entire period. The trees fertilized in October
only appeared nitrogen deficient during the
months of May, June, and July, and at that
time had extremely low levels of nitrogen in
the leaves. Also, leaves from trees fertilized
in October only increased in nitrogen content
and improved in appearance during the sum-
mer although no nitrogen had been applied;
after the fall fertilization, the nitrogen con-
tent of these leaves greatly increased so that
they were equivalent in nitrogen content to
those of the January only plots and the plots
receiving three applications. The trees fertil-
ized in May only paralleled in nitrogen con-
tent the trees fertilized in October only, up to
the point when in May the fertilizer was ap-
plied. After this application, the leaves in-
creased markedly in nitrogen content but did
not reach the level attained by the leaves in
the January only or the three application
treatments. This parallels the observation that
while the trees fertilized in May only had
generally very dark green color, this was due


Fig. 1. Nitrogen analysis of leaves from fruiting
twigs of selected treatments.





REITZ: TIMING FERTILIZATION


to tile appearance of the old leaves and that
the appearance of the spring flush leaves of
1953 remained poor. It is also notable that as
the 1954 flush of growth came out on trees
fertilized in May only, the new leaves were
lowest in nitrogen. It is assumed that data for
trees receiving two applications per year
would be intermediate between the extremes
given here.
Among other major elements, the most con-
spicuous differences were in potassium and
calcium. The treatment receiving all fertilizer
in October was conspicuously high in potas-
sium and low in calcium throughout the
greater part of the year. The May only treat-
ment was just the reverse. Differences in
magnesium were erratic and differences in
phosphorus were of small magnitude.
As already noted, during 1954 and 1955
there was very little difference in appearance
of the trees regardless of treatment and this
was reflected in leaf analysis. Table 2 shows


the analysis of spring flush leaves taken from
non-fruiting twigs on two dates. This type of
sample is more nearly the conventional sample
taken in studies of leaf analysis. In most cases
no significant differences were found. The
most notable feature in Table 2 is the dif-
ference in analysis between 1954 and 1955.
In 1954, leaves generally were low in nitro-
gen, phosphorus and potassium and high in
calcium.
Fruit Quality-In each year except 1952-53,
at least one sample of fruit was picked for
juice analysis. Part of these results are pre-
sented in Table 3. Soluble solids in four of the
six years for which records are available were
highest for fruit from the trees fertilized only
in October; however, the two remaining years,
the soluble solids level was lowest. This shift
in relative level of soluble solids appeared to
be of some consequence as it was supported by
a significant interaction between years and
treatment when subjected to analysis of va-


Table 2. Analysis of spring flush leaves taken from
non-fruiting twigs July 26, 1954, and August 2, 1955
LEAF ANALYSIS

TREATMENT Nitrogen Phosphorus Potassium Calcium Magnesium
1954 1955 1954 1955 1954 1955 1954 1955 1954 1955


Feb. 2.04 2.59 0.107 0.123 0.71 0.99 7.18 5.77 0.173 0.195
Feb. and June 2.06 2.74 0.103 0.124 0.61 0.95 7.52 5.59 0.151 0.183
May 2.17 2.54 0.109 0.123 0.68 0.89 7.31 5.89 0.176_0.198
May and Oct. 2.17 2.47 0.110 0.122 0.72 0.94 7.21 5.91 0.242 0.194
Oct. 2.14 2.47 0.116 0.114 0.73 0.94 6.74 6.02 0.194 0.206
June and Dec. 2.20 2.52 0.111 0.122 0.74 0.82 6.81 6.05 0.219 0.186
Feb., June and Nov. 2.16 2.52 0.108 0.124 0.67 0.98 7.02 5.71 0.244 0.188

Statistical
Significance(a) N.S. N.S. N.S. N.S. N.S. N.S. ** c

(a) N.S. non-significant
a significant at 5% level
S significant at 1% level
c analysis run on composite samples only






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


Table 3. Summary of fruit characteristics

JUICE ANALYSIS FRUIT SIZE
TREATMENT ABrix Diameter, Avg. Wt.
Brix Acid Acid mm. grams


Feb.


Feb. and June

May

May and Oct.

Oct.


11.73 1.06 11.26


11.63


1.07


11.70 1.03

11.48 1.09
11.63 1.07


June and Dec. 11.63

Feb., June, and Nov. 11.62


1.06


1.06


Statistical


Significance(a):

Treatments N.S.

Interaction **


N.S.

N.S.


(a) N.S. non-significant

significant at $5 level
S significant at 1% level

riance by split-plot methods, using treatments
as the main plots and years as the sub-plots as
suggested by Pearce (2). This would be in-
terpreted to mean that the treatments had a
real effect on soluble solids but that the effect
varied to some extent depending upon the
season. No significant difference was discov-
ered in acidity or ratio of soluble solids to
acidity although the trees fertilized entirely or
partly in October were among those giving
fruit with highest acidity and lowest ratio.
Juice content was quite uniform and the dif-
ferences were of no statistical significance in
any case. Vitamin C was determined in only
three years, but no differences of practical or
statistical consequence were found. The in-
teraction noted above for soluble solids
(Brix) was not significant for any ,other
juice characteristic.


Fruit Size-One of the more noticeable ef-
fects of the treatments was the effect of the
October treatment in producing fruit of larger
than average size. This effect was noted
strongly in the crops picked in 1952, 1954,
and 1955. Measurements were taken of this
characteristic by two methods, first, as the
measured diameter of the fruit on the tree in
1951, 1952, 1954, and 1955, and second, as
the average weight of the fruits which were
sampled for fruit analysis in 1954, 1955, and
1956. The summary of both weight and diam-
eter measurements is given in Table 3. Size
differences were more noticeable in the diame-
ter measurements. These measurements of
diameter made in the field were largely done
in the early years of the experiment while the
weight measurements were done in the last
three years of the experiment. Here again it


11.04

11.53

10.72

10.95

11.05

11.14.


70.5

71.5

71.3

71.6

73.1

71.7

71.0


N.S.

N.S.


N.S.




REITZ: TIMING FERTILIZATION


is noted that the greater effects were obtained
in the earlier years of the experiment than in
the later ones. The significant interaction of
fruit weight with years reflects relatively larger
fruit in the October plots in 1954 than in 1955
and 1956.
External Characteristics rf the Fruit -
Studies were made on color and grade of
fruit, both in the field and to a limited extent
in the Citrus Experiment Station packing-
house at Lake Alfred. It was observed on
many occasions that the color of fruit on trees
fertilized in October only was outstanding in
December and January; however, during
February this difference diminished greatly
so that when the fruit was mature enough to
pick, the advantage had been completely lost.
Packinghouse studies confirmed the field ob-
servation that little difference existed in the
latter part of the season. The loss in the ad-
vantage for the October treatment was due
to re-greening of fruit in that treatment and
to improved color of fruit in other treatments.
When fruit was picked late in the season
and judged for fruit color as well as coarse-
ness, and later graded into United States
grades, there was no advantage for any treat-
ment over the other in any of these character-
istics.
Yield-Yield results are given in Fig. 2. Al-
though there were some obvious differences
in average yield, the differences obtained
were not statistically significant. Treat-
ments involving application of fertilizer in
October were lowest in average yield. The
yield figures for these treatments include a
great deal of late-bloom fruit which would
be of no value for fresh fruit production unless
it were handled separately. The yield from
trees receiving all fertilizer in May was high-
est, but this high yield was the result of ex-
ceptional yield on two plots of the four
replications and somewhat less than average
yield on the remaining two. Yields from the
other four treatments were intermediate be-
tween these extremes.

DIscussION
The results indicate that no large benefit
in yield or fruit quality can be obtained under
the conditions of this experiment by simply
varying the time of application of fertilizers.
Some smaller advantages or disadvantages can,


however, be assigned the individual treat-
ments.
Applications made in October (before the
end of the rainy season in this area) had sev-
eral disadvantages. In addition to low yield,
the trees bloomed dangerously early, showed
nitrogen deficiency severely during post-bloom
and early summer periods and set much late-
bloom fruit. Aside from larger fruit (of doubt-
20-



17-


15-



2 14


o l


7a

0
F- 61lesO -
a / _..,


Feb Feb May May Oct. June Feb.
June Oct. Dec. June
Nov.
TREATMENT
Fig. 2 Accumulative yield by years during the last
six years of the experiment.
ful value for this variety), such treatments had
no advantages.
Single annual application of fertilizer in
May produced greatest average yield, but the
result lacked statistical significance. The treat-
ment had nothing else to recommend it, and
the tree condition in the post-bloom period
would not be satisfactory to many growers.
The remaining four treatments prevented
unfavorable tree condition and were satisfac-
tory in all respects. Three applications per year
had no advantages over treatments using few-
er applications, and hence cannot be recom-





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


mended. When all fertilizer was applied in
February, quite satisfactory results were ob-
tained and might be recommended. By com-
parison, February and June applications or
December and June applications would per-
haps reduce leaching loss if exceptional rain-
fall occurred after the single annual applica-
tion and would reduce the hazard of excessive
salt concentration if high rates of fertilization
were used. Neither of these conditions was
important in the experiment.
Similar conclusions might not be drawn if
early orange varieties or grapefruit had been
used in the experiment. The earlier coloring of
the fruit, the larger fruit size, and the higher
soluble solids frequently occurring in the
treatments receiving October applications
might be sufficient to justify their use for
these varieties. Such comments are, of course,
speculative in relation to the data presented
here.
It is probable that fertilizer rate played an
important role in the results. In later years,
with higher rates, results were less pronounced
than in earlier years with lower rates. Evi-
dently striking results from timing experi-
ments must depend upon attaining nutritional
extremes at some period of the year (1). At
high fertilizer rates, such extremes cannot be
produced under the soil conditions existing in
this experiment. Under other soil conditions,
where less clay and organic matter is found
in the soil, nutritional extremes may occur
much more readily than was the case in this
experiment. However, experiments performed


in Central Florida (3, 4) have not shown as
much difference as had previously been anti-
cipated and it is probable that the effects
spoken of above could be obtained only in the
least fertile and coarsest textured soils.

SUMMARY
A fertilizer timing experiment using Valen-
cia trees on sour orange rootstock planted on
calcareous hammock soil was conducted over
a seven-year period. The seven treatments in-
volved one, two, or three applications per
year, using a constant total amount of mixed
fertilizer annually on all plots. Results indicate
that applications made before the end of the
rainy season (prior to November 1st) are un-
desirable; that three applications per year are
unnecessarily expensive; and that satisfactory
results can be obtained by using two applica-
tions, one after the end of the fall rainy season
and a second before the beginning of the
summer rainy season, or by a single applica-
tion made in winter.
LITERATURE CITED
1. Martin, W. E. 1942. Physiological studies of
yield, quality and maturity of Marsh grapefruit in
Arizona. Ariz. Agr. Expt. Sta. Tech. Bul. 97.
2. Pearce, S. C. 1953. Fruit experimentation with
fruit trees and other perennial plants. Tech. Com-
munication No. 23, Commonwealth Bureau of Horti-
culture and Plantation Crops, East Mailing, England.
Section 25, p. 14.
3. Reuther, Walter, and Paul F. Smith. 1954. Ef-
fect of method of timing nitrogen fertilization on
yield and quality of oranges. Proc. Fla. State Hort.
Soc. 67: 20-26.
4. Sites, John W., I. W. Wander, and E. J. Des-
zyck. 1953. The effect of fertilizer timing and rate
of application on fruit quality and production of
Hamlin oranges. Proc. Fla. State Hort. Soc. 66:54-62.





KNORR AND PRICE: GRAPEFRUIT STEM PITTING

IS STEM PITTING OF GRAPEFRUIT A

THREAT TO THE FLORIDA GROWER?


L. C. KNORR AND W. C. PRICE
Florida Citrus Experiment Station
Lake Alfred

Before attempting to answer the question
raised in the title to this paper, it is necessary
to consider two subsidiary questions. The first
of these is this: What is stem pitting?
The term "stem pitting" was first used by
Oberholzer, Mathews, and Stiemie (16) in
South Africa to designate a specific disease of
grapefruit trees on rough lemon rootstock.
Subsequently, the term came also to be used
in a different sense: to designate a symptom, or
set of symptoms, occurring in the wood of
various kinds of citrus trees when infected
with, or presumed to be infected with, one
or another virus. This double usage has re-
sulted in a certain amount of confusion.
The term stem pitting has been applied by
others to the pitting that occurs under the
bark of Key lime seedlings serving as indicator
plants for tristeza virus (3). It has also been
applied (1) to various types of pitting present
in many varieties of citrus-for example, to
the pitting in such varieties as trifoliate
orange and sour orange, which varieties are
found (5) to be free of pitting in Argentina
where the stem-pitting disease abounds.
We are concerned with the disease of
grapefruit known as stem pitting. According
to Oberholzer, Mathews, and Stiemie (16),
stem pitting is characterized by corrugations
or longitudinal pits on the outer surfaces of
trunks of affected trees; trees showing stem
pitting of the trunk become stunted and
bushy, giving rise to the name stunt bush;
their foliage is sparse, small, mottled, and
chlorotic; and their fruit are small with thick
rind, high acid content, and low juice con-
tent. In severely affected trees, scaffold
branches tend to grow downward at sharp
angles, crowns are flat, and the rough-lemon
rootstock suckers profusely.
According to McClean (12, 13), the symp-
toms described by Oberholzer et al. are second-

Florida Agricultural Experiment Stations Journal
Series, No. 567.


ary ones that develop as affected trees mature,
the important primary symptoms being those
that are revealed by stripping off bark from
the trunk and large limbs. In the surface of the
underlying wood, there is to be found pits,
shallow grooves, or channels with their long
axes paralleling the grain of the wood. The
channels give the unaffected wood the ap-
pearance of ridges resembling loose strands
of twine. Channelling is well-defined and
characteristically present in the trunk and
lower branches but may be lacking in twigs
and young branches.
Oberholzer (17) in 1953 estimated that
stem pitting had destroyed 40 per cent of the
grapefruit groves in South Africa, and Oxen-
ham and Sturgess (19) report that stem pit-
ting, or dimples, of grapefruit, "is the most
serious problem affecting the Queensland cit-
rus industry," with most plantings becoming
unproductive by the 15th year. This terrible
destruction results apparently from injury to
phloem and xylem tissues in the scaffold of
the tree, thus rendering tissues incapable of
supplying either tops or roots with the water
and food needed for growth and fruiting.
Oberholzer, Mathews, and Stiemie (16)
showed that stem-pitting disease is perpetu-
ated by vegetative propagation and discovered
that some sources of budwood carry a milder
form of the disease than others. McClean (12,
13) proved the disease to be infectious and to
be capable of transmission by grafting or by
means of the brown citrus aphid', Toxoptera
citricidtus (Kirk.) (syn. Aphis citricidus Kirk.).
He considered stem pitting to be caused by a
virus that is widespread in citrus in South
Africa, and he also reported that at least two
'/At this point it might prove helpful to point out
that a certain amount of confusion has arisen with
respect to common names for Toxoptera (Aphis)
citricidus (Kirk.), the highly efficient vector of
tristeza in South America, South Africa, and Aus-
tralia, and Toxoptera aurantii (Fonsc.), the mark-
edly inefficient vector that is present in Florida.
In the American literature the common name for T.
citricidus is the brown citrus aphid, and for T.
aurantii. the black citrus aphid (cf. "Common names
of insects approved by the Entomological Society of
America," Bul. Ent. Soc. of America 1 (4) : 1-34.
1955). In the literature of certain other countries
however, the order is reversed: it is T. citricidus that
is called the black citrus aphid (cf. "Common names
of insects," Commonwealth Sci. & Ind. Res. Org.
Australia, Bul. 275, 32p. 1955). and T. toxoptera
the brown citrus aphid.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


strains of the virus exist. Both strains induce
veinal flecking in West Indian (Key) lime
seedlings and both stunt such seedlings rather
severely, one more so than the other.
The second subsidiary question that must
be considered is this: What is the relationship
between stem pitting and tristeza? This is cer-
tainly not an easy question to answer, as will
presently become evident. On the one hand,
there are reasons for believing that these two
diseases are caused by the same virus. Mc-
Clean (18) has pointed out that the causal
agents of both diseases are transmitted by
Toxoptera citricidus and that both diseases
are universal in South Africa. He thinks that
it would be strange indeed for two distinct
viruses to be transmitted by the same insect
and also to be ubiquitous in the same crop. It
is certainly tempting to regard the two dis-
eases as specific host responses to the same
virus but there may be good reasons for re-
sisting such temptation.
Costa, Grant, and Moreira (3) suggested
that stem pitting might be caused by the same
virus as that which causes tristeza, or by a
closely related virus, and McClean (18) con-
curred in this opinion. The virus responsible
for stem pitting in South Africa is also be-
lieved to cause a die-back of lime in the Gold
Coast, where at least two strains of the virus
are reported to exist (8, 9), and to cause in
South Africa (13) a severe decline of Tahiti
lime on the tristeza-tolerant sweet-orange root-
stock. Stem pitting has been reported to oc-
cur in Argentina (11), apparently having been
introduced there simultaneously with tristeza.
It is also known in the Belgian Congo (20).
McClean and van der Plank (14) postulated
that the tristeza-virus complex has two com-
ponents, a stem-pitting component and a
seedling-yellows component. They postulate
further that the stem-pitting disease is induced
in grapefruit by the stem-pitting component
whether the seedling-yellows component is
present or not. It is not clear from the paper
by McClean and van der Plank whether stem-
pitting virus alone can cause decline of sweet
orange on sour-orange rootstock or whether
the seedling-yellows component must also be
present. However, sour orange is thought to
be more tolerant of stem-pitting virus alone
than of the stem-pitting seedling-yellows com-


Another reason for considering that tristeza
and stem-pitting viruses are not identical is
this: although tristeza virus is supposed to be
universal in citrus of South Africa, many 25-
year-old grapefruit trees there do not have
the stem-pitting disease (15). This could be
interpreted to mean 1) that tristeza virus is
different from stem-pitting virus despite being
closely associated with it in nature, or 2) that
some strains of tristeza virus are so mild that
they do not cause stem pitting.
Stem-pitting disease of grapefruit does not
occur in Florida, nor, to our knowledge, does
it occur elsewhere in the United States. Triste-
za is in Florida (7), however, and is reported
to be spreading in some areas, such as Lake
and Orange Counties (2). We know of a few
grapefruit trees in Florida infected with tris-
teza virus that display a pitting of twigs and
small branches comparable to the pitting that
frequently develops in Key lime seedlings
when infected by tristeza virus; these
grapefruit trees, however, do not have
the striations and channeling of wood of
the trunk or large limbs, symptoms said
by Oberholzer et al. to be the characteristic
manifestations of stem pitting disease;
neither do these trees show any indications of
decline nor deviations from normal fruiting. In
Florida, we have examined a large number of
grapefruit trees, many of which have been
demonstrated to be carrying the virus of tris-
teza, but in none of these trees have we found
the stem-pitting disease. Because of these ob-
servations, it seems safe to conclude that at
present stem pitting occurs rarely, if at all, in
Florida.
The virus, or virus complex, that causes
seedling-yellows disease of grapefruit, sour
orange, and Eureka lemon seedlings in Aus-
tralia and South Africa also does not occur in
Florida. When Florida tristeza virus is trans-
mitted to these three species by budding from
infected sweet-orange trees, it does not pro-
duce seedling yellows in them.
This certainly seems to be a paradox: al-
though tristeza is not uncommon in Florida,
neither the seedling-yellows component nor the
stem-pitting component of the complex ap-
pears to occur here! How can this be ex-
plained?
One possible explanation is to assume that
the seedling-yellows component is present in




KNORR AND PRICE: GRAPEFRUIT STEM PITTING


Florida but that by itself it cannot produce
seedling yellows, that seedling yellows devel-
ops only when the stem-pitting component is
also present. If this is assumed, then it needs
further to be assumed that only the seedling-
yellows component of the complex, not the
stem-pitting component, is present in Florida
and that seedling-yellow virus by itself causes
the mild form of tristeza to be found here. Al-
though we do not have the experimental evi-
dence necessary to rule out this possibility, we
prefer a simpler hypothesis.
Our hypothesis is that tristeza, stem pitting,
seedling yellows, and the Gold Coast's lime
die-back are caused by a single virus that ex-
ists in the form of numerous strains. [It seems
likely that this is about what Costa, Grant, and
Moreira (3) had in mind when they sug-
gested that tristeza and stem pitting are caused
by the same virus.] It may further be sup-
posed that naturally-infected trees can harbor
two or more strains simultaneously and that
one or another of these strains predominate,
depending upon the species or variety of citrus
in which they occur. The strain of virus pre-
dominating in sweet orange of South Africa is
usually, though not always, one that will in-
duce seedling yellows in grapefruit, Eureka
lemon, and sour orange seedlings. We can
designate it as the seedling-yellows strain. It
apparently is not well adapted to the grape-
fruit. Consequently, when a mixture of strains
is transmitted by Toxoptera citricidus from
naturally-infected sweet orange to grapefruit,
another strain better adapted to the grapefruit
soon predominates; this may be a strain that
causes stem pitting or another that is consid-
erably less severe than the stem-pitting strain.
Even when transmission is by grafting and
when seedling yellows develops, the grapefruit
tends to lose the component that causes seed-
ling yellows while retaining the component
that causes stem pitting (15); this observation
can better be explained by assuming the stem-
pitting and seedling-yellows components to be
strains of the same virus than by assuming
them to be distinct and separate entities.
It is not necessary to assume that strains of
tristeza virus exist; their existence has been
demonstrated in South America (4) and in
the United States (18). It is necessary to as-
sume only that the strains of tristeza virus
commonly found in the United States cause


neither seedling-yellows disease nor stem-
pitting disease.
Although there is no substantial body of ex-
perimental evidence on which to base a judg-
ment of the validity of the hypothesis that tris-
teza seedling yellows, and stem pitting involve
not a complex of viruses but a group of closely
related strains, an experimental check of the
hypothesis can readily be made in Australia
or South Africa, where presence of a seedling-
yellows factor is said to occur. Evidence is now
available for the statement that a mild strain
of tristeza virus will protect citrus from more
severe forms of the virus (4, 6, 18). Conse-
quently, a grapefruit seedling invaded by the
stem-pitting component of the tristeza virus
complex should be refractory to infection by
the seedling-yellows component, whether in-
troduced by means of grafting or by Toxoptera
citricidus, if the two components are closely
related strains but not if they are separate and
distinct viruses. So far as we can learn from
the literature, this test has not been made.
Let us now return to the main question of
this paper: is stem pitting a threat to the
Florida grower? We believe that it is a threat,
but one that should not be taken too seriously
so long as an efficient vector of tristeza like
Toxoptera citricidus is kept out of the state.
If stem-pitting virus is a strain of tristeza virus,
the possibility that it will arise by mutation of
the mild strains of tristeza virus present in
Florida is a virtual certainty. If an efficient
vector of the virus, such as Toxoptera citrici-

dus, should feed on the tree in which the mu-
tant arises, there will be a good possibility of
spreading the virus to healthy trees in the
neighborhood. In the absence of such a vector,
the possibility of spread is very small indeed.
Tristeza has been present in Florida for a good
many years (10) and it is likely that the
strains of virus in existence here are well
adapted to the crop; they are more or less in
equilibrium with the crop. This equilibrium is
not likely to be upset except by some radical
change, such as appearance of an efficient vec-
tor.
If stem pitting is caused by a separate and
distinct virus that does not now exist in Flori-
da, it should by all means be prevented from
entering here. Quarantine measures against
importation of budwood is the most practical
means by which to exclude it.







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


REFERENCES TO THE LITERATURE
1. Bitters, W. P.. N. W. Dukeshire, and J. A.
Brusca. 1953. Stem pitting and quick decline symp-
toms as related to rootstock combination. California
Citrog. 38: 154, 170-171.
2. Cohen, M. 1956. Injury and loss of citrus trees
due to tristeza disease in an Orange County grove.
Florida State Hort. Soc. Proc. 69: 19-24.
3. Costa, A. S., T. J. Grant, and S. Moreira. 1950.
Relatives of tristeza. A possible relation between
tristeza and the stem-pitting disease of grapefruit
in Africa. Citrus Leaves 30 (2): 12-13, 35, 38.
4. Costa, A. S., T. J. Grant, and S. Moreira. 1954.
Behavior of various citrus rootstock-scion combina-
tions following inoculation with mild and severe
'strains of tristeza virus. Florida State Hort. Soc.
Proc. 67: 26-30.
5. DuCharme, E. P., and L. C. Knorr. 1954. Vas-
cular pits and pegs associated with diseases in citrus.
U. S. Dept. Agr. P1. Dis. Reptr. 38: 127-142.
6. Grant, T. J., and A. S. Costa. 1951. A mild
strain of the tristeza virus of citrus. Phytopathology
41: 114-122.
7. Grant, T. J., and H. Schneider. 1953. Initial
evidence of the presence of tristeza. or quick decline,
of citrus in Florida. Phytopathology 43: 51-52.
8. Hughes, W. A., and C. A. Lister. 1949. Lime
disease in the Gold Coast. Nature 164: 880.
9. Hughes, W. A., and C. A. Lister. 1953. Lime
dieback in the Gold Coast, a virus disease of the
lime, Citrus aurantifolia (Christmann) Swingle. Jour.
Hort. Sci. 28: 131-140.


10. Knorr, L. C. 1956. Suscepts, indicators, and
filters of tristeza virus, and some differences be-
tween tristeza in Argentina and in Florida. Phyto-
pathology 46: 557-560.
11. Knorr, L. C., E. P. DuCharme, and A. Banfi.
1951. The occurrence and effects of "stem pitting"
in Argentine grapefruit groves. Citrus Mag. 14 (2):
32-36.
12. McClean, A. P. D. 1950. Possible identity of
three citrus diseases. Nature 165: 767-768.
13. McClean, A. P. D. 1950. Virus infections of
citrus in South Africa. III. Stem-pitting disease of
grapefruit. Farming in So. Africa 25: 289-296.
14. McClean, A. P. D., and J. E. van der Plank.
1955. The role of seedling yellows and stem pitting
in tristeza of citrus. Phytopathology 45: 222-224.
15. McClean. A. P. D. 1956. Tristeza and stem-
pitting diseases of citrus in South Africa. FAO P1.
Prot. Bul. 4: 88-94.
16. Oberholzer, P. C. J., I. Mathews, and S. F.
Stiemie. 1949. The decline of grapefruit trees in
South Africa. A preliminary report on so-called
"stem pitting." Union So. Africa Dept. Agr. Sci. Bul.
297. 18p.
17. Oberholzer, P. C. J. 1953. Degeneration of our
citrus clones. Farming in So. Africa 28: 173-174.
18. Olson, E. 0. 1956. Mild and severe strains of
tristeza virus in Texas citrus. Phytopathology 46:
336-341.
19. Oxenham, B. L., and 0. W. Sturgess. 1953.
Citrus virus diseases in Queensland. Queensland
Dept. Agr. and Stocks. Pamphlet 154. 8p.
20. Steyaert, R. L., and R. Vanlaere. 1952. La
"Cannelure" ou "Stem-Pitting' du Pamplemoussier
au Congo Belge. Bul. Agr. du Congo Belge 43: 447-
454.


SEASONAL CHANGES IN THE JUICE CONTENT

OF PINK AND RED GRAPEFRUIT

DURING 1955-'561


E. J. DESZYCK AND S. V. TING

Florida Citrus Experiment Station

Lake Alfred

Pink and red grapefruit in the early season
does not always meet the minimum juice re-
quirements as established by the Florida State
maturity laws (3, 4). Because of the low juice
content, harvest of these two varieties is often
delayed, especially since the adoption of high-
er juice standards; these being raised approx-
imately 10 percent during August 1 to October
15, and approximately 5 percent during Octo-
ber 16 to November 15. For the remainder of
the season, the lower juice requirements de-
fined by the Citrus Code of 1949 remain in
effect. The relatively high juice required in the
early season delays harvest of much of the
pink and red grapefruit until the period of low

'/Cooperative publication by the Florida Citrus
Experiment Station and the Florida Citrus Commis-
sion. Florida Agricultural Experiment Station Journal
Series No. 565.


juice standards of November 16 to July 31
during each season.
Several factors influence juiciness of citrus
fruit. Generally, juice content varies markedly
with and during seasons; it is relatively low in
the immature fruit and high in the fully ripen-
ed fruit late in the season. High rainfall and
irrigation tend to raise juice volume, such fac-
tors accounting for variations from year to
year. Still other factors are: location, variety,
rootstock, age of trees, time of bloom, shape
of fruit, and certain cultural deficiencies. Oil
(7) or arsenic (1, 2) sprays have not been
found to affect significantly the amount of
juice in the fruit.

The Florida Citrus Commission has been
conducting a four-year survey of red and
pink grapefruit to obtain a better understand-
ing of the internal quality and maturity chac-
acteristics of these varieties. When the survey
was begun in the fall of 1953, the soluble
solids content in much of the fruit did not
meet standards; however, since the juice re-





DESZYCK AND TING: SEASONAL CHANGES


SAMPLING PERIOD

Fig. 1. Seasonal changes in the average juice con-
tent of pink (P.S.) and red (R.R.) grapefruit of three
sizes (96, 70, 54) grown on sour orange (S.O.) and
rough lemon (R.L.) rootstocks during 1955-56.


quirements were raised in 1955, juice content
became the limiting factor in maturity. There-
fore, a study of juiciness was included during
the 1955-56 season.

A preliminary report is here presented for
the purpose of ascertaining the juice content
of pink and red grapefruit of three sizes
grown throughout the State during the 1955-
56 season. Special emphasis was placed on its
relationship to legal juice requirements. In ad-
dition to seasonal changes in juice content, the
variations among samples during each sam-
pling period as well as the daily increases in
the juice are included.

EXPERIMENTAL

For this survey, 137 groves were selected
throughout the citrus area of Florida, including
the Ridge section, and the East and West
coasts. Of the total number, 68 groves were
Ruby red and 41 pink seedless on rough lemon,
and 20 groves were red and 8 pink on sour
orange rootstock. Fruit sampling was similar
to that used commercially; that is, each sam-


pie consisted of six fruit of one size picked
from different trees. Three sizes (96, 70, and
54) were collected from tagged trees at in-
tervals of 14-16 days during the 1955-56 sea-
son, extending from September to March.
Juice was expressed at the rate of 40 fruit per
minute using a Food Machinery In-Line ex-
tractor (5) with a flush setting, i' inch orifice
tube, strainer tube of 3/32 inch openings, and
a cup of six inches in diameter. The juice was
then passed through a Chisholm-Ryder fin-
isher of the tapered screw type equipped with
0.033 inch perforated screen, weighed and ex-
pressed as milliliters in each sample of six
fruit. In compiling the data the average juice
volume for each period of 14-16 days was used.







s... 0










i)-





0 R..2.
.S S 5454






050. -0
--- m---..

...... .....




-S.e 7O







SAMPLING PERIOD

Fig. 2. Seasonal changes in the average juice con-
tent of two varieties of fruit of three sizes grown on
two rootstocks during 1955-56.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


RESULTS AND DISCUSSION
In general the average juice content of pink
and red grapefruit of three sizes on rough
lemon and sour orange rootstocks gradually
increased with the advance of the season, with
some exceptions (Fig. 1). Some irregularities
were apparent for size 54 fruit on sour orange
rootstock. In addition the juice volumes in the
fruit of the three sizes decreased slightly dur-
ing January and February (Fig. 2-A).

Rootstock apparently does not influence
juice content in white varieties of grapefruit
(6). However in the pink and red varieties,
significantly more juice is found in fruit grown
on sour orange than on rough lemon rootstock
during the latter part of the season (Fig. 2-B).
This variation was first apparent in December
for size 54 fruit, and during March for size
96. On the average for the season more juice
was found in fruit on sour orange than on
rough lemon rootstock.

The seasonal trends in the juice of two
varieties and three sizes are shown in Fig.
2-C. The red variety contains significantly
higher juice content than the pink grapefruit
during the latter part of the season, January


to March. However, it is similar in the two
varieties during the early season from Septem-
ber to January. On the average for-the season
Ruby red fruit contains more juice than the
pink variety.
The percentages of samples of size 96
grapefruit meeting the legal juice require-
ments through December are listed in Table 1.
Very little fruit can be picked under the 1955
juice standards, since only 7.7 percent of the
samples attained sufficient juice (1110 ml.) at
that time. During October 1 to 15, 32.1 per-
cent of the fruit met the strict regulations.
When the requirement is lowered to 1080 ml.
during October 16 to November 15, 63.2 per-
cent of the fruit met the standard during the
first part of this period, and 84.5 percent dur-
ing the latter part. Although the lower stand-
ard is restrictive, the majority of the samples
acquired adequate juice. After November 15
when the requirement is lowered to 1020 ml.
most of the fruit had enough juice for harvest.
The size of the fruit appears to have no influ-
ence- on the time of attainment of the high
juice standards effective through October 15
since approximately one-third of the samples
of each size met the standards during the
period.


Table 1. Percentage of grapefruit samples picked throughout the State attaining
juice standards from September to December, 1955 (size 96)


Sampling Period
Juice Requirements Sampling Period
September October November December
15-30 1-15 16-31 1-15 16-30 1-15 16-30

ml/6 fruit Percent
1110 (a)
and
above 7.7 32.1 46.5 76.8 85.0 81.1 96.3
1080 (b)
above 12.8 41.9 63.2 84.5 85.0 86.9 97.3
1020 (c)
and
above 31.7 69.5 81.3 93.6 95.0 90.8 100.0
Below
1020 68.2 30.4 18.7 6.4 5.0 9.2 -0-


(a) Minimm juice requirement for Aug. 1 Oct. 15
(b) Minimum juice requirement for Oct. 16-Nov. 15
(c) Minimum juice requirement for Nov. 16-July 31.





DESZYCK AND TING: SEASONAL CHANGES


Table 2. The average juice content and standard deviation for
grapefruit of size 70 for 13 sampling periods during
1955-56.


Sampling Period Juice Standard
(nl/6 fruit) Deviation

Sept. 15-30 1171 122.2
Oct. 1-15 1332 125.5
Oct. 16-31 1392 126.7
Nov. 1-15 1465 122.7
Nov. 16-31 1495 114.7
Dee. 1-15 1541 126.2
Dec. 16-31 1571 125.7
Jan. 1-15 1590 108.2
Jan. 16-31 1603 139.7
Feb. 1-15 1568 104.7
Feb. 16-29 1585 103.0
March 1-15 1604 109.7
March 16-31 1609 110.7



The average juice content and the standard
deviations for size 70 fruit for 13 sampling
periods are shown in Table 2. The standard de-
viations are generally higher during the earlier
part of the season than during the latter part
with some exceptions. The average juice and
the standard deviation can be helpful in as-
certaining the range distribution about the
mean, especially if used in the early season.
For example, during September, the average
juice content for size 70 fruit was 1171 ml.
with a standard deviation of 122.2 ml. Of the
samples tested, approximately one-third fell
between 1171-1293 ml., and one-sixth fell
above 1293 ml. It is evident that with the
juice requirement of 1380 ml., less than one-
sixth of the samples met this high requirement,
and therefore fruit cannot be picked because
of low juice volume.

The daily average increases in juice volume
for one fruit of each size during sampling
periods from October through December, are
shown in Table 3. Large daily increases for
all three sizes occurred during the October 8
sampling period, with smaller amounts during
the remaining periods. With sizes, the highest
daily increase in juice was found for size 54,
and the lowest for size 96. On the average the


juice increased by 0.6, 0.7, and 0.9 ml for
sizes 96, 70, and 54, respectively. An estimate
of the time of meeting juice regulations can be
made by knowing the average daily increase
in the juice. Of course, these values will vary
with location, seasons, and other factors but
can be useful as a guide to the time of har-
vesting.

SUMMARY AND CONCLUSIONS

A preliminary report of the juice content of
seedless pink and red grapefruit of sizes 96,
70, and 54 grown on rough lemon or sour
orange rootstocks is presented. The samples
were collected twice monthly from 137 groves
during the 1955-56 season. In general, the
juice content increased with the advance of
the season, increasing approximately one-third
from September to March. In the latter part
of the season, the red fruit contained more
juice than the pink variety. Likewise, fruit on
sour orange .rootstock contained more juice
than that grown on rough lemon. On the aver-
age, the red grapefruit on sour orange had
the most juice while the pink variety on rough
lemon had the least amount.

As far as meeting the high juice standards
in effect from August 1 to October 15, ap-
proximately 8 percent of the fruit in Septem-
ber and 32 percent in October met the strict
juice regulations. At the time of the medium
juice requirements from October 16 to Novem-
ber 15, approximately 63 and 85 percent met


Table 3. Average daily increase in juice content per fruit
of grapefruit of three sizes (96, 70, and 54)
during October to December 1955.


Sampling Period Size
96 70 54
ml/fruit/day
Oct. 1-15 1.1 1.7 2.1
Oct. 16-31 0.5 0.5 0.8
Nov. 1-15 0.9 1.0 0.8
Nov. 16-30 0.1 0.3 0.4
Dec. 1-15 0.4 0.5 0.8
Dec. 16-31 0.4 0.2 0.4

Average 0.6 0.7 0.9







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


regulations in October and November, respec-
tively. After November 15, most of the fruit
met the low juice standards then in effect.
The variations in the juice content for each
sampling period as well as the daily increases
in juice volumes are presented.

LITERATURE CITED
1. Deszyck, E. J. and J. W. Sites. 1954. The effect
of lead arsenate sprays on quality and maturity of
Ruby red grapefruit. Proc. Fla. State Hort. Soc. 67:
38-42.


2. Deszyck, E. J. and J. W. Sites. 1955. Juice con-
tent in early Ruby red grapefruit. Proc. Fla. State
Hort. Soc. 68: 47-49.
3. The Florida Citrus Code of 1949. Chapter No.
25149. State of Fla. Dept. Agr. Citrus & Vegetable
Inspection Div.
4 General Laws of Florida. 1955. Minimum juice
content for grapefruit. Chapter 29760, Senate Bill No.
562.
5. Gerwe, R. D. 1954. Extracting citrus juices.
Proc. Fla. State Hort. Soc. 67: 173-176.
6. Harding. P. L. and D. F. Fisher. 1955. Seasonal
changes in Florida grapefruit. U. S. Dept. Agr. Tech.
Bul. 886.
7. Taylor, O. C., G. E. Carman, R. M. Burns, P.
W. Moore, and E. M. Naeur, 1956. Effect of oil and
parathion sprays on orange size and quality. Calif.
Citrograph 41: 452-454.


EFFECTIVENESS OF DIFFERENT ZINC

FERTILIZERS ON CITRUS


C. D. LEONARD, IVAN STEWART
AND GEORGE EDWARDS

Florida Citrus Experiment Station
Lake Alfred

Zinc foliage sprays have been used for more
than 20 years for the correction and preven-
tion of zinc deficiency or frenching in Florida
citrus groves. Such sprays are reasonably ef-
fective in controlling wrenching in most groves
even though the zinc sources now used are
very slowly absorbed and highly inefficient
(7). Sprays have the additional disadvantage
of leaving a residue on the leaves which in-
creases the scale population. Hence there is
need for an effective and inexpensive method
of supplying zinc to citrus trees by application
of a suitable zinc fertilizer to the soil. The
studies reported here were carried out in an
effort to find such a method.
Soil application of zinc, chiefly as the sul-
fate, has been far less dependable than foliage
sprays as a method of supplying zinc to citrus.
Camp (3) reported in 1934 that in some cases
no visible result was obtained from soil appli-
cations of zinc sulfate, whereas in others ap-
plication of from 5 to 15 pounds per tree
broadcast gave good responses. Even where
soil applications of zinc are effective absorp-
tion of zinc and correction of the zinc defi-
ciency leaf pattern are relatively slow. The
effectiveness of soil applications of zinc varies
greatly with various soil characteristics; for ex-

Florida Agricultural Experiment Stations Journal
Series, No. 559.


ample, this element is much less available at
a soil pH of 6.0 or 7.0 than at more acid soil
reactions.
Jones, Gall, and Barnette (6) reported that
when zinc compounds are applied to the soil,
they react to form three types of compounds:
(a) water soluble zinc compounds, (b) com-
binations formed by the reaction of soluble
zinc compounds and the organic and inorganic
colloidal complex of the soil (replaceable
zinc), and (c) combinations insoluble in
water and not in combination with the colloi-
dal complex of the soil (not replaceable). They
found that when low concentrations of soluble
zinc compounds react with the soil, the major
portion of the zinc enters into combination
with the colloidal complexes and may be re-
placed by a normal ammonium chloride solu-
tion. Under these conditions they found a near
equivalence between the replaceable zinc of
the soil and calcium removed from the colloi-
dal complex. When high concentrations of
soluble zinc compounds react with the soil,
they found that the zinc is present not only
in water soluble and replaceable forms but
also in an insoluble form. They state that or-
ganic matter, clay, replaceable bases, carbon-
ates and phosphates influence the fixation of
zinc in the soil.
Jamison (4), however, reported little dif-
ference in the fixation of zinc in the presence
and the absence of superphosphate in the soil.
He states that the forces which retain zinc in
these soils are far stronger than those holding
zinc as phosphates or basic compounds ordin-
arily considered insoluble.






LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS


Jamison (5) found that zinc applied as the
sulfate leached from the soil faster where
larger crystals or lumps were applied than
where a fine powder was used. Most of the
zinc from the fine source materials remained
adsorbed in the surface three inches of soil
while much of the zinc from coarse materials
had penetrated into the deeper layers of soil
or had leached. He attributed this difference
to saturation with zinc of small local zones of
soil beneath the lumps or large crystals.
Brown (2) mixed zinc sulfate thoroughly
at the rate of 100 pounds per acre with five
major citrus-producing soils which had been
adjusted to pH levels of 4, 5, and 6. At pH's 4
and 5, the zinc content of the leaves of orange
and grapefruit seedlings grown in these soils
was very high, but in leaves of the plants
grown in soil at pH 6 it was much lower. The
uptake of zinc at different pH levels varied
for the five soils, but with Lakeland soil at
pH's 4, 5, and 6 the zinc contents of orange
leaves were 202, 317, and 44 ppm, respective-
ly.
LEACHING OF ZINC
The high uptake of zinc by citrus seedlings
from different soils at pH 4 and 5 with which
zinc sulfate had been mixed, as reported by
Brown (2), shows that this material is an ex-
cellent source of zinc for citrus when distrib-
uted within the rooting zone of the trees.
Since most of the zinc from finely-divided zinc
sulfate becomes fixed near the soil surface (5),
the poor results obtained from soil applica-
tions of this material in citrus groves appear to
be due to its failure to leach downward into
the rooting zone. In an effort to find a method
of getting zinc deeper into the soil, two zinc
chelates, zinc 1, 2 diaminocyclohexane tetra-
acetate (ZnDCTA) and the zinc chelate of
Table 1. Effect of soil pH on amount of radioactive
zinc leached through lakeland soil from t.o
zinc chelates.


pH of soil ZnDCTA ZnAPCA
ctM (a) cp

4 901 0
5 2230 0
6 2776 0
7 3153 12

(a) Counts per minute


an aromatic polycarboxylic acid (ZnAPCA)
were tagged with radioactive zinc-65 and
leached through Lakeland soil adjusted to
pH's of 4, 5, 6, and 7. Counts made on the
leachates showed that ZnDCTA was very ef-
fective in solubilizing zinc, and its effective-
ness showed marked increases as the soil pH
rose from 4 to 7 (Table 1). ZnAPCA was
highly ineffective as a solubilizer for zinc.
Zinc sulfate and several zinc chelates were
tagged with zinc-65 and leached through pots
of Lakeland soil at pH 5.4. Counts on the
leachates indicated that much more zinc in
ZnEDTA remained soluble than in zinc sul-
fate (Table 2). Increasing the amount of
EDTA applied with the same amount of zinc
(varying the molecular ratio of zinc to EDTA)
increased the amount of zinc leached. Addi-
tion of non-ionic or anionic wetting agents also
substantially increased the solubility of the
zinc in this chelate, but addition of a cationic
wetting agent reduced it. Zinc gluconate and
zinc naphthenate were relatively ineffective as
solubilizers for zinc. Zinc sulfate, with or with-
out a wetting agent, was extremely ineffective
in these leaching trials. These results show
the great fixing power of the Lakeland soil
for zinc.
The distribution of the zinc in the soil was
determined by taking three cores of soil from
each pot with a special soil sampling tube with

Table 2. Aounmt of radioactive sine fr different
*ouce. leched through pots of Iakeland
soil at pH 5.4.


Zinc Source Other Material Cpm (a)
Zn EDTA 214
Zn EDTA 1 PR-51 498
Zn DTA 5 g. HR-51 876
Cationic vetting agent 81
SAnionic vetting agent '61
SNon-ionic vetting agent 687
Zn ErTA (1:2) (b) 740
S (1:5) (b) 1621
Zn gluconate 14
Zn Naphthenate 2
Zn SO 4 I
zn so4 P0 5 Sg. m-51

(a) Counts per minute
(b) Molecular ratio of zinc to EATL






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


a narrow slit in the side and making radio-
active counts directly on the soil at depths of
one to six inches. These counts showed that
most of the radioactive zinc applied in the
form of zinc sulfate remained in the top few
inches of soil, while that applied as ZnEDTA
was much more uniformly distributed (Fig.
1). The total of the counts for the six-inch
layers sampled was considerably greater for
zinc sulfate than for ZnEDTA at pH's of 5
and 6, indicating much greater fixation of zinc
from the sulfate. There was little difference in
the total counts for these two zinc sources at
pH's of 4 and 7. Radioactive counts made on
the leaves of citrus seedlings grown in the
pots showed a close correlation between the
movement of zinc through the soil and the
amount of zinc uptake by the plants.
FIELD EXPERIMENTS
Since the pot studies reported above showed
considerably more leaching of zinc and greater
uptake of zinc by citrus seedlings from che-
lated zinc than from zinc sulfate, field experi-
ments were carried out in several commercial


Fig. Residual concentrations o
leaching of ZnEDTA and Zi
adjusted to different pH le


I000-


PH 4






ZnSO,
ZnEDTA








24624


citrus groves to compare the effectiveness of
chelated zinc with zinc sulfate. Two such ex-
periments are reported below.
In December, 1952, a field plot experiment
was started in a grove of 8-year-old Pineapple
orange trees growing on Lakeland sandy soil
with a pH of about 6.0. This grove was
sprayed with zinc until 1951. The linear four-
tree plots were completely buffered by other
trees from adjoining plots, and replicated three
times in randomized blocks. Zinc sulfate
monohydrate, containing 36 percent zinc, was
applied at rates of 100, 164, and 328 grams of
zinc per tree per application. Each rate was
applied once a year to one series of plots, and
three times a year to another series. Three zinc
chelates, ZnEDTA (zinc ethylenediamine
tetraacetate), ZnHEIDA (zinc hydroxyethyl
iminodiacetate), and ZnEDTA-OH (zinc hy-
droxyethyl ethylenediamine triacetate), were
applied once a year at rates of 12.5, 25, 50,
and 100 grams of zinc per tree. These chelates
were also applied at rates of 12.5 and 25
grams of zinc per tree three times a year until
1955, when the use of ZnHEIDA was dis-


f Zn65 following application and
n SO, to pots of Lakeland sand


Depth, Inches


W)

N
800-
W
3 600-
C

(D)
CL 400-

0
200-




LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS


continued. In September, 1955 the 12.5-gram
rate for ZnEDTA and ZnEDTA-OH applied
three times a year was changed to 50 grams,
and the 25-gram rate was changed to 100


grams. All materials were broadcast by hand
under the spread of the trees. Leaf samples
taken in August, 1955 (1955 summer flush)
and in August, 1956 (1956 spring flush and


Table 3. Effect of soil application of zinc compounds on
the zinc content of leaves of Pineapple orange
trees on acid soil.


(b)
Source of Zinc gm. Zn No. ppm zinc in leaves
applied (a) Applications Summer Spring Summer
per tree) per year Flush Flush Flush
per appl. 1955 1956 1956

Zn SO H20 100 1 33 28 30
164 1 29 28 27
328 1 44 44 35
100 3 35 30 29
164 3 42 42 37
328 3 48 53 42

Zn EDTA 12.5 1 28 21 24
25 1 29 21 21
50 1 33 25 24
100 1 33 26 27
12.5 3 34 31 26
25 3 33 38 29

Zn HEIDA 12.5 1 29 -
25 1 34 -
50 1 35 -
100 1 37 -
12.5 3 32 -
25 3 33 -

Zn EDTA-OH 12.5 1 32 26 28
25 1 29 25 26
50 1 29 28 24
100 1 32 33 25
12.5 3 31 28 26
25 3 30 29 27

Check None 31 23 24

(a)All applications broadcast.

(b)
1955 summer flush sampled in August, 1955. 1956 spring flush and summer
flush sampled in August, 1956.





FLORIDA STATE HORTICULTURAL SOCIETY, 1956


summer flush separately) were analyzed for
total zinc by the polarographic method of Bar-
rows, Drosdoff, and Gropp (1).
The highest zinc contents were found in the
leaves from trees that received the higher
amounts of zinc sulfate (Table 3). Zinc sul-
fate applied three times a year resulted in
higher zinc content of the leaves than the
same amount of zinc per application applied


once a year. Application of 100 grams of zinc
per tree as the sulfate and in the chelate form
showed about equal effectiveness in increas-
ing zinc in the leaves. The lower rates of ap-
plication of the chelates showed little advan-
tage over the untreated checks. These field re-
sults do not bear out the increased availability
of zinc shown by the chelates in the pot ex-
periment reported above. In the pot experi-


Table 4, Effect of amount and method of application
of zinc chelates on the zinc content of
Pineapple orange leaves. (a)


.. Treatment
Chelate Other Material Gmo Zn How Zinc b)
Applied Applied Spring Summer
.... ,., tree I F1ih Fluh

Zn pED_& 328 Band 2 29
5 lbs soda ash 100 Chunks 25
N 5 328 26
5 WS 100 23
S5 328 25
S3 oz. AP-78 (c) 100 25
S8 ozo (c) 328 23
S328 Smo piles 25 30
5 lbs soda ash 328 39 25
5 100 26
N 100 23

Zn EDTA-OH 328 Band 29 25
" 10 Ibe soda ash 328 a 28 24
5 1" I 100 Chunks 25
5 328 29
5 S 100 25
5 328 28
3 oz. AP-78 (c) 100 23
8 oz. (c) 328 28
328 Piles 23 27
100 30
5 Ibs soda ash 328 32 23
a" n oa 5 100 25

Check None 23 25


(a) Each treatment applied one time*
(b) 1956 flushes, sampled in August, 1956.
(c) Anionic wetting agent (Antara Chemical Company).





LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS


ment, ZnEDTA was more effective than zinc
sulfate in penetration of soluble zinc through
the soil and also in bringing about uptake of
zinc by citrus seedlings.
A second experiment was started in the fall
of 1955 in another part of the same Pineapple
orange grove. It consisted of about 70 different
zinc treatments, including sprays and soil ap-
plications, each applied to three individual
trees. Some of these treatments were applied
in the spring of 1956. Three methods of soil
application were used: (a) broadcast in a
band 3 to 4 feet wide, (b) applied in harden-
ed chunks made by mixing the zinc sources
with water and drying, and (c) in small piles
of loose material distributed around the trees.
In some treatments, the zinc sources were
mixed with soda ash (NaCO,) to raise the
soil pH, wettable sulfur to lower the pH, or
with a wetting agent. Zinc sulfate was also
applied in mixtures with calcium chloride.
Foliage sprays of zinc sulfate neutralized with
hydrated lime were applied for comparison
with the soil treatments.
In this experiment two zinc chelates (Zn-
EDTA and ZnEDTA-OH) were tested at a
rate much higher than in the first experiment,
but were again found to be relatively ineffec-
tive as sources of zinc regardless of the method
of application (Table 4). A small increase in
zinc in the spring flush leaves was brought
about by mixtures of chelated zinc and soda
ash applied in small piles, when compared
with the chelates applied alone. However,
none of the chelate treatments brought about
any substantial increase in the zinc content of
the summer flush leaves, when compared with
the untreated checks. These results are in
general agreement with those obtained in the
first experiment.
Five pounds of zinc sulfate applied broad-
cast twice a year showed only a small increase
in zinc uptake over similar application once
a year, and the addition of wettable sulfur
showed no advantage over zinc sulfate alone
(Table 5). When applied in chunks, addition
of wettable sulfur gave a small increase over
application of zinc sulfate alone.
Zinc sulfate applied as a foliage spray in
January, 1956 gave a progressive increase in
the zinc content of the 1956 spring flush
leaves as the concentration of the spray was
increased from three to 12 pounds of zinc sul-


fate per 100 gallons. However, the sprays gave
no increase in zinc content of the 1956 sum-
mer flush leaves when compared with the
untreated checks. This failure of the sprayed
zinc to move in substantial amounts into the
newer flush tends to explain why such sprays
must be repeated every year or two in most
groves.
Application of zinc sulfate to the soil in
small piles is comparable to the use of hard-
ened chunks in that both methods give a high
concentration of zinc over numerous small
local soil zones. The work of Jamison (5) in-
dicates that this should induce greater total
movement of zinc down through the soil. In
this experiment, application of zinc sulfate in
small piles, either alone or with wettable sul-
fur, gave slightly lower zinc levels in the
leaves than similar amounts applied broad-
cast or in chunks. However, when five pounds
of zinc sulfate was mixed with five pounds
of calcium chloride and applied in small piles,
it gave a very striking increase in the zinc
content of the leaves. The 1956 spring flush
leaves contained 170 ppm. of zinc. This is
nearly three times as high as that obtained
from a foliage spray at 12 pounds of zinc
sulfate per 100 gallons, and is four times
greater than that obtained from any other
soil treatment. The younger 1956 summer
flush leaves contained 82 ppm of zinc, which
is twice as much as the highest level from any
other treatment. Several extra samples of
leaves were taken and analyzed to verify these
unusually high values. In the spring flush they
approach the high leaf zinc levels reported by
Brown (2) for citrus seedlings grown in pots
of soil in which zinc sulfate had been mixed
at the rate of 100 pounds per acre.
It would appear that the high concentra-
tion of soluble calcium supplied by the cal-
cium chloride replaced most of the zinc fixed
by the soil in exchangeable form, or by satur-
ating the exchange complex with calcium, pre-
vented fixation of zinc in exchangeable form.
This would permit more of the zinc to leach
downward into the root zone where it could
be taken up by the trees.
It was not possible to prepare hardened
chunks by mixing zinc sulfate and calcium
chloride with water even when cement was
added, but satisfactory chunks were made by
mixing five pounds each of zinc sulfate, cal-





78 FLORIDA STATE HORTICULTURAL SOCIETY, 1956


cium chloride, and wettable sulfur with water.
Application of these chunks, however, showed
no advantage over similar chunks containing
only zinc sulfate and wettable sulfur, and
both of these treatments gave leaf zinc levels


far below those given by the mixture of zinc
sulfate and calcium chloride applied in piles.
This may be due to the slow breakdown of
the chunks, but it may also be due in part to
lowering of the soil pH by the sulfur. Various


Table 5. Effect of amount and method of application of
zinc sulfate on the zinc content of Pineapple
orange leaves


STreatment M 5nf (b)
Zinc sulfate Other Material No* of Gmso Zn. How Spring Sumer
Lbs/tree Lbs/tree times applied applied Flush Flush
applied per tree
(a) .

2 1 328 Band 21
2 2 656 32
2 5 WS 1 328 9 26 28
5 1 820 38 33
5 2 1640 N 42 35
5 5 WS 1 820 32 29
5 5 WS 2 1640 33 33

5 1 820 Chunks 30
5 2 1640 35
5 5 Vs 1 820 38 35
5 5 vs 2 1640 40 41
5 5 VS
150 ml Ethomeen T-15(c)1 820 X 30
5 5 WS
5 CaO12 1 820 36 35


5 1 820 Sm. piles 26 28
5 5 vS 1 820 31 26
5 5 CaC1: 1 820 170 82

3/100 gal 1 Ca(0)2/1 gal. 1 Foliage 31 22
6 2 1 Spray 44 23
12 4 1 60 24

(Plots) Check None 23 25


(a) Where 2 applications are shown, they were made
one being made in Apr. 1956.

(b) 1956 flushes, sampled August, 1956.


about 6 moso apart, the second


(c) Cationic vetting agent (Armour Chemical Division, Armour & Coo)





WENZEL AND MOORE: GRAPEFRUIT UTILIZATION


mixtures of zinc sulfate and calcium chloride
are being studied further as a possible source
of zinc suitable for soil application to citrus
trees.
SUMMARY
A study was made to compare the effective-
ness of soil application of different zinc
sources to citrus trees growing on acid soil.
Zinc sulfate and chelated forms of zinc were
tagged with radioactive zinc-65 and leached
through pots of Lakeland soil adjusted to dif-
ferent pH levels to study their leaching prop-
erties. Counts made on the leachates indi-
cated that ZnEDTA and ZnDCTA (zinc 1, 2
diaminocyclohexane tetraacetate) were much
more effective in carrying zinc through the soil
than was zinc sulfate. Virtually none of the
zinc sulfate was leached through the pots.
In a field experiment with Pineapple orange
trees, zinc sulfate and three zinc chelates were
about equal in increasing the zinc content of
the leaves when each was applied once a year
at 100 grams of zinc per tree per application.
The highest zinc contents were found in the
leaves from trees that received two pounds of
zinc sulfate per tree per application.
In a second field experiment, a single ap-
plication of five pounds zinc sulfate per tree,
applied broadcast, in hardened chunks made
by mixing it with water, or in small piles scat-
tered around the trees gave a slightly higher
zinc content of both spring and summer flush
leaves than foliage sprays applied at the rate
of three pounds of zinc sulfate per 100 gal-
lons. Foliage sprays at 6 and 12 pounds of
zinc sulfate per 100 gallons substantially in-


,creased the zinc content of the spring flush
over that obtained with the three-pound rate,
but failed to increase the zinc content of the
summer flush leaves. A mixture of five pounds
zinc sulfate and five pounds calcium chloride,
applied in small piles beneath the trees, increas-
ed the zinc content of the spring flush leaves to
170 ppm, and that of the younger summer
flush leaves to 82 ppm. Both figures are un-
usually high for mature citrus trees growing
in the field.
LITERATURE CITED
1. Barrows, Harold L., Matthew Drosdoff, and
Armin H. Gropp. 1956. Rapid Direct Polarographic
Determination of Zinc in Plant Ash Solutions. Agri-
cultural and Food Chemistry 4: 850-853.
2. Brown, J. W. 1955. Absorption of Zinc by Citrus
from Various Soil Types. Thesis, University of Flori-
da.
3. Camp, A. F. 1934. Studies on the Effect of
Zinc and Other Unusual Mineral Supplements on the
Growth of Horticultural Crops. Fla. Agr. Exp. Sta.
Annual Report, page 67.
4. Jamison, Vernon C. 1943. The Effect of Phos-
phates upon the Fixation of Zinc and Copper in Sev-
eral Florida Soils. Proc. Fla. State Hort. Soc. 56:
26-31.
5. Jamison, Vernon C. 1944. Citrus Nutrition
Studies. Fla. Agr. Exp. Station Annual Report, page
192.
6. Jones. H. W., 0. E. Gall, and R. M. Barnette.
1936. The Reaction of Zinc Sulfate with the Soil. Fla.
Agr. Exp. Station Bul. 298.
7. Stewart, Ivan, C. D. Leonard, and George Ed-
wards. 1955. Factors Influencing the Absorption of
Zinc by Citrus. Proc. Fla. State Hort. Soc. 68: 82-88.
ACKNOWLEDGMENT
The authors express their appreciation to the
Minute Maid Corporation and to its repre-
sentatives for their cooperation and for per-
mitting the use of the grove in which the
field experiments reported here were carried
out. Appreciation is also expressed to the Dow
Chemical Company and to Geigy Agricultural
Chemicals for supplying the zinc chelates used.


INCREASED UTILIZATION OF GRAPEFRUIT

THROUGH IMPROVEMENT IN QUALITY

OF PROCESSED PRODUCTS'


F. W. WENZEL AND E. L. MOORE
Florida Citrus Experiment Station

Lake Alfred
Increased utilization of grapefruit is needed
because the present supply is in excess of de-

1/Cooperative publication by the Florida Citrus
Experiment Station and Florida Citrus Commission.
Florida Agricultural Experiment Station Journal
Series No. 564.


mand. The average financial return to grape-
fruit growers has been small during recent
years. During the 1955-56 season 48 percent
of the grapefruit crop used was for processed
products, such as canned grapefruit juice,
canned grapefruit sections, and frozen con-
centrated grapefruit juice. Obviously, large
amounts of these products are being bought
by consumers, but improvements in the quality
of some of the products packed could and







FLORIDA STATE HORTICULTURAL SOCIETY, 1956


should be made. Better quality in processed
grapefruit products should lead to increased
demand and subsequently to increased utiliza-
tion of grapefruit.
This paper will discuss briefly (a) utiliza-
tion of Florida grapefruit for processed prod-
ucts, (b) factors which affect the quality of
processed grapefruit products, and (c) past
and current investigations of the Florida Citrus
Experiment Station and the Florida Citrus
Commission concerning factors upon which
the quality of processed grapefruit products
depends.
UTILIZATION OF FLORIDA GRAPEFRUIT
There has been a gradual increase in the
production of Florida grapefruit from about
18 million boxes for the 1936-37 season to a
peak production of about 42 million boxes dur-
ing the 1953-54 season; for the past two sea-
sons approximately 35 and 38 million boxes


have been produced. During the same time
production of Florida oranges has increased
from 19 million boxes in 1936-87 to over 91
million boxes during the 1955-56 season. It
may be seen from the figures in Table 1 that
the utilization of grapefruit by the Florida
citrus processing industry has gradually in-
creased over the years. For example, about 38
percent of the grapefruit used in the 1936-37
season went into processed products com-
pared to 48 percent during 1955-56. The
maximum utilization occurred in 1945-46
when 69 percent was processed. The use of
oranges for processing has increased from 3
percent during the 1936-37 season to about
37 percent in 1946-47 and to 71 percent in
1955-56. This, it is evident that currently al-
most 50 percent of the grapefruit and over 70
percent of the oranges grown in Florida are
being used for processed products. This is in
marked contrast to the situation in and prior


TAEB 1
Utilization of Florida Grapefruit Fresh and Processed 1, 2
Fresh fruit Fruit Fresh and
sales processed processed
Season Processed
Thousands Thousands Thousands % of total
of boxes of boxes of boxes
1936-37 11,233 6,759 17,992 37.6

1941-42 8,956 10,143 19,099 53.1
1946-47 10,414 15,866 26,280 60.4

1951-52 19,172 13,678 32,850 41.6

1952-53 17,305 15,035 32,340 46.5

1953-54 20,451 20,089 40,540 49.6

1954-55 19,263 15,660 34,923 44.8

1955-56 19,925 18,661 38,586 48.4
1 Figures above for boxes for 1953-54 and previous seasons from Florida Citrus Fruit -
1955 Annual Sunary, prepared by Paul E. Shuler and J. C. Townsend, Jr., with the
cooperation of Florida Crop and Livestock Reporting Service, Orlando, Florida,
Florida Citrus Comission, Lakeland, Florida, Florida Department of Agriculture,
Nathan Mayo, Commissioner, and Agricultural Marketing Service, U.S. Department of
Agriculture.
2 Figures above for boxes for 1954-55 and 1955-56 from Annual Reports, Citrus and
Vegetable Inspection Division, Florida Department of Agriculture, Winter Haven,
Florida.






WENZEL AND MOORE: GRAPEFRUIT UTILIZATION


TABLE 2
Quantity of Florida Grapefruit Used for Packs of Major Processed Products prior to the 1952-53 Season 1, 2
Processed 1936-37 1941-42 1946-47 1951-52
grapefruit Boxes % Boxes % Boxes % Boxes %
product
Canned juice 3,057,179 51.9 5,683,874 58.0 7,584,708 49.0 6,812,089 56.3
Canned blended juice 90,367 1.5 1,123,932 11.5 4,273,355 27.7 2,736,950 22.7
Canned sections 2,701,714 45.8 2,852,107 29.2 3,453,827 22.4 2,290,301 19.0
Canned citrus salad 49,205 0.8 122,694 1.3 140,357 0.9 238,054 2.0
Totals 5,898,465 100.0 9,782,607 100.0 15,452,247 100.0 12,077,394 100.0
1 Figures above for field boxes furnished by and used through the courtesy of the Florida Canners'
Association, Winter Haven, Florida.
2Figures above do not include utilization of grapefruit for other processed products, such as processed
grapefruit concentrate.


to 1936, when most of the oranges and grape-
fruit from Florida were sold as fresh fruit. In
view of these facts, it is time that more em-
phasis be placed by growers and processors
on the production and use of citrus fruits hav-
ing internal quality necessary for the produc-
tion of processed products of good quality.
The quantity of grapefruit used for the pro-
duction of the more important processed
grapefruit products is shown in Table 2 for
some seasons prior to the 1952-53 season.
Statistics presented in Table 3 show that the
four products that have been the best outlets
-for grapefruit during the past five seasons
have been canned grapefruit juice, canned
grapefruit sections, canned blended juice, and
frozen grapefruit concentrate. Perhaps it


should be pointed out, since both seedless and
seedy grapefruit are produced, that during
the 1955-56 season 75 percent of the seedy
grapefruit was sent to commercial canneries
but the corresponding amount of seedless
fruit was 32 percent.
During the last five years utilization of
grapefruit (Table 3) for canned juice has
varied from less than 7 to more than 11 mil-
lion boxes, while that for blend has varied
only slightly; these two products in 1955-56
provided an outlet for about 11.8 million
boxes or 66.4 percent of the total grapefruit
used by processors in the major processed
products.
Since the 1946-47 season, the pack of
canned grapefruit sections and citrus salad


TABLE 3
Quantity of Florida Grapefruit Used for Packs of Major Pro-essed Products front the 1951-52
Season through the 1955-56 Season 1, 2
Processed 1951-52 1952-53 1953-54 1954-55 1955-56
grapefruit Boxes % Boxes % Boxes % Boxes % Boxes %
product


Canned juice


6,812,089 50.6 8,338,569 56.2 11,459,550 58.0 8,226,991 53.8 9,585,095 53.8


Canned blended juice 2,736,950 20.4 2,371,543 16.0 2,797,251 14.1 2,074,358 13.6 2,236,437 12.6
Canned sections 2,290,301 17.1 2,553,104 17.2 3,111,999 15.7 3,367,061 22.0 3,179,466 17.8


Canned citrus salad 238,054 1.8


289,489 1.9 379,686 1.9 326,857 2.1 295,622 1.7


Frozen concentrate 1,084,986 8.1 1,159,173 7.8 1,682,141 8.5 1,065,480 7.0 2,128,620 12.0
Frozen blended 268,231 2.0 133,785 0.9 358,429 1.8 224,586 1.5 365,110 2.1
concentrate
Totals -13,430,611 100.0 14,845,663 100.0 19,789,056 100.0 15,285,333 100.0 17,790,350 100.0
1
Figures above for field boxes furnished by and used through the courtesy of the Florida Canners' Association,
Winter Haven, Florida.
2 Figures above do not include utilization of grapefruit for other processed products, such as processed grapefruit
concentrate, frozen grapefruit sections, chilled grapefruit sections and salad, or chilled grapefruit juice.






FLORIDA STATE HORTICULTURAL SOCIETY, 1956


has ranged from approximately 4 to 6 million
cases (24/2's). During the 1955-56 season al-
most 83' million boxes of grapefruit were used
for canning about 5,. million cases of grape-
fruit sections and salad, which corresponded
(Table 3) to 19.5 percent of the total grape-
fruit used. Through the use of grapefruit of
suitable quality and good processing pro-
cedures, canned sections of excellent quality
may be obtained. Such a product has always
met with good consumer acceptance, and it is
believed that the increased sale of canned
grapefruit sections, both in this country and
in foreign countries, would provide a means
for the utilization of some of the excess grape-
fruit now available. Since Florida produces
over 70 percent of the world crop of grape-
fruit, it would seem that the potential possi-
bilities for export of canned grapefruit sec-
tions should be very great. It is difficult to
understand why in recent years the grapefruit
section pack continues to be only approxi-
mately double what it was in the 1930-31
season.
The largest production of frozen concen-
trated grapefruit juice occurred during the
1955-56 season, when over 2,2 million gallons
were produced from about 2% million boxes of
fruit. In contrast to this, during the same sea-
son over 70 million gallons of frozen con-
centrated orange juice were produced. Thus,
it is evident that the acceptance and use of
frozen grapefruit concentrate by consumers
has been far below that of frozen orange con-
centrate. There was a sharp drop in produc-
tion during the 1950-51 season of frozen
grapefruit concentrate to only about 188,000
gallons caused by poor acceptance of the 1.6
million gallons of this product packed in the
previous year. The size of the frozen grape-
fruit concentrate pack has just in recent seasons
reached and during 1955-56 exceeded what
it was six years ago in its second season.
About 179 million boxes of grapefruit were
used in 1955-56, by the processing industry
for the production of the major grapefruit
products listed in Table 3. Canned grapefruit
juice provided an outlet for 53.8 percent of
this fruit and 17.8 percent was used for the
canning of grapefruit sections. In the produc-
tion of the canned blended juice and frozen
grapefruit concentrate packs, 12.6 and 12.0
percent of fruit were used, respectively.


Canned citrus salad and frozen concentrated
blended juice together accounted for 3.8 per-
cent. The utilization figures given in Tables 2
and 3 are only for the more important products
listed and, therefore, are slightly less than the
actual total amounts of grapefruit used for
processing. Some fruit also was used for
products such as concentrated processed grape-
fruit juice, chilled grapefruit juice, and chilled
grapefruit sections and salad. Thus during the
1955-56 season, 544,070 boxes and 262,099
boxes of grapefruit were used for chilled sec-
tions and juice, respectively.
QUALITY OF PROCESSED GRAPEFRUIT PRODUCTS
The meaning of the term, quality, depends
upon both the person using the term and the
products to which the term is applied. For ex-
ample in speaking of fresh grapefruit, growers
and shippers place considerable emphasis on
the external appearance of fruit, provided it
meets maturity standards for internal quality,
while processors are chiefly concerned with the
internal characteristics of the fruit. Thus, the
concentrator is more interested in the total
soluble solids in the juice than he is in having
fruit free of external blemishes. In packing un-
sweetened canned grapefruit juice, the use of
fruit containing juice of low acidity and high
Brix/acid ratio is extremely important, while
fruit with a greater acid content, provided that
it is not excessive, may be used for the pro-
duction of sweetened processed grapefruit
products.
The definition of quality for processed citrus
products should be based upon the desires and
opinions of consumers, because the demand
for these products depends to a great extent
upon such desires. Of course, the price that
consumers have to pay for these products is
another factor and perhaps the major one
which influences total demand; also, today
ease of use or convenience is becoming con-
tinually of greater importance to the house-
wife. Recently, Florida Citrus Mutual has re-
viewed (22) some of the consumer surveys (5,
7, 24) which have been made during recent
years to determine the characteristics of pro-
cessed grapefruit products which consumers
considered to be acceptable and of good qual-
ity. The canned grapefruit juices used for one
of these surveys (4, 5) were packed in the
pilot plant at the Citrus Experiment Station.
Other reports on consumer surveys (4, 6) con-









WENZEL AND MOORE: GRAPEFRUIT UTILIZATION


cerned with this problem have also been pub-
lished. Very briefly and in general, most of
the results from these surveys have indicated
that most consumers prefer grapefruit products
that have a typical grapefruit flavor, are mod-
erately sweet and not excessively bitter.
Therefore, these three characteristics may be
used as an indication of quality in canned
grapefruit juice and other grapefruit products.
Characteristics other than these also influence
the quality of such products. For example,
canned grapefruit sections of good quality
should also be firm and uniform in size and
appearance; discoloration and undesirable fla-
vors in sections, caused by poor storage con-
ditions, are not desirable. Likewise frozen
concentrated grapefruit juice should show no
tendency to gelation, should reconstitute easi-
ly and then be free from indications of sepa-
ration or clarification.
To improve the quality ot processed citrus
products, both growers and processors should
consider factual information that has been
made available through past research investi-
gations concerning the factors that affect the
quality of these products. They should also be
aware of current research projects, the ulti-
mate practical object of which is the profit-
able utilization of the entire grapefruit crop
either by improvement in the quality of the
major processed products that are now
packed, thereby causing better acceptance
and more demand, or by the development of
new processed products or by-products that
will provide other outlets for this fruit. Some
of these research investigations, that have been
completed or are in progress, at the Citrus
Experiment Station will be discussed briefly.
Principal emphasis concerning processed prod-
ucts has been placed on the factors affecting
the quality of canned grapefruit sections,
canned grapefruit juice and frozen concen-
trated grapefruit juice.
An investigation on the effect of storage
temperature on quality of canned grapefruit
sections was discussed by Huggart, Wenzel
and Moore (9). Results indicated that for
maintenance of original good quality in
canned sections, the products should be held
at 700 F. or lower. Marked changes in color,
flavor and firmness that result in lower quality
in this product occurred at storage temper-
atures of 80 F. or above. Another study (10)


recently completed has shown that the dis-
coloration or browning of canned grapefruit
sections during storage is related to the acidity
in the canned product, which is dependent
upon the acid content of the grapefruit used.
In general, browning occurred during storage
more frequently in the canned sections with
the greater acidities.
The effect of cultural practices on the
quality of canned grapefruit sections has been
subject to investigation during the past three
seasons. Discussion of the data obtained when
canned grapefruit sections were processed
commercially from fruit grove plots that were
treated with fertilizer containing various
amounts of potash has been reported (27). It
was found, as is generally known, that the
time at which grapefruit are harvested is a
factor affecting the quality of canned sec-
tions; also that when grapefruit were picked
at the same time from trees which had re-
ceived fertilizer containing 0, 3, and 10 per-
cent potash, the firmness of the canned sec-
tions decreased with increase in the amount
of potash. A similar study using arsenated and
unarsenated grapefruit will be completed this
season.
Research has been done on various problems
concerning the production and storage of froz-
en concentrated grapefruit juice. Data on
changes that occur in this product during stor-
age, such as gelation, clarification, sugar hy-
drate formations and the very slight- loss of
ascorbic acid have been published in various
articles (2, 8, 13, 14, 15, 18, 25). Thermal
stabilization of grapefruit juice for the produc-
tion of frozen concentrate has been found
necessary to prevent the occurrence of gela-
tion and clarification in this product during
storage and distribution. Atkins, Rouse and
others (1, 2, 3, 19, 20) have reported results
obtained from several investigations of this
process for the production of frozen grape-
fruit concentrate of good quality. During stor-
age at 0 F. or lower, undesirable flavors may
develop in frozen grapefruit concentrate. Such
off-flavors are usually described as being simi-
lar to tallow, castor oil, or cardboard. Results
of the study since 1953 of this problem were
recently reported (17). Oxidative changes are
believed to be involved in the development of
these off-flavors and it has been found that
the maintenance of a sufficiently high peel oil




Full Text

PAGE 1

of the FLORIDA STAT0 HORTICULTURAL SOCIETY VOLUME 69 Published by the Society

PAGE 2

FLORIDA STATE HORTICULTURAL SOCIETY, 1956 SIXTY-NINTH ANNUAL MEETING of the FLORIDA STATE HORTICULTURAL SOCIETY held at ORLANDO, FLORIDA November 7, 8 and 9 1956

PAGE 3

II FLORIDA STATE HORTICULTURAL SOCIETY, 1956 FLORIDA STATE HORTICULTURAL SOCIETY Executive Committee 195 6 PRESIDENT R. A. CARLTON West Palm Beach SECRETARY TREASURER DR. ERNEST L. SPENCER R. R. REED Bradenton Tampa PUBLICATION SECRETARY EDITING SECRETARY RALPH P. THOMPSON W. L. TAIT Winter Haven Winter Haven SECTIONAL VICE-PRESIDENTS CITRUS VEGETABLES C. A. ROOr Louis F. RAUTH Winter Garden Delray Beach KROME MEMORIAL ORNAMENTAL Boy 0. NELSON DR. T. J. SHEEHAN South Miami Gainesville PROCESSING DR. R. D GERWE Lakeland MEMBER.S-AT-LARGE HOWARDA. THULLBERY, Lake Wales D. F. S. JAMISON, Gainesville FRANK L. HOLLANDWinter Haven J. ARTHUR LEWJS, Miami E. S. REASONER, Bradenton

PAGE 4

FLORIDA STATE HORTICULTURAL SOCIETY, 1956II FLORIDA STATE HORTICULTURAL SOCIETY Executive Committee 195 7 P RESIDENT ROBERT E. NORRIS Tavares SECRETARY TREASURER DR. ERNEST L. SPENCER R. R. REED Bradenton Tampa PUBLICATION SECRETARY EDITING SECRETARY RALPH P. THiompsoN W. L. TAIT Winter Haven Winter Haven SECTIONAL VICE-PRESIDENTS CITRUS VEGETABLES CHARLES D. KIME, JR. NORMAN C. HAYSLIP Waverly Ft. Pierce KROME MEMORIAL ORNAMENTAL DR. PAUL L. HARDING S. A. ROSE Orlando Gainesville PROCESSING DR. JAMES M. BONNELL Plant City MEMBERS-AT-LARGE R. A. CABLTON, West Palm Beach FRED J. WESEMEYER, Ft. Myers FRANK L. HOLLAND, Winter Haven DR. GEORGE D. RUEHLE, Homestead DR. R. D. GERWVE, Lakeland

PAGE 5

IV FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Article I--NAME-This organization shall be Article X-SUCCESSION-In the absence known as the Florida State Horticultural Soof the President or his inability to serve temciety. porarily the Vice President of the Citrus SeeArtile 1-OJECIVE-he bjetiv ofton shall serve instead. If the position of this Society shall be the advancement and desPaesidensnated ths s xe tveCor.te velopment of horticulture in Florida. saldsgaehsscesr Article III-YEAR-The year shall begin Article XI-EXECUTIVE COMMITTEE January I and close December 31. The Executive Committee shall consist of not more than 15 persons including the immediate Article IV-CLASSIFICATION OF MEMPast President and all Officers above named, BERSHIP-There shall be three classifications the others to be elected at same time and of membership, all of which carry voting in same manner as prescribed in Article IX. privileges: The President shall be chairman of the ExecA-Annual utive Committee. The Executive Committee B-Sustaining shall have authority to act for the Society beC-Patrontween annual meetings. Nothing in this article shall be construed as Article XII-MEETINGS OF THE EXECoperating against or cancelling the privileges UTIVE COMMITTEE-The Executive Comof Life Members accepted as Life Members mittee shall meet upon call of the Chairman prior to the adoption of this constitution. at such time and place as may be approved by a majority of the Committee. A majority of Article V-ELIGIBILITY FOR MEMBERthe Committee shall constitute a quorum. The SHIP-Any individual, firm or partnership inCommittee may be canvassed by mail and terested in the development and advancement vote by ballot in like manner. of horticulture in Florida shall be eligible for membership. Article XIII -COMMITTEES -The PresiArticle VI-DUES-Dues shall be paid andent shall with the approval of the Executive nually according to classification at rate as Comrmittee appoint all standing or special prescribed in By-laws. committees as provided in the By-laws. Article VI-ANNUAL MEETING -The Article XIV-DUTIES OF OFFICERS Society shall hold an annual meeting each year The President shall be the official head of the in accordance with the By-laws unless preSociety to preside at all Executive Committee vented from doing so by causes beyond its meetings and at the general session of the control. annual meeting. He shall be directly responArtile IIISCTIOS -TheSocety sible to the Executive Committee and may be sarlle dviI -sEC tions Tesoet removed from office for cause by an affirmashal bedivied ntosectonsreprsening tive vote of a majority of the full Executive various horticultural interests as provided in Committee. the By-laws. Article IX-OFFICERS-The officers shall The Vice Presidents shall be members of the consist of a President, a Vice President from Executive Committee. The Vice President of each section, a Secretary, a Publication Secthe Citrus Section shall assume the duties of retary, an Editing Secretary, and a Treasurer, the President in the temporary absence of the which officers shall be elected by a majority President. The Vice Presidents of the various vote of the membership present at the annual sections shall preside over the particular secmeeting and shall assume their respective oftons of which they are representatives at the fices at the beginning of the new year. annual meeting.

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 V The Secretary shall record all records of all countersign all vouchers paying bills or acmeetings of the Executive Committee and shall counts against the Society. The Treasurer be responsible except as may otherwise be shall be placed under bond in an amount dedesignated in the By-laws for, recording and termined by the Executive Committee, prekeeping proceedings of the annual meeting. mium on which shall be paid by the Society. He shall likewise issue and mail out statements AtceX-MNMNSTi osi of dues to the membership, notices of meetings Aticle may MNMETi beCodensan nua etiand perform such other dutes as ordinarily tigon thy e reamenddatianyo annuajort-o hthe Executive Committee when approved by The Publication Secretary and Editing Seca majority vote of the membership present. retary shall perform such duties as .may .be Article XVI-EFFECTIVE DATE -This presmibtede. uhrzd yteEeui Constitution shall become effective immediateCommitee.ly upon approval by a majority vote of the The Treasurer shall be responsible for all membership at the annual meeting in October funds paid into the Society and shall issue and 1951. 1. The Society's year shall begin January 5. SECTIONS-The Society shall consist 1 and end December 31. of the following sections: 2. Dues-dues shall be paid annually for Citrus Section the current year and shall be payable to the Vegetable Section Treasurer of the Society. Dues shall be as Krome Memorial Institute follows: (Tropical and Sub-Tropical Fruits) Annual Membership $ 4.00 Ornamental and Floriculture Section Sustaining Membership $ 10.00 Processing Section Patron Membership $100.00 Other sections may be added on recommenda3. AnualMeeing-he ociey sall old tion of a majority of the Executive Commita. annual meetingthe falofieacy shar at tee when approved by a majority vote of the an nnalmetin i te al ofeah ea a membership present at an annual meeting. a place and time selected by a majority vote of the Executive Committee. The order of COMMITTEES business at the annual meeting shall be deNominating Committee-The President not tiermm iadateethy arbe.eExc less than thirty days before annual meeting shall appoint a nominating committee consist4. The meetings of the Society shall be ing of not less than two persons from each devoted only to horticultural topics, from scisection, which committee shall make nominaentific and practical standpoints, and the pretons at the annual meeting of the Officers and siding officer shall rule out of order all moother members of the Executive Committee for tions, resolutions, and discussions tending to the ensuing year; Provided that the members commit the Society to partisan politics or merrepresenting various sections shall seek advice cantile ventures. of each section in open meeting concerning

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VI FLORIDA STATE HORTICULTURAL SOCIETY, 1956 the nomination of Vice President for that secbonds unless it is ordered by the Executive tion. Such nominations by the committee howCommittee of the Society that such earnings ever shall not preclude nominations from the can be made available for operating expense. floor.APPROVAL OF BILLS Program Committee-The Vice Presidents of All bills before being paid shall be approved the various sections shall constitute a Program btePeietScea rTesrr n Committee of which the President shall be the by th PrsdnSceay rTesrrn Chairman and the Secretary and Treasurer vouchers drawn to pay such bills shall be shal. .ee fiiommes signed by the President or in his absence the shal be x oficiomembrs.Vice President of the Citrus Section and counAtiditing Committee -The President with tersigned by the Treasurer. the approval of the Executive Committee shall HNRR EBR appoint an auditing committee which commitHNRR EBR tee shall confer with the Treasurer in preparAny individual who has rendered especially ing an audit to be presented by the Treasurer meritorious service to the Society and to the at the annual meeting. The President shall advancement of horticulture in Florida may be appoint such other committees as may be designated by a two-thirds vote of the full deemed advisable and approved by the ExecExecutive Co'mmittee and approved by a mautive Committee. jority vote of the .-Society as an Honorary DEPOSTORYMember of the Society. Such honorary memDEPOSTORYbers shall not be required to pay dues. The Executive Committee shall have auAMENDMENTS thority to select a depository or establish a trusteeship for funds of the Society as it may These By-laws may be amended at any andeem in the best interest of the Society. All nual meeting by an affirmative majority vote Patron Membership dues and all donations, of the membership present when such amendunless otherwise specified by donor, shall be ments have been approved and recommended invested by the Treasurer in United 'States by a majority of the Executive Committee. Government bonds. The earnings from these .These By-laws shall take effect immediately bonds shall be left as accrued values or reupon adoption by the membership at the aninvested in the United States Government nual meeting in October, 1951.

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FLORIDA STATE HORTICULTURAL SOCIETY, 11956. VII of the FLORIDA STATE= 1956 ..I .-|.* VOLUME LXIX PRINTED 1957 CONTENTS O f i erfo r 15f-----e-----s----------r---------------_ _-_ _--------I I--I Constitution and By-Laws IV President's Annual Address, R. A. Carlton, W est Palm Beach -------------------------1 Plant Research in the Atomic Age, George L. McNew, Boyce Thompson Institute for Plant R esearch, Inc., Yonkers, N .Y .__ __---_ _ __-----------------__ -------------------_4 The Mediterranean Fruit Fly Eradication Program in Florida, Ed L. Ayers, Plant Commissioner, State Plant Board of Florida, Gainesville, and G. G. Rohwer, Area Supervisor, U. S. Department of Agriculture, Lake Alfred ---------------12 A w ard of H onorary M em berships _ _ _._------------------_ ___ ____----------------------15 CITRUS SECTION Injury and Loss of Citrus Trees Due to Tristeza Disease in an Orange County Grove, Mortimer Cohen, State Plant Board of Florida, Gainesville _---------__--------19 Effect of Phosphate Fertilization on Root Growth, Soil pH, and Chemical Constituents at Different Depths in an Acid Sandy Florida Citrus Soil, Paul F. Smith, U .S. D .A. H orticultural Station, Orlando _ ___---------------_--------_---___--25 Starting -and Maintaining Burrowing Nematode-Infected Citrus Under Greenhouse Conditions, William A. Feder and Julius Feldmesser, U. S. D. A. Hort icultural S tation O rlan d o -------_----_-------------_-----_----_-------__--2 9

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e-4 o a e Ca o in o cq a) I ce cc M C, co CID 't m mo 1 x0 ) M C a S a*t e~oto o -0 pp i S -c-a 0 --z i u 1 0 AN *0 0 cnal Q -C S S8 cdd a > .L, cz Q)o Q) P-4C ,.: M a S* a S -st<* Qao o .* 5 -.5 e e -.-0 * -a S S.* a 3 0 0 -. -S -a S S,. ,. .0o .5e. E o 8 e t 0 2 e .c *ia ) Sz m Z U C, ;14

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 IX PROCESSING SECTION Rapid Determination of Peel Oil in Orange juice for Infants, R. W. Kilburn and L. W. Petros, Florida Citrus Canners Cooperative, Lake WNales_--_.-_-__________--------107 Effects of Finisher Pressure on Characteristics of Valencia Orange Concentrate, 0. W. Bissett and M. K. Veldhuis, U. S. Citrus Products Station, Winter Haven__-___ 109 A Study of the Degrees Brix and Brix-Acid Ratios of Grapefruit Utilized by Florida Citrus Processors for, the Seasons 1952-53 Through 1955-56, E. C. Stenstrom and G. F. Westbrook, Citrus and Vegetable Inspection Division, State Departm ent of A griculture, W inter H aven __ ._ __ __ _ _-------------------------------------113 Diacetyl Production in Orange juice by Organisms Grown in a Continuous Culture System, Lloyd D. Witter, Metal Division, Research and Development Department, Continental.Can Co., Inc., Chicago, II-.__-______ 120 Standardization of Florida Citrus Products, Arthur R. Pobjecky, Southern Fruit DisCitrus Vitamin P, Boris Sokoloff, Isidor Chamelin, Morton Biskind, William C. Martin, Clarence Saelhof, Shiro Kato, Hugo Espinal, Taekyung Kim, Maxwell Simpson, Norman Andree and George Benninger, Southern Bio-Research Laboratory, Florida Southern College,' Lakeland ______--------------__------___----128 Vacuum Cooling of Florida Vegetables, R. K. Showalter and B. D. Thompson,, Florida Agricultural Experiment Station, Gainesville _____________ 132 The Quality Control of Chilled Orange juice from the Tree to the Consumer, Leo J. Lister, Halco Products, Inc., Fairvilla, and Arthur C. Fay, H. P. Hood, and S o n s, B o ston M a ss.-_ -__ -----_ _ __------_ _----_ __ _------_ ---_ ___---1 3 6 Hydrocooling Cantaloupes, K. E. Ford, Georgia Experiment Station, Experiment, G e o r g ia ---_ ---_ _----_ ----_ ----_ ---_ _---_---_----_ __---_ _----_ __---_ _------1 3 The Sloughing Disease of Grapefruit, W. Grierson and Roger Patrick, Florida Citrus Experim ent Station, Lake A lfred _--------------------_ __ __-------------------140 Effect of Variety and Fresh Storage Upon the Quality of Frozen Sweet Potatoes, 00 Maurice W. Hoover and Victor F. Nettles, Florida Agricultural Experiment Storage Studies on 42* Brix Concentrated Orange juices Processed from juices Heated at Varying Folds. 11. Chemical Changes with Particular Reference 'to Pectin; A. H. Rouse, C. D. Atkins and E. L. Moore, Florida Citrus Experiment StaPurification of Naringin, R. Hendrickson and J. W. Kesterson, Florida Citrus Experiment Station, Lake Alfred _____ ___ _ ___ _ 149 Sectionizing Marsh Seedless Grapefruit, Gray Singleton, Shirriff,Horsey Corporation, St .l n C i 4 __ _C-_ _ _ __ _ __ _ An Effective Highl Pressure Cleaning System for Citrus Concentrating Plants, D. I. M 0 0 Mud c an C. -4 Brk w Mi-t Mai Cop rain Ora d S-------------15

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X FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Some Studies on the Use of Sodium Nitrite as a Corrosion Inhibitor in the Canning Industry, J. R. Marshall, Tampa Laboratory of Research and Technical Department, American Can Co., Tampa___-------------------------------__------------159 Reducing Losses in Harvesting and Handling Tangerines, W. Grierson, Florida Citrus Experim ent Station, Lake Alfred ____---------_ --_ _------------------_------------_ 165 Quality of Canned Grapefruit Sections from Plots Fertilized with Varying Amounts of Potash, F. W. Wenzel, R. L. Huggart, E. L. Moore, J. W. Sites, E. J. Deszyck, R. W. Barron, R. W. Olsen, A. H. Rouse and C. D. Atkins, Florida Citrus Experiment Station, Lake Alfred _-_-_--_-_--------_-___-----------170 Storage Studies on 42* Brix Concentrated Orange juices Processed from juices Heated at Varying Folds, I. Physical Changes and Retention of Cloud, E. L. Moore, A. H. Rouse and C. D. Atkins, Florida Citrus Experiment Station, Lake Alfred 176 Effect of Thermal Treatment and Concentration on Pectinesterase, Cloud and Pectin in Citrus juices Using a Plate Type Heat Exchanger, C. D. Atkins, A. H. Rouse and E. L. Moore, Florida Citrus Experiment Station, Lake Alfred------_ __-___-----181 Distribution and Handling of Frozen Fruits, Vegetables and juices, George J. Lorant, Birds Eye Laboratories, Albion, New York___-----_----------------_ _-_---______-----185 Dried-Citrus-Pulp Insect Problem and Its Possible Solution with Insecticide-Coated Paper Bags, Hamilton Laudani, Dean F. Davis, George R. Swank and A. H. Yeomans, Stored-Products Insects Laboratory, Savannah, Georgia -.._----------_-191 VEGETABLE SECTION Progress Report on Cantaloupe Varieties, B. F. Whitner, Jr. Central Florida Experim ent Station, Sanford ____-__---------.. -----_ ----------------_---------------------195 Phytotoxicity of Fungicides to Cantaloupes, Robert A. Conover, Sub-Tropical Experim ent Station, H ~om estead _______-------------------------------------------------198 Irrigation of Sebago Potatoes at Hastings, Florida, Donald L. Myhre, Florida Agricultural Experiment Station, Potato Investigations Laboratory, Hastings_______------200 Use of Certain Herbicides in Fields of Growing Tomatoes -Progress Report, John C. Noonan, Sub-Tropical Experiment Station, Homestead -__-________-_-_----------204 Crop Production in Soil Fumigated with Crag Mylone as Affected by Rates, Application Methods and Planting Dates, D. S. Burgis and A. J. Overman, Gulf Coast E xperim ent Station, Bradenton _-------------------_ -_ _---_------______---------_ -207 Breeding Objectives and the Establishment of New Breeding Lines of Southernpeas, A. P. Lorz, Florida Agricultural Experiment Station, Gainesville_-_---------_---210 Factors Influencing Consumer Preference of Southern Peas (Cowpeas), Maurice W. Hoover, Florida Agricultural Experiment Station, Gainesville_--_____------------_ -213 Outlook for the Production of Southern Field Peas for Freezing, James Montelaro, M inute M aid Corporation, Plym outh----------------------__ __--_____-_-__---_-_---_-_-_--_ 216

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 XI Insect Problems in the Production of Southern Peas (Cowpeas), John W. Wilson, Central Florida Experiment Station, Sanford, and W. G. Genung, Everglades Experiment Station, Belle Glade _________-___ _____ -217 Influence of Nitrogen., Phosphorus, Potash and Lime on the Growth and Yield of Strawberries, R. A. Dennison and C. B. Hall, Florida Agricultural Experiment S ta tio n G a in esv ille _----_ -_ _------_ __ __-_ __ _ _ __---------------------------2 2 4 Lime-hIduced Manganese Deficiency of Strawberries, C. B. Hall and R. A. Dennison, Florida Agricultural Experiment Station, Gainesville _____--------____------__---_228 Cucumber Fungicides for the West Coast of Florida, Grover Sowell, Jr., Gulf Coast 0p E xperim ent Station, Bradenton ----_ __.__------------_ _----_ _----_--_ __ _ _ __--------230 Notes on Current Developments of Gray Mold, Botrytis Cinerea Fr. of Tomato and Its Control, R. S. Cox, Everglades Experiment Station, Belle Glade, and N. C. Hayslip, Indian River Field Laboratory, Ft. Pierce_ ________---------------------235 Evaluation of Control Methods for Blackheart of Celery and Blossom-End Rot of Tomatoes, C. M. Geraldson, Gulf Coast Experiment Station, Bradenton__----___--236 Control of Diseases in the Celery Seedbed, R. S. Cox, Everglades Experiment StaThe Assay of Streptomycin as it Relates to the Control of Bacterial Spot, Grover Sowell, Jr., Gulf Coast Experiment Station, Bradenton _____-------------------244 Control of Pole Bean Rust with Maneb-Sulfur Dust, Robert A. Conover, Sub-Tropical Experim ent Station, H om estead _ _____-------------------------____----------247 Fungicidal, Herbicidal and Nematocidal Effects of Fumigants Applied to Vegetable Seedbeds on Sandy Soil, A. J. Overman and D. S. Burgis, Gulf Coast Experim ent Station, B radenton __------__ _ ------_ _---_ _ ___---------_ _---_----_---_ --_250 Variety Tests of Commercial Types and New Breeding Lines of Southernpea, L. H. Halsey, Florida Agricultural Experiment Station, Gainesville__ _______------------255 Results of Different Seeding and Fertilizer Rates for Potatoes at Hastings, E. N. McCubbin, Florida Agricultural Experiment Station, Potato Investigations L ab oratory H astin g s --_ _ _-------_ __------_ _----_--___------_ _----_2 5 9 Production of Spinach for Processing on Muck Soils of Central Florida, M. M. Hooper, V vegetable G row er, A popka ___---------------------_ _ _ ___------------------261 KROME MEMORIAL SECTION The Concept, Duties, and Operations of the Florida Avocado and Lime Commission, C. F. Ivins, Florida Avocado and Lime Commission, Homestead_________---------262 Notes on Tropical Fruits in Central America, Wilson Popenoe, Escuela Agricola Panamericana, Tegucigalpa, Honduras -----------------------------------267 Marketing of Limes and Avocados in Florida, Harold E. Kendall, South Florida G row ers Association, Inc., G oulds _ ___-----------------------------------270

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XII FLORIDA STATE HORTICULTURAL SOCIETY, 1956 The Sub-Tropical Fruit Program of Dade County, John D. Campbell, County Agricultural A gent, H om estead __---------____------------__-----_---------------272 Some Observations on Lime and Avocado Grove Cultural and Maintenance Practices in Dade COUnty, Norman E. Sutton, Grove Management, Inc., Goulds_---_----_274 Future of Florida Minor Tropical Fruit Industry in Doubt, Nixon Smiley, Miami' Herald Farm and Garden Editor and Director, Fairchild Tropical Garden, M iam i --_-___----------------------_ __-------------------------------------2 75 Krome Memorial Avocado Variety Committee Report, F. B. Lincoln, Chairman, H om estead -__-------------------------_ --__ -__------------------_-------------------276 Pollination and Floral Studies of the Minneola Tangelo, Margaret J. Mustard, S. John Lynch and Roy 0. Nelson, Division of Research and Industry, University of M iam i, C oral G ab les ___ -----------. _ _--_ _--_ _--_-_-_ __--------_-----_2 7 7 Changes In Physical Characters and Chemical Constituents of Haden Mangos During Ripeninig at 80' F., Mortimer J. Soule, Jr., and Paul L. Harding, U. S. D. A. H orticultural Station, O rlando _--____--_ _-_ _-----------_-----------------------___--282 Further Rooting Trials of Barbados Cherry, Roy 0. Nelson and Seymour Goldweber, Division of Research and Industry, University of Miami,* Coral Gables ---------285 Research on Sub-Tropical Fruits as a Result of Mediterranean Fruit Fly Eradication Program, Geo. D. Ruehle, Sub-Tropical Experiment Station, Homestead__.----___287 Some Effects of Nitrogen, Phosphorus and Potassium Fertilization on the Yield and Tree Growth of Avocados, S. John Lynch and Seymour Goldweber, Division of Research and Industry, University of Miami, Coral Gables---------__ _-_------289 A Comparison of Three Clones of Barbados Cherry and the Importance of improved Selections for Commercial Plantings, R. Bruce Ledin, Sub-Tropical Experim ent Station H om estead _-.__ _____--------------_------_---------------------_. _ _-----293 Rare Fruit Council Activities, 1956, William F. Whitman, Salvatore Mauro, Seymour W .Younghans, M iam i Beach------------------_-_--_-_ _--____---------.--297 Some Notes on a Weevil Attacking Mahogany Trees, F. Gray Butcher and Seymour Goldweber, Division of Research and Industry, 'University of Miami, Coral 00 Gabes__a --_ _----_ ---------------------305 H ome0 ea 0_ _ _ .*__ ___ 30 Some Aspects of the Lychee as a Commercial Crop, Gordon Palmer, Florida Lychee Growers Association, Osprey -_____ _ ___ _ ______________309 The Effects of Longtime Avocado Culture on the Composition of Sandy Soil in Dade County, John L. Malcolm, Sub-Tropical Experiment Station, Homestead_______---313 Rooting of Peach Cuttings Under Mist as Affected by Media and Potassium Nutrition, Mario Jalil, Escuela Agricola Panamericana, Honduras, and Ralph H. Sharpe, Agricultural Experiment Station, Gainesville__----------------_-------------------324

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 XIII Some Effects of Nitrogen, Phosphorus and Potassium Fertilization oil the Growth, Yield, and Fruit Quality of Persian Limes, Seymour Goldweber, Manley Boss and S. John Lynch, Division of Research and industry, University of Miami, C o r lra b l s G---b---s_--_ _----__---_ _---_----_-__ ________ __--------__ _ ---23 2 ORNAMENTAL SECTION Mist Propagation of Roses, S. E. McFadden, Jr., Department of Ornamental Horticulture, University of Florida, Gainesville ______----------------__--------__ ---333 Gladiolus Botrytis Control, R ..Magie, Gulf Coast Experiment Station, BradenSome Notes on Philodendron Hybrids, Erdman West and H. N. Miller, Florida Agricultural Experim ent Station, Gainesville_ __ _---------_ ___ __ __-------------------343 Fertilization of Gladiolus, S. S. Woltz, Gulf Coast Experiment Station, Bradenton ---------347 Studies on the Nutritional Requirements of Chrysanthemums, S. S. Woltz, Gulf Coast Experim ent Station, Bradenton _____-----------------_-----------------352 Virus Ring Spot of Peperomia Obtusifolia and Peperomia Obtusifolia var. Variegata, M. K. Corbett, Florida Agricultural Experiment Station, Gainesville -------------357 How to Landscape Our Outdoor Space for Living, Thomas B. Mack, Florida Southern College, Lakeland _______0 -_ __ ___-_ -____ _-_ 360 Regional Performance of Hemerocallis in Florida, Eunice T. Knight, Apopka ------------363 The Palm Society, Dent Smith, The Palm Society, Daytona Beach--_ --___ 366 Comparison of Happiness Rose Production on Four Rootstocks, S. E. McFadden, Jr., Department of Ornamental Horticulture, University of Florida, Gainesville __----__368 Florida Nursery Law, Paul E. Frierson, State Plant Board of Florida, Gainesville ._---__-____370 Research in the Ornamental Field in Control of Mediterranean Fruit Fly, E. W. MeElwee, Florida Agricultural Experiment Station, Gainesville -____-------_---__ -----379 The Florida Flower and Nursery Industry, Cecil N. Smith, Florida Agricultural Exp erim en t Station G ain esv ille .. ______---_____ ___--------_ __ ---_______ _____ _ _ __--------3 80 The Downward Movement of Phosphorus in Potting Soils as Measured by P", Daniel 0. Spinks and William L. Pritchett, University of Florida, Gainesville___-------385 Twelve Bauhinias For Florida, R. Bruce Ledin, Sub-Tropical Experiment Station, Pesticides and Plant Injury, S. H. Kerr, Florida Agricultural Experiment Station, G a in e sv ille ---_ ------------_ _. -_---------------------------_ __ _ _ _ _---3 9 8 The Effect of Parathion as a Corm and Soil Treatment for Gladiolus, E. G. Kelsheimer, Gulf Coast Experiment Station, Bradenton ---_ -----___ ------__ _---I______ -----403 The Genus Solandra in Florida, R. D, Dickey, Florida Agricultural Experiment Statio n G ain esv ille --_ ------_----__ _--_----------_ _----__ ---_ _____ __----4 6 5

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XIV FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Studi-s on Chemical Weed Control in Plumosus Fern, C. C. Helms, Jr., J. M. Call and E. 0. Burt, Watermelon and Grape Investigations Laboratory, Leesburg -_-----407 Fungicides and Plant Injury, Albert P. Martinez, State Plant Board of Florida, Gainesville _--------------I-------------------------------------------------------413 The Hunting Billbug a Serious Pest of Zoysia, E. G. Kelsheimer, Gulf Coast Experiment Station, Bradenton -_-------------------------------------------------------------415 ANNUAL REPORTS Necrology --------------------------------------------------------------------------------------419 Report of Executive Committee -----------------------------------------------------------421 G eneral Business M eeting ------------------------------------------------------------421 Resolutions--------------------------------421 Report of Treasurer-----------------422 L ist of M em bers -----------------------------__-------------------------_--423 Index------_ -.---------------------------------------------------------------------------433

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AA R A. CARLTON WGST PALM BE-ACH President of the Sc etv -956

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THE PRESIDENT'S ADDRESS R. A. CARLTON it is to talk too much. Anyway, during those West Palm Beach years working with Colonel Floyd I gained a deep appreciation of the problems he had One of the duties imposed upon the Presifaced through the years and sincerely redent of this Society is an annual address on gretted any criticism I ever bad of his efforts. the activities of your Society and the general His untimely death in 1945 prevented the state of Horticulture in Florida. I am glad to Society from ever awarding him any honorarireport that your Society is now the third largum, if it had been possible for the Society to est Horticultural Society in the United States accord him anything commensurate with the and the seventh oldest society. It is exceeded services he had rendered. in membership by the Wisconsin and Michigan It affords me great pleasure to report that Horticultural Societies in that order. The oldest during the past year your Society operated society is in Ohio and was organized in 1847.. under a new deal compared to the years outThe Wisconsin Society which has the largest lined above. This year it was a pleasant ex. membership has received State aid since 1879 perience to see how all your General Officers. which may account in some measure for the worked together as a team to develop the prosize of its membership. gram and arrangements for this meeting. The In the preparation of this address it was Chairman of each Section readily accepted natural to reflect upon the changes that have the responsibility of developing the program occurred in the activities of the Society in the for his Section, and the Executive Committeemore than 30 years in which I have been a men from the Society at large were most helpmember, and more or less active in the Soful to the General Officers in arranging the ciety's functions. When I became a member, many details of this meeting. I wish to express the horticultural crops of the State were strug-my sincere appreciation for the help and cogling along on an unbalanced program of nuoperation I have received from one and all. trition, and your Society was struggling in Some of my foregoing remarks have emphaabout the same manner. sized the fact your Society has been most forColonel Bayard F. Floyd had been Secretunate in the selection of a Secretary. This tarysine 117 ad mst f th Prsidntsgood fortune still prevails in Dr. Ernest L. tar. .ic 97adms ftePeiet Spencer. He has all the attributes of other good and Executive Committeemen of those days secretaries with an additional one of getting insisted on the Colonel running it as a one more work out of other people without making man show, and imposed upon him the comanybody mad. plete responsibility for the program, arrangements for the meetings, and everything else During the past two years your Society requiring much work and time. I recall that created a Fellowship in Virology at the Unisome of the young upstarts in the Society versity of Florida. This Fellowship was about 25 years ago, myself included, became awarded to Mr. Robert Bozarth, a graduate of somewhat critical of some of the Colonel's Everglades High School in 1948 and the Colbest efforts at program and meeting arrangelege of Agriculture, University of Florida, in ments. As usual, everybody thought something 1952. He is presently directing' his study on should be done but nobody wanted to do any the viruses of gladiolus. When these viruses work. This state of mild criticism prevailed have been isolated they will be identified by until about 1939 when the speaker and some symptoms, host reaction, cross protection, and others approached the Colonel about forming by the use of the Spinco Ultra Centrifuge ata Vegetable Section of the Society. The tempts will be made to purify and crystallize Colonel was quite agreeable and cooperative the viruses. These studies will aid in the debut flatly declined to accept any responsibility veloping of practical and economical control for a program for such a section. Being brash measures that can be applied by the growers. and bold, I accepted this responsibility and Realizing full well the complex field involved during the next five years I learned how easy in research on crop viruses, the recipient of

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PAGE 20

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MNEW: PLANT RESEARCH, 5 fly bad as much as a few micrograms of the principles of life which he can exploit in makchemical in her body. ing plants more serviceable to man. By the This example could be multiplied a bullsame token, the man who would control indred-fold by choice of other devices and techsects, diseases and weeds has an obligation to niques-the' physical chemist who pulls two study them carefully to determine their closely related viruses apart in an electrophorestrengths and weaknesses. sis apparatus by minute differences in their By so doing, the biologist can orient the efsurface charges 'or by differences in their mass forts of the chemist in developing new types or density in an ultracentrifuge, or the X-ray of chemicals to solve many problems in plant crystallographer who plots the arrangement culture. The examples we will consider here of' invisible and active atoms one to another today lie in this general area on the frontiers in a crystal lattice that one barely sees under of .science. They are chosen from work of the most powerful microscope. Thiis is a great various scientists at Boyce Thompson Institute, era in which to live. Every scientist worthy of not because they are the only work in the area the name should thrill to the opportunities beor even superior to that of others but because fore him to understand the universe. of my familiarity with them. For many decades the botanist and hortiFUNGICIDAL BULLETS culturist have been interested in the outside of plants. They did a necessary job of describMen have been at war with, the fungi since ing the organs and determining the relation time eternal. You people here in Florida need of one plant to another. We learned how to not be reminded that tremendous quantities of change these external appearances by breedchemicals must be applied to plants to prevent ing, altering their nutrition, or exposing them fungous diseases. You contribute a substantial to chemicals. However, no one knew exactly share. of the 125 million dollars spent each what bad been done or why plants reacted th'e year in the United States on control of plant way they do. Today a new viewpoint is comdiseases; ing into plant research. We are more interested In spite of this terrific investment we are in what a plant does than what it looks like. only partially successful in reducing the ravThe activities going on inside of millions ages by fungi. According to our best estimates of -tiny cells in each tissue arouses one's they still destroy 7% of our potential agriculturimagin'ation. There is a beehive of activity in al productivity, This amounts to about 2.8 one of these cells--with a volume of less than billion dollars a year. To get down to brass one-billionth of a cubic inch-that would put tacks it means that every man, woman and the best man-made factory to shame. For exchild in the United States pays $24.20 a year ample, if one provides the leaves of a plant in tribute to the fungi. Each family would be with labelled C"O., within five minutes there horrified if it entered $96 a year in its housemay be detected 57 new organic compounds bold budget as the cost of plant diseases but in the tissue. Within a couple of hours some such are the facts. of the very complex new molecules are being Obviously we need better methods of consecreted from the roots. One must admit that trolling diseases. Some people may make their the dynamics of cell operations are tremendcontribution by breeding resistant plants, imOtis. proving crop rotations etc., but we have elected The activities of these cells are of interest to see what call be done in improving fungito men because anyone who call control the cides. There are several good fungicides but cell can change the 'tissue and thereby regulate we need more and the only way we are going the entire plant to our selfish purposes. One to get them is invent them. We have decided can make cells grow faster, change their shape,' to learn all we can about the ones now availinactivate them completely, change their able so we can develop better ones. Here are heredity; render them more nutritious or make a few examples of recent developments, them immune to disease by use of the approSulfur operates in a unique fashion. The priate chemicals. Therefore the scientist who particle of sulfur deposited on a leaf or fruit will take the time and effort to understand volatilizes and reaches the spore in tile -vapor cell functions should be able to uncover basic phase. By use of radioactive sulfur (SI) Drs.

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6 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Miller and McCallan have shown that the sultributes. Dr. Owens has cast much light in fur atom is taken up by the spore and is almost this area by recent studies on the effect of immediately reduced to hydrogen sulfide. It is several dozen quinones and hydroquinones on released within a couple of minutes from the enzyme systems. Hie found that there was a spore and, contrary to previous conceptions, very close correlation between fungitoxicity the H2,S does not act as a fungicide in destroyand ability to inhibit sulfhydryland aminoing the spore. Please note that facts such as bearing enzymes. An exception was observed these could be determined only by using isoin comparing benzoquinone and naphthoquintope tracer techniques. one analogues. He was finally able to show Once these facts were out in the open our that benzoquinone appeared to be less active scientists began to wonder how sulfur could than naphthoquinone because it was detoxidestroy a spore without entering into cell refied more readily by entering into extraneous actions. Biochemical studies have shown that reactions. Dark-colored spores secrete subthe spore suffers irremedial damage when it stances that inactivate much of the benzogives up two hydrogens to reduce each sulfur. quinone before it can penetrate and destroy For each molecule of sulfur reduced, the spore the spore. releases a molecule of carbon dioxide. By the Most of us have wondered what roles are time the spore has reduced 15,000 to 25,000 played by the halogens on the organic moleparts of sulfur per million units of body weight cules so commonly used as insecticides, fungiit succumbs. cides and herbicides. Dr. Burchfield has careThe search in this area goes on to determine fully studied the effect of placement of two what organic acid in the spore is undergoing types of chlorine in the symmetrical triazines, decarboxylation. Insofar as we know, sulfur is a new class of fungicides developed by Dr. unique among the fungicides in its ability to Schuldt in cooperation with chemists of the destroy a spore solely by robbing it of maEthyl Corporation. These compounds have the terials. All other fungicides enter the spore following structure: and react with vital cell constituents. Sulfur is a hit and run bullet that bleeds the spore to 0 death. H The organic fungicides are far more fas1 -Ncinating. They can be designed in a wide variety of forms with only minor differences in configuration. By trial and error, chemists have learned that there is a rigid requirement of chemical structure to attain effective fun6(chloroanilino)-2,4-dichloro--triazine gitoxicity. Why does a minor change in chemical structure affect the fungicidal activity so The two chlorines on the triazine nucleus drastically? It is becoming increasingly clear were found to be essential for reaction with that the changes either influence the ability sulfhydryl-bearing enzymes and related comto penetrate the fungus body, to enter into pounds. if they are replaced with other groups certain vital cell reactions and disrupt them, the molecule becomes impotent because it canto change resistance to the cells detoxification not react in the cell environment. The chlorine mechanisms or to modify the stability and peron the anilino group serves a multiple function. sistence of the molecule. When placed ortho to the nitrogen it activates Most of you know that there are two quinthe chlorine on the triazine nucleus. One one fungicides on the market under the trademight describe it as a booster charge because names of Spergon (chloranil) and Phygon of its effect on electron density at the vital (dichlone). Many of you may have beard me part of the molecule. Therefore, if the chlorine say in years past that diclone was aat this point activity may be intimes as fungicidal as chloranil. This appears creased several-fold, depending upon the to be true when one measures their effect on species of fungus affected. spore germination but it is contrary to what This booster effect declines as the chlorine one would expect from their chemical atis pushed farther away into the ineta or para

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McNEW: PLANT RESEARCH 7 positions on the phenyl ring. In spite of this we can design one that will penetrate the diminishing effect the parachloroanilino comfungous body, enter into a vital reaction with pound is much more active than its meta anaan enzyme or metabolite, but not be detoxilogue. This has been shown to be due to its fied by extraneous reactions. This is a big greater ability to penetrate the spore wall of order but it is not an impossible one,. certain fungi. The concepts on spore penetration have VIRUS MULTIPLICATIONS AND PATHOGENESIS changed drastically in the last three years. We One of the great areas of knowledge to be are learning that certain groups such as the developed is the nature of virus infections in parachlorophenyl, or the long alkyl chain of plants. In spite of the monumental strides for14 to 17 carbon atoms alter the lipoid soluward in the past thirty years, the riddle of how bility of a molecule enough to regulate comviruses multiply and cause disease remains unpletely the ability to penetrate the waxy and solved. The presence of virus protein does not oily layers in the fungus wall. Merely by necessarily cause disease symptoms. Investichanging the length of the carbon chain in gators have isolated and identified heavy the 2-position of the imidazoline nucleus it is weight proteins from apparently normal possible to render the molecule safer for use plants so removal of proteins from normal on plants and more destructive for spores at pathways of metabolism does not explain the the same time. Glyodin was developed by Drs. disease conditions. As a matter of fact nuWellman and McCallan merely by lengthening cleic acid may be combined with proteins the carbon chain from eleven atoms where it without inciting symptoms as witnessed by the rendered the molecule violently injurious to research on recovery of tobacco from ring the plant and relatively weak for the fungus to spot done by Dr. Price, a former member 17 carbon atoms where the reverse situation of our staff, 'now with the Citrus Experiment heldStation. In studies employing radioactive molecules, On the assumption that there is some physioDr. Miller has been able to show that fungilogical disturbance other than the abnormal cides not only penetrate the spore wall at unuse of protein, Dr. Porter has been investibelievably fast rates but may also change the gating the biochemical changes in plants durpermeability of spore membranes. If spores ing the incipient stages of infection before are placed in a suspension containing 2 p.p.mdisease symptoms appear. The first reaction of of glyodin they will accumulate up to 6000 a plant to the tobacco mosaic virus appears to p.p.m. of their own body weight within 2 to 5 be an abnormal synthesis of amino acids. By minutes. Interestingly enough, such a spore use of paper chromatography he has been destroyed by this organic chemical will take able to demonstrate a net increase in alanine, up just as much mercury or silver fungicide threonine, aspartic acid, lysine, gamma aminoas a normal living one. Likewise, lie found butyric acid, asparagine and serine within 72 that mercury and silver did not interfere with to 96 hours. After attaining this peak conceneach other although it bad been assumed that tration they began to decrease so they were heavy metals might be expected to occupy present in subnormal concentrations after 192 similar reaction sites. The spores actually took hours. Glutamine followed the same pattern up more mercury after they had been exposed except that it attained a much higher peak to silver than comparable untreated spores. and within a shorter period after inoculation This was traced to a change in the semiof the virus. Apparently there is some mechanpermeable membranes of the spore. Silver afism of nitrogen assimilation triggered by the fects the spore so its cell constituents are lost virus before it begins to multiply much less more readily and external chemicals penetrate create symptoms. As soon as the virus begins to more actively. multiply, the concentration of amino acids By patient studies such as these we are declines. The mechanism by which these cataloguing the effects of changes in chemical changes are implemented is imperfectly unstructure on the activities of various, types of derstood and obviously justifies much more molecules. The ultimate goal of course is to investigation if we are to understand the define all the characteristics of a fungicide so physiological basis of pathogenesis by viruses.

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8 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Within the past five years the scientific are obtaining considerable information on world has come to understand much more what happens when an insect becomes resistabout the virus particle itself. Dr. Magdoff ant. has been studying the physical properties of Dr. Moorefield has continued studies which southern bean mosaic virus by X-ray diffrache began while be was a student at the Unition. Interest is being directed primarily tovarsity of Illinois. The flies resistant to DDT ward the spatial relationship of nucleic acid to have a new type of enzyme known as dehydrothe protein and to the packing of subunits of chrns.Tisatramksitpsbefr Z1 cboi e Ti maera mae it posil fo the virus in crystals. We now know that the insect to detoxify the chemical by removviruses may be degraded by removing nucleic igHlfo h oeue h nyede acids and can be restored to activity by ret I not reur a meali cosiun toatvt combination of these two components,' so it and appears to be a specific sulfhydryl type Sof material. Within the past year, Dr. Mooreportant' field has shown that the ability to produce There is no more exciting area of research this enzyme is latent in the larvae of an ordinthan these on virus proteins. The very basis of ary population of DDT-susceptible insects but life is involved in, the studies on ribonucleic probably does not occur uniformly in all inacid and protein synthesis. In due season, as dividuals. When larvae are exposed to DDT techniques are perfected on viruses, one may only those with exceptional ability to generate expect such studies to be extended to the this enzyme mature. Because of this, the remechanisms of heredity. Far in the future the sistant adults have demonstrable quantities of redesigning of chromosomes by chemical dehydrochlorinase while comparable susceptimethods far more advanced than the primitive ble insects do not. use of colchicine today to induce polyploidy. It is perfectly obvious that we need to know more about the metabolic processes of insects THE MECHANISM oF ACQUIRED RESISTANCE which permit them to detoxify chemicals or OF INSECTS TO INSECTICIDES develop alternate metabolic pathways to escape the lethal effects of insecticides. Since One of the serious problems facing the sulfhydryl compounds allegedly play such an agriculturist is the tendency of insects to acimportant role, Dr. Cotty and Dr. Hilchey quire resistance to insecticides. For example, have been studying sulfur metabolism, Congreenhouse operators have found that red trary to ordinary beliefs that animals must obspider mites develop resistant populations tain their sulfur from organic materials in within a few months to two years after a newv plants, these investigators have demonstrated chemical is introduced. In 'the past decade that insects can convert sulfates 'into sulfur they have run through five new chemicals amino acids. By use of paper chromatography that were found only by a tremendous invest. to separate the various acids and measure their meant in funds and research time. The mites concentrations and by feeding sulfates and are so tiny that we have not had the courage other materials labelled with S' they have bbeen able to trace the process in aseptically interesting cases of resistance in houseflies, reared cockroaches and houseflies. The sulmosquitoes, flea beetles, lice, etc., that can be fates are converted into methionine and the used. Currently our people are working on methionine is changed into cystine through an the resistance of houseflies to chlorinated hyintermediate cystathionine. The cystathionine drocarbons since they present an excellent seems to serve as a unidirectional regulant subject for study on the comparative biochemsince cystine cannot be converted back into istry of resistant and susceptible populations. methionine. The cystine may be converted into By use of pure culture techniques to avoid taurine and excreted as such. microbiological contaminants, paper chromaPreliminary evidence indicates that some retography to separate and measure cellular sistant houseflies have exceptional ability to components such as amino acids, and use of synthesize glutathione but further research Geiger counters to follow the pathway of along these lines will be required to establish metabolism of unstable atoms such as S" we the point.

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MeNEW: PLANT RESEARCH 9 THE PROCESSES OF ABSCISSION FoRMIATION to cotton, the number of free amino acids in One of the very vital processes in plants is the petiole increases from three to about the bilty o sed eavs ad bossms.The twelve. A similar phenomenon has been ob4e deped lpave a oaon The served i the leaves of deciduous trees in the prosesso deperd on elsa the boraseo of the fall and Dr. Weistein found that rose petals ascision blayessos bell at these ofedge undergo an increase in soluble nitrogen after leveor lesows Wuteynd this knywldge cutting. This promising lead suggested that the disease agents produce a biochemical change ulion stag maiso acdpomation ans th t that causes diseased leaves to fall so one may ulthese amino acid prulddfciltteoratnd ofa assume that chemical messengers are involved c lsi thesamo abcsiwon aclaefrmon in abscission cell formation, Since we know so nw esmthabisonay. little about the chemical stimuli we have very Unfortunately the story on abscission will imperfect control over defoliation of cotton to not prove so simple. A careful study of the facilitate picking or removal of leaves from total nitrogen balance indicates that the amino nursery stock to improve its storage qualities. acids are the result of senescence in which Neither do we know bow to prevent shatterproteolysis occurs rather than the incitants of ing of foliage from forage legumes, or loss a.new process. However, we do have one fasof leaves from diseased plants and blossoms cinating lead in Dr. Plaisted's work. He has from cut flowers such as the rose. found an active principle in shattered blosSometime ago we set out to design a new soms that causes abscission of foliage in nortype of heterocyclic sulfur fungicide. We mal healthy plants. Studies are underway to failed completely insofar as making a fungicide isolate this factor and learn more about its bewas concerned but we did notice that some of savior. The significance of this research to the compounds bad ability to cause the leaves date is that we are building tip a set of exto drop from beans. Over a period of two perimental procedures for regulating and years we have synthesized a variety of related studying this vital, but very seriously neglected compounds andf succeeded in developing a field. new class of defoliants that can be applied THE REGULATION OF PLANT GROWTH either through the roots or directly to the foliage. If studies such as those described on the The remarkable thing about these new fungicides, viruses, insecticides and foliage materials is that they cause a simple physioabscission seem far-fetched, unrealistic and not logical defoliation without burning or distortlikely to ever produce significant practical reing the leaves. As a matter of fact they duplisults, I would like for you to bear with me a cate the natural processes of leaf shedding moment while we outline the consequences of almost precisely. A couple of days after the material is added to soil the innermost leaves ya r as estieh prsigneda D. Abimme2 begin to change color. Some members of the yasaoteIsiueasge r imr series cause the leaves to take on a red tinge, man and Dr. Hitchcock to a study of how then become yellow and finally drop from plants grow. They were free to study any the plant. Defoliation proceeds steadily outaspect of plant growth and differentiation that ward and upward until the entire plant is deappealed to them. Their attention was gradfoliated. If the plant is held for several weeks ually focused oil methods of altering the norit completes its dormant period. New buds mal balance of growth hormones or chemical break forth and the plants resume normal stimuli in plants by adding chemicals to the growth. These materials offer such a wonderplant ful opportunity to study the biochemistry of defoliation that we were prompted to organFrom this research there came knowledge ize a study of defoliation by natural processes, on the use of ethylene gas to anaesthetize cells freezing and chemicals. or regulate maturation 'processes in cells, and Dr, Plaisted has found that within a matter root-inducing substances that have been useof a couple of days after a defoliant is applied ful in plant propagation. Interest in indole and

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10 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 naphthalene compounds led to a study of The 2,4-D molecule has three significant other types of acids, especially chlo-inated defeatures. These are the two chlorine on the rivatives of benzoic acid and eventually to benzene ring: aryloxy acids such as 2,4-D. By 1941 they had described the selective growth regulant 2 ability of 2,4-D and opened the doors to a new era in weed control and the development of specific growth regulants. There is no need to dwell upon how the American public grasped the opportunity to 0 remove broadleafed weeds from lawns, roadC sides, wheatfields, pastures and cornfields. the oxygen linkage between the ring and acid Within ten years, consumption of 2,4-D exgroups, and the free carboxyl group, Exploraceeded 25 million pounds a year. Even more tory research has indicated that the oxygen important was the contagious enthusiasm of linkt may be replaced with nitrogen to give a dozens of chemical companies to hunt for weaker class of regulant but so far nothing other classes of regulants and selective herbiof practical significance has developed in this cides and of scores of experiment stations to area. employ weed specialists to study the chemical Study soon showed that the halogens played control of weeds. An entire new profession very dominant roles. The chlorine para to the sprang up within a decade. A national society oxygen was found to be indispensable but the and four regional weed control conferences ortho chlorine could be eliminated or replaced were organized so thousands of scientists meetbyamtlgrutoivacmpndny anull. tohiscs proy ss bndpafo thetpslightly less effective. However, when a third gure. Tnd. dyobablyia brnhe mos pgiutrochlorine was added to one of the free positions gsi e n d dya ic branc df ariduts.a a gamut of effects was obtained. A chlorine sciece n th pat to deade. i the 3-position to give the 2,3,4,-triehloro Peculiarly enough, 2,4-D came into existcompound has very little effect on regulant ence because someone was interested in ability. When added in the 6-position so both growth processes. These men were not as-, positions ortho to the oxygen are blocked, the signed to work on weed control. There is good compound is essentially inactive. When the reason to believe that they might never have chlorine is added in the 5-position to give discovered such a material had they been told 2,4,5-trichlorophenoxyacetic acid there is a that they were to study weed control because slight diminution of regulant activity for some they would have had no background, either plants and an increase in the caustic or lethal from experience or literature knowledge to effect on others. This new compound will suggest that selective growth regulants should destroy raspberries and woody plants that are have been used. If ever there was an example very resistant to 2,4-D. This was the first major to show how science makes its big steps forstep forward and has been tremendously imward, this is one. portant in brush control on ranges and farm Sciece nedsdept andbredth f uner-pastures. Sciece eed deth nd beadh o uner~ The next step came from a study of the carstanding. The men of science must dig beboxyl grouping. McNew and Hoffman found neath the surface to find more than meets their in 1946 that the acid group could be converted eyes. If research projects are defined so speci,to a salt, amid or ester without destroyfically that scientists must follow narrow, ing activity, In other words the O=C--OH rigidly prescribed objectives, their effectivegroup could be changed without des Itroying ness will be minminzed because it is these big regulant ability provided a free carbonyl steps forward that clear the way for the work(C=0) grouping remained. This fact was exmen of science to build a new house of knowlploited fully in the next few years by three edge. Let us look at four rooms in the 2,4-D lines of development. The volatility of the mahouse to see what has happened since 1941. terial was reduced so it would be less hazard-

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McNEW: PLANT RESEARCH 11 ous for use around valuable susceptible plants not hurt them even as it destroys wild mustard by converting it to metallic or other salts. The and other weeds growing in pea or alfalfa. acid was rendered readily dispersible in water fields. by converting it to the very soluble triethanoThese four developments within the first lammne salts, Finally, it was converted to one decade of the 2,4-D era show what can be of the esters which were more effective in done by the ingenuity, curiosity and alertness the and western areas than the salts because of scientists once they are given a new tool to of their volatility and lipid solubility properwork with. Of course these four achievements ties. stand out like brilliant gems of intellectual atThe third change came from further studies tainment but one must remember the tens of in the Institute laboratories on 2,4-dichlorothousands of hours of patient research and phenoxyethanol and its sulfate ester. Dr. King hundreds of ideas that failed. They are the found that these materials were essentially inoverhead that must inevitably be paid for active on plants normally susceptible to 2,4-D. every advance in research. Thus the replacement of the free carbonyl group by a hydroxyl group was fatal to the SUMMARY herbicidal activity. The project might have died at this point bad be not noticed that the ethyl hee toay, Sormed ofr yfe our sonussdby sulfate ester, since named Crag Herbicide I, ther coday.eximy of you deayl bset chuedicay would prevent germination of weed seed' th opeI fhedaisstohmca whenit as prayd o th soi. H shwed structures or the nature of cell activities. You hatn tecmn was cnthved in. He serbhave my humble apologies for overburdening thaide odund s btivte bnt stam seriyou. However, the details are not too importcized sy Irdinaid bo y. 0.st shew ant. They are nothing more than illustrations thae soils Itres far. y ies a ow of the basic principles we have been elucisoat Bacillum, rus a suata cmon dating. If you can leave here with a positive that removes the sulfate radicle. Other bacteria in the soil oxidize the resultant ethanol derivavolved we will feel that all the hours spent in tive to 2,4-D acid. Thus soil microorganisms preparation and travelling down here were can generate 2,4-D in the soil in sufficient well spent. Let us look at these principles. quantities to kill weeds. This is a safer, more Principle 1. The scientific agriculturist is selective type of compound than 2,4-D. By turning his attention from exterior consideraextending this principle to other analogues of tions to a study of cell metabolism. This new the phenoxy-ethanol series a whole completrend is absolutely necessary if we are to make ment of new compounds is being evolved that systematic progress in the future. Remember, can be used to destroy weeds in fields of such the person who can control the operation of sensitive crops as tomato. cells can determine the fate of the individual The fourth development came from studyplant, the disease agent, the insect, etc. ing the effect of increasing the length of the Principle 2. It is possible to design molecarbon chain in the acid, Dr. Wain of England cules to do almost fantastic things to a cell. has confirmed earlier observations by SynerAlthough our knowledge is in a most primiholm and Zimmerman that 2,4,-dichloroarytive state there is a great gleam of light shinloxy compounds with an even number of caring down upon Lis. It is possible to design molebon atoms in the side acid are more toxic than cules that fit like the key in the lock of cell the compounds with an odd number. This has morphology and physiology. Molecules can be been shown to be due to the ability of plants made to penetrate one type of tissue and not to metabolize this part of the molecule by reanother, to change cell permeability, to enter moving two carbons at a time to convert the into different metabolic pathways, and even material back to 2,4-D. Because of this 2,4to differ in their stability and reactiveness. Redichlorophenoxybutanol may be converted member that the future' will see new kinds of into 2,4-D by some plants, Peculiarly enough, molecules in the garden. They will take the the legumes such as peas and alfalfa do not place of insects, diseases and weedy plants have this ability so the butanol derivative does and make plants rebel at their own genetics.

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12 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Principle 3. The type of basic research that technological strides of our lifetime but the must be pursued in this great development long range view is that more good will come does not come easily. It takes time, patience from it than harm. People will be fed better, and many, many dollars. It is necessary that clothed warmer, and housed more satisfactorievery one of us understands this and encourly because of scientific progress. We are conages it. Men must be encouraged to seek basic fident that the future is brighter for having principles of life processes so investigators knowledge of the atom even though it may such as themselves can use intelligence in do great damage in the bands of a moron or creating new processes of farming and new a moronic society. products. The scientist who operates from a Before every scientist there is an opportunity sound set of basic principles is efficient, efto serve as never before, There are available fective and adaptable. Without these principles new tools, more money, and more challenge he must experiment by blind probing. Eventhan ever before. If this nation and its demotually blind research becomes too expensive to cratic processes are to continue strong, healthy support because of the low, rate of progress. and progressive its security will come through Principle 4. There never was a time when skillful use of every mental and physical rebiologists had better research tools at their source at our command. Therefore it is not disposal than today. The things that can be only a privilege to be a scientist in such a done in a-most routine fashion simply were great era; it is a moral obligation to serve not dreamed of twenty years ago. There is a skillfully and progressively with the long certain measure of hazard to the tremendous range viewpoint uppermost in our minds. THE MEDITERRANEAN FRUIT FLY ERADICATION PROGRAM IN FLORIDA E L. AYERS, COMMISSIONER In addition, the arsenic used in spraying host Stat Plat Bord o Floidaplants did much damage to those plants and Stat Plat Bord o Floidatrees. Gainesville That was modern warfare in those daysutilization of the best known methods of eradG. G. RorwvER, AREA SUPERVISOR icating a fly that had seriously affected fruit U. S. Department of Agriculture and vegetable production in other parts of the Lake lfredworld. Regardless of procedures followed the Lake lfredoutcome was the successful eradication of the Modern warfare against a major agricultural Medfly, the only time in agricultural history insect-enemy in Florida has come into its own that this insect had been eradicated from any in the present Mediterranean Fruit Fly Eradcountry. ication Program. The combination of aircraft .The present campaign. against the Medfly and improved chemical control procedures, began only a few days after a Miami resident supported by an intensive inspection program, reported to the Dade County Agent's office has beaten the fly back and should effect comthat larvae had been found in a backyard plete eradication within a matter of months. planting of grapefruit, Tentative identification More than 25,years ago this same insect in.of the larvae as that of the Medfly was made vaded Florida and was eradicated after a long by state and federal laboratories, and the posiand expensive fight that exhausted 18 months tive identification followed the receipt by these in time and $7,5 00,000 in state and federal same laboratories of fly specimens trapped in appropriations. That was a campaign that the Miami area. created a great deal of criticism with its poliThe early weeks of the campaign could not cy of destroying all host fruits and vegetables. have been much different from those of the

PAGE 30

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AWARD OF HONORARY MEMBERSHIPS 15 festations, since the winters in Germany are Although the program is many months away considered severe enough to eliminate local from that successful conclusion, there is every incidences of the fly. Nevertheless, the peach reason to believe that eradication will be accrop in Germany has been infested in particuaccomplished within the space of one year. The lar cases to 100 percent, enough to affect the program is being financed by state and federal national economy. Apricots, apples, pears, and governments, with each appropriating an tomatoes also have been infested in that counequal half of the over-all eradication fund of try. $10,000,000. That is a small figure on the Peaches grown in Egypt also have been 100 basis of the present day dollar value when percent infested when no control is applied; compared with the cost of the first fight. certain parts of Brazil no longer export citrus, The cooperation of personnel of the Florida and Spain ships only early varieties of citrus Department of Agriculture, State Experiment which must be marketed before ripening propStations, other civilian and military governerly. mental agencies and the general public has Reports of this kind emphasize the fact that been of inestimable value to the eradication the Medfly must be eradicated from Florida. program. AWARD OF HONORARY MEMBERSHIPS LLOYD STANLEY TENNY 1929-30; and General Manager of the Chicago Lloyd Stanley Tenny was born near Hilton, Mercantile Exchange from 1929 to 1943 when N.Y. eighty years ago this month and was be retired. He is now livig in Hendersonreared on a farm. He received his A.B. Degree vle ot aoia from the University of Rochester in 1902, Few men have so profoundly influenced served as Assistant Pathologist with the U. S' Florida Agriculture in five short years as did Department of Agriculture from 1902 to 1904, Mr. Tenny. He was one of the BIG FIVE as Assistant Pomologist 1904 to 1907 and a' (consisting of P. H. Rolfs, H. Harold Hume, Pomologist for the U.S.D.A. until 1908 when W., J. Krome, Wilmon Newell and Lloyd S. he returned to Cornell for further study. From Tenny) who played a tremendous part in 1911 to 1913 Mr. Tenny was with Cornell's Florida Horticulture. Mr. L. B. Skinner (for Agricultural Extension D'epartment, being adyer Prsdn fti ocey ruh r vanced to Professor of Extension. He was the Tenny to Florida to organize the Grower's and first state leader of county Agricultural Agents Shipper's League in 1913. Soon thereafter Dr. in NewYork and helped organize the first E. W. Berger took to his office samples of Farm Bureaus. Citrus Canker because Mr. Tenny had been a Pathologist. Mr. Tenny recognized it as a very Mr. Tenny was Secretary-Manager of the serious threat and "sold" the Florida authoriFlorida Growers & Shippers League from 1913 ties on the idea that eradication would be to 1916, Secretary of Florida East Coast Ascheaper in the long run than control. How sociates 1916-17, and Secretary-Treasurer of right be turned out to be!!! the Coral Reef Nurseries from 1917 to 1918. Soon, the eradication of Citrus Canker was Mr. Teny was Vice President of the Eastmade number one objective of the Growern Fruit and Produce Exchange of Rochester, er's and Shipper's League because Florida had N. Y., and of the North American Fruit Exno department in its government which could change of New York City and president of undertake it, no funds and no law. just the Southern States Produce Distributors from imagine!!! Mr. Tenny threw himself into the 1918 to 1921. The Bureau of Agricultural fight with all of his tremendous energy, skill, Economics called him as Assistant Chief 1921 knowledge and resourcefulness. He whipped to 1926 and as Chief in 1928. He was Vice together an organization, raised the finances President of the California Vineyardists Asand together with others of the BIG FIVE sociation in 1928-29; President of the Federal drew up and secured the passage of the Fruit Stabilization Corporation of California "FLORIDA PLANT ACT OF 1915." Having

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16 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 secured the law that was necessary, he helped the Citrus Experiment Station has grown in the others select the "PLANT COMMISSIONboth size and stature until it now occupies ER" Dr. Wilmon Newell; the "State Nursery and enjoys an outstanding position in the field Inspector" and the "Port Inspection Departof horticultural research. ment," which in cooperation with the U.S.D.A. Dr. Camp has over one-hundred publications was responsible for the inspection of all plants on citrus and other tropical and sub-tropical entering the State from foreign countries, crops. Some of these publications, especially Having helped make the Plant Board a gothose dealing with the fertilization and nutriing concern, Mr. Tenny turned his attention tion of citrus have been and are being used to the task for which he had been brought to as guideposts in production management. His Florida, that of getting better rail rate scheddevelopment of a coordinated system of sprayules for Florida growers and shippers. ing and fertilizing citrus is in a large measure It is not too much to say that but for the responsible for the tremendous per-acre protimely arrival of Mr. Tenny the Florida citrus duction citrus growers now enjoy as comindustry might very easily have been wiped pared to the 1930s. The development of such out by Citrus Canker. Like all other members a program has been worth untold millions to of the BIG FIVE, Mr. Tenny was a giant. the citrus industry, as it has enabled growers The Florida State Horticultural Society takes to maintain a rather uniform per-box cost over pleasure in making Mr. Lloyd Stanley'Tenny the last twenty-five years while per-acre costs an Honorary Member and regrets that the have gone steadily upward. state of his health requires that it be in abAs an agent of the Florida Citrus Commissentia. sion, Florida Citrus Mutual and the Florida State Plant Board, Dr. Camp has been called ARTHUR FORREST CAMP upon for fact-finding trips to South and CenDr, Arthur Forrest Camp came to Florida trial American countries, Spain, Japan, Califrom California in 1923, and during the enforma, and Texas. His reports following these suing thirty-three years has compiled a record trips enabled the various agencies to formulate plans to protect and promote citrus i Florida. osrased by fewHe is considered the citrus industry's outstandSg ing spokesman on technical subjects, and has Herndated frnors the U9ndvwst ofwaded been called on many times to state the idus*i wto ors in 192 by washwgrdn try's case before legislative committees of both University, St. Louis, Missouri, and immedis Dr Cam ha don g eg cosltn wor on ately started on a career that was to be devoted not only to horticultural advancement Citrus production, marketing and processing in Florida but to advancement on an internain many foreign countries for governments, tonal scale, companies, cooperatives, and individuals From 1923 to 1929 Dr. Camp served in including Cuba, Jamaica, Haiti, Honduras, several important research positions with the Nicaragua, Costa Rica, Guatemala, Argentina, Florida Experiment Station at Gainesville, and Brazil, Paraguay, Peru, Surinam, Bermuda, in 1929 was made Horticulturist In Charge, Mexico, Sweden, Spain, and Japan. He was Department of Horticulture. This same yea' made an Honorary Citizen of Argentina in he was made an agent of the U.S.D.A., and recognition of assistance given the citrus inplayed an outstanding part in the eradica_ dusty in that country. tion of theMediterranean fruit fly. In 1930 he Dr. Camp was instrumental in setting up returned to the Experiment Station and served and carrying out research into the tristeza as head of the Horticulture Department until problem, a new disease that posed a threat 1936 when he became Horticulturist In Charge, to Florida citrus and one that decimated many Citrus Experiment Station. Since 1944 Dr. groves in South America. Thanks to this work Camp has served as Vice-Director, Agriculture tristeza no longer poses the threat that it once Experiment Stations, in charge of the Citrus did. Experiment Station. He personally carried on Dr. Camp is an honorary member of the research until 1944, and under his guidance Kiwanis Club and Gamma Sigma Epsilon,

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AWARD OF HONORARY MEMBERSHIPS 17 and a member of the Florida State Horticulone child, Peggy, who is now Mrs. Peggy tural Society, American Society for HorticulClayton May, and two' grandchildren. tural Science, American Association for the As Secretary to the State Agricultural AdAdvancement of Science. He is in American justment Administration Committee, a memMen of Science, Who Knows-and What and ber of the State Defense Council, Chairman Who's Who in American Education. He is a of the State USDA War Board during World grove owner, and the president of the Haines War II, he rendered outstanding service to City Citrus Growers Association. Florida agriculture by arranging for the proIt is with tremendous pleasure that the curement and proper distribution of vital Florida State Horticultural Society recognizes agricultural supplies and by stimulating farm the great service that Dr. Camp *has rendered people to extraordinary effort in war crop to the horticulture of the State of Florida and production, in buying U.S. War Bonds, in other countries and his leadership in the field salvage drives, and in other activities conof citrus research that has been largely renected with the war effort. sponsible for the enviable position the Florida Through his knowledge of Florida agriculCitrus Industry holds today. ture, his careful study and understanding of HAROLD G. CLAYTON the functions of all agencies concerned with agriculture, and his persistent efforts to work It is a great privilege to present to the in close harmony with all agencies and groups, membership of this Society a distinguished nahe has been instrumental in bringing about tive Floridian who has, by unanimous vote effective working relationships between these of the Executive Committee, been designated agencies and groups for the maximum service to receive an Honorary Membership in the to Florida agriculture and the solution of Society. major agricultural problems. Harold G. Clayton was born, February 27, While serving as district agent, be was ac1892, at Ocala, Fla. He grew up and attended tive in promoting 4-H1 Club work and in copublic schools in Tampa; received B.S. Degree operation with the state 4-H Club agents he in agriculture from University of Florida in helped to start the state's 4--H camping sys1914; received M.S.A. Degree from same intem, which today is outstanding in the Nation. situation in 191 6. After a brief period of farm From 1947 be served as Administrator to work he was made County Agent in Manatee the State Soil Conservation Board, He was County, in March 1917. He entered military appointed to this position by two different service in World War I on May 15, 1918 and boards since the State Soil Conservation served until December 6, 1918. Early in 1919 Board was completely reorganized by the 1953 be returned to county agent work and in Legislature. October 1919 he was made District Agent HesrdasCimnofteSteed with the Agricultural Extension Service at eserveondisoCara Comite.atSe Gainesville. He continued as District Agent until November 1934, at which time he was He was a member of the Farmers Home asked by the Director of the Extension Service Administration State Advisory Committee. to assume administrative direction of the He was a member of the State Agricultural Agricultural Adjustment Administration, later Stabilization and Conservation Committee. the Production and Marketing Administration, eclaoae ihFoiaFrs ev and now Agricultural Stabilization and Con' Hce ancolaboatedvation FSrida Fnreterservation Committee. He served in thisposition until July 1, 1947. During this period he modification evaluation study. continued to bold a cooperative appointment During his service as Director of the Floriwith Extension Service. On July 1, 1947 he da Agricultural Extension Service the number was made Director of the Florida Agricultural of county agents increased from 61 to 66. Extension Service, the position he held until (Florida has one county which is not classiMay 31, 1956 when be retired. fied as an agricultural county.) The number H. G. Clayton married the former Miss of assistant county agents has increased from Harriet Ray, of Tampa. The Claytons have 18 to 54; the number of home .demonstration

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18 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 agents from 41 to 52, and the number of asAlways modest-never once grasping for sistant home demonstration agents from 9 to spotlight or for front page-devoted to Florida, 22. The total staff of specialists has been inher horticulture, her agriculture, her farm creased from 14 to 33. Mr. Clayton's wide youth-never asking for anything for himself knowledge of and service to horticulture in other than an opportunity to serve others Florida is reflected again by the fact that this always trying to see the other fellow's point of increase in.specialists' services covers every view. A person whose soundness of judgment phase of horticulture in our state. has been recognized by those at the highest Mr. Clayton has for many years been a levels in our state government and institutions. faithful member of this Society and a regular A man who has by both precept and example attendant and keen observer at its meetings; rendered outstanding service to this Society learning the needs, problems, views, of people and to Florida horticulture. Always a gentleactually engaged in various horticultural enterman-a person of highest character-whohas prises; using his knowledge and his ability to in every way measured fully to the highest strengthen and direct the Agricultural Extenstandards of honorary membership in this dission Service for the common good. tinguished Society.

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COHEN: TRISTEZA DISEASE 19 INJURY AND LOSS OF CITRUS TREES DUE TO TRISTEZA DISEASE IN AN ORANGE COUNTY GROVE' MORTIMER COHEN This grove has been mapped twice a year since July 1952, the last mapping having State Plant Board been completed in July 1956. The entire Gainesville area included in the study is shown in Figure 1, which also provides a graphic comparison Soon after the discovery of tristeza in between the condition of the grove in July Florida, it became apparent that careful study 1952 and in July 1956. The entire grove area over an extended period of time would be consists of about 80 acres. Approximately 20 necessary to assess accurately the amount of acres, planted entirely to Temple oranges on damage done by this disease. and to make sour orange stock, are not included in our predictions regarding future losses. In July statistical summary because many trees in 1952, therefore, a large grove near Winter that portion of the grove showed signs of deGarden in which many trees with tristeza had cline from water damage in 1954 and it was been found, was mapped tree-by-tree, by a desired to restrict the study, as much as group of Plant Board inspectors. possible, to the effect of tristeza only. The In the mapping, trees were rated on the remaining 60 acres consists of 4169 trees, of folloing sale:which 88 per cent are Temples on sour orange rootstock, mainly 26 to 30 years old. 0 -Healthy Also in the grove are 297 Valencia trees on I -Slight decline sour orange stock, about 200 trees on grape2 -Moderate decline fruit stock, and a small number for which the 3 -Severe decline rootstock is undetermined. Properties owned X-Dead or missing by 4 different individuals are included in this R-Replant tree 60 acre block. It should be stressed that this Infected trees in this grove are of mature is not a neglected planting but that normal size and are not stunted. The large size of practices of cultivation and fertilization are the trees and the observable spread of disease being followed. in the planting are taken to indicate that the Figure I shows only trees rated 2, 3, X or disease was brought in by natural means, II, that is, trees in definite decline, missing or probably by aphids, rather than through inreplanted. Trees rated 1, those in slight defected budwood. This is in contrast to the cline, are not included, because slight sympsituation in other parts of the state where toms are sometimes due to transient causes the majority of infected trees apparently had and not to tristeza. This map contrasts trees tristeza virus introduced with the original affected in July 1952 (shown as O's) with bud. the large number of additional trees affected 'by July 1956 (shown as X's). The many to hthe e frtsmofa ingleindividua butr istheoresult trees which went into serious decline in the of the cooperative work of many individuals now or 4-year interval between the 2 mappings can wvhonse effyortshhav mtallytaidedA in thet colectin be clearly seen. All portions of the grove and assembly of the data Presented in the Paper are were not affected equally. Some of the older J. N. Buby K. E. *n A. C. Crws L. W. Holley, Dr. L. C. Knorr, Mrs. Enid Matherly, John areas planted with Temple orange on sour Pery, C. R. Roberts, Mrs. Jean Smith, Howard Van Pet orng stoc wer th mos seerl afece

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Fig. 1. Spread of disease in an orange grove near Winter Garden from July 1952 to July 1956. Map shows trees in moderate or severe decline, dead, missin s r replanted. Trees with slight symptoms of decline are not shown. All trees are of the Temple orange variety except for the indicated block of X 0 0 X 0 0 0 0 X 0 3 0 0 0 X I X XI X X 0 0 0 X UX 0 0 0 X 0 0 0 00 X 0 0 X 0 1 0 X X X XO 0 X X 0 X X X X 0 X 0 X X X X X X X XO 0 X X X 0 0 0 X X X X 0 K X 0O 0 X 0 OX 0 0 0 00 X 0 X K 0 X 00 X X X .0 X 0 f0 0 q X 0 X X X 0 X XX XXX 0 X 0 0 0 0 t 0 X X X X X X 'X X X XX X XX XX X X OX X X X X X X 0 0> X X 0 0 X X X X XX X X 0 X X X X 0 C S X X X X X 0 K X X X X X X 0 X F S X X X 4 0 0 0X 0 0 0 0 X X X0 X X 00 X X X 0X X K X X X 00 0 0 000 X X X X X X 0X> X X X X X 0 X X X X X 0 X X X X X 0 OX X X X 0X X X 00 0 00 0X X IC0X 0 X 00 0 X X X X X X X X X 0X 0 0 0 X X X X X 0x X X X X X X X X X X 0 0 X X X X X 0 X X X X X X X X X XO 0 X 0 X X X X X X 0 X X 0 0 0 X X X 0 X X X 0 0 X X X 0 X X X X X X 0 0 0 X 0 0 0 0 X X0 S XXX XXX X X X X X 0 0 X X X Xd X X X X X X X X X X X X 0 X X X X X X X X X X X X X X X X X X X X X 0 0 0 XX 0 X X X X X X0 X X 0 X 0 X 0 X X X X X X X 0X 0 0 0 .X X 0 X X X X X X C X 0 0 0 X 0 0 -X X X X X X X XX X X X 0 X X X 0 X X 0 0X 0 0 0 X 0 0 0 X X X X 0 0 X 0 X '0 0 0 C 0 X X 0 X X X X X 0 X ..D 0 X XX 0 X X X O X X I X X X X X LX X X X X. X X X X X X X X 0 X X X 7 XX X X X 00X X X X X X XXX 0 X 0 0 ] 0X X X 00XK X 0 X X X X X 0 XX X X 0 X X XXX 00XX 0 X X X X 0X X X X X X 0 0 X X 0 X 0 Y X X X X X XX X X X X X X 0X OX X 0X X C X XX X X X X X XO X X X X X X X 1)X X X X X 0 X X X X X X0 X X X 1 X X X 0 X X X X ~ X 0 X 0 X X X X 000X X X X X0 X X X 0 0X X X0 X X 0 0 X X0 X OX X X X X 00 X X -X X X 0X X X X X X X X X X 0 0 0 X X 0 0 0 0 0 X X X X 0 X 0 0 X X X X X X X X X X 0 X X X X X 0X 0 X 0 0 X X X. X X0 X X X 0 X X X X X X 0 X 0 0 0 0 X X X X X X 0 X X X X 0 X X C X X .X X IXI0 I I0 0 X XX 0 X XI X1 1 0 0 0 X X 0 X X 0 0 0 X X 0T X X X 0 X X 0 X 0 X X 0 X X X X 0 0 X X X 0 0 X X X X X I IX XXI X X X 0 X X0 X X XXI X X X 01 X 0 I X X X X X 000X 0 X X X X X X X X X X X XX0X XX0 0 X X X 0 0, X X 0X X X X X X X 0 0 0 0 0 X X X X X 0 X X X X X' X X X X X X X 0 X X X X X X0 .X X X X X X X MAP: 0 -Trees in decline, dead, missing or replanted in July, 1952 X -Additional trees affected by July, 1956

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COHEN: TRISTEZA DISEASE 21 but the eastern portion of the area studied TREE uATE 2, 3, X AWD R IN AN 0RMGE MIUNTY' WRMV1 was not as badly affected as the middle por-. 2J U tion. Trees in the Valencia .orange block, -which is thoroughly infected with psorosis as well as tristeza, were not as severely injured, TU on the average, as trees in the Temple blocks. -2 The western-most planting consists of Temple W trees which are approximately 8 years old. A relatively low proportion of these trees showed symptoms of decline. Most striking is the relative absence of disease in all trees on grapefruit rootstock. These are located in some of the rows direct6 ly south of the Valencia block. This situation 0 is discussed below. The increase in the number of trees in deo cline from 1952 to 1956 did not come about abruptly, but was the result of a steady trend, as is shown diagrammatically in Figure 2 w where the number of trees in classes 2, 3, X and R at each mapping is indicated by a line graph. Trees in class 1, those in slight J decline, are not included in this graph. The "'" 1. 1" MTABLE 1 DISEASED, MISSING, AND REPLANT TREES IN AN ORANGE GROVE NEAR WINTER GARDEN NUMBER OF TREES CLASS OF DECLINE PERCENTAGE DEAD OR TOTAL OF ALL DATE SLIGHT MODERATE SEVERE MISSING REPLANTS AFFECTED TREES July 1952 285186 22 19 107 619 14.8% Dec. 1952 360 173 160 27 100 820 19.6 JulY 1953 241 201 267 30 135 874 .20.9 Feb. 1954 452 264 235 37 137 1125 26.9 Aug. 1954 444 298 220 137 213 1312 31.4 Mar* 1955 1540 307 66 7 346 2266 54.3 Aug. 1955 393 209 227 127 365 1321 31.6 Jan. 1956 433 196 251 175 327 1382 33.1 July 1956 385 158 220 269 479 1511 36.3

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22 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 total number of trees in classes 2, 3, X and R mission test also, to be carrying the tristeza increased from 334 in July 1952 to 1126 .in virus. July 1956, Thus 27 per cent of all trees in It is interesting to contrast the results of the grove were in definite decline or missing, these histological tests with similar tests made dead, or replanted by July 1956. If this rate on trees in the 20-acre area previously menof increase of diseased trees continues for the tioned as having been excluded from the next 4 years, July 1960 will see 46 per cent study because its trees had suffered from of all trees in the grove in this category of water damage. Bark samples from 11 trees seriously affected trees. in decline in the water-damage area were It is i interesting also to compare the numeamine anr treste a. ber of trees in all classes during the succesneaiefr rsea sive mappings from 1952 to 1956 as shown .It is quite. clear, therefore, that, in the 60 in table 1. The major increase in "total trees acres under study, tristeza was the major affected" during this period is in replant cause of decline. On the basis of this evitrees and trees dead or missing, but the numdence it can be estimated that upwards of ber of trees in intermediate stages of decline 90 percent of the diseased trees studied were has also remained at a higher level than was injured by tristeza disease. observed during the first two mappings. In When trees in this grove once begin to March 1955, a three-and-one-half-fold in.. deteriorate, they do not recover, but concrease over the previous reading in the numtinue to decline and eventually die. This can ber of trees in slight decline was recorded. b enb bevn h aeo re on The count occurred after a relatively dry winin decline when the grove was first mapped ter. The transient nature of this apparent dein July 1952. Figure 3 summarizes the icline is indicated by the fact that most of formation on all the trees rated as being in these trees were again rated as healthy in slight, moderate, or severe decline in July the subsequent 3 mapping. If one projects 1952. Of a total of 483 trees i all categories the data in Table 1 to July 1960, and in.. in 1952, 294 were dead, missing or replanted eludes also trees showing slight symptoms of by July 1956, and 396 trees or 82 percent decline, it will be found that 57.8 per cerit were more seriously in decline than in 1952. of all trees in this grove will have been afAs might have been expected, more of the fected by the end of 4 more years, provided trees at first judged to be in slight decline the present rate of increase in the number of via trees in decline continues, R 19 S--h i St, Mo -,-te. -nd S-e-.What is the evidence that these trees are 0 suffering from tristeza disease? Numerous trees have been examined for the presence of -. honeycombing-that pattern of tiny holes inthe bark below the bud union which has 19695 proven to be quite reliable in Florida as a field test for the presence of advanced tristeza in trees on sour orange rootstock. A high proportion of the trees examined have 1 shown this symptom. 9 -----A more specific method for determining if plants are suffering from tristeza disease is 4 ... the histological examination of the bark from 192 (PVeo f.ni1P the bud union of suspect trees as describedPI by Schneider (1). Bark samples collected at random from 33 trees in decline in the grove were examined using this method. Of the 33 -e trees examined, 30 were found to be positive for tristeza Six of the histologically tristezapositive trees were indexed on key lime 1,1NMM seedlings, and all 6 were found, by the transH.althy slit -oo-rte S.. -,

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COHEN: TRISTEZA DISEASE 23 proved to have been affected by a temporary FLO. condition, and a higher proportion of these COLDITION OF tO IN A PLANTING ON MU~D SOUR ORANG4 trees showed recovery. If the 203 trees which A APUT R 955CK were found to be in moderate or severe deICY~y e 7 3 2 1n cline are considered alone, it is seen that 189 smr o m trees or 93 percent were more seriously in Q0(Q0Q/00E0-E 0000I decline in 1956 than-in 1952. ME The fact that trees in decline generally do 00 ot improve but continue to decline further ME A -n 3 0 *0A00 A.0eM oo is an additional indication that tristeza is 000 0 responsible for the condition of the grove. It M 000 is enlightening, in this connection, to com.... pre v theifatew of te n that area of he E I 21 1A 0~~ *D E* Eg 009@e@@.fOLU with trees from an area in which tristeza was the prime disease factor. In a portion of the oo water damage area in August 1954, 274 0-So ,1 fl~ trees were rated as showing some degree of 0 -o~i Mo t Dal *GU~ ~ ~~ Ur. Uf~lO 0I= n decline. Two years later only 22 percent of 16 these trees showed any deterioration; some 'I of these, no doubt, were suffering from tristeFigure 4 will reveal that very few of the trees za. On the other band, in a comparable area on grapefruit rootstock are in decline while in another part of the grove where no water a very high proportion of the adjoining trees damage bad been noted and where 180 trees on sour orange rootstock are diseased. Bark were in decline in August 1954, 52 percent samples were taken from 9 of the grapefruit of the trees bad deteriorated by July 1956. trees which did show some sign of decline, When tristeza was first found in Florida, and were examined microscopically. None of most pathologists expected to see a repetition thedscimns was fordsteza.itoogca of the damage done in South Amrica. One of the warnings issued by pathologists was These observations do not prove that citrus to avoid planting citrus on grapefruit roottrees on grapefruit rootstock cannot be instock because it, iiesu rnerosok ured by tristeza in Florida, since these trees had been found in South America to make may eventually show tristeza injury, but it is a combination non-tolerant to tristeza. After very apparent that grapefruit cannot be con.extensive examination of Florida citrus groves, sidered to be in the same class as sour orange however, State Plant Board inspectors have insofar as susceptibility to tristeza in Florida not been able to find any trees on grapeis concerned. fruit rootstock which were in decline beOne of the purposes for undertaking the cause of tristeza infection. When the grove in study of the grove near Winter Garden was this study was examined, it was found that to explore the possibilities for predicting futhe bud union on about 200 trees bad a conture outbreaks of tristeza in Florida. To figuration which indicated that the rootstock carry out this aim, two small plots containing was grapefruit rather than sour orange. 58 trees in all were set up for special study of These trees have been watched since 1952 trees on sour orange rootstock. Trees in one and it is of interest to examine Figure 4 plot bad Valencia orange tops, and Temple which is a map of the portion of the grove orange tops were used in the second plot. containing the trees on grapefruit rootstock. Bark samples have been taken periodically Figure 4 shows both the rootstock and tree from trees in these plots and prepared for condition in August 1955. Trees on grapemicroscopic examination. In the course ofthis fruit rootstock are mixed in with trees on sour study, 6 previously healthy trees in these orange rootstock thusproviding an excellent plots have developed histological symptoms comparison of the behavior of trees on these of tristeza. These histological symptoms were two rootstocks under identical environmental evident from six months to 2 years before conditions. Even a casual examination of there was any visual indication in the field

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24 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 that these trees were diseased, This confirms tristeza; have been found elsewhere in the observations made by Schneider (1) on Orange county, and a few have been found trees with quick decline disease in California. in other counties in the state (2). The signiThus, a tool actually is available for shortfinance of this finding is not fully undertime prediction of future deterioration of stood. It may be that the virus has an excitrus trees from tristeza disease. tremely long incubation period before it be0 ..gins to affect the phloe of the host tree. tm ot is obv must betpr ca sy en(Phloemn breakdown is one of the earliest faatras of trez usito b reed by of tors of the histological picture of a tree in b tnceof rthe v r es weo rein e, on num e y decline with tristeza disease). Another citrus lieheah-pedring teesterie idexed o khey virus disease with an incubation period of limeseelins t deermm ifanyof hem many years is already known-psorosis disease were carry the virus of tristeza. In this -gested previously way it was hoped the interval between the tht t h t be t s production of the virus and the first apa sehis pib t s the a s e ith tion a .pearance of histological symptoms could also Ao sedkpowsbit itan addition a fath c-ru be approximated. This phase of the work has tordexe, ustnwn be prese t ioe o the diss produced most surprismg results. So far, 21 a eind, mt rbn ptrse. Inefyorse th iss trees in this grove which are histologically cattrn begiorn isue acIney and casn-i normal have been checked by transmission mtned isbserin stuie tesely tree coan-y test for the presence of tristeza. Of these, 15 sinned thsrvaw o mofgt o the pescrtablym trees or 71 percent have been found to be hul thbove moresierton sheu prtobpositive for tristeza. Furthermore, 4 out of 5 s rThe a entraco astd tatorn s ezauldiseaseobn trees on grapefruit rootstock which were Fcured th a cta fthatse serio st disse s itrs similarly indexed proved to be carrying trislog hs ae r seri b es od it rs teza virus although, as previously mentioned' Alstngogr t ni, paapter grcrbe oieos in there is no indication, in Florida, that trees a snge gove ony, mansewher grves ben ni damaged by tristeza. At present, many of the disease. If the foregoing sampling of the factors involved in producing an outbreak of trees in this grove can be considered reprethis disease are not understood and cannot be tentative it must be concluded that about predicted. Growers who plant groves on sour three quarters of the healthy-appearing trees orange rootstock, the only rootstock used in Sthis grove are carrying the virus of tristeza. The most surprising aspect of this project is tolerant to tristeza, are risking the life of their that only one of the trees tested has so far planting. Is it wise, therefore, to continue the shown histological signs of tristeza disease, use of this dangerous rootstock where other although -a few of these trees are known by rootstocks can do the job safely? indexing to have been carrying the virus for LITERATURE CITED almost 3 years, and most of the trees are 1. Schneider, Henry. 1954. Anatomy of bark of known to have been infected for almost 2 bud union. trunk, and roots of quick-decline-affected years. It should be mentioned that similar gardia 22 56ng7-581. su rag oosok.Hl virus-carrying susceptible trees, which appear 2. Cohen, Mortimer. 19&6. Incidence of tristeza healthy and do not show histological signs of sy"pto"s.F Phyopath. tre:s9 (~abstract)s.wn il

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SMITH: PHOSPHATE FERTILIZATION 25 EFFECT OF PHOSPHATE FERTILIZATION ON ROOT GROWTH, SOIL pH, AND CHEMICAL CONSTITUENTS AT DIFFERENT DEPTHS IN AN ACID SANDY FLORIDA CITRUS SOIL, PAUL F. SMIrH pate. The soil is a transitional type between Lakeland and Eustis fine sands, previously Horticultural Crops Research Branch identified as Lakeland (7, 8). The plan foIAgricultural Research Service lowed is to apply 0, 1, 3, and 8 units of United States Department of Agriculture P.A., respectively, to different plots for each 4 units of nitrogen used, There are six 12Orlando tree plots for each phosphate level. The P2O, comes from 20 percent superphosphate, and In recent years, certain studies (4, 10) compensatory amounts of gypsum are given have been made to explore the relation beso that all plots receive the amount of CaSO, tween fertilization practices and root develcarried by the highest level of superphosphate. opment of citrus in the sandy soils of Florida. The highest rate of PO, was the usual cornThose reports were concerned primarily with mercial rate at the time the experiment was the effect of nitrogen sources and rates and started, but current recommendations (6) call methods of timing on the density of roots in for a drastic reduction. The experimental rates the top 5 feet of soil, where the changes in of P.O. described above will be referred to as chemical composition were relatively small. none, low, medium, and high in discussing With adequate liming, nitrogen appears to treatments. have little or no permanent effect on soil All trees have regularly received 3 applicacomosiio (1).tions a year of a mixed fertilizer containing The present studies involved deep sampling little or no organic material and no superin a long-term phosphate experiment in phosphate. The current mixture is 10-0-10-3 which there has been a large permanent (MgO) -0.5 (MnO)-O.5 (ZnO)-0.1 (B20s) apchange in the phosphorus status of the soil plied at the rate of 24 lb. per tree per year. because of the accumulation of applied phosCopper also was included for the first 10 years pate. Previous reports (7, 8) describing the but omitted since. Zinc was applied in spray results from this experiment for the first 6 form only once and that was in the spring of years, failed to show any beneficial response 1954. For the first 9 years the appropriate in tree growth, yield, or fruit quality to apquantities of superphosphate and gypsum plied phosphate. No additional data on these were also applied 3 times a year and to the factors are presented here, but the results same area as covered by the mixed fertilizer. through the 13th year are still essentially the From the 10th year on, these materials have same. The present report is concerned with been applied all in one spring application. No the density of small roots, soil pH, and cerattempt has been made to compensate for the tain chemical constituents in the soil in relacalcium carried as the phosphate salts, but a tion to the rate of phosphate fertilization. relatively high rate of dolomitic limestone has EXPERIMENTAL METHODS been regularly applied to all plots. Pineapple orange trees on Rough lemon In July 1955 eight 2-inch cores of soil were' stock were planted on a virgin plot of ground taken from each plot. The most uniform trees in a random block experiment in 1942 and were selected, and in most cases only one certain plots have never received any phoscore was taken per tree. The cores were taken at the tree-drip line and to a depth of 5 feet.'/This study was made possible by the generous The samples were taken by depths of 0-6 in., cooperation of Loren H. Ward of Orlando, Flo~rida, in 61 n 22 n 44 n n 26 n whose grove the experiment es. The technical assistance of G. K. Scudder, Jr., and G. Hrneiar is The 8 cores of soil for the respective depths gratefully acknowledged.

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26 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 500 5.0 40Q LSD 0 0.05 1 4. LSD 0.05 3PA0. 3.0. P 200. 02.0. 0S0 100.i 1.0. OLMH OLMH OLMH OLMH OLMH OLMH OLMH OLMH OLMH LMH 6.5. -25. 6.0.i L SD 0 0.05 20. L SD 0 0.05 5.5 -pj5. 5.0 K 1 o 4.5. 5. 4.Q 0. OLM OLMH OLMH OLMH OLMH 2 58 280 60 15. PPM IQ PPM* Cu 5 IlMN2 612 *-24 24-42 420 0 -12 1 24-42 4 0 Fig. 1-G. Root growth and various soil factors found at different depths (in inches) in an experimental Pineapyl orange grove onpacidndy ol afte ,3 ydadrs of dif ferential fertilization with superphosphate. total soil phosphous; Fi.n2per rght) igcaconcentrations of small "feederroots found; Fig. e3 (center let)roil pH; g .nes rt e xchareasb e tsium; dig ere f o cppe ai. 6h (lwe riht toa magnee Th L D bar inict th reuie difrnefrsgnfcnea h 5% lee bewe an tw tramet ordpts

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SMITH: PHOSPHATE FERTILIZATION 27 were composited, screened to remove the because the groves were grown before the fibrous "feeder" roots, and thoroughly mixed general drop in applied phosphate in comby rolling on a canvas cloth, and portions were mercial groves. saved for laboratory analyses. Rootlets smaller While the data in Fig. 2 are less consistent than about 1/16 inch in diameter were sorted than those for the concentration of P in Fig. 1, out, dried, and weighed. In addition to pH, they clearly indicate that high-phosphate total amounts of P, Cu, Mn, and Zn were defertilization somehow causes a sharp reductermined on certain soil samples after total tion in the quantity of feeder roots in the top digestion in sulfuric-nitric acid mixtures. Ex12 inches of soil. In the 6 to 12-inch zone all changeable K, Ca, and Mg were determined 3 levels of applied phosphate significantly reby neutral ammonium acetate extraction. ducked root growth. It is probable that the effect on root growth is somewhat exaggerated RESULTS AND DISCUSSION in the area sampled because of the uneven distribution of applied phosphate. Even so, it is Phosphorus status of soil--The values found difficult to avoid the conclusion that applied for total P are shown in Fig .The data are phosphate has had no beneficial effect on root very consistent and show that while most of growth in this experimental grove. The dethe applied P is held in the top foot of soil, pression of root growth below 12 inches is not there is a gradual accumulation throughout statistically significant, but the trend is still the top 5 feet. This is in agreement with the present to the 42-inch depth. Even to the 60findings of Spencer (11) that superphosphate inch depth there is no suggestion of increased gradually distributes itself through the top root growth as a compensation for the reducfew feet of soil. Actually, more total P was tion in growth at the shallower depths. found than was applied to the plots receiving Since tree size, appearance, and yield superphosphate for 13 years. This is doubtrecords do not yet reflect the density of roots lessly due primarily to the fact that the lowas measured here, it remains to be seen hanging foliage interferes somewhat with the whether such a reduction is a definite handimachine spreading of the superphosphate, and cap to the tree. No explanation is offered as there would be a zone of relatively high P to why superphosphate depresses root just outside the foliage line due to the deflecgrowth, but the effect is somewhat similar to tion of particles. Sampling in this area showed that found with a high rate of ammonium nian increase of 1900 lb. of P per acre through rate (4). the 5-ft. column, whereas only about 1250 lb. Soil pH-Inereased acidity at all soil depths of P bad been applied. Thus, the sampling was associated with the use of superphosphate. method may also exaggerate the other effects Fig. 3 shows the pH values found at differassociated with differential phosphate fertilient depths in relation to treatment. In the zation. It is felt, however, that the trends two upper sampling depths there is a gradwould be indicative of the nature of the renation in pH values corresponding to treatsponses even though the magnitudes might ment. At the 3 lower depths, there was little differ somewhat from those shown. or no difference among the pH values for the Density of feeder roots-The distribution of 3 rates of superphosphate, but those for the feeder roots is shown in Fig. 2. The data are plots that received none were appreciably presented as the weight of roots found in a higher. square foot of soil 6 inches deep taken from Superphosphate is not a simple material as each depth zone. The total dry weights of it contains a mixture of phosphatic salts, gypfeeder roots expressed as grams of roots per sum, iron and aluminum oxides, silica, and square foot column 5-ft. deep are as follows: trace quantities of several other substances. No phosphate 23.8; low phosphate 21.4; It is. mildly acidic and gives a pH reading of medium phosphate 21.3; and high phosphate about 3 when mixed with water. The acid16.3. It is of interest that Ford (3) also found ulating effect of superphosphate on most soils 16.3 as an average weight of roots in comis of little or no practical significance bemercial groves of this age category. These cause of the suffering action of the soil. Howsoils too, would have been high in phosphate ever, with very sandy soils of low exchange

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28 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 capacity and high rates of application, addiin the fertilizer. No Cu was applied during tional liming apparently is required to offset the interval, and Cu status of the soil is virthe acidifying effect of superphosphate. tally unchanged. The effect of superphosphate in lowering GENERAL DISCUSSION pH is particularly evident in the top 12 inches Several studies (1, 5, 7, 8, 11, 12) have of the soil and corresponds to the area of maxishown that phosphate accumulates in Florida mal phosphate accumulation and maximal decitrus groves. Removal of this element by the pressing in root growth. Yet it appears doubtcitrus crop is not large, being about 0.5 lb. of ful that there is a simple cause and effect reP per ton of fruit (9). Application of superlation between pH and root growth. Previous phosphate does not markedly increase the abstudies (10) in which the pH was varied in sorption of phosphorus by the tree in ordinthis same general range, but without superary acid, sandy Florida grove soil (7). The phosphate as a variable, showed no depreseiec hsfrfist hwaybnfca sion in root growth due to lowered pH. Likeeffect of applied phosphate on citrus in this wise, studies with different levels of phosphate State except in a few cases, such as on muck in solution cultures did not show any adverse soil or very light sands where the content of effect of high phosphate on root growth (2)4 native phosphate is very low. Thus, while it is not yet established what Wander (12), studying soil factors in recauses the depression in root growth, it is aplation to presence or absence of liming, noted parent that superphosphate does not have a that a phosphate differential existed in the beneficial effect on soil reaction. topsoil and concluded that the greater retenEffect of phosphate level on exchange K, tion of Mg and Mn in the limed plots was due Mg, and Ca-There was practically no effect to the absorptive capacity of the accumulated of phosphate treatment on the extractable calcium phosphate. The present results, i adquantities of the three base elements (K, Mg dition to previously published data (8), fail and Ca). The only difference of consequence to show any relation between large phosphate was the tendency for more K to be retained accumulations and the retention of Ca, Mg, in the upper depths where the greatest amount Mn, Cu, or Zn. Thus, it appears possible that of phosphate had accumulated in the soil the effect noted by Wander was not 'attribu(Fig. 4). Mg values were virtually identical table to phosphate but to pH. Liming probably at all depths in all treatments and the respecretarded the losses of phosphate, Mg and MR tive total pounds per acre in 5 ft. of soil were for the same reason rather than through the no phosphate 340; low phosphate 321; meindirect method postulated. dium phosphate 349; and high phosphate 330. um g Ca showed a slight, but irregular and noncuulation would also result in greater Ca significant, increase with values of 1176, 1090, accumulations in the soil, particularly if there 1307, and 1290 lb. per acre for the same was a reversion to calcium phosphate. Howrespective treatments. This Ca trend was not ever, neither exchange Ca nor total Ca (7, 8) accentuated in the upper soil depths where is appreciably changed. The work of Spencer the phosphate accumulation was the greatest. (11) offers an explanation since be found that most -of the phosphate accumulated in Effect of phosphate level on the total Florida sandy grove soils is in the form of amounts of Cu, Zn, and Mn-There was no iron and aluminum phosphates rather than significant effect of phosphate level on the calcium phosphate. total amounts of any of these metals found in the soil. The concentrations of Cu and Mn are SUMMARY shown in Fig. 5 and 6. Zn showed a mean Soil samples to a depth of 60 inches were value of 19 p.p.m. in the top soil and about 8 taken in a Pineapple orange grove on an acid, p.p.m. in all lower depths regardless of treatsandy soil after 13 years of differential ferment. These results are in harmony with the tilization with superphosphate. Data derived results found in a topsoil sampling 5 years pre-from these samples showed that (1) the viously (8). Both Zn and Mn show increases largest increase in P was in, the top 12 inches as a result of continued use of these elements of soil, but some increase was noted at all

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FEDER AND FELDMESSER: BURROWING NEMATODE 29 depths, (2) the total weight of "feeder" roots 4. W. Reuther and P. F. Smith. The ffet of nitrogen on root development of Valencia in the 60 inches was nearly one-third less in .range trees. Proc. Amer. Sue. Hort. Sci. (MS subthe high phosphate plots than where none "mitte" fo ubiation). tde o ol ro rd was applied, (3) appreciable acidity was imcitrs groves. Fla .Exp. Sta. Tech. Bull. 340. parted to the soil by the superphosphate, par6. Reitz, H. J., et al. Recommended fertilizers and ticularly in the top 12 inches, and (4) there Sta.Bull 36 1954.tu.Unv f l.Ag.Ep was somewhat more exchangeable K found 7. Reuther, W., F. E. Gardner, P. F. Smith and as a result of increased phosphate but the ext.ial with oranges n Flida. Proc a.ate eort changeable Ca and Mg were unaffected and Sec. 61: 44-60. 1948i.SmtadA..Sph.A8. Rethr W. P. F. Smt n AW. 44eht Ac.there were no differences in the total amount cumulation of the major bases and heavy metals in Florida citrus soils in relation to phosphate fertilizaof Cu, Zn, or Mn regardless of treatment. tion. Soil Sci. 73: 375-381. 1952. N9. Smith, P. F. and W. Reuther. Mineral content of Noneof hes fining ca be onsrue as oranges in relation to fruit age and some fertilization being high beneficial to the culture of citrus. practices. Proc. Fla. State Hort. Soc. 66: 80-86. 1953. 10. Smith, P. F., and W. Reuther. Preliminary report on the effect of nitrogen source and rate and LITERATURE CITED lime level on pH, root growth, and soil constituents in 1. Bryan, 0. C. The accumulation and availability of a Marsh grapefruit grove. Pro. Soil Sci. Soc. Fla. IS: phosphorus in old citrus grove soils. Soil Sci. 3S: 108-116. 1955. 245-259. 1933. 11. Spencer, W. F. Phosphatic complexes in the soil. 2. Chapman, H. D. and D. S. Rayner. Effect of Ann. Rpt. Fla. Agr. Exp. Sta. P. 193, 1952; p. 218, various maintained levels of phosphate on the growth, 1953. yield, composition, and quality of Washington navel 12. Wander, 1. W. The effect of calcium phosphate oranges. Hilgardia 20: 325-358. 1951. accumulation in sandy soil on the retention of 3. Ford, H. W. The influence of rootstock and tree magnesium and manganese and the resultant effect age on root distribution of citrus. Proc. Amer. Soc. on the growth and production of grapefruit. Proc. Hort. Sci. 63: 137-142. 1954. Amer. Sue. Hort. Sci. 55: 81-91. 1950. STARTING AND MAINTAINING BURROWING NEMATODE-INFECTED CITRUS UNDER GREENHOUSE CONDITIONS WILLIAM~ A. FEDER AND JULIUs FELDMESSER Studies, which will be reported elsewhere, indicate that the burrowing nematode will Fruit and Nut Crops Section and infect and reproduce 'readily in citrus seedNematology Section lings growing under normal greenhouse conHortculuralCros Reearh Brnch ditions in Florida. It was also found that HortculuralCros Reearh Brnch grove subsoil, turned up while digging for Agricultural Research Service nematode-infected roots, contained many United States Department of Agriculture small nematode-bearing root fragments, and that citrus seedlings planted into this soil in Orlando pots under greenhouse conditions were read 'ily infected and supported a burrowing nematode The current nematode research program population, requires the use of large numbers of burrow.hs .bevtoswr tlzdi ud ing nematode-infected citrus seedlings as Teeosrain eeuiie ud well as a large and reliable supply of burrow-. ing the construction of two drained concrete ing nematodes. Large numbers of infected soil tanks. These concrete block tanks were seedlings are needed for the chemical screenconstructed on a 4-inch thick, poured coning program and for various biological studies crete slab and the soil-bearing portions had and other fundamental work. Obtaining suf inside dimensions of 10' x 4' x 2' and 16' x 4' fcetburrowing nematodes from naturally x 2', respectively. The bottom of the soilinfected grove trees requires a great deal of bearing portion of the tank is raised one block time and labor. A method of raising and mainwidth above the concrete slab and is containing burrowing nematode populations on structed of /'"' No. 9 expanded metal resting citrus in the greenhouse was, therefore, deon cross bars of 2" x 2" x 4" angle iron. The vised. metal surfaces are all coated with red lead

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30 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 prit ier itil(d )s h i it i Ii ) ( (o le( I sill 1-i Y (' atlid w 'rl c' litivat e(I alid fertilized ill a a1 l e()rosiI (li T lii is l()\\I tinitito( nloini r. It wls folild that the small ill Fi. I. r(ot friioeits, wdIlich seemitiglv contained 0w bulk of tematOdes found in the subsoil, di( not wiash (S()wt upmt watering, bu t instca~d, some \worked to the surface of the soil, if wtterig w-as excessive. It was necessary to us h them bclow the surface when this ocCI irred. Water, which Cleached through the soil, \\its Collected in lairi.e palls and examined periodically for the presence of burrowing tes. T() date, niiitirrowing nemiatodes Li x been recotver(d from the leaching water. After 6\ week., burrowing -nematode -inNedtt Seedlilts \ere harvested from the tank. These seedIlinffS bore few to manix lesions Fig. 1. Inside of soil tank shoving cross supports, Oni titt roots tiand all states of the borrowing expanded metal bottom, and a portion of the walls. ncinatod were tfotnd withiii the lesions. The stall er tank holds about 1,300 growing seedIt filling the tank with soil a 2-inch layer lins when loaded to capacity, and the larger of Nt" lime rock was first potired onto the exotne about 2,100 seedlings. Seedlings usually pailded l metal bottom. Sterilizd field soil was are roiwn 3 months in[ the tank before they then placed on the lile rock layer to a depth anr harvested. This period is sufficient for of .4 inches. FiTniall tite r jmaiti ) space iij heim to oercotm thei initial shock of traitsthe tank was filled withI the te Itquired lonpilatltilg and to develop an adequate top ber of yards of sobsoil taket from beneath and root system. Danping off occurs infretrees kilown to harbor the birrowitng t emquietly and is controlled byi applications of Atode in their roots. This soil was brought wettable captain to the soil between the rows. from the grove in closed Ital 'rbage catis It order to miiiiniize trap-croppitig, a fex to ivoii colititaittitilhol of citrus plainttiings infected roots are cut ttp) and buried after each etroute. The soil it the tinik was wet dtwn row of seedllittgs is (d11ig 1i). In this manner, iad tamped and iiltwcd to settle for a fc\w ant active hurrowit ig litematode population has days. Seedlints of Bottlh letoitl altof DUnnitat beetnvl matinttined in one tank since January gra pcfrtit anud -(cds (of both these varieties 1t56. This populatioti has now survived a were theil plaIted int the tatik it rtws, and witIter and a summer itI the tank under normal the row\s were imirkedo with plitntbtitng dite and grtrtlhlloise conditions. Approximately. 800 intype of miaterial planted. These platltin g.s feeted seedlils(s have bet harvested since wvere wiatlre(d careftih to avoid waterr
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GRIMM: DIEBACK INVESTIGATIONS 31 PRELIMINARY INVESTIGATIONS ON DIEBACK OF YOUNG TRANSPLANTED CITRUS TREES' GORDON R. GRIMM 'PROCEDURES AND RESULTS Horticultural Crops Research Branch Temple orange and Glen Navel orange on Cleopatra mandarin rootstock, 312 and % inch Agricultural Research Service in diameter, were used in transplanting tests Unitd Sttes-Deprtmnt o Agiculure to determine the effect of top pruning, the abUnitd SatesDeprtmet o Agrculure sence of fibrous roots, and defoliation. TransOrlando planting experiments were begun in November and March at the U. S. Department of INTRODCTIONAgriculture experimental farm 7 miles west of INTRODCTIONOrlando, Florida. Each experiment was comDieback of transplanted citrus trees refers posed of eight treatments with eight trees to a progressive dying of a pruned branch or each replicated four times, making 32 trees trunk from the cut surface toward the root. It per treatment (table 1). Each treatment was has been recognized in Florida for as long as a combination of three separate operations; groves have been planted. Usually the losses e.g., the trees for treatment I had branches, from this disease have been minor, but within fibrous roots and leaves; those for treatment' the past few years they have increased suf8 had their branches, fibrous roots, and leaves ficiently to warrant investigation. Large acreremoved. Branched trees were pruned to ages have been planted at all seasons of the leave 4-to-6-inch branches; the trees without year, and it has become apparent that losses branches were pruned to trunks approximately of young trees from dieback have increased 16 inches high; all fibrous roots and all leaves disproportionately with the increased acreage remaining after top pruning were removed planted. with pruning shears in the groups indicated. A sudyof he atue ad cuseof iebck The trees were planted with a 5 x 5 foot wA startdy ren the natretndodss of treans spacing and the entire area was kept free of planting citrus trees. No general agreement wes was found among growers or nurserymen as Excellent, good, fair, and poor were used to to the best method of transplanting. Practices describe the subsequent growth of the tree. An in top pruning the trees varied considerably. excellent tree had little or no dieback on the Methods of handling, watering, and subsecut branches or main trunk and vigorous quent care also varied. A diversity of opinion sprout growth; good and fair trees bad relaprevailed on the importance of fibrous roots tively increased amounts of dieback and relaand of the leaves at the time of transplanting. timely decreased sprout growth; poor trees To determine the role of all of the various either had died back far enough to make resteps involved in transplanting on the inciplacement desirable or were dead. Observadence of dieback, controlled experiments were tions were continued until no further changes performed under field conditions. In con. in growth habit were apparent. junction with these tests, laboratory isolations TalIshwtenubrofxcln, wssecae tohdete thes disease good, fair, and poor trees withm each treattment for the November and March plantings. tAs a group, trees with fibrous roots present and donationof citrus tr ees knowme Mr Che F. Fat were distinctly better in both the November Jrorando Fla. rser:ake and March plantings than those with fibrous Nurseries Co., Winter Haven, Fla.; Grand Island Nurroots removed. As a group, trees with branches series, Eustis, Fla.; and Ward's Nursery, Avon Park a Fa. preen were bete tha tre with branches

PAGE 49

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GRIMM: DIEBACK INVESTIGATIONS 33 Table 2. 14aan inches of dieback and new sprout growth 6 weeks after .transplanting Parson Brown orange trees, as influenced by exposure, defoliation, and delay in initial watering Treatment Dieback Sprout growth in. in, Exposlure to the sun 0 hour 1.58 32.53 1 425**17.02*** 21 5.12***, 3.85*** Lesives present 3,02 18.99 Leaves removed 4.28* 16.i6 Watering at planting 3.59 17.63 delayed for 3 hours 371 -17,97 *Indicatestatistical significance at odds of 19:1 ***Indicates statistical significance at odds of 999:1 The results are summarized in Table 2 in 6 percent of the trees showed measurable terms of average inches of dieback of the dieback, and this seemed to occur regardless main trunk and average inches of total Dew of the presence or absence of wound paint. sprout growth per tree for the respective Several fungi and an unidentified bacterium treatments. Trees exposed to the sun for 133 have been isolated from trees affected with or 21/ hours prior to planting bad considerably dieback. However, investigations to date have more dieback and less sprout growth than not shown any one organism to be consistently trees that bad been protected from drying associated with dieback. Colletotrichuln gloeowith wet sphagnum moss. Statistically the difSporioides was isolated from 60 percent of the ferences are very highly significant. It should trees; Diplodia natalensis, Phomlopsis citri, also be noted that trees without leaves at the Fusarium spp., and bacteria were isolated from time of transplanting had significantly more 10 to 30 percent of the trees. dieback than trees with leaves at the time of DSUSO transplanting. ,Time of initial watering did Dsuso not affect the amount of dieback or sprout Field observations and experimental data growth of the trees in this experiment. indicate that dieback of transplanted citrus trees is largely a result of mishandling the Preliminary observations on the effectivetrees at some point during transplanting. ness of various pruning paints for the control Transplanting citrus trees involves many opof dieback were made during February, erations such as pruning, digging, transporting, March, April, and May on sweet orange trees planting, watering, and fertilizing and any one with various amounts of top pruning and deor all may be done carelessly enough to injure foliation, De-Ka-Go, Carbolineum, and pastes the tree. Environmental conditions at the time of Zineb, Orthocide, and neutral copper were of operations, such as temperature, humidity, applied to the cut surfaces immediately after wind and water, and soil characteristics may pruning and before the trees were dug at the also have direct influences oil the success of nursery. The treated trees were planted at transplanting. random with non-treated trees and compariThe presence of healthy fibrous roots and sons were made in the same planting. Only their protection from drying at all times have

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34 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 proved to be important for vigorous tree fibrous roots, leaves, and branches, coupled growth, which apparently provides the best with the fact that at present nIO One organism defense against dieback of transplanted citrus has been isolated consistently from all dietrees. back trees, suggests that good transplanting The presence of leaves can have a marked methods offer the best control of this disease. influence in preventing or checking dieback of It is evident that during transplanting of citrus the tree. It is not uncommon for dieback to the entire tree, particularly the fibrous roots, proceed down one side of a limb or trunk on should be protected from drying at all times. which no leaves are present and to stop on Once the tree has been set in the grove it the other side at the first leaf. Exactly bow a should be watered at planting and again the leaf stops dieback is not known; it may be second or the third day afterward; and, in only by sustaining healthy tissue through the Central Florida sandy soils, every 3 to 5 days normal leaf functions. Even though the leaves thereafter for the first few weeks as weather are lost shortly after planting, they may be conditions require, beneficial to the tree during transplanting. In SUMMARY the third experiment, trees with leaves during Dieback and new sprout growth of young exposure to the sun lost their leaves 2 or 3 transplanted citrus trees were measured in re-days later, yet they had significantly less die0 nation to (1) top pruning, (2) defoliation, (3) back than trees without leaves. root pruning, (4) exposure of the entire tree From the data obtained thus far it would to the sun before transplanting, and (5) deseem advisable to top prune trees only modlayed watering after transplanting. The preerately, maintaining 4-to-6-inch branches, This liminary results indicate that dieback may be was particularly true for fall-planted trees, a result of injurious transplanting operations. which were larger and stronger, and had less Healthy fibrous roots were shown to be very dieback 4 months after planting. Incidental important for vigorous tree growth and to observations have shown that the advance of constitute one of the best defenses against dieback down a branch is often checked temdieback. The presence of leaves appeared to porarily and sometimes permanently at the be beneficial in limiting the amount of diecrotch. back, especially in fall-planted trees. A causal organism of dieback cannot be enInvestigations to date give no definite intirely ruled out. However, the fact that a tree dications that fungi or bacteria are primary has less dieback because of the presence of causal agents of dieback. THE POSSIBILITY OF MECHANICAL TRANSMISSION OF NEMATODES IN CITRUS GROVES A. C. TARJAN dispersal of the organism has been impleFlorda itrs EperientStaionmented mainly by the widespread disseminaFlorda itrs EperientStaiontion of infected citrus nursery stock and other Lake Alfred cultivated plants. It generally has been assumed that various implements and mechanThe somewhat phenomenal spread of the ical devices also play a role in the spread of burrowing nematode, Radopholus similis the burrowing' nematode as in the case of (Cobb) Thorne, in recent years has been atcertain other plant pathogenic nematodes tribute to subsoil drainage (3), to the move(1, 2, 5). Although shovels, cultivators, and meant of the nematode itself, and to the acmobile harvesting machinery have been imtivities of humans (4). This latter means of plicated, it was suspected that bulldozers *were mainly responsible. The "pull and treat" Series, No. 529.utrlEprmn tto ora program (6) of the Florida State Plant Board,

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TA-RJAN: TRANSMISSION OF NEMATODES 35 which is accomplished by the destruction of been suspected that other species are capable burrowing nematode infected citrus and subof inflicting serious root damage. Likewise, in Sequent soil treatment with D-D soil fumithe "Suspected Plant Parasite" group, the gant, uses bulldozers for elimination of desiggenus Dorylahnus probably contains species nated trees. The machines enter the groves, that are plant parasites as well as those which fell the trees and place them in piles for burnare predatory in feeding habit, ing. If infested soil and infected roots were Data in Table 2 shows that most of the capable of being picked up and transported, samples obtained yielded from 26 to 75 nemathe bulldozers, with their undesired cargo, todes and that in no case did a sample fail to might be assigned on the following day to yield living nematodes. This is especially signieither clearing virgin land for future groves ficant when it is taken into account that the or pushing out old or undesirable trees to major part of this survey was conducted in make way for a new planting. In either case the winter and spring months of 1956 during it was assumed that nematode inoculum an extended drought. Occasionally a sample might, in this manner, be disseminated to nonconsisted of only a small number of apparentinfested land, ly desiccated roots and soil which was scraped With the cooperation of Mr. Charles Pouchoff the body of the bulldozer, while at other er, Florida State Plant Board, Lake Alfred, times the sample was found packed under and the various contractors involved in clearpressure in crevices in the tracks and had to ing infested grove sites, a study was underbe forcefully pried out. In one case, the taken to determine (1) if bulldozers and culmachine operator' had finished for the day tivators were carrying soil and debris infested and in an attempt at disinfestation had sprayed with nematodes, (2) the relative kinds and the tracks with diesel fuel, a substance which frequency of occurrence of these nematodes, has been assumed to be nematocidal. The soil and (3) whether clods of soil and debris insample, obtained about one hour after the fested with burrowing nematodes might be spraying, yielded numerous active, apparently suitable inoculumn for infecting potted citrus healthy nematodes when processed in the plants. The vast majority of the sites visited laboratory the next day. were groves affected by spreading decline, but Ironically, the only time that Radopholus in a few cases noninfested groves were also similis was obtained was from a sample taken inspected. Soil, including roots when availfrom a machine pushing out apparently able, was scraped off bulldozer tracks and healthy grapefruit trees for purposes of rewas obtained also from various locations on planting with orange. the "dozer" body. Samples thus obtained were stored in pint jars, returned to the The imposing list of plant parasites shown laboratory, and processed for nematodes. in Table 0 disproves the conception that such nematodes cannot possibly survive in soil During the course of this study, 63 samples clods or debris exposed to air and sun. Where, were collected from 23 different groves in in the case of certain plant parasites, adequate Lake, Polk, and Orange Counties. General of moisture is needed to prevent desiccation, nematodes identified are listed in Table I matter containing adequate moisture can be while the relative abundance of nematodes in found tightly packed on the bulldozer tracks, each of the samples is shown in Table 2. In one case, a bulldozer being transported by Nematode genera with saprozoic or predatruck was intercepted about two miles from tory feeding habits comprise the longest list the grove site in which it had been working. in Table 1. There were additional genera of As expected, numerous nematodes were obthis group that were not identified principally tained from the soil samples collected from because only spear-bearing nematodes were of the machine. primary interest in this study. The bulb and Although the foregoing data proved that stem nematodes, Ditylenchus spp. were the certain machinery is capable of disseminating most numerous among the plant parasites nematodes, the question remained whether found. Although many species of this genus inoculum thus translocated was capable of inare not parasites of higher plants, it has long stituting an infection at a new location. Con-

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36 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 sequently tests were conducted on potted to maintain as constant a soil temperature as seedlings simulating actual conditions as possible within the cans. Inoculum consisted closely as possible. of finely cut citrus feeder roots which were Thirty 9-month-old grapefruit seedlings moderately infected with burrowing nemagrowing in autoclaved soil in 46 oz. cans were toes. In simulating the physical state of podivided into five lots of six plants each. These tential inoculum as it had been observed on were placed evenly in large flats of autothe bulldozers, various combinations of inclaved soil, so that only the upper fifth of the fected roots, mashed citrus fruit, clay, and can projected above the soil. This was done soil were mixed and shaped by hand into Table 1. Genera of nematodes found in soil collected from bulldozers Plant Parasites Suspected Plant Parasites Sprozoites and Predators Tylenchulus (1) a/ Aphelenchoides (31) Rhabditis (17) Radopholus (1) Paurodontus (1) Diplogaster (5) Tylenchorhynchus (2) Dorylaimus (11) Acrobeles (8) Criconemoides (1) Xiphinema (3) Gephalobus (2) Tylenchus (6) Tylencholaimus (3) Tripylidae (1)b/ Ditylenchus (18) Pseudhalenchus (5) _e/ Diplogasteroides (2) Meloidogyne (1) Belondira (1) Rhabditolainus (1) Dolichodorus (4) .Nothotylenchinae (1) 1/Monhystera (2) Heraicycliophora (1) Aleimu (1) Pratylenchus (12) Prismatolaimus (1) Trichodorus (3) Acrobeloides (2) Hoplolaimus (2) Discolaimus (2) Rotylenchus (3) Mononchus (2) Belonolaimus (1) Vilsonema (2) Tylenchidae (2) b/Eucephalobus (2) Plectus (1) Aporcelaimus (1) Chiloplacus (1) Cervidiellus (1) Aphelenchus (10) a/ Numeral indicates frequency of occurrence. bfIdentified only to family or sub-family. c/New genus-technical descript .on currently being prepared.

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TARJAN: TRANSMISSION OF NEMATODES 37 Table 2. Relative number of nematodes recovered was combined with clav, crushed citrus fruit, from so i samples. soil, or any combination of these. These results, although derived from tests with notted seedlings, indicate that situations No, of Nematodes Frequency in Sanples cudarise in the field where nematode151 or more 12 infected inoculum might be carried into Don76-150 13 infested land, come into contact with the soil in a shaded area prior to or following a rain, 275 22 and could institute ant infection of host plants 11-25growing in the immediate vicinity. 11*-5 8010 or less SUMMAY none 0 A survey was undertaken in which soil and root samples were obtained mainly from the tracks of bulldozers employed in eradicating smal clds.All f teseinoclumcomincitrus groves afflicted with spreading decline. sml cld.Al of teeiourncm0 0 ations were either placed on or partially imTh is survey was conducted mainly during the bedded in the soil contained in the cans, some winter and spring months when the citrus area of which had been watered immediately prior had received a minimum rainfall. Sixty three to inoculation. This was done to approximate soil and root samples were collected from the condition where infested material bad tw Iytregoe nPlLkadOag either fallen from a bulldozer to the ground Counties. Fourteen different genera of known or had been pushed into the ground by the plant parasitic nematodes including Radophomachine tracks. Watering the soil in some of his similis, the burrowing nematode, were the cans simulated rainfall prior to inoculaidentified. Experiments were conducted in tion. After the inoculum was introduced which burrowing nematode infected citrus water was applied to those cans which bad roots in combination with clay, crushed citrus not been pre-wetted. One flat was placed in fruit, and soil were introduced into pots cona room provided with artificial illumination, a taining 9-month-old citrus seedlings. After constant temperature of approximately 78" F., inoculation, these plants were either exposed and a relative humidity which averaged about to sunlight or placed in shaded areas. Only in 80 percent during hours of illumination and the latter -case did plants incur burrowing 95 to 100 percent in total darkness. Two flats nematode infections. It is concluded that were placed outside exposed to sunlight, while mechanical equipment such as bulldozers are another flat was placed in the partial shade capable of transmitting nematodes which, of a slat house. A control flat containing under the proper conditions, can institute inplants which had received combinations of fections of citrus. nematode-free citrus roots, citrus pulp, clay LITERATURE CITED and soil was placed outside exposed to weath1. de Carvalho, J. Cj 1953. Ditylenchus destructor em Tuberculo-Semente Importado da Holanda. Rev. er conditions' Inst. Adolfo Lutz. 13: 67-74. Plants were harvested and screened for burvestigatin ot'n theB~eant Grass Nemtode, Anguina rowing nematodes by the root incubation Agrostis (Steinbuch. 1799) Filipjev, 1936, U. S. Dept. Agr., Pl. Dis. Rptr. 36 (3):75-83. technique (7) approximately 10 weeks after 3. DuCharme, E. P. 1955. Subsoil Drainage as a this experiment was initiated. It was found Factor in the Spread of the Burrowing Nematode. Fla. State Hort. Soc., Proc. 68: 29-31. that only plants which had been protected 4. Simanton, W. A. 1956. How Has Spreadjing Defrom exposure to direct sunlight, i.e. those cline of Citrus Spread ? Sunshine State Agr. Res. Rpt. 1 (3) : 5, 7. placed in the constant temperature room and 5. Steiner, G., A. L. Taylor, and Grace S. Cobb. thos >lcedin he lat ous beamein1951. Cyst-forming Plant Parasitic Nematodes and thos plcedin te sat ouse beameintheir Spread in Commerce. Helm. Soc. Wash., Proc. fected with burrowing nematodes. It did not 18 (1) : 13-18. appear to make any difference whether the 1955. Effien[,ess of the Phull and-Treat Methooko. plants were watered prior to or after inocula_ Controlling the Burrowing Nematode on Citrus. Fla. State Hort. Soc., Proe. 68: 36-38. tion, whether the inoculum rested oin or was 7. Young, T. W. 1954. An rneubation Method for inserted in the soil, and whether the inoculum Collecting Migratory Endo-parasitic Nematodes. U. S. Dept. Agr., Pl. Dis. Rptr. 38 (11): 794-795.

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38 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 TRANSMISSION OF T.RISTEZA VIRUS BY APHIDS IN FLORIDA PAUL A. NORMAN Leaf pieces from the T, and T2 sources were Entomology Research Branch used to inoculate greenhouse-grown citrus seedlings. The Valencia and Florida sweet THEODORE J. GRANT seedlings were considered to be nucellar, and Horticultural Crops Research Branch the Temple oranges were sexual seedlings Agricultural Research Service selected for characteristics of the parent varieUty. Presence of the tristeza virus in these U. S Deprtmnt o Agiculureplants was confirmed by retransmission with Orlando leaf-piece transfers to Key lime plants. The infected Valencia and Florida sweet seedlings The mild tristeza virus was transmitted were transplanted to a field and the infected from temple orange trees to Key lime. test Temple orange plants were kept in pots in a plants by two species of aphids in preliminary screen-house. Individual plants were reexperimental work (16). The green citrus checked by leaf-piece inoculations into Key aphid (Aphis spiraecola Patch) gave positive lime plants for proof of continued presence of transmissions to 9 of 128 test plants and the the virus in the young growth at the time of melon aphid (A. gossypii Glover) to I of 26 each acquisition feeding by aphids. plants. Higher ratios of infection have been In the previous tests (16), in the present obtamed m recent tests with the combined use tests with the black citrus aphid, and in of controlled sources of mnoculum in several studies of Meyer lemon as a source of virus, varieties of citrus seedlings, multiple-branched small Key lime plants 8 to 12 inches high within Key lme test plants, larger numbers of aphids single stems and 25 to 150 aphids were em. per plant, and timely observations to detect ployed. In the other tests healthy Key limes 18 initial symptoms. This report presents results to 20 inches high were cut back or the tops obtained with this improved technique. It inbent over to stimulate rebranching, and colcriminates the black citrus aphid (Toxoptera onies of 300 to 700 aphids were used. aurantii (Fonsc.) ) as a vector, and describes tests with other insects and mites, so far neg-. Pathological investigations had indicated ative, as vectors. Studies of Meyer lemon trees that the optimum time to observe initial sympas sources of inoculum are also discussed. -toms of vein clearing associated with the mild tristeza virus was 20 to 40 days following tisMETHODS sue inoculation. In insect-inoculated Key lime In order to establish tristeza virus in plants plants 30 to 60 days following infestation was of different citrus varieties, two Key lime found to be the optimum period. Thereafter plants (T, and T,) were selected as standard the symptoms might diminish, especially under sources of the virus inoculum. These plants summer conditions in the greenhouse. Initial had been infected in March 1953 as a result Symptoms did not always occur on all of aphid transmissions from a stunted Temple branches. The branches showing symptoms orange tree on a red lime (Rangpur type) were tagged so that they could be observed rootstock (16). Green citrus aphids were frequently and used for testing retransmission transferred to these plants after they had fed by means of leaf inoculations into Key lime on the Temple orange for 116 hours, 75 to plants. the T. plant for a 1-hour transmission feeding Isolated aphid colonies of single species period and 30 to the T, plant for 23 hours' were placed on young, succulent growth of feeding. Both these Key lime plants have been healthy citrus seedlings and allowed to feed used in other pathological investigations (8) for 24 hours, since previous tests with other and the reactions on the Key lime are considspecies (3, 5) had indicated that such feedered typical of the mild tristeza virus in ing would free them of tristeza virus. The Florida. yotng shoots with the aphids were then trans-

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NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION 39 ferred to the infected seedlings that had been TESTS WITH THE BLACK CITRUS APHID previously tissue-inoculated and tested, andthe aphids were allowed to move over voluntarily. One positive transmission of tristeza virus After a 25-hour period to acquire the virus, was obtained in five tests with the black citrus aphids on shoots from the infected seedling' aphid. In this test 25 alate adults and nymphs, were placed on the multiple-branched Key all reared from one adult, were given an aclime test plants in separate cages at the labor_ acquisition feeding period of 48 hours on an atory. Again the aphids were allowed to move infected Valencia orange scion grown on a over voluntarily.'At the end of 24 hours counts potted Key lime rootstock in the greenhouse. per unit of leaf area were used as a basis for The transmission feeding period was 4 hours. estimating the total number of aphids present Presence of the virus in the aphid-infected Key on each test plant. Representative aphid speclime test plant was confirmed by leaf-tissue imens were collected for positive identificatransfers. The identity of the aphid species tion. The test plants were sprayed twice with was confirmed by Louise M. Russell, of the 0.04 percent nicotine sulfate before they were Entomology Research Branch. This is the first transferred to, the greenhouse. record of positive transmission of tristeza virus TESTS W H GREEN CITRUS AND MELON APHIDS MEYERt LEMON As A SOURCE The results given in table 1, from tests OF TRISTEZA VIRUS carried out in March and April 1956, show Meyer lemon trees are present in dooryards that the green citrus aphid transmitted the or small plantings in most citrus areas. Some virus from three varieties of infected citrus Mever lemon trees have been found to carry seedlings to Key lime plants. All test plants tristeza virus (11, 17, 20), but investigations infested with melon aphids became infected. in Texas (4, 18) indicate that its spread from The proportion of successful transmissions by this host is not common. Because of the wide both species was much higher than in the interest in Meyer lemon as a host, tests were previous tests (16). made to transmit the virus from it. Three aphid Table 1.-rnmsinof tristesa virus by aphids from various citrus species were used as vectors. Colonies of 5 to seedlings to multipl0-branched Key lime plants. 50 apterous adults were employed. In 16 tests with the black citrus aphid and 21 tests with the melon aphid no transmissions were obTest P I -u b la r n tainted. In 107 tests where the green citrus Orson citrus aphid, aphid was used, 2 transmissions were secured. val~nia 30 3 1In the first positive transmission a Meyer 400 14 2 lemon tree at Minneola, Fla., was the source Floria ....t 304 3 of inoculum. Thii-ty apterous adult green Temple 4002 1 citrus aphids fed for 42,12 hours on this tree -elon aphids and 42 hours on the test plant. Scattered but distinct clearing of veins occurred on the young leaves of the Key lime test plant 5 months later. These symptoms became less In these tests initial symptoms of tristeza evident as the leaves matured, and subsequent were detected on one or more branches of the new growth showed no further symptoms. test plants 5 to 6 and, in one case, 8 weeks While these transmission tests were being carafter inoculation. New young leaves of inried out, budwood from the Meyer lemon fested branches showed distinct vein clearing branch that the aphids had fed on was and a veinlet pattern that frequently faded as brought to the greenhouse and side-grafted the growth matured. After the initial veininto 5 Key lime plants. All these plants showed clearing symptoms disappeared, some leaf strong veinand veinlet-clearing symptoms, cupping and deficiency signs remained, Preswhich were evident for a longer period and ence of the virus in all aphid-infected plants were more distinct than those observed on the was confirmed by tissue transmissions to adKey lime plant infected as a result of aphid additional Key lime plants. inoculation.

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40 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 The Meyer lemon scion on one of the graftTEST PLANTS AS A MEASURE inoculated Key lime plants was allowed to deof Vimus TiRANSMISSION velop, and subsequently green citrus aphids were fed on it for 24 hours and then transTristeza of citrus was first recognized as a ferred to two Key lime plants for another 24 disease of sweet orange on sour orange roothours. One plant, on which 75 aphids fed, stock. This scion-rootstock combination was showed no symptoms, but the other, on which used in initial studies, which showed that the 50 aphids fed, developed transitory leaf sympdisease is caused by a virus and can be transtoms 4 months later. This limited symptom mitted by tissue grafts (1, 6) and by Aphis expression of tristeza suggested that either the citricidus (Kirk) (1, 3, 13, 15). As informasource of inoculum contained only a very mild tion advanced, West Indian, Mexican, and Key tristeza-virus strain or the aphids had sorted lime plants were employed as means of deout and transmitted only a portion of the virus tecting this virus (9, 10, 14, 19). strain' mixture. The primary symptoms of vein and veinlet In~~~ ~ .re ooti uterifrain ef clearing and stem pitting on the Key lime ic traners nd btion gthrat erein maea. plants are useful. Improvements in the propheey ranses indoclate grathssee made. duction and detection of symptoms on the The ey ime inculted ithtisue rom test plants have been sought as means of obthe Meyer lemon at the end of 2 months tann0ute nomtino iu rnms showed striking veinand veinlet-clearing sinIn futher prnormatigionvrs transmissymtm.TeKyms ouae ihts standardized sources of inoculum, multisues from the aphid-transmitted source showed branched Key lime plants, large aphid popula-. only slight deficiency symptoms and a tendentions, and observations at critical periods have cy for slight cupping of some leaves. Three gIve ihrto vrstasiso ne months 'after the inoculations observations gier -spig ra dtiosnvs thremisoner ndrm weret tiade-iouthed roene Mee slem.To initial symptom expression in the summer sugpourcs badsserouaed ofro the anye 10iter gests that the Key lime plants are not as good s1ucenhadmeergs of tnd of phres pnt indicators of tristeza virus under high-tempertissue-nocumeters fo tm; tw opidiftree plnt ature conditions. Temperatures appear to aftisue-noclatd fom he phi-inectd Ky fect not only the occurrence of vein clearing lime source had no pits, and one plant had I on the leaves, but also stem-pitting symptoms, pit per 10 centimeters of stem. These results as noted by Grant and Higgins (8). show that a milder form of tristeza virus was Teitniyo yposo h etpat ahdtnwstransmitted by hssu Meerreanbyte also varies with the virus strain. Recent pathofphod thame wsouranmtcdbesu gat logical investigations indicate that the mild fromthesamesouce'tristeza virus in Florida may be a mixture of TESTS WITH OTHER INSECTS AND MITES strains (8). By use of the aphid-transmitted mild-virus source plants T, and T,, and with Tests were also made with other insects leaf-piece transmissions to Key lime plants and and mites found on citrus in Florida. The successive selections of leaf pieces and transsources of inoculum were tristeza-infected Key missions to other Key lime plants, evidence lime seedlings. Thus far there have been no was obtained of virus strains that cause many positive transmissions. The species tested as stem pits and some that cause few to no pits. vectors, with the number of Key lime plants Apparently the tristeza virus strains could infested, were as follows: green peach aphid exist in varying mixture levels in infected (Myzis persicae (Sulz.) ) 4, citrus mealybug plants. Work in South Africa (12) and Brazil (Pseudococcus citri (Risso) ) 49, leafhopper (7) has shown that aphids have transmitted Homnalodisca triquetra (F.) 35, blue sharpa mild foim of the virus from trees known to shooter leafhopper (Oncometopia undata be carrying the severe form. In the present (F.) ) 7, big-footed plant bug (Acanthocephastudy of Meyer lemon as a virus source, the la femorata (F.) ) 14, southern green stink two transmissions obtained by means of aphids bug (Nezara viridula (L.) ) 29, stink. bug produced notably milder symptom expression Euschistus obscutrus (P. de B.) 7, citrus red on Key lime plants than those obtained by mite (Metatetranychus citri (McG.) ) 8. tissue transmission.

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NORMAN AND GRANT: TRISTEZA VIRUS TRANSMISSION 41 TRANSMISSION OF TRISTEZA VIRUS seldom exceeded two new infections each year IN CITRUS GROVES from each diseased tree. They noted, however, that the most rapid spread was generally The green citrus aphid is the most abundant in th'e intermediate area where most orchards aphid on Florida citrus. It usually limits its were ruined commercially about five years feeding to seasonal growth flushes of succuafter the disease was first reported in them. lent terminals which vary with the citrus This area bad the largest number of flying variety and rainfall conditions, and its feeding aphids. curls the tender foliage. The black citrus aphid, In Florida the visible spread of the disease appearing later in the season, feeds on more has been greatest in a Temple orange grove mature leaves. The melon aphid, although ess where all trees were reported as being on sour prevalent on citrus than the green citrus orange rootstock. Actually some were growina aphid, is also found on young growth-e Recent studies in California (5) indicate onve t heat these tree scs anesevd itas bethat in four districts where measurements lievred rhttesers hav vrservephd asranswere taken the yearly average number ofavsoablenresevisboy dirseaseahd tr n s-u aphids of all species flying to a single orange mirain rtsnthevsil isak.te nsu tree ranged from 185,725 in the coast area to 956,238 in the area around Covina and The more infected trees available, the greatAzusa called the intermediate district' The er is the chance for aphids to acquire the virus respectiv Ie figures for the melon aphid alone and transmit it to other trees. In Florida the were 3,200 and 35,600. Since the melon aphid number of visibly diseased trees is not always is the demonstrated vector of tristeza virus in a reliable measure of the number of infected southern California, it is not surprising that trees, for frequently there are mixtures of the disease spread most rapidly in the interrootstocks. mediate district. Green citrus aphids made tip Surveys made by the State Plant Board of more than 85 percent of the aphids caught Florida (2) show -a widely scattered distribuflying to the orange trees, but neither this tion of tristeza-infected trees. These trees species nor the black citrus aphid has been serve as sources of virus, and as aphid infestashown to carry the tristeza virus in,'California. tions are not usually controlled by present We do not have comparable data for aphid spraying practices, the number of infected populations in Florida. However, our studies trees in the State may be expected to inshow that all three species are potential veccrease. tors of the tristeza virus. Each tristeza-infected tree serves as a reservoir from which the aphids can obtain The green citrus aphid was found to transthe virus. There are two types of reservoirsmit the tristeza virus from infected Valencia (A) an infected tree on a nontolerant rootand Florida sweet seedlings as well as from stock, as sour orange, which shows decline the Temple orange variety previously reported. symptoms and produces delayed, weak flushes The black citrus aphid was shown for the first of new growth; and (B) a tree on a tolerant time to be a vector of the virus. Seven other rootstock which has apparently healthy insects and one mite species did not transmit growth but carries the tristeza virus. The latter the virus. is a more dangerous source of the virus, beImproved techniques have given high cause the succulent flushes of new growth are. ratios of transmission by the melon and green suitable for aphid feeding and transmission of citrus aphids. The techniques utilize 9conthe virus at the time other normal, healthy trolled sources of inoculum in several varieties trees are flushing. The visibly diseased trees of citrus seedlings, multiple-branched Key (type A) seem to be less dangerous sources of lime test plants, 300 to 700 aphids per test, inoculumn because of their 10-day to 2-week and timely observations to detect initial sympdelay in producing new flushes of growth that toms. are less vigorous. In California Dickson et al (5) reported Transmissions of virus by the green citrus that the rate of spread of tristeza in the groves aphid from Meyer lemon produced notably

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42 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 milder symptom expression on Key limes than Further information on the reactions of grapefruits, limes, lemons, and trifoliate hybrids to tristeza. Calif. those obtained by tissue transfers to Key Citrogr. 36: 310, 311, 324-329. limes from the same Meyer lemon source. 10. Knorr, L. C., and W. C. Price. 1954. Diagnosis and rapid determinations of tristeza. Fla. Agr. Expt. REFERENCES CITED Sta .Rpt., pp. 196-197. 1. Bennett, C. W., and A. S. Costa. 1949. Tristeza -1l. McClain, R. L. 1956. Quick decline (tristeza) of disease of citrus. Jour.. Agr. Res. 78 (8): 207-237. ei rus. Calif. Dept. Agr. Bul. 45(2): 177-179. 2. Cohen, M., and L. C. Knorr. 1953. Present status 12. McClean, A. P. D. _1954. Citrus vein-enation viof tristeza in Florida. Proc. Fla. State Hort. Soc. 66: rus. So. African Jour. Sci. 50(6): 147-151 20-22. 13. McClean, A. P. D. 1950. Virus infections of 3. Costa, A. W., and T. J. Grant. 1951. Stu citrus2i(South Africa. Farming in So. Africa 25 (293); transmission of the tristeza virus by the vector Aphis citricidus. Phytopathology 41 (2): 105-113. 14. McClean, A. P. D. 1950. Possible identity of 4. Dean, H. A., and E. 0.. Olson. 1956. Preliminary three citrus diseases. Nature, (London) 165: 767.768. studies to determine possibility of insect transmission 15. Meneghini, M. 1946. Sobre, a natureza e transof tristeza virus in Texas. Jour. Rio Grande Valley missibilidade da doenca "tristeza" dos citrus. Biologico Hort. Soc. 10: 25-30. 12.: 285-287. 5. Dickson, R. C., Metta McD. Johnson, R. A. Flock 16. Norman, Paul A., and Theodore J. Grant. 1953. and Edward F. Laird, Jr. 1956. Flying aphid popular Preliminary studies of aphid transmission of tristeza tions in southern California citrus groves and their virus in Florida. Proc. Fla. State Hort. Soc. 66: 89-.92. relation to the transmission of the tristeza virus. 17. Olson, Edward 0., and Bailey Sleeth. 1954. TrisPhytopathology 46 (4): 204-209. teza virus carried by some Meyer lemon trees in 6. Fawcett, H. S., and J. M. Wallace. 1946. Evidence South Texas. Proc. Rio Grande Hort. Inst. 8: 84-88. of the virus nature of citrus quick decline. Calif. 18. Sleeth, Bailey. 1956. Occurrence of tristeza in Citrogr. 32 (2): 50, 88, 89. two citrus variety plantings. Jour. Rio Grande Valley 7. Grant, T. J., and A. S. Costa. 1951. A mild strain Hort. Soc. 10: 31-33. of the tristeza virus of citrus. Phytopathology 41(2) 19. Wallace, J. M., and R. J. Drake. 1951. Newly 114-122. discovered symptoms of quick decline and related 8. Grant, T. J., and Richard P. Higgins, 1956. Oc-. diseases. Citrus Leaves 31: 8, 9, 30. currence .of mixtures of tristeza virus strains in 2 alcJ ..C .OehleadJ .J a Hofmeyer. 1956. Distribution of viruses of tristeza 9. Grant, T. J., A. S. Costa, and S. Moreira. 1951. and other diseases of citrus in propagative material. Studies of tristeza disease of citrus in Brazil. V. U. S. Dept. of Agr. Plant Disease Rptr. 40(): 3-10. PHYSIOLOGIC RACES OF THE BURROWING NEMATODE IN RELATION TO CITRUS SPREADING DECLINE E. P. DUCHARME' ANDW. BIRCHFIELD' rowing nematode, it is important to know The urroing ematde, adopo .sn.whether physiologic races of burrowing nema(todes occur in nature and whether there are a s(Cbb T*re-s ow nan oaarsiiz. ..more than 125 different species of plants. races that do not parasitize citrus. A physioloSome species show no evident effects of the gcrc sgnrlyudrto ob dni cal with the species in morphological respects parasite, whereas other species such as rough bttodfe frmiins eapct fis lemon suffer severely. Many of the susceptible phsogysuhaprsism species are grown as ornamentals around homes and, if parasitized by burrowing nema.a a a ..an .spetm r fe lne n todes, may be a source of infection for citrus .bu irsgoe odrn aemrhs growing close by. If all the burrowing nematodes that parasitize these plants are alike. then any infected plant could spread the in-. .eto tnerycr. O h te ad physiologic race of burrowing nematodes that should some colonies of burrowing nematodes difr.rmtebrown eaoe asn be ~ ~ so .pcaie htthyd o edo spreading decline came from such a clump of baan pats.Te Aan rot er havl citrus, then their presence on host plants .. would not be a threat to adjacent groves. Be. Sthe citrus roots were not. Roots from this location were examined four times during the folFlorida Agricultural Experiment Station Journal lowing year. Each time the citrus roots were Series No. 540. free of burrowing nematodes although the /Florida Citrus Experiment Station. Lake Alfred. -. 2/Florida State Plant Board, Gainesville, Florida. rus roots were intermingled with the para-

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DUCHARME AND BIRCHFIELD: PHYSIOLOGIC RACES 43 sitized banana roots. Attempts to infect the lemon roots and attacked the banana roots as roots of sour orange seedlings with burrowing well. 50 0 ~ nematodes from this location were not successIn another study, nematode-free sour orange ful. The burrowing nematodes from this locaseedlings and banana plants growing in steamtion, although they would not feed on citrus, sterilized soil were cross-inoculated with burcould not be' distinguished morphologically s from those causing spreading decline. in this in the preceding experiment. The soil temdiscussion burrowing nematodes that parasitperature was maintained at 75" to 78* F. The ized banana but not citrus will be designated burrowing nematodes from banana reinfected as the "banana race." Ibanana but not the sour orange seedlings, and Clumps of banana plants in or next to 39 those from a spreading decline affected grove citrus groves and other clumps in 30 locaparasitized both the sour orange and banana tions where there was no citrus were examined test plants. The results of these experiments for presence of burrowing nematodes. In the confirmed the existence of two of the three 39 locations next to groves, the citrus and physiologic races found in the field. banana plants were close enough for root conBurrowing nematodes that cause spreading tact. Among these places examined, burrowdecline are physically like those of the banana ing nematodes had parasitized banana but race. The average length and width of female not citrus in 9 locations, both banana and nematodes from both races was almost identicitrus in 4, and only citrus roots in 3. No cal and there was no significant difference in burrowing nematodes were found in the rethe physical proportions. No morphologic mining 23 locations. Of the 30 isolated character was found that Could be used to clumps of banana, 13 were parasitized by burdistinguish one physiologic race from the rowing nematodes and 17 were not. None of other. The two physiological races of the burthe parasitized banana plants appeared to be rowing nematode' (Radopholus similis) that diseased, whereas all infected citrus bad have been found in nature have been separated symptoms of spreading decline. These obonly by differences in parasitic activity on servations indicated the existence of three citrus and banana. The existence of a possible physiologic races of burrowing nematodes, third race, found in the field on citrus only, separable by their ability to parasitize either was not studied in the laboratory experiments banana or citrus or both. undertaken. Experiments were conducted under conit is likely that other physiological races of trolled conditions to test the hypothesis dethis nematode can be detected by using addirived from observations made in the field that tional species of host plants. Burrowing nemaat least three strains of burrowing nematodes todes collected from several kinds of ornaexist. In the first experiment, sour orange seedmental plants failed to parasitize citrus in exlings planted in sterile soil maintained at ploratory tests, possibly because they may be temperatures of 7 5" to 78' F. did not become similar to the banana race. On the other hand, parasitized when inoculated with the banana we know that the physiologic race causing race of burrowing, nematodes. In another exspreading decline will infect Persea americana periment, nematode-free banana plants and Mill., (avocado); Malpighia glabra L., (Barrough lemon seedlings planted side by side in bados cherry); Hedychittm coronarium Koenthe same container were inoculated with colig, (ginger lily); and Musa paradisiaca var. lections of the banana race and the race sapientum Kuntze, (common banana in Floricausing citrus spreading decline. The inocuda). At present it is not known how many lated test plants were grown for six months physiological races of the burrowing nematode with the soil temperature maintained at '75' to are involved in the spreading decline disease 78" F. The burrowing nematodes from banana of citrus, but the existence of such races could infected the banana test plants, but not the explain some of the variation that occurs in rough lemon seedlings although the roots of the severity of disease expression among afboth plants were intermingled. In contrast, the fected groves, In the search for resistant citrus burrowing nematodes from a grove affected by rootstocks, it will be necessary to test prospecspreading decline readily parasitized the rough tive plants against different populations Of 0

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44 FLORIDA-STATE HORTICULTURAL SOCIETY, 1956 burrowing nematodes from numerous locathere is some practical way to distinguish these tions. races, it is necessary for growers to take utSince one of the physiological races paramost precaution to avoid introducing any bursitized both citrus and banana, it becomes rowing nematodes by planting infested ornanecessary to determine which race is present mentals in or next to citrus groves. The existbefore deciding whether or not infected banence of physiologic races of burrowing nemaana or other plants should be considered potodes does not minimize the gravity of the tential reservoirs of infection for citrus. Until spreading decline problem. CITRUS ROOTSTOCK SELECTIONS TOLERANT TO THE BURROWING NEMATODE HARRY W. FORD Ten trees were entered in the test program. Florida Citrus Experiment Station The sweet orange scions of two trees were suspected as the source of the tolerant factor and Lake Alfred were therefore included in the test program The purpose of this paper is to report the and coded sweet oranges E and F. Two trees evaluation of certain rootstock material that were seedling sweet oranges and were coded seemed to show resistance to spreading desweet oranges G and H. One tree was a seedcline. Spreading decline caused by the burling of Cleopatra mandarin and coded Cleorowing nematode Radopholus similis (Cobb) patra I. The rootstocks of four of the trees apThorne (7) generally affects all citrus rootpeered to be rough lemon and were coded stocks used commercially in Florida. Between rough lemon. The abbreviated designations 1951 and 1955, a total of 54 trees were found were RL-A, RL-B, RL-C, and RL-D. The that appeared healthy although surrounded by rootstock of the last candidate was unidentidecline trees. The trees were reported by Exviable as a common citrus species and was periment Station personnel, extension workers, coded Clone X. production managers, growers, and inspector' In order to obtain test material, roots of of the Florida State Plant Board. Most trees the desired tree were severed and both cut were eliminated as possible burrowing nemaends of each root lifted above the surface of tode resistant candidates after a preliminary the ground and tied to stakes.: Five to 40 perinspection. A few trees showed potentialities cent of the severed roots of rough lemon and worthy of intensive study for burrowing nemafive to 12 percent of sweet orange stocks protode resistance. ducked sprouts. The sprouts were permitted to METHODS grow until eight to 15 expanded leaves were The feeder roots of each tree recommended present. The sprouts were removed and cut for study were sampled for the presence of into leaf bud cuttings by severing the stem the burrowing nematode by the root incuba-above and below the bud with pruning shears. tion technique suggested by Young (10). A Henceforth the term cutting will be used in feeder root distribution pattern was compiled this report to indicate a rooted leaf bud cutting for comparison with a representative standard in which the bud has developed into a leafy for healthy trees. The method of root sampling shoot. The propagating procedure is conis described in mother papei (4). Trees were tained in a separate report by Ford (3). accepted as candidates for the test program if Root sprouts of promising candidates have the root profile compared -favorably with that -been topworked to older citrus trees to obtain of a healthy tree even though burrowing seed to determine if the nematode tolerant nematodes were found associated with the factor is seed transmitted. roots. Forty-four of the 54 candidates were The following tests were performed to evaleliminated by this test. tate the material: I. A candidate rootstock Florida Agricultural Experiment Station Journal clone was first evaluated by comparing the Series No. 551. rowth of six cuttings planted i sub-soil i-

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FORD: CITRUS ROOTSTOCK SELECTIONS 45 fested with the burrowing nematode and six Clone X were grown in decline sub-soil to cuttings in non-infested citrus grove sub-soil. determine the influence of N and K on the Separate 1.25 gallon containers were used for population of burrowing nematodes. Two each cutting. The containers were placed in a levels of N and K in factorial combination water cooled temperature tank that maintained were applied as nutrient solutions twice weekly the soil temperature at 78' F. The plants in for four months. The following concentrations each container of decline soil were inoculated in ppm were used: N, 25 and 200; K, 0 and three times with burrowing nematodes ob300. Also, 24 cuttings of Clone X were ditained from different commercial groves. The vided into two groups. One group was planted cuttings were permitted to grow for three to in burrowing nlematode infested soil and the six months depending on rate of growth and other in non-infested soil. Each group was time of year. sub-divided into two groups of six plants each I1. Six Clone X cuttings were planted in to which two levels of N were applied. Nitrocontainers filled with steam sterilized soil. gen at 25 and 210 ppm in the nutrient soluTwo hundred hand picked burrowing nemation was applied twice weekly. todes were placed on the roots of each plant V. The ability of the nematode to peneand permitted to develop for six months. rate the feeder root, lay eggs and reproduce was determined by an aceto-osmic staining II1. Six months old cuttings of RL-A, RL-B, procedure developed by Tarjan and Ford (8). and Clone X were budded with Parson Brown, Rooted leaf-bud cuttings of clones RL-A, RLValeemandgraefrit sion byusig a B, and Clone X were planted in'sterilized soil patch bud technique (2). Three to six months in separate petri dishes with a one half inch after budding, the plants were tested for square of No. 41 Whatman filter paper under growth and nematode infestation im the temthe root tip. Twenty-five female burrowing perature tank. nematodes in 0.3 ml. of water were placed on IV. Sweet orange E and sweet orange F the root tip and covered with a layer of soil. were budded on susceptible rough. lemon seedThe inoculated roots were stained and cleared, lings to determine if nematode tolerance in after two to 26 days at 78* F. under artificial The roots could be induced by the scion of a light, so that nematodes and eggs could be budded tree. seen inside the roots. V. Twelve cuttings of RL-A, RL-B, and VII. The number of eggs in the cortex and Table 1. Root distribution of the parent tree of selected rootstock clones as compared to susceptible rough lemon. Rootstock clone Feeder roots in indicated 10 inch depth zones 0-10 10-20 2C-30 30-40 40-50 50-60 Total Clone X -9.2 11.2 160 12.6 8.8 5.9 63.7 Rouh lemon B 1.9 6. 20 uh lemon C 3.o 2 .2 .1 6.9 Ro 1. 1. .5 Rou,-h lemion P 3.9 2.2 4.4 3.3 .9 .3 15.0 Lemon (Check) -/.7 2.1 5.3 4.3 3.7 2.0 22.1 M Idean of 4 samples to a depth of 5 feet expressed as erams dry weiSht in a colum one foot square. b Sean o^ 120 trees 25 Years old in soil not infested with spreading decline.

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46 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 stele of the feeder root of Clone X as comVII1 From October 1955 to January 1956, pared to RL-A was determined by comparing fruit samples were collected from the Parson single roots from a cutting of each clone Brown scion of Clone X and compared with placed together in a petri dish. Fifty female Parson Brown on rough lemon. Measureburrowing nematodes were placed between ments were made of internal fruit quality. Apthe two roots and incubated for four days after pearance and palatability were evaluated by a which the roots were stained and cleared. panel. Table 2. Growth and R. similis population of cuttings from selected rootstock clones after 3-4, months in temperature tank Clone Soil Shoot Growth Fresh wt, Fresh wt. Number b Condition m. Shoot Roots R. similis (grams) (grams) 'Per cutting Rough lemon A Infested 45 28 21 117 ;L e81 Pon infested 48 30 26 Rough lemon Infested 1 7 34 25 201 113 Non infested 51 37 31 Oour-h lemon C Infe sted 39 32 23 123 .75 Pon infested 44 35 28 Rough lemon D Infested 43 46 61 352 :L 203 Non infested 51 55 66 Sweet Orange E~c Infested 29 9 7 25 :L 11 Non infested 38 12 12 Street 10range c Infested 29 16 13 37 :t 16 !:,on infested 35 22 16 Sweet Cran -e G d Infested 4 .4 39 :L 21 Pon infested 9 7 5 Sweet Orange Ed Infested 5 3 2 41 :t 11S on infested 7 4 3 Cleopatra I Infested 10 2,12 seedling Yon infested 24 5 3 Clone X Infested 28 45 !19 3 i3 Yon infested 27 37 3 a 1ean of 6 plants front separate containers. b Incubated in fruit jars for 4 hours. 7 The scion of a tree being tested as a potential rootrtock,. d Parent plant a sendlin!tree. e Standard dleviation of the mean.

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FORD: CITRUS ROOTSTOCK SELECTIONS 47 Table 3. Growth and R. s imilis population of clone X cuttings in steam sterilized soil inoculated with 200.R. similis per plant, Treatment 3 months 6 months Shoot growth Shoot aib Number' Shoot growth ShootzraibNumberaw cm. Ro-t R. similis cm. Root R. similis per -cutting per cutting Inoculated 21 .9 2 2 49 .9 1 t I Untreated 19 .9 47 .8 a Mean of 6 plants from separate containers. b Fresh weight of shoot divided by fresh weig[,ht of roots. SPlants removed froia containers and roots incubated in fruit jars for 48 hours. RESULTS depression of growth by the burrowing neIn Table I feeder root measurements of the matode.e etofab d dsc non e atd parent trees of four rootstock candidates grow, Sur viVal and plant growth of RL-A, RL-B, and ing in decline soil are compared with the root Clone X is presented in Table 4. Growth comdensity of trees on ordinary rough lemon in parisons between grafted combinations of the non-infested soil. Rough lemon B had a root different clones are not entirely valid because density comparable to a healthy tree to a all of the tests were not Iperformed at the same depth of five feet while Clone X had three time. Growth of grapefruit and Parson Brown times the root density of ordinary rough lemon. scions on RL-A was reduced 10 and 18 perThe growth and burrowing nematode incent respectively. The Valencia bud on RL-B festation of cuttings taken from 10 candidate was taken from the parent tree of RL-B so rootstock clones is shown in Table 2. Shoot, that the budded combination was genetically growth of RL-A and RL-B was reduced seven the same as the original tree in the field. This percent by the presence of the burrowing combination showed a 10 percent reduction nematode. Both rough lemon clones supported .in growth. The growth, of cuttings of Clone X a population of burrowing nematodes combudded with Parson Brown from the original parable to spreading decline susceptible parent tree was not reduced in decline soil rough lemon. There was no reduction in shoot and the burrowing nematode population comlength or root weight of Clone X when grown pletely disappeared. Studies of Ruby Red in burrowing nematode infested soil and the grapefruit and Temple budded on Clone X population of burrowing nematodes was rewere in progress only two months when this duced to a very low level in all replicates of manuscript was written. The burrowing nethe test. matode population consisted of two to four Nematode survival and plant growth when adult females. No larvae were present indi200 hand picked burrowing nematodes were eating that the nematode population was not placed on the roots of six individual cuttings increasing. Sweet orange E and sweet orange of Clone X in sterilized soil are shown in F when budded on susceptible rough lemon Table 3. After six months, the burrowing were retarded in growth 65 percent by the nematode population had disappeared from nematodes so that the results are not reported. the roots of 50 per cent of the cuttings and Unbudded cuttings of sweet orange E and F one to three nematodes were found on the were also reduced in growth (Table 2). The roots of the remaining plants. There was no data indicate that the two sweet orange clones

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48 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Ia Table 4 Growth and R. similis population of budded rootstock cuttings Graft comScion Soil Duration Shoot growth Fresh wt. Nwber b bination Condition (months) cm. of plant .similis Rootstock (grams) per cuttinF Rough lemon A Grapefruit. Infested 3 13 21 75 & 47 Non infested 14 28 Rough lemon A Parson Brown Infested 3 35 97 156 81 Non infested 43 124 Rough lemon B Valencia c Infested 3 26 -84 +. 23 Non infested 29 Clone X Parson Browne Infested 4 29 112 0 Non infested 30 103 Clone X Ruby Red Infested 2 .2 t 1 Clone X Temple Infested 2 4 1 1 a Mean of 6 plants from separate containers. b Incubated in fruit jar for 48 hours. c Combination genetically the same as original tree found in the field. do not have nematode tolerant characteristics Studies of burrowing nematode activity by that originate in the top of the trees as origstaining in sitit indicated that reproduction of finally suspected. burrowing nematodes was depressed in the The effect of N and K nutrition on nemacortex of the feeder roots of Clone X cuttings tode infestation of the host has attracted the as compared with the cortex of RL-A, RL-B3 attention of several workers (1, 5, 6). Oteifa or ordinary rough lemon cuttings. Oc(5) found that nutrition was of considerable casionally nematodes penetrated the stele imortance in determining the development of Clone X and after 21 days there was an intilne of root knot nematodes Meloidogyne increase in the nematode population. There was cognita. no indication of an exit of nematodes from the Nitrogen and K levels had no significant efstele. No burrowing nematodes penetrated the fect on the burrowing nematode population of stele of RL-A, RL-B or rough lemon under the RL-A, RL-B, and Clone X so that the results conditions of this experiment. Eighty-five tests are not reported. The growth of Clone X cutwere made on the rough lemon clones. Aptings was modified, by increased N and K, parently there is a difference between species from that reported for citrus in sand culture from the standpoint of burrowing nematodes (9). Additional studies are in progress to entering the stele. Nematodes were found in evaluate the -effect of nutrition on growth of the stele of pumnmelo, for example. Clone X cuttings. A detailed comparison was made between The effect of N level on growth of Clone X Clone X and RL-A by placing female burrowin infested as compared to non-infested citrus ing nematodes between single roots from each grove sub-soil is shown in Table 5. Shoot clone. The results of this test are shown in growth was not affected by the burrowing neTable 6. There were 60 times more eggs in matode infested soil condition at either of the the cortex of RL-A than in the cortex of Clone two N levels. X. In the cortex of RL-A eggs were scattered

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FORD: CITRUS ROOTSTOCK SELECTIONS 49 throughout the tissues while in tile cortex of identified as the cause of spreading decline. Clone X all eggs that could be found were RL-B, the rootstock of an 18 year Valencia close to the body of the nematode. When netree from a grove in southern Polk County matodes penetrated the stele of Clone X, a was transplanted into spreading decline soil condition that occurred in 11 percent of the in 1941. Thus the feeder roots have been insamples, considerably more eggs were found fested with the burrowing nematode for at per nematode. least 14 years. The tree was considerably A panel of Experiment Station personnel larger than surrounding decline trees even preferred the external fruit appearance of Parthough some feeder root damage was detected. son Brown on rough lemon to that of Parson Below five feet the root. density fluctuated Brown on Clone X. However the panel preconsiderably during a one year period. ferred Parson Brown on Clone X for eating The results of growing plants of RL-A and quality. juice characteristics of Parson Brown RL-B under controlled conditions in infested on Clone X and rough lemon are shown in soil and inoculation of individual roots in Table 7. petri dishes indicate that the two rough lemon DISCUSSION clones are reasonably tolerant to the damage RL-A was secured from the rootstock ot a of the burrowing nematode. The number of Valencia orange tree in Lake Alfred that bad burrowing nematodes and the damage within been in spreading decline infested soil for four the root cortex of the two tolerant clones are years prior to 1951. Dense foliage covered the comparable to susceptible rough lemon. The tree with leaves of normal size which was in nature of the tolerance of these rough lemon marked contrast to adjacent trees with sympclones is not understood; however, the rapid toms of spreading decline. The grove was rate of shoot growth and development of new pulled before the burrowing nematode was feeder roots is probably an important factor. Table 5. Effect of IT on F.Iros th and R. similis population of Clone i. cuttings in infested and non infested soil after 3 months in temperature tank Treatment Soil Sboot growth Shotratioc 'Number d Condition CM. Root R. similisd -per cutting Low Y Infested 26 1.3 6 + 3 t'on infested 23 1.3 High I Infested 29 1.0 3 t 2 Pon infested 27 .8 Significance N.S. IT.S. r.S. a ,.ean of 6 plants from separate containers. b 25 Ppm and 210 ppm of N respectively applied twice weekly. C Fresh weight of shoots divided by fresh weight of roots. dRoots incubated in fruit jars for 48 hours.

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50 FLORIDA STATE HORTICULTURAL SOCIETY 1.956 Table 6. Number of R. similis and eggs found in feeder roots of Clone X a and Rough lemon A cuttings four days after nematode inoculation. Rootst ock Cortex Steleo SI. -sI Is Lggs d.similis Eggs Rough lemon A 10.1 97.2 Clone X 5.2 1.6 3 9 Significance L.S.D. at .05 3.1 21.2 Fifty female burrowing nematodes placed between a feeder root of Clone X and a feeder root of Itough lemon A in a petri dish. b Mean of 35 replicates in which the nematodes invaded the cortex. SThe mean of 4+ replicates in which the nematodes invaded the stele. Statistical significance at 5 percent level. **.Statistical significance at 1 percent level. It is conceivable that the burrowing nematode Florida in 1954. The tree was 16 feet high and could damage RL-A and RL-B under poor yielded six boxes. Root samples taken at the grove management practices. This possibility periphery of the tree over an 18 month period will have to be evaluated under field condiwere devoid of burrowing nematodes. Feeder tions. At the present time RL-A and RL-B are roots from the four adjacent trees were alpropagated by cuttings although an evaluways found to harbor the nematode. With the action of seed propagation is in progress. It is exception of an area nine feet square near the essential that the seed produce a very high southeast corner of the tree, feeder roots of percentage of nucellar plants as assurance that adjacent rough lemon trees did not penetrate the rootstock will be genetically the same as the dense root system of Clone X. The rethe original parent. Tests for susceptibility to sistance of the feeder roots to the burrowing tristeza and xyloporosis are in progi-ess. nematode and the dense nature of the root Clone X, a rootstock that has not been idensystem suggests that the stock may also be tified, is resistant to the burrowing nematode of value as a biological barrier against the found in citrus groves. The clone is not comspread of the burrowing nematode. pletely immune because nematodes penetrated Fruit of Clone X are not available at the the feeder roots and in 50 percent of the present time so that all progeny have been plants one to .four nematodes survived three obtained from leaf bud cuttings. The clone is to six months. In every test conducted with more difficult to propagate and grows slower cuttings of Clone X, the rate of growth in nethan rough lemon. The leaves appear to be matode infested soil was equal to or better resistant to anthracnose caused by Colletotrithan in non-infested soil. Laboratory studies chum gloeosporioides Penz but susceptible to indicated that the resistant factor was consour orange scab caused by Elsinoe 'Fawcetti fined to the root cortex and had a detrimental Bitancourt and Jenkins. In containers, the roots effect on the eggs laid by the nematode. were more frequently damaged by excess The 25-year-old parent tree of Clone X water than roots of rough lemon. was discovered in a grove near Davenport, The reaction of Clone X to other diseases

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FORD: CITRUS ROOTSTOCK SELECTIONS 51 such as tristeza and xyloporosis is unknown to the root cortex and had a detrimental efat present, The stock should be evaluated in fect on the eggs laid by the nematode. The the field for general horticultural characterisabsence of information on general horticultural ties before being recommended for use in characteristics, mineral nutrition, tristeza and Florida citrus groves. xyloporosis, indicate that field tests must be SUMMARY evaluated before this clone can be recomBetween 1951 and 1955 a total of 54 trees mended for planting in Florida citrus groves. were found that appeared healthy although LITERATURE CITED surrounded by decline trees. Most trees were 1. Chitwood B. G. and B. A. Oteifa. 1952. Nemeliminated as potential burrowing nematode atoe parasitic on plants. Ann. Rev. Microbiol. resistant candidates after a preliminary in2. Ford. Harry W. 1956. Unpublished data. -3. Ford, Harry W. 195. A method of propagating spection. Ten trees were entered im the test .citrus rootstock clones by leaf bud cuttings. Proc. Amer. Soc. Hort. Sei. (In press). program. 4. Ford, Harry W., Walter Reuther, and Paul F. The results of growing cuttings of candiSmith. 1957. Effect of Nitrogen on root development of Vaeni orng tr----ees .Po. Amer .Sc. ot date clones in spreading decline infested soil .ci (I pres. c SdOtifa, B. A. 19 .Development of the root and noclatin o indvidal rots i er knot nematode Meloidogyne incognita as effected by dishes indicated that two rough lemon clones potassium nutrition of the host. Phytopath. 43: 171-174. were tolerant to the burrowing nematode 6. Oteifa, Bakir A. 1955. Nitrogen source of the even though a high population of burrowing host nutrition in relation to infection by a root-knot 6 nematode Meloidogyne incognita. Plant Disease Renematodes was found on the roots. Growth porter 39 (12): 902-903. 7. Suit, R. F., and E. P. DuCharme. 1953. The of plants was reduced 10 to 18 percent. burrowing nematode and other parasitic nematodes A third rootstock, that has not been identiin relation to spre-ading decline of citrus. Plant Disease Reporter 37(7). 379-383. fied, was found to be resistant to the burrow8. Tarjan, A. C .W. Ford. 1957. A modified ...aceto-osmium staining method for demonstration of ing nematode fectg citrus groves. Plant nematodes in citrus root tissues. Phytopath. (In growth was not reduced in infested soil and press) .beJ .n achlr .D 98 h the population of burrowing nematodes alCitrus Industry. Vol. I. Univ. of Calif. Press. Berkeley Calif. ways decreased and frequently disappeared. 10. Young, T. W. 1954. An incubation method for The resistant factor was found to be confined collecting migratory endo-parasitic nematodes. Plant Disease Reporter. 38(11) : 794-795. Table 7. Juice characteristics of Parson Brown on Clone X compared to Parson Brown on rough lemon, 1955-56. Rootstock Date Juice by Soluble Acid Soluble Mgs. Vitamin Weight Volids olids to */.001. -. % f Acid Ratio Clone X Oct. 7 52.0 9.2 1.10 8.3 69.2 Rough lemon Cet. 7 50.7 9.4 1.21 7.7 58.4 Clone X Yov. 8 54.6 10.3 1.05 9.8 55.0 Rough lemon Yov. 8 50.9 1.127 .955.0 Clone X Dec. 13 .50.0 11. .97 11.7 63.1 .tough lemon -ec. 13 54.7 10.7 .94 11.4 60.0 Clone X Jan. 3 53.8 11.8 .81 14.6 66'1 Rouh lemon Jan. 3 58.8 11.4 .88 13.0 64.6

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52 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 THE NEW 4-H CLUB PROGRAM FOR CITRUS PRODUCTION TRAINING JACK T. MCOWN 5. Keep neat and accurate records in a Florida Agricultural Extension Service record book, showing the work that has been done, and write a story about your citrus acGainesville tivity. Agricultural progress in America during reSECOND YEAR'S REQUIREMENTS cent decades has been astounding. Looking 1. At least 6 months after completion of at agricultural history it can be seen that this the first year map, make another map showprogress is closely associated with the eming the location of (1) healthy trees, (2) phasis agriculture has placed on developing missing trees, (3) dead trees, (4) diseased its youth. Major agricultural enterprises have trees, (5) young resets. had specific programs to inspire youth. This 2. When the map is completed, it should is a part of the citrus industry that is lacking show the total number of trees in the block, today. Realizing that many boys do not have the number of healthy trees and number of the opportunity to study citrus the Agriculdiseased, dead and missing trees. Refer to tural Extension Service is expanding its citrus your first year map and copy the comparable youth program to meet this need, This paper figures and set them down below the first will outline the Extension, Service's citrus year's figures. Note whether the general conyouth program in order that you may become dition in the grove is (1) improved, (2) better acquainted with its aims and objecworse, (3) the same. Mention the progress ties. The Extension Citrus Advisory Comof the grove in the story at the end of the mittee which plays an important part in deyear veloping this program, has outlined a 5-year .B bet dniyery isao n project for 4-H Club boys wishing to become more intimately acquainted with the industry. late oranges, two kinds of grapefruit and one The 5-year program as outlined below will kind of tangerines. It is not necessary to, idenmeet all requirements for a 4-H Club project. tify by variety, but the club member should Upon completing each year's requirements, be able to examine the fruit and determine the youth may continue his work toward the' whether it is early, midseason or late. following year's requirements without wait4. When the seedbed is between 12 and 18 ing foran Wend of a calendar year. months old, line out the seedlings. Discuss The requirements for the first year are: location of nursery and its size with the local 1. Map a 10-acre bearing grove showing leader or Extension Agent. the location of (1) healthy trees, (2) missing 5. Be able to identify 5 pests of citrus (may trees, (3) dead trees, (4) diseased trees, (5) be insects, diseases or both). young resets. 6. Keep neat and accurate records and 2. When the map is completed, it should write a story on the, second year's citrus acshow the total number of trees in the blocks, tivity. the number of healthy trees, and the number THIRD YEAR's REQUIREMENTS of diseased, dead and missing trees. 1. About 9 months after making the second 3. Be able to identify citrus fruits that map, make a third one the same way. have been injured by (1) rust mites, (2) scale, 2. Determine the number of skips in the (3) melanose. 10-acre plot due to missing, dead, or diseased 4. Plant a citrus seedbed either as an trees. From this figure, calculate the perindividual home project, or in a cooperat--ive centage of trees missing. The percentage of club project. Discuss size and location of crop loss in the grove would be about the your seedbed with your local leader, or Exsame. Knowing what price per box the fruit tension Agent. (Minimum size of seedbed brought, calculate the financial loss to the to be determined.) grower.

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McCOWN: CITRUS PRODUCTION TRAINING 53 3. Bud the nursery. The 4-H Club memFIFTH'YEARS REQUIREMENTS ber should demonstrate to the local leader or 1. Keep the following record on a bearing the Extension agent his ability to bud and grove from September 1 to August 31. Fertiliproperly care for the nursery. The budded zation: date, analysis, number of pounds per trees should be properly labeled. Certified tree, method of application. Actually be on budwood should be secured if possible. if band and watch the entire operation for at certified budwood is used, the buds should least one application. Know bow to correct be selected and the budding done under direct or prevent nitrogen, magnesium, manganese, supervision of the leader and the State Plant zinc and iron deficiencies. Br rep aentati-dentify and know the apSpraying: Date, what is being sprayed for, proximate harvest season--whether early, midmaterials used in the spray, approximate galseason or late-of the following citrus fruits: lonage or pounds of dust per tree. Oranges--Parson Brown, Hamlin, Navel, PineCultivation: Date, kind (disc, plow, acme). apple, Jaffa, Valencia, Lue Gimn Gong. GrapeCover crop: Date planted, kind and seedfruit-Duncan, Marsh Seedless, Foster Pink, ing rate per acre (if not volunteer), Know Thompson Pink, Red; Tangelos -Orlando, why cover crops are needed in Florida citrus Minneola, Thornton; Miscellaneous, one groves. Observe harvesting operations and variety of lemon, Persian (Tahiti) lime, Merspend at least half a day with a picking crew. Cott. 1 2. Know what "top working" means and 5. Be able to identify four insects and how it is done. three diseases that are of economic import~ 3. Draw a floor plan of a fresh fruit packance in citrus production. ing house, single strength, sectionizing plant 6. Keep neat and accurate records and or concentrate plant ,and know the fundawrite a story of the year's activities. mental of their operation. FoURTH YEAR's REQUIREMENTS 4. Keep neat and accurate records and 1. Be able to identify leaf symptoms of the write a story of the year's activity. following mineral deficiencies in citrus: nitroBy providing this type of program we gen, magnesium, zinc, manganese and iron. should achieve many objectives, First of all, 2. The club member should be able to the youth, through his association as a 4-H demonstrate his ability to stake out a grove Club member would develop his leadership for planting. abilities. (2) Such a program would inspire the 3. Sell or plant out the nursery trees. Learn boy's interest in citrus through a closer 'associato plant nursery trees in the grove by planttion with many segments of the industry. (3) ing under the supervision of the club leader Provide the citrus industry with better trained or Extension agent. Keep a record of bow personnel upon completion of this project. (4) these trees are cared for the first year. InPrepare some of these young men to achieve clude dates for each operation, including a better job by becoming better skilled. (5) amount of water per tree, banking, planting Inspire a desire in some to further their educacover crop, analysis and amount of fertilizer, tional training by attending college. insect and disease control. Now comes the question of what course of 4. Be able to identify five citrus insects and action must be taken in order that we may four diseases and tell how they can be conachieve these aims and objectives. A 4-H Club trolled. member who enrolls in a citrus project will 5. Explain what is meant by the "on tree" through his local leader or county agent's price growers get for citrus. Keep a record of leadership be made aware of the require"on tree" prices for one season from October I ments necessary to carry on a project for 5 to June 15 for oranges and grapefruit. (Conyears. He will also be instructed in the protact the same grower, grove caretaker, or cash cedure of keeping records, as a project record buyer once each week and ask him the "on book will be provided outlining each year's tree" price. Record this information, in table work. Upon completion of a year's project, form in the record book, showing if it is early, several boys will be selected from each county midseason or late fruit prices.) to attend the annual junior Citrus Institute.

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54 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 This Institute is held at 4-H Camp Cloverleaf and taking an active part in local project for the purpose of putting a final touch to the work. We may also inspire the youngsters citrus project work for the year. Attending through encouragement and recognizing a job the Institute will be an award for the boy dowell done. In some instances financial aid may ing the best project work in his county. The be necessary for clubs to develop local projjunior Citrus Institute this past year was ects. Examples would include: nursery jointly sponsored by the Chilean Nitrate Eduprojects, small groves for demonstration purcational Bureau of Orlando and Dolomite poses, tours and training schools. OrganizaProducts Inc., of Ocala. In addition to the tons and individuals may help by making junior Citrus Institute, we are preparing to available funds for this purpose. We feel that promote additional interest among the club the program outlined will be successful. Howmembers in citrus by providing fruit judging ever, greater goals may be achieved if we reacontests and similar activities at the various lize the importance of such a youth program county fairs throughout the state. At this and show an interest by putting forth a contime the boy will also be given the opporcerted effort to insure success. The young tunity to participate in insect, disease and people of Florida are a part of the citrus inother identification contests. dusty. Let us prepare them to accept its fuIt is important that the citrus industry take ture responsibilities in order that our industry part in developing this program. Men in the may continue to be a leader among the various industry can be of help by showing an interest American agricultural enterprises. FIELD OBSERVATIONS OF SEVERAL METHODS OF MANAGING CLOSELY SET CITRUS TREES FRED P. LAWRENCE 25, having the parts near together, is the one Florida Agricultural Extension Service that seems most appropriate for our use. GeApplying this definition,, consider first the Gainevillecitrus tree spacings of the various producing ROBERT E. NoRRI areas of the world. In Italy and other MediFlorida Agricltural Extension Service terranean countries citrus trees are usually spaced 10'x10' or 10'x12' which results in 300 Tavares to 450 trees per acre. The Japanese orchards You will note from your program that the average 240 to 300 trees per acre. Egypt's title of this presentation is "Field Observapredominant spacing is 12'x18'; Peru 18'xl8 ; tions of Several Methods of Managing CloselyBrazil 21'x24'; California 22'x22' and Florida Set Citrus Trees." That title sounded simple 25'x25'. enough when it was submitted to the program The planting distance in a given area dechairman but now that we have bad more pends upon such things as variety, species of time to contemplate we are not so sure. For rootstock used, type and fertility of the soil, instance, how close is close? To help answer, the length of the growing season, and, to a this question we turned to Webster's Collelarge extent, upon the attitude of the indigiate dictionary only to find more confusion vidual doing the planting. To illustrate the than enlightenment, We were reminded first latter point it might be well to point out that of all that it depends how you pronounce the quite a number of California growers, accordword. If you put a "z" in the pronunciation-. ing to an article in the October '55 issue of cloze-it means to "shut up" and considering Citrograph, are turning to what they call the small amount of actual data we have, that hedgerow plantings and some groves are might not be a bad idea. There are many planted as closely as 8x10 which gives some other meanings, of course, but Definition No. 490 trees per acre,

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LAWRENCE AND NORRIS : FIELD OBSERVATIONS 55 All of these plantings, or at least a major should be confined to the removal of dead portion of them soon reach a point where the wood and occasional broken limbs. This limbs and branches of the various trees interrecommendation, plus the fact that pruning lock and overlap and unless special manis an expensive operation, has also brought agement practices of pruning are applied the about the situation that pruning in Florida bearing surface of such trees diminishes and until comparatively recently has been connaturally the production declines in proporfined to the inside of the tree and to the retion. moval of dead wood. According to the best estimates available Insofar as the records show, no effort has Florida has 497,400 acres of bearing trees, been made to limit the size of citrus trees in 333,690 acres or 67% of which are 16 years of Florida or to control crowding by judicious age or older. A grat many of these groves are pruning of the periphery of the tree until some planted on spacings of 15x30, 20x24, 25x25 growers began to hedge tho periphery of their and similar distances and if we apply definitrees in the late 40's. tion No. 25 to the word close we will find that most of these trees have their parts near I1. HegnZf irsisafr o rnn together; hence we can apply the term closedesigned to facilitate grove management pracly planted and in need of some form of pruntices and to improve the quality of fruit proing. -duced. It is a practice that is becoming in'. .creasingly popular among Florida citrus growTime will not permit our discussing the ers as a way to alleviate the problem of overvaried and many methods of pruning emcrowding which ultimately results in a loss of ployed in the various citrus producing areas production. of the world--or even all of those practiced in Hedging provides a means by which the Florida-so we will confine our remarks to bearing surface of trees is reduced in area some field observations of several methods of without greatly reducing their b earing ability. managing closely-set citrus trees; to narrow Indeed, in the case of some varieties, especialit down even more we propose to discuss ly tangerines, hedging actually increases the briefly the following practices: per cent pack-out of fresh fruit in the first 1. Hedging crop following the pruning operation by in2. Heading back creasing fruit size. Fruit color and textures 3. Thinning by tree removal also are often improved because of increased 4. Topping-a form of rejuvenation prunsunlight and more effective insect and disease ing control. In fairness to those who may read this One of the most valuable advantages of paper in the printed proceedings we should hedging, and the primary reason for its use state that from this point on our talk will be in the first place, is to open the tree middles illustrated with color slides and we shall atby removing interlocking branches. This altempt to present, as clearly as possible, a lows for the movement of tractors, discs, spray word picture of these various methods of and dust equipment and trucks through the pruning. grove without damage to the trees and fruit Despite the difficulties associated with or to the equipment and operator. It speeds crowded groves, very little pruning of any up grove operations generally, thereby reducnature has been undertaken in Florida either ing cultural costs. to prevent or to correct the situation. This has If you would like additional information on probably been due to the fact that earlier exhedging or plans for a hedging machine we peniments suggested that pruning was an opsuggest you obtain Experiment Station Bulleeration that contributed very little to over-all tin 519 by D. S. Prosser and Extension Servfruit production. In instances of moderate to ice Circular 115 by R.. Norris. severe pruning, a loss of fruit was noted with2. Heading Back-This term and the type out any apparent compensating effect on operation it implies is seldom used in Florida quality or fruit sizecitrus; however, it is used rather extensively On the basis of these earlier experiments, in the California lemon industry as well as recommendations were made that pruning throughout most of the other citrus producing

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56 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 areas of the world. It consists of removing a It required 3 men 5 days to run all brush portion of the tree at regular intervals in order from the 10 acres through the chipping mato retain a rather constant size of the tree. chine. It took 4 men 3 days to haul out all There are certain advantages and disadvanlimbs above 4 inches in diameter. It should tages to this method of pruning but since it be pointed out that this grove bad a problem appears to be of little value under present of no place to haul and burn the brush so it Florida conditions we will pass over it. had to be disposed of in place. 3. Thinning by tree removal-This is a pracTo dispose of the trees in the manner tice that has long been contemplated by described the owner figured the total cost, of Florida growers but one that has seldom been the operation at $1.50 per tree. practiced. Numerous Florida groves planted Of particular interest in the group of slides during the last 30 years were spaced 15x,30, shown on this operation is the one showing or a similar distance, with the idea of rehow rapidly the remaining trees are filling in. moving every other tree. Few growers, howBased on the progress the trees have made ever, have actually removed these trees and this year, it is believed that the grove will be many have practiced little or no heading back back to normal production next year. or pruning of any kind. Some comments on similar operations: Only in recent years have some few growBlock B-Red grapefruit on rough lemon ers actually thinned their groves by removing stock 10 years old was planted 123x30 on trees in the closely-spaced rows. We regret Lakeland fine sand. Every fourth tree on the that we da not have more yield and cost data diagonal was sawed off flush with the ground to present on these operations but the pracwith a pulpwood saw, dragged out and tice is not general and accurate data is scarce. burned. The following year there was no We do have slides of one complete operation noticeable reduction in crop. At 12 years of to show and some yield and cost data on the age (next year) the grower plans to remove one operation: every other tree on the diagonal-thus reducing The grove, consisting of a 10 acre block of the spacing to 25x30 at -which time he will Hamlins budded on rough lemon root, was begin a program of hedging. Based on preplanted in 1939 with a tree spacing of 15x25. vious experience the grower feels there will The soil type is deep phase Lakeland fine be very little per acre loss in production-if sand. The trees were never beaded back or any. hedged and as a result the limbs were interBlock C-Twenty-five year old Valencias locked badly and many of the lower branches on rough lemon stock were planted 15x3O on were dying as a result of shading.During the Eustis fine sand. The trees were very crowded last 5 years production decreased, very markso every other tree was "buckhorned," bulledly so during the past two seasons, which, dozed and replanted. The year before moving as you know, were dry. During January and the production on the block was 4400 boxes. February 1956 every other row was removed Fifty trees were removed and the following by sawing the limbs off with a power saw and year the production dropped to 3960 boxes. running all wood under 4 inches in diameter The plan is to move 50 trees per year until through a chipping machine. The stumps the operation is completed. After the third were treated with a tree killer (without sucyear it is anticipated that the loss of 50 trees cess) on two occasions and as a final effort per year will not result in any loss of total the stumps were sawed level with the ground crop produced. and a chopper run down the row to remove Some figures on this operation: all suckers. It took 2 men 312 day to saw and re-sa-w 20 The crop has not yet been harvested but the trees; one man 312 to whitewash (by hand) 20 owner estimates his crop loss at 25% over the trees; one man one day to remove (by drag) previous year's yield. the brush from 20 trees; four men, a bullSome figures on the operation: dozer, a flat truck and a water wagon one The rows were 21 trees long-2 men cut 2 day to push, haul 1. mile and re-plant 20 trees. rows per. day. Two men could trim the large The total cost of labor for this operation exlimbs7,and stack the brush on 5 rows per day. clusive of equipment was $2.60 per tree.

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LAWRENCE AND NORRIS: FIELD OBSERVATIONS 57 The re-set trees began bearing the second Grove A-Cut back every other row in year at the rate of about 4 box per tree averJanuary 1947 just after the fruit was picked. age and in the third year they were yielding The trees were whitewashed immediately. a box average. The fourth year's yield will They started to sprout out in about six weeks probably be between three and four boxes. and grew very vigorously the first year. The And now the last practice to considersecond year they put on only a few scattered 4. Toppirng, a form of rejuvenation pruning: fruit. The third year the growth was very Rejuvenation pruning is a term used by hordense and possibly because of the large trees ticulturists to describe the objective of reon two sides, tended to grow upright but proinvigorating trees by stimulating more and duced better than a box average of fruit. By better shoot growth and fruitfulness. This the fourth year it was obvious that although the trees had good big broad leaves and were pruning must be severe enough to remove sufrwgvgrusythywudsobebk Se ike the old trees so it was decided to cut much of the tree. back the trees on both sides of the row. Some When enough of the top is cut off, a trees bore as much as 8 boxes of fruit the growth response usually occurs throughout fourth year. These trees (as you can see by the woody framework. In order to produce, the slides) now have the characteristic apfrom pruning, an invigorating effect in a large pearance of budded trees and are yielding 10 old tree, it is necessary to make many small boxes per tree. The new wood is quite thorny cuts or remove some of the large branches. and some pruning to thin and shape is necesThe method we have chosen to report on sary, is that of removing the complete top of old Grove B-The initial operation was begun seedling trees at varying heights from ground in February 1947. In this block it was noted level to eighteen feet. This, too, is a new that trees cut below 5 feet did not appear to practice in Florida and although again, facts come back as rapidly as did ones cut at a and figures are not abundant, we have some greater distance from the ground. Those trees slides that are at least interesting. This practopped above 5 feet were more difficult and tice might well be described as an act of expensive to handle in the original operation desperation brought on in many groves by inand did not respond any faster. It now appears creased overlapping of limbs which resulted that the trees cut 10 feet and higher will in a marked increase of pest and disease and never "head-out" low and will ultimately be a gradual dying of lower limbs. In some old right back like they were originally; whereas seedling groves it is 10 to 15 feet from the the trees cut at 5 to -10 feet take on the charground to the first limb. The tops are sparse, acteristics of budded trees and will apparentthe foliage is small, production is down and the ly remain relatively "low-headed" -provided cost of picking (usually from a 40 foot ladder) they are hedged to prevent inter-locking. Of is such that it makes the operation very exspecial interest in Grove B was one particular pensive. tree that yielded 16 boxes the fifth year. All trees in Grove B are currently producing an During the last ten years many growers average of 10 to 12 boxes of fruit.' have been experimenting with various meth~ I umr eaanws opitotta ods of pruning to try to alleviate this condiIh ns ar we agaper wiret poirelyu thare tion. From these various methods of pruning shecotets of thi pbservtarns wuthln theh rewe will discuss only the one wherein the -enmaking rffeldobserdations awithso thomg. Howtire top of the tree is removed, The data preemerig seomndagioas tat is tiany Hnstnwe sented is from two different blocks of old ever itoseysemres loa hti an prdintane seedling trees owned by two different growbf clasly-aed trreainedhthrouon cfath ers. Both growers topped only a few trees in bermsainpraing orutegined ithosg paper:fth 1947. Grower A started by topping trees in frso rnn ulndi hsppr every other row at a relatively constant height 1. Hedgying: of roughly 5 feet from the ground. Grower B A comparatively new method of pruntopped about 20 trees in a block. These trees ing which is rapidly being adopted by were topped from 1 foot to 15 feet in height. Florida growers to relieve the. adverse ef-

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58 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 fects of crowding and shading found in time) to prove or disprove the value of most Florida groves 15 years old and older. the operation. It would appear from the Advantages: limited operations we have observed that a. Increased effectiveness of pest control. if a grower has access to additional land b. Decreased damage to trees and equipand in instances of healthy trees a new ment. grove that will bear heavily in 4 to 5 c. Faster more economical grove operayears can be established at an economic tons. figure. d. Decreased dead wood. -4. Topping, a form o rejuvenation pruning. e. Increased "pack-out" of fresh fruit. It is too early to make positive statef. Better sizes and better color of fruit. ments relative to this operation; howg. More attractive appearance of grove. ever, it appears that by topping two or Disadvantages: more rows per year (beginning on the a. Usually a reduced yield for at leastotsdrw)hiscudrsepdctn one year .and reduce cost of harvesting in old b. A fairly costly operation (varies from canopied groves. 732c to 78c per tree)'/ Advantages: 2. Heading back: a. Reduces height of tree. We have not observed enough of this b. Greatly improves tree vigor. type of pruning in Florida to offer any md. Produces increased cover crop growth. 3. T'binning by tree removal: Disadvantages: As we have pointed out there are now a. Complete loss of crop for two years. quite a number of growers who have reb. An expensive operation. cently turned to this method of relieving c. New trees quite thorny. a crowded condition but very few have d. If trees are not whitewashed and cuts adequate records (because of length of coated with water repelling paints the V/Agricultural Extension Service Circular 115. trees will be weak and soon rot away. TIMING FERTILIZATION OF CITRUS IN THE INDIAN RIVER AREA HERMAN J. REITZ cations are made during the drier part of the 0yea Florida Citrus Exeriment Station Lake Alfred The experiment to be described was begun S. in January, 1949, and was terminated with eese yera ieale o trest ws the .1955-56 crop. The trees used were Valesed fmig teretie, Paly as aresut sf encia oranges on sour orange rootstock planted this intiming seerleerarmeyts wre in on single beds in 1940. The soil in the exithis toressver exerions wre inperimental area was classified Parkwood loamy epiet s etral Some fhe fine sand with pH ranging from 6.8 to 8.3 in ee po d rct 03 r F)orid pape the surface and with pH values above 6.8 in preent reted result (o, 4). Thpeisen paper all depths to 42 inches. The surface samples percent the resdits Rive aneprden Lao-r contained carbonates equivalent to about 14 duced t te Idia Rier iel Laoraor percent calcium carbonate and organic matter near Fort Pierce. The results agree with the ofapoiaey3pren.Tesi locn or A prxmtl 3 Secn.Tesi locn th r Fti da dfatpatcied bofveiie r is d a tained 12 to 30 percent clay plus silt (partithlatie io appidation if ether a 1. les less than 0.05 mm. in diameter) in various reltivly ino cosidratonif he PP~ layers, thus being much finer in texture than Fla. Agri. Expt. Sta. Journal Series No. 546. soils used for citrus in Central Florida. in

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REITZ: TIMING FERTILIZATION 59 this soil, the trees were known through Treatment 6: measurement to have 75 percent of their fine One-half fertilizer applied June 15th and root system in the upper 19 inches from the one-half applied December 15th. crown of the bed. Treatment 7: The seven experimental treatments conOne-third fertilizer applied February 15th, sisted only of variations in the time of applione-third June 1st, and one-third November cation of mixed fertilizers during the year. Dur1st. ing each calendar year, every tree in the exThe schedule was adhered to within pracperiment received the same amount and tical limits. All the treatments were replicated analysis of fertilizer. The yearly total rates four times, at first using six trees per plot. Later and analysis used were changed several times it became recognized that several of the trees during the course of the experiment, as shown were affected by crinkle scurf and that addiin Table 1. Rates were increased up to 1953 tional trees were non-typical of the Valencia to achieve a greener, more dense foliage, and variety. These trees were then discarded and increased further after 1953 to achieve greater the results quoted are based upon the typical trees remaining in the plots insofar as this -Table 1. Amounts and analyses of fertilizer used was permitted by the records. In the experiment RESULTS Year Analysisa) Annual Rate, Plot Observations-At the beginning of the per tree experiment in January, 1949, the trees were Pounds somewhat small for trees nine years of age 1949 3-6-8-3-0-1 16 and also were showing the symptoms of low fertilization level. In August, 1949, a severe 1951 4-6-8--0-1 20 hurricane struck the grove and caused about 1951 4-6--5-01 2090 percent defoliation on all trees and almost 1952 5-6-8-5-0-1 30 complete loss of the fruit crop. Throughout 1953 6-6-8-5-0-0 30 1950 and 1951, the foliage on all trees was 1954 8-4-10-7-0-0 24 light green and sparse, but this condition improved slowly throughout the period and was 1955 B-4-10-7-0-0 24 fairly satisfactory by the end of 1952. (8)N-P205K20-Mgo--Mno-Cu0 respectively. Through 1953 to the end of the experiment, all trees had satisfactory foliage conditions except when modified by treatments as noted yield, as was indicated might be possible by below. an adjacent experiment involving different The most' conspicuous changes in tree aprates of fertilization. The changes in analysis paac eebogtaotb plcto wer inlunce bytrndsin enralFloi. of all fertilizer in October. In the last four fertilizer practice during the period. The timyears of the experiment, all trees so treated ing treatments were as follows: 'were notably earlier in blooming and coming Treatment 1: into growth in the spring than other trees. The All fertilizer applied February 15th. extreme example of this was observed JanuTreatment 2: ary 7, 1954, when approximately one-third of One-half total fertilizer applied Februall trees so treated were in full bloom from ary 15th and one-half June 15th. leafless inflorescenses while the trees in other Treatmnt treatments were completely without bloom. Trlltmertize aple :yIt Twig growth on these trees was also early All ertiize appiedMay st.in development, and the twigs were long and Treatment 4: bad many leaves per twig. These leaves in One-alffertlizr aplie May1stand most years did not become dark green -as did one-half October 15th. leaves from other treatments, and in some Treatment 5: years the trees became conspicuously nitrogenAll fertilizer applied October 15th. deficient and sparse of foliage during the post-

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60 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 bloom and early summer season. In late sumwith the fruit. It was coincidental that the mer, some greening of foliage occurred even severity of the leaf symptoms observed was before fertilization, presumably due to breakgreatest in the year that was picked for this down of organic matter in the soil. Trees given study, so the differences found are doubtless one-half the fertilizer in May and one-half in greater than would have been found in other October were similarly but less conspicuously years. affected. The analytical results for nitrogen are preTrees given all fertilizer in May were at sented in Fig. 1. These results correlate with the opposite extreme in appearance comthe appearance of the trees. For example, the pared with trees fertilized only in October, trees fertilized only in January and those These trees bad limited spring growth, in numfertilized three times per year maintained a ber of twigs or length of twigs, and this spring reasonably good green color of leaves and growth became dark green slowly. The bloom relatively high nitrogen level throughout the was sometimes very late, not reaching a peak entire period. The trees fertilized in October in 1954 until about April 9, and not then beonly appeared nitrogen deficient during the ing profuse or conspicuous. The general leaf months of May, June, and July, and at that color in the post-bloom period was fairly dark time had extremely low levels of nitrogen in green due to the color of the old leaves and the leaves. Also, leaves from trees fertilized the absence of new flush. In the early sumin October only increased in nitrogen content mner period, the characteristic appearance of and improved in appearance during the sumthese trees was dull grayish green, the foliage mer although no nitrogen bad been applied; was thin, and there were numerous dead twigs after the fall fertilization, the nitrogen conin the trees. During the late summer and fall tent of these leaves greatly increased so that the trees were of average foliage appearance, they were equivalent in nitrogen content to but this was generally the case with nearly all those of the January only plots and the plots of the trees except possibly those fertilized receiving three applications. The trees fertilonly in October. ized in May only paralleled in nitrogen conThe general appearance of trees in all of tent the trees fertilized in October only; up to the other treatments was not outstanding in the point when in May the fertilizer was apany respect and the trees were fairly green plied. After this application, the leaves inthroughout the year. ,creased markedly in nitrogen content but did I Tre Sze-Te crcuferece f th trnksnot reach the level attained by the leaves in ofthtree in-the exrperente was theasredk the January only or the three application first in August, 1950, and again in January, whretet.Ti aall the tressertvied aony thad 1956. The averages showed that the increase whinerathy vrye darilgreen Mayor onls adu in trunk circumference was smaller for the geealvrydkgencortiwsdu trees receiving all the fertilizer in October -1EAMN than for any other treatment. However, difFebTuENT ferences in neither the actual trunk circumferences nor in the increases during the period 2, clba were large enough to be of statistical signi--Dots fertilized finance, indicating that the timing of fertiliza0 tion bad doubtful effect on tree size.2. Leaf Analysis-Leaf samples were taken for 0 mineral analysis on a number of occasions d zing the course of the experiment, beginning in W F. 1952. In one series, samples of leaves from 1F F F fruit-bearing twigs were collected from four of the treatments at approximately monthly intervals from March, 1953, to May, 1954. This 12 M A M j A S 0 less commonly used type of sample was select095A 0 19JA ed because it was desired to study the nutriSAMPLING DATE tional status of leaves most closely associated Fig ".Ntoe analyss of leaves from fruitng 0ig of 0eece 060reatmen0ts *6.0

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REITZ: TIMING FERTILIZATION 61 to the appearance of the old leaves and that the analysis of spring flush leaves taken from the appearance of the spring flush leaves of non-fruiting twigs on two dates. This type of 1953 remained poor. It is also notable that as sample is more nearly the conventional sample the 1954 flush of growth came out on trees taken in studies of leaf analysis. In most cases fertilized in May only, the new leaves were no significant differences were found. The lowest in nitrogen. It is assumed that data for most notable feature in Table 2 is the diftrees receiving two applications per year ference in analysis between 1954 and 1955. would be intermediate between the extremes. In 1954, leaves generally were low in nitrogiven here. gen, phosphorus and potassium and high in Among other major elements, the most concalcium. spicuous differences were in potassium and 'Fruit Qiiality-In each year except 1952-53, calcium. The treatment receiving all fertilizer at least one sample of fruit was picked for in October was conspicuously high in potasjuice analysis. Part of these results are presium and low in calcium throughout the sented in Table 3. Soluble solids in four of the greater part of the year. The May only treatsix years for. which records are available were ment was just the reverse. Differences in highest for fruit from the trees fertilized only magnesium were erratic and differences in in October; however, the two remaining years, phosphorus were of small magnitude. the soluble solids level was lowest. This shift As already noted, during 1954 and 1955 in relative level of soluble solids appeared to there was very little difference in appearance be of some consequence as it was supported by of the trees regardless of treatment and this a significant interaction between years and was reflected in leaf analysis. Table 2 shows treatment when subjected to analysis of vaTable 2. Analysis of spring flush leaves taken from non-fruiting twigs July 26, 1954, and August 2, 1955 LEAF ANALYSIS TREATMENT Nitrogen Phosphorus Potassium Calcium Magnesium 1954 1955 1954 1955 1954 1955 1954 1955 1954 1955 Feb.. 2.014 2.59 0.107 0.123 0-71 0.99 7-18 5.77 0.173 0.195 Feb. and June 2.o6 2.74 0.103 0.124 o.61 0.95 7.52 5.59 0.151 0.183 May 2.17 2.54 0.109 0.123 0.68 0.89 7.31 5.89 0.176-0.198 May and Oct. 2.17 2.47 0.110 0.122 0.72 0.94 7.21 5.91 0.242 0.194 Oct. 2.14 2.47 o.116 0.114 0.73 0.94 6.74 6.02 0.194 0.206 June and Dec. 2.20 2.52 0.111 0.122 0-74 0.82 6.81 6.05 0'.219 o.186 Feb., June and Nov. 2.16 2.52 0.108 0.124 o.67 0.98 7.02 5.71 0.244 0.188 Statistical Significance (e) N.S. ** N.S. N.S. N.S. N.S. N.S. ()N.S. -non-signific ant -significant at 5 level *significant at 1% level C .analysis run on composite samples only

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62 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 3. Summary of fruit characteristics JUICE ANALYSIS FRUIT SIZE OBrix % Acid OBrix Diameter, Avg. Wt. % Ac6d mm. gram Feb. 11.73 1.06 11.26 70.5 187 Feb. and June 11.63 1.07 11.04 71.5 196 May 11.70 1.03 11.53 71.3 187 May and Oct. 11.-48 1.09 10.72 71.8 200 Oct. 11.63 1.07 10.95 73-1 203 June and Dec. 11.63 1.06 11.05 71.7 .193 Feb., June, and Nov. 11.62 -1.06 1114 71.0 193 Statistical Signific ance (a): Treatments N.S. N.S. N.S.* Interaction N.S. N.S. N.S. (a) N.S. non-significant *-4significant at 5% level S -significant at 1% le vel riance by split-plot methods, using treatments Fruit Size-One of the more noticeable efas the main plots and years as the sub-plots as fects of the treatments was the effect of the suggested by Pearce (2). This would be inOctober treatment in producing fruit of larger terpreted to mean that the treatments had a than average size. This effect was noted real effect on soluble solids but that the effect strongly in the crops picked in 1952, 1954, varied to some extent depending upon the and 1955. Measurements were taken of this season. No significant difference was discovcharacteristic by two methods, first, as the ered in acidity or ratio of soluble solids to measured diameter of the fruit on the tree in acidity although the trees fertilized entirely or 1951, 1952, 1954, and 1955, and second, as partly in October were among those giving the average weight of the fruits which were fruit with highest acidity and lowest ratio. sampled for fruit analysis in 1954, 1955, and juice content was quite uniform and the dif1956. The summary of both weight and diamferences were of no statistical significance in eter measurements is given in Table 3. Size any case. Vitamin C was determined in only differences were more noticeable in the diainethree years, but no differences of practical or ter measurements. These measurements of statistical consequence were found. The indiameter made in the field were largely done teraction noted above for soluble solids in the early years of the experiment while the ('Brix) was not significant for any other weight measurements were done in the last juice characteristic. three years of the experiment. Here again it

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REITZ: TIMING FERTILIZATION 63 is noted that the greater effects were obtained however, be assigned the individual treatin the earlier years of the experiment than in ments. the later ones. The significant interaction of Applications made in October (before the fruit weight with years reflects relatively larger end of the rainy season in this area) had sevfruit in the October plots in 1954 than in 1955 eral disadvantages. In addition to low yield, and 1956. the trees bloomed dangerously early, showed External Characteristics of the Fruit -nitrogen deficiency severely during post-bloomn Studies were made on color .and grade of and early summer periods and set much latefruit, both in the field and to a limited xtent bloom fruit. Aside from larger fruit (of doubtin the Citrus Experiment Station p acking20 house at Lake Alfred. It was observed on 9 many occasions that the color of fruit on trees 8 fertilized in October only was outstanding in December and January; however, during 17 February this difference diminished greatly so that when the fruit was mature enough to 5 pick, the advantage had been completely lost. Packinghouse studies confirmed the field observation that little difference existed in the c 3 latter part of the season. The loss in the ad--195155 vantage for the October treatment was due W to re-greening of fruit in that treatment and a 1 to improved color of fruit in other treatments. J loWhen fruit was picked late in the season 0 9.49 5 and judged for fruit color as well as coarseM ness, and later graded into United States J8 grades, there was no advantage for any treatt7ment over the other in any of these charactert6--915 istics. 0Yield-Yield results are given in Fig. 2. Although there were some obvious differences in average yield, the differences obtained 3 were not statistically significant. Treat2 ments involving application of fertilizer inI October were lowest in average yield. The yield figures for these treatments include a 0 e.Fb.MyMy Oc .June Feb. great deal of late-bloom fruit which would June OctDec. June be of no value for fresh fruit production unless T RE AT MENT Tov it were handled separately. The yield from F'ig. 2 Accumulative yield by years during the last trees receiving all fertilizer in May was high_ six years of the experiment. est, but this high yield was the result of exful value for this variety), such treatments had ceptional yield on two plots of the four no advantages. replications and somewhat less than average Single annual application of fertilizer in yield on the remaining two. Yields from the May produced greatest average yield, but the other four treatments were intermediate beresult lacked statistical significance. The treattween these extremes. ment had nothing else to recommend it, and DiscusIONthe tree condition in the post-bloom period DISCUSIONwould not be satisfactory to many growers. The results indicate that no large benefit The remaining four treatments prevented in yield or fruit quality can be obtained under unfavorable tree condition and were satisfacthe conditions of this experiment by simply tory in all respects. Three applications per year varying the time of application of fertilizers. bad no advantages over treatments using fewSome smaller advantages or disadvantages can, er applications, and hence cannot be recom-

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64 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 mcrnded. When all fertilizer was applied in in Central Florida (3, 4) have not shown as February, quite satisfactory results were obmuch difference as had previously been antitained and might be recommended. By comcipated and it is probable that the effects parison, February and June applications or spoken of above could be obtained only in the December and June applications would perleast fertile and coarsest textured soils. baps reduce leaching loss if exceptional rainfall occurred after the single annual applicaSUMMARY tion and would reduce the hazard of excessive A fertilizer .timing experiment using Valensalt concentration if high rates of fertilization cia trees on sour orange rootstock planted on were used. Neither of these conditions was calcareous hammock soil was conducted over important i the experiment. a seven-year period. The seven treatments inSimilar conclusions might not be drawn if volved one, two, or three applications per early orange varieties or grapefruit had been year, using a constant total amount of mixed used m the experiment. The earlier coloring of fertilizer annually on all plots. Results indicate the fruit, the larger fruit size, and the higher that applications made before the end of the soluble solids frequently occurring inm the rainy season (prior to November Ist) are untreatments receiving October applications desirable; that three applications per year are might be sufficient to justify their use for unnecessarily expensive; and that satisfactory these varieties. Such comments are, of course, results can be obtained by using two applicaspeculative in relation to the data presented tions, one after the end of the fall rainy season here. and a second before the beginning of the It is probable that fertilizer rate played an summer rainy season, or by a single applicaimportant role in the results. In later years' tion made in winter, with higher rates, results were less pronounced than in earlier years with lower rates. Evi. LITERATURE CITED dental striking results from timing exeri.1. Martin, W. E. 1942. Physiological studies of yield, quality and maturity of Marsh grapefruit in ments must depend upon attaining nutritional Arizona. Ariz. Agr. Expt. Sta. Tech. Bul. 97. extremes at some period of the year (1). At 2. Pearce, S. C. 1953. Fruit experimentation with fruit trees and other perennial plants. Tech. Comhigh fertilizer rates, such extremes cannot be munication No. 23, Commonwealth Bureau of Hortiproduced under the soil conditions existing in Section 25 p. 1ntt4. rps atM inEgad this experiment. Under other soil conditions, 3. Reuther, Walter. and Paul F. Smith. 1954. Ef.feet of method of timing nitrogen fertilization on where less clay and organic matter is found yield and quality of oranges. Proc. Fla. State Hort. in the soil, nutritional extremes may occur Soc. 6:2.026.,Iw.wnrndEJ.es much more readily than was the case in this zyck. 1953. The effect of fertilizer timing and rate experiment. However, experiments performed Of'applicato onfru>it ulaisy and podctionrof Hali orngs Pro. Fla Stt Ht Soc 66:54-62

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KNORR AND PRICE: GRAPEFRUIT STEM PITTING 65 IS STEM PITTING OF GRAPEFRUIT A THREAT TO THE FLORIDA GROWER? L. C. KNORR AND W. C. PRICE ary ones that develop as affected trees mature, Florda itrs EperientStaionthe important primary Symptoms being those Florda itrs EperientStaionthat are revealed by stripping off bark from Lake Alfred the trunk and large limbs. In the surface of the underlying wood, there is to be found pits, Before attempting to answer the question shallow grooves, or channels with their long raised in the title to this paper, it is necessary axes paralleling the grain of the wood. The to consider two subsidiary questions. The first channels give the unaffected wood the apof these is this: What is stem pitting? pearance of ridges resembling loose strands The term "stem pitting" was first used by of twine. Channelling is well-defined and Oberholzer, Mathews, and Stiemnie (16) in characteristically present in the trunk and South Africa to designate a specific disease of lower branches but may be lacking in twigs grapefruit trees on rough lemon rootstock. and young branches. Subsequently, the term came also to be used Oberholzer (17) in 1953 estimated that in a different sense: to designate a symptom, or stem pitting had destroyed 40 per cent of the set of symptoms, occurring in the wood of grapefruit groves in South Africa, and Oxenvarious kinds of citrus trees when infected ham and Sturgess (19) report that stem pitwith, or presumed to be infected with, one ting, or dimples, of grapefruit, "is the most or another virus. This double usage has reserious problem affecting the Queensland citsulted in a certain amount of confusion. rus industry," with most plantings becoming The term stem pitting has been applied by unproductive by the 15th year. This terrible others to the pitting that occurs under the destruction results apparently from injury to bark of Key lime seedlings serving as indicator phloemn and xylemn tissues in the scaffold of plants for tristeza virus (3). It has also been the tree, thus'rendering tissues incapable of applied (1) to various types of pitting present sppygetertsorrtswtthwar in many varieties of citrus-for example, to and food needed for growth and fruiting. the pitting in such varieties as trifoliate Oberholzer, Mathews, and Stiemie (16) orange and sour orange, which varieties are showed that stem-pitting disease is perpetufound (5) to be free of pitting in Argentina ated by vegetative propagation and discovered where the stem-pitting disease abounds. that some sources of budwood carry a milder We are concerned with the disease of form of the disease than others. McClean (12, grapefruit known as stem pitting. According 13) proved the disease to be infectious and to to Oberholzer, Mathews, and Stiemie (16), be capable of transmission by grafting or by stem pitting is characterized by corrugations means of the brown citrus aphid', Toxopter~a or longitudinal pits on the outer surfaces of ecitricidus (Kirk.) (syn. Aphis citricidus Kirk.). trunks of affected trees; trees showing stem He considered stem pitting to be caused by a pitting of the trunk become stunted and virus that is widespread in citrus in South bushy, giving rise to the name stunt bush; Africa, and he also reported that at least two their foliage is sparse, small, mottled, and chlorotic; and their fruit are small with thick -t thirs pointmout mightonrosehelpfuls toapipsent out rind, high acid content, and low juice conrespect to common names for Toxoptera (Aphis) citricidus (Kirk.), the highly efficient vector of tent. In severely affected trees, scaffold tristeza in South America, South Africa, and Ausbranches tend to grow downward at sharp traia, nd Toxopte'r a aa" tis (Fnsc.) theF' mak angles, crowns are flat, and the rough-lemon In the American literature the common name for T. citricidus is the brown citrus aphid, and for T. rootstock suckers profusely. aurantii, the black citrus aphid (cf. "Common names of insects approved by the Entomological Society of According to McClean (12, 13), the sympAmerica," Bul. Ent. Soc. of America 1 (4): 1-34. toms described by Oberholzer et al. are second1955). "t hte rliteratuered certain othetrcodustries is called the black citrus aphid (cf. "Common names of insects," Commonwealth Sci. & Ind .Org. Florida Agricultural Experiment Stations Journal Australia, Bul. 275, 32p. 1955). and T. toxoptera Series, No. 567. the brown citrus aphid.

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66 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 strains of the virus exist. Bothi strains induce Another reason for considering that tristeza veinal flecking in West Indian (Key) lime and stem-pitting viruses are not identical is seedlings and both stunt such seedlings rather this: although tristeza virus is supposed to be severely, one more so than the other. universal in citrus of South Africa, many 25The second subsidiary question that must year-old grapefruit trees there do not have be considered is this: What is the relationship the stem-pitting disease (15). This could be between stem pitting and tristeza? This is cerinterpreted to mean 1) that tristeza virus is tainly not an easy question to answer, as will different from stem-pitting virus despite being presently become evident. On the one band, closely associated with it in nature, or 2) that there are reasons for believing that these two some strains of tristeza virus are so mild that diseases are caused by the same virus. Mcthey do not cause stem pitting. Clean (13) has pointed out that the causal Stem-pitting disease of grapefruit does not agents of both diseases are transmitted by occur in Florida, nor, to our knowledge, does Toxoptera citricidus and that both diseases it occur elsewhere in the United States. Tristeare universal in South Africa. He thinks that za is in Florida (7), however, and is reported it would be strange indeed for two distinct to be spreading in some areas, such as Lake viruses to be transmitted by the same insect and Orange Counties (2). We know of a few and also to be ubiquitous in the same crop. It grapefruit trees in Florida infected with trisis certainly tempting to regard the two disteza virus that display a pitting of twigs and eases as specific host responses to the same small branches comparable to the pitting that virus but there may be good reasons for refrequently develops in Key lime seedlings sisting such temptation. when infected by tristeza virus; these Costa, Grant, and Moreira (3) suggested grapefruit trees, however, do not have that stem pitting might be caused by the same the striations and channeling of wood of virus as that which causes tristeza, or by a the trunk or large limbs, symptoms said closely related virus, and McClean (13) conby Oberholzer et al. to be the characteristic curred in this opinion. The virus responsible manifestations of stem -pitting disease; for stem pitting in South Africa is also beneither do these trees show any indications of lieved to cause a die-back of lime in the Gold decline nor deviations from normal fruiting. In Coast, where at least two strains of the virus Florida, we have examined a large number of are reported to exist (8, 9), and to cause in grapefruit trees, many of which have been South Africa (13) a severe decline of Tahiti demonstrated to be carrying the virus of trislime on the tristeza-tolerant sweet-orange root.. teza, but in none of these trees have we found stock. Stem pitting has been reported to octhe stem-pitting disease. Because of these obcur in Argentina (11), apparently having been servations, it seems safe to conclude that at introduced there simultaneously with tristeza. present stem pitting occurs rarely, if at all, in It is also known in the Belgian Congo (20). Florida. McClean and van der Plank (14) postulated The virus, or virus complex, that causes that the tristeza-virus complex has two comseedling-yellows disease of grapefruit, sour ponents, a stem-pitting component and a orange, and Eureka lemon seedlings in Ausseedling-yellows component. They postulate tralia and South Africa also does not occur in further that the stem-pitting disease is induced Florida. When Florida tristeza virus is transin grapefruit by the stem-pitting component mitted to these three species by budding from whether the seedling-yellows component is infected sweet-orange trees, it does not propresent or not. It is not clear from the paper duce seedling yellows in them. by McClean and van der Plank whether stemThis certainly seems to be a paradox: alpitting virus alone can cause decline of sweet though tristeza is not uncommon in Florida, orange on sour-orange rootstock or whether neither the seedling-yellows component nor the the seedling-yellows component must also be stem-pitting component of the complex appresent. However, sour orange is thought to pears to occur here! How can this be exbe more tolerant of stem-.pitting virus alone plained? than of the stem-pitting seedling-yel lows comOne possible explanation is to assume that plex. the seedling-yellows component is present in

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KNORR AND PRICE: GRAPEFRUIT STEM PITTING 67 Florida but that by itself it cannot produce neither seed ling-yel lows disease nor stemseedling yellows, that seedling yellows develpitting disease. ops only when the stem-pitting component is Although there is no substantial body o~f exalso present. If this is assumed, then it needs perimental evidence on which to base a judgfurther to be assumed that only the seedlingment of the validity of the hypothesis that trisyellows component of the complex, not the teza seedling yellowvs, and stem pitting involve stem-pitting component, is present in Florida not a complex of viruses but a group of closely and that seedling-yellow virus by itself causes related strains, an experimental check of the the mild form of tristeza to be found here. Alhypothesis can readily be made in Australia though we do not have the experimental evior South Africa, where presence of a seedlingdence necessary to rule out this possibility, we yellows factor is said to occur. Evidence is now prefer a simpler hypothesisavailable for the statement that a mild strain Our hypothesis is that tristeza, stem pitting, of tristeza virus will protect citrus from more seedling yellows, and the Gold Coast's lime severe forms of the virus (4, 6, 18). Consedie-back are cause 'd by a single virus that exquently, a grapefruit seedling invaded by the ists in the form of numerous strains. [It seems stem-pitting component of the tristeza virus likely that this is about what Costa, Grant, and complex should be refractory to infection by Moreira (3) had in mind when they sugthe seedling-yellows component, whether ingested that tristeza and stem pitting are caused troduced by means of grafting or by Toxoptera by the same virus.] It may further be supcitricidtis, if the two components are closely posed that naturally-infected trees can harbor related strains but not if they are separate and two or more strains simultaneously and that distinct viruses. So far as we can learn from one or another of these strains predominate, the literature, this test has not been made. depending upon the species or variety of citrus Let us now return to the main question of in which they occur. The strain of virus prethis paper: is stem pitting a threat to the dominating in sweet orange of South Africa is Florida grower? We believe that it is a threat, usually, though not always, one that will inbut one that should not be taken too seriously duce seedling yellows in grapefruit, Eureka so long as an efficient vector of tristeza like lemon, and sour orange seedlings. We can Toxoptera citricidus is kept out of the state. designate it as the seedling-yellows strain. It If stem-pitting virus is a strain of tristeza virus, apparently is not well adapted to the grapethe possibility that it will arise by mutation of fruit. Consequently, when a mixture of strains the mild strains of tristeza virus present in is transmitted by Toxoptera citricidus from Florida is a virtual certainty. If an efficient naturally-infected sweet orange to grapefruit, vector of the virus, such as Toxoptera citricianother strain better adapted to the grapefruit dus, should feed on the tree in which the musoon predominates; this may be a strain that tant arises, there will be a good possibility of causes stem pitting or another that is considspreading the virus to healthy trees in the erably less severe than the stem-pitting strain. neighborhood. In the absence of such a vector, Even when transmission is by grafting and the possibility of spread is very small indeed. when seedling yellows develops, the grapefruit Tristeza has been present in Florida for a good tends to lose the component that causes seedmany years (10) and it is likely that the ling yellows while retaining the component strains of virus in existence here are well that causes stem pitting (15); this observation adapted to the crop; they are more or less in can better be explained by assuming the stemequilibrium with the crop. This equilibrium is pitting and seedling-yellows components to be not likely to be upset except by some radical strains of the same virus than by assuming change, such as appearance of an efficient vecthem to be distinct and separate entities. tor. It is-not necessary toq assume that strains of If stem pitting is caused by a separate and tristeza virus exist; their existence has been distinct virus that does not now exist in Floridemonstrated in South America (4) andin da, it should by all means be prevented from the United States (18). It is necessary to asentering here. 0 0Q0arantine Seasures -agis sume only that the strains of tristeza virus importation of budwood is the most practical commonly found in the United States cause means by which to exclude it.

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DESZYCK AND TING: SEASONAL CHANGES 69 9pie consisted of six fruit of one size picked from different trees. Three sizes (96, 70, and 20oC 54) were collected from tagged trees at inS.9 s4 tervals of 14-16 days during the 1955-56 sea9 .. *son, extending from September to March. 80 juice was expressed at the rate of 40 fruit per minute using a Food Machinery In-Line ex7C tractor (5) with a flush setting, / inch orifice --tube, strainer tube of 3/32 inch openings, and a cup of six inches in diameter. The juice was -then passed through a Chisholm-Ryder finisher of the tapered screw type equipped with 0.033 inch perforated screen, weighed and exS 140C pressed as milliliters in each sample of six 0 IMC fruit. In compiling the data the average juice -* volume for each period of 14-16 days was used. 00C e*_--RR/SO, 0 e.....ePs/1SO S4023 OcQ.3 d u23 Dec.23 Jon23 Feb.23 M.2% siz. 70 SAMPLING PERIOD Fig. 1. Seasonal changes in the average juice content of pink (P.S.) and red (R.R.) grapefruit of three S "".9 sizes (96, 70, 54) grown on sour orange (S.O.) and rough lemon (R.L.) rootstocks during 1955-56. n quirements were raised in 1955, juice content became the limiting factor in maturity. There" fore, a study of juiciness was included during the 1955-56 season. A preliminary report is here presented for --the purpose of ascertaining the juice content of pink and red grapefruit of three sizes f grown throughout the State during the 1955856 season. Special emphasis was placed on itsrelationship to legal juice requirements. In ad... .. dition to seasonal changes in juice content, the variations among samples during each sam-* pling period as well as the daily increases in the juice are included.< EXPER1IMENTAL 4 For this survey, 137 groves were selected i.9 throughout the citrus area of Florida, including the Ridge section, and the East and West coasts. Of the total number, 68 groves wereRuby red and 41 pink seedless on rough lemon, SAPLNG PERIOD and 20 groves were red and 8 pink on sour orange rootstock, Fruit sampling was similar Fig. 2. Seasonal changes in the average juice conto tat sed ommrcial ;thatis ach amtent of two varieties of fruit of three sizes grown on to tat ued ommecialy; hat s, ach amtwo rootstocks during 1955-56.

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70 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 RESULTS AND DISCUSSION to March. However, it is similar in the two In gnerl te aerae jiceconentof ink varieties during the early season from Septemn generapteaveragfjhree sieonn oupgh ber to January. On the average for-the season and ed rapfrui ofthre sies n rugh Rubv red fruit contains more puice than the lemon and sour orange rootstocks gradually pink Ivariety. increased with the advance of the season,' with some exceptions (Fig. 1). Some irregularities The percentages of samples of size .96 were apparent for size 54 fruit on sour orange grapefruit meeting the legal juice requirerootstock. In addition the juice volumes in the ments through December are listed in Table 1. fruit of the three sizes decreased slightly durVery little fruit can be picked under the 1955 ing January and February (Fig. 2-A). juice standards, since only 7.7 percent of the samples attained sufficient juice (1110 ml.) at Rootstock apparently does not influence that time. During October I to 15, 32.1 perjuice content in white varieties of grapefruit cent of the fruit met the strict regulations. (6). However in the pink and red varieties, When the requirement is lowered to 1080 mi. significantly more juice is found in fruit grown during October 16 to November 15, 63.2 peron sour orange than on rough lemon rootstock cent of the fruit met the standard during the during the latter part of the season (Fig. 2-B1). first part of this period, and 84.5 percent durThis variation was first apparent in December ing the latter part. Although the lower standfor size 54 fruit, and during March for size ard is restrictive, the majority of the samples 96. On the average for the season more juice acquired adequate juice. After November 15 was found in fruit on sour orange than on 'when the requirement is lowered to 1020 ml. rough lemon rootstock. most of the fruit had enough juice for harvest. The size of the fruit appears to have no influThe seasonal trends in the juice of two enceon the time of attainment of the high varieties and three sizes are shown in Fig. juice standards effective through October 15 2-C. The red variety contains significantly since approximately one-third of the samples higher juice content than the pink grapefruit of each size met the standards during the during the latter part of the season, January period. Table l. Percentage of grapefruit samples picked throughout the State attaining juice standards from September to December, 1955 (size 96) Juice Requirements sampling Period September October November December 15-30 1-15 1631 1-15 1630 1-15 16-30 ml/6 fruit Percen 1110 (a) and above 797 32.1 46.5 76.8 85.0 81.1 96.3 1080 (b) and above 12.8 41.9 63.2. 84.5 85,0 86.9 97.3 1020 (c) and above 31.7 69.5 81.3 93a6 95.0 90.8 100,0 1020 68.2 30.4 18.7 6.4 5.0 9.2 -0(a) Minimum juice requirement for Aug. I -O0t 15 (b) Minim% juice requirement for Dta 16-Nov. 15(c) Minimum juice requirement for Nov. 16-July 3

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DESZYCK AND TING: SEASONAL CHANGES 71 Table 2. The average juice content and standard deviation for juice increased by 0.6, 0.7, and 0.9 ml for grpfri of sie'0fr1apigprosdrn 1955-56. 7 or1 smligprid drn sizes 96, 70, and 54, respectively. An estimate of the time of meeting juice regulations can be made by knowing the average daily increase Sampling Period Juice Standard in the juice. Of course, these values will vary (ml/ fruit eviation with location, seasons, and other factors bti Sept. 15-30 1171 122.2 can be useful as a guide to the time of barvesting. Oct. 1-15 1332 -125.5 Oct. 16-31 1392 3.26.7 SUMMARY AND CONCLUSIONS Nov. 1-15 1465 122.7 Nov. 16.-3 195 114.7 Apreliminary report of the juice content of Dec. -15 541 26.2 seedless pink and red grapefruit of sizes 96, Dec. -15 541 26.2 70, and 54 grown on rough lemon or sour Dec. 16-31 1571 125.7 orange rootstocks is presented. -The samples Jan. 1-15 1590 108.2 were collected twice monthly from 137 groves Jan. 16-31 1603 139.7 during the 1955-56 season. In general, the Feb. 1-15 1568 104.7 juice content increased with the advance of Feb.16-9 155 13.0 the season, increasing approximately one-third from September t March. In the latter part March 1-15 1604 109.7 of the season, the red fruit contained more March 16-31 1" no.? juice than the pink variety. Likewise, fruit on sour orange .rootstock contained more juice than that grown on rough lemon. On the average, the red grapefruit on sour orange had Sd he most juice while the pink variety on rough deviations for size 70 fruit for 13 sampling lemon had the least amount. periods are shown in Table 2. The standard deviations are generally higher during the earlier As far as meeting the high juice standards part of the season than during the latter part in effect from August I to October 15, apwith some exceptions. The average juice and proximately 8 percent of the fruit in Septemthe standard deviation can be helpful in asber and 32 percent in October met the strict pertaining the range distribution about the juice regulations. At the time of the medium mean, especially if used in the early season. juice requirements from October 16 to NovemFor example, during September, the average ber 15, approximately 63 and 85 percent met juice content for size 70 fruit was 1171 ml. with a standard deviation of 122.2 mn]. Of the samples tested, approximately one-third fell Table 3. Average daily increase in juice content per fruit between 1171-1293 mi., and one-sixth fell of grapefruit of three size. (96, 70, and 54) above 1293 ml. It is evident that with the during October to December 1955. juice requirement of 1380 ml., less than onesixth of the samples met this high requirement, Sampling Period 96 Size and therefore fruit cannot be picked because 05 of low juice volume. mi/fruit/day Oct. 1-15 1.1 1.7 2.1 The daily average increases in juice volume Oct. 16-3 0.5 0.5 0.8 for one fruit of each size during sampling Nov. 1-15 0.9 1.0 0.8 periods -from October through December, are 0 shown in Table 3. Large daily increases for Nv 63 ... all three sizes occurred during the October 8 Dec. 1-15 0.4 0.5 0.8 sampling period, with smaller amounts during Dec.16-31 0.4 0.2 0.4 the remaining periods. With sizes, the highest daily increase in juice was found for size 54, Average o.6 0.7 0.9 and the lowest for size 96. On the average the -.* I0

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72 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 regulations in October and November, respec2. Desc, J. an J. .Sit. 15 J F ontively. After November 15, most of the fruit Hort. Soc. 68: 47-49. m. .-3. The Florida Citrus Code of 1949. Chapter No. 25149. State of Fla. Dept. Agr. Citrus & Vegetable The variations in the juice content for each Inspection Div.so lrd,195 iiu uc sampingperod a wel a th daiy icreseS content for grapefruit. Chapter 29760, Senate Bill No. in jice olues ae pesened.5.| Gerwe, R. D. 1954. Extracting citrus juices. Proc. Fla. State Hort. Soc. 67: 173-176. 6. Harding. P. L. and D. F. Fisher. 1955. Seasonal LITERATURE CITED changes in Florida grapefruit. U. S. Dept. Agr. Tech. Bul. 886. 1. Deszyc<, E. J. and J. W. Sites. 1954. The effect 7. Taylor, 0. C., G. Carman, R. M. Burns, P. of lead arsenate sprays on quality and maturity of W. Moore, and E. M. Naeur, 1956. Effect of oil and Ruby red grapefruit. Proc. Fla. State Hort. Soc. 67: parathion sprays on orange size and quality. Cal. 28-42. Citrograph 41: 452-454. EFFECTIVENESS OF DIFFERENT ZINC FERTILIZERS ON CITRUS C. D. LEONARD, IVAN STEWART ample, this element is much less available at a soil pH of 6.0 or 7.0 than at more acid soil AND GEORGE EDWARDS reactions. Florida Citrus Experiment Station Jones, Gall, and Barnette (6) reported that Lake lfredwhen zinc compounds are applied to the soil, LakeAlfrd -they react to form three types of compounds: Zinc foliage sprays have been used for more (a) water soluble zinc compounds, (b) comthan 20 years for the correction and prevenbinations formed by the reaction of soluble tion of zinc deficiency or frenching in Florida zinc compounds and the organic and inorganic citrus groves. Such sprays are reasonably efcolloidal complex of the soil (replaceable fective in controlling frenching in most groves zinc), and (c) combinations insoluble in even though the zinc sources now used are water and not in combination with the colloivery slowly absorbed and highly inefficient dal complex of the soil (not replaceable). They (7)'. Sprays have the additional disadvantage found that when low concentrations of soluble of leaving a residue on the leaves which inzinc compounds react with the soil, the major creases the scale population. Hence there is portion of the zinc enters into combination need for an effective and inexpensive method with the colloidal complexes and may be reof supplying zinc to citrus trees by application placed by a normal ammonium chloride soluof a suitable zinc fertilizer to the soil. The tion. Under these conditions they found a near studies reported here were carried out in an equivalence between the replaceable zinc of effort to find such a method. the soil and calcium removed from the colloidal complex. When high concentrations of fate, happbaeen zesseeybl th solg soluble zinc compounds react with the soil, spay, has beetho oar esudeplnabin to coirge they found that the zinc is present not only sapry (3s reoted in s1pp4ytngtin o catrs.s in water soluble and replaceable forms but Cam (isb) reputd wa o9btai at fro some asesi also in an insoluble form. They state that orcationsbe rezisul ase wbhedreas snother apganic matter, clay, replaceable bases, carbonpcation of zrom su te, whereas pters trpe ates and phosphates influence the fixation of broadcast gave good responses. Even where zinc in the soil. soil applications of zinc are effective absorpJamison (4), however, reported little diftion of zinc and correction of the zinc defiference in the fixation of zinc in the presence ciency leaf pattern are relatively slow. The and the absence of superphosphate in the soil. effectiveness of soil applications of zinc varies He states that the forces which retain zinc in greatly with various soil characteristics; for exthese soils are far stronger than those holding FloidaAgrculurl Epermen Satins ouralzinc as phosphates or basic compounds ordinSeries, No. 559. rlcosdedioub.

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LEONARD, STEWART AND EDWARDS: ZINCFERTILIZERS 73 Jamison (5) found that zinc applied as the an aromatic polycarboxylic acid (ZnAPCA) sulfate leached frorn the soil faster where were tagged with radioactive zinc-65 and larger crystals or lumps were applied than leached through Lakeland soil adjusted to where a fine powder was used. Most of the pH's of 4, 5, 6, and 7. Counts made on the -zinc from the fine source materials remained leachates showed that ZnDCTA was very efadsorbed in the surface three inches of soil fective in solubilizing zinc, and its effectivewhile much of the zinc from coarse materials ness showed marked increases as the soil pH had penetrated into the deeper layers of soil rose from 4 to 7 (Table 1). ZnAPCA was or had leached. He attributed this difference highly ineffective as a solubilizer for zinc. to saturation with zinc of small local zones of Zinc sulfate and several zinc chelates were soil beneath the lumps or large crystals. tagged with zinc-65 and leached through pots Brown (2) mixed zinc sulfate thoroughly of LIakeland soil at pH 5.4. Counts on the at the rate of 100 pounds per acre with five leachates indicated that much more zinc in major citrus-producing soils which had been ZnEDTA remained soluble than in zinc suladjusted to PH levels of 4, 5, and 6. At pH's 4 fate (Table 2). Increasing the amount of and 5, the zinc content of the leaves of orange EDTA applied with the same amount of zinc and grapefruit seedlings grown in these soils (varying the molecular ratio of zinc to EDTA) was very high, but in leaves of the plants increased the amount of zinc leached. AddigYrown in soil at PH 6 it was much lower. The tion of non-ionic or anionic wetting agents also uptake of zinc at different pH levels varied substantially increased the solubility of the for the five soils, but with Lakeland soil at zinc in this chelate, but addition of a cationic pH's 4, 5, and 6 the zinc contents of orange wetting agent reduced it. Zinc gluconate and leaves were 202, 317, and 44 ppm, respectivezinc naphthenate were relatively ineffective as ly. solubilizers for zinc. Zinc sulfate, with or withLEACHING OF ZINC out a wetting agent, was extremely ineffective The high uptake of zinc by citrus seedlings in these leaching trials. These results show from different soils at pH 4 and 5 with which the great fixing power of the Lakeland soil zinc sulfate bad been mixed, as reported by for zinc. Brown (2), shows that this material is an exThe distribution of the zinc in the soil was cellent source of zinc for citrus when distribdetermined by taking t hrtee cores of, soil from uted within the rooting zone of the trees. each pot with a special soil sampling tube with Since most of the zinc from finely-divided zinc sulfate becomes fixed near the soil surface (5), Tabl. 2. lwmut of radioactiv. Sim fro. different the poor results obtained from soil applicasouce leahe through pot. of lakeland tions of this material in citrus groves appear tosolaPH54 be due to its failure to leach downward into the rooting zone. In an effort to find a method Zinc souxte Oth.r matral Oe. (a) of getting zinc deeper into the soil, two zincenET 2 chelates, zinc 1, 2 diaminocyclohexane tetraz i2 acetate (ZnDCTA) and the zinc chelate of Zn EDT I g. M-51 48 Zn EDTA 5 g a. -51 8% Table 1. Effect Of soil pH On amount of radioactive "Cationic vettiNg agent .81 zinc leached through Lakeland soil frost, two zinc chelates. "Anionic vetting agent '6U4 .No-ionic wetting agent 687 Zn EDTA (1:2) (b) 740 IV of soil ZnCAZnAFCA (1:5) (b) 1621 cpm (1) epm Zn gluconmte 3.4 S901 0 Zn Naphthenate 2 3.2230 0 Zn so 4 H2 1 6 2776 0 ZS s0 -2 5 gm. R-51 S 7 3153 3.2 (a) Counts per minute (a) Counts per minute (b) Molecular ratio of zinc to EDT

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74 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 a narrow slit in the side and making radiocitrus groves to compare the effectiveness of active counts directly on the soil at depths of chelated zinc with zinc sulfate. Two such exone to six inches. These counts showed that periments are reported below. most of the radioactive zinc applied in the In December, 1952, a field plot experiment form of zinc sulfate remained in the top few was started in a grove of 8-year-old Pineapple inches of soil, while that applied as ZnEDTA orange trees growing on Lakeland sandy soil was much more uniformly distributed (Fig. with a pH of about 6.0. This grove was 1). The total of the counts for the six-inch sprayed with zinc until 1951. The linear fourlayers sampled was considerably greater for tree plots were completely buffered by other zinc sulfate than for ZnEDTA at pH's of 5 trees from adjoining plots, and replicated three and 6, indicating much greater fixation of zinc times in randomized blocks. Zinc sulfate from the sulfate. There was little difference in monohydrate, containing 36 percent zinc, was the total counts for these two zinc sources at applied at rates of 100, 164, and 328 grams of pH's of 4 and 7. Radioactive counts made on zinc per tree per application. Each rate was the leaves of citrus seedlings grown in the applied once a year to one series of plots, and pots showed a close correlation between the three times a year to another series. Three zinc movement of zinc through the soil and the chelates, ZnEDTA (zinc ethylenediamine amount of zinc uptake by the plants. tetraacetate), ZnHEIDA (zinc hydroxyethyl FIELD EXPERIMENTS iminodiacetate), and ZnEDTA-OH (zinc hydroxyethyl ethylenediamine triacetate), were Since the pot studies reported above showed applied once a year at rates of 12.5, 25, 50, considerably more leaching of zinc and greater and 100 grams 4 zinc per tree. These chelates uptake of zinc by citrus seedlings from chewere also applied at rates of 12.5 and 25 lated zinc than frm zinc sulfate, field experigrams of zinc per tree three times a year until ments were carried out in several commercial 1955, when the rise of ZnHEIDA was disFig. Residual concentrations of Zn65 following application and leaching of ZnEDTA nd Zn S04 to pots of Lakeland snd adjusted to different pH levels. 10000 PH 5 PH 4 Zn S4 PH 6 -PH 7 S 0-*Zn S04 800Z ZnnS04 (D ZnEDTA S400-ZE7. --ZnEDTA 200-0 0T DTA S --* 2 6 2 4 6 2 4 6 6 2 4 6 2 4 6 2 4 6 Depth, Inches

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LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS 75 continued. In September, 1955 the 12.5-gram grams. All materials were broadcast by hand. rate for ZnEDTA and ZnEDTA-OH applied under the spread of the trees. Leaf samples three times a year was changed to 50 grams, taken in August, 1955 (1955 summer flush) and the 25-gram rate was changed to 100 and in August, 1956 (1956 spring flush and Table 3. Effect of soil application of zinc compounds on the zinc content of leaves of Pineapple orange tree-on acid soil. Source of Zinc gm. Zn NO. ppm zinc in leaves~b applied ()Applications Summer Spring Summer per tree per year Flush Flush Flush per appl. 1955 1956 1956 Zn S04 H20 100 1 33 28 30 164 1 29 28 27 328 1 44 44 35 100 3 35 30 29 164 3 42 42 37 328 3 48 53 4 Zn EDTA 12.5 1 28 21 24 25 1 29 21 21 50 1 33 25 24 100 1 33 26 27 12.5 3 .34 31 26 25 333 38 29 Zn BEIDA 12.5 1 29-25 1 34-50 1 35-100 1 37 -12.5 3 32 -25 333 -e5 Zn EDTA-OH 12.5 1 32 26 28 25 1 29 25 26 50 1 29 28 24 100 1 32 33 25 12.5 3 31 -28 26 25 3 30 29 27 Check None -31 23 24 (a)A*1 applications broadcast. ()1955 summer flush sampled in August, 1955. 1956 spring flush and sinner flush sampled in August, 1956.

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76 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 summer flush separately) were analyzed for once a year. Application of 100 grams of zinc total zinc by the polarographic method of Barper tree as the sulfate and in the chelate form rows, Drosdoff, and Gropp (1). showed about equal effectiveness in increasThe highest zinc contents were found in the ing zinc in the leaves. The lower rates of apleaves from trees that received the higher plication of the chelates showed little advanamounts of zinc sulfate (Table 3). Zinc sultage over the untreated checks. These field refate applied three times a year resulted in sults do not bear out the increased availability higher zinc content of the leaves than the of zinc shown by the chelates in the pot exsame amount of zinc per application applied periment reported above. In the pot experiTable 4. Effect of amount and method of application of'zinc chelates on the zinc content of Pineapple orange leaves. (a) Treatment Chblate Other Material Go. Zn HOW p Zinc _(b) Applied Applied Spring Summer Er -tree I* l -lush ,Zn EpA32J. Band 29 5 T soda ash 100 Chunks -25 5 0 328 26 5 W00 -23 5 " 3.6" -25 3 oz. AP-78 100 -25 "8 oz. (g) 328 -623 328 Sm. piles 25 30 5 lba soda ash 328 " 39 25 5 " 100 " -26 100 " -23 Zn EDTA-OH 328 Band 29 25 .10 l soda ash 28 28 24 -__L, 5 100 Chunks 25 "5 " "328 "29 a "5 "100m" 25 "5 ""328 "28 3 oz. AP-78 () 100 -" .oz " 2 28 "328 Piles 23 27 "0100 6" -430 "5 Tbe soda ash 328 "32 23 --5 Check None 23 25 (a) Each treatment applied one time. (b) 1956 flushed, sampled in August, 1956. (c) Anionic batting agent (Antara Chemical Company).

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LEONARD, STEWART AND EDWARDS: ZINC FERTILIZERS 77 ment, ZnEDTA was more effective than zinc fate per 100 gallons. However, the sprays gave sulfate in penetration of soluble zinc through no increase in zinc content of the 1956 sumthe soil and also in bringing about uptake of mer flush leaves when compared with the zinc by citrus seedlings. untreated checks. This failure of the sprayed A second experiment was started in the fall zinc to move in substantial amounts into the of 1955 in another part of the same Pineapple newer flush tends to explain why such sprays orange grove. It consisted of about 70 different must be repeated every year or two in most zinc treatments, including sprays and soil apgroves. plications, each applied to three individual Apiaino ieslaet h oli trees. Some of these treatments were applied small piles is comparable to the use of hardin the spring of 1956. Three methods of soil ened chunks in that both methods give a high application were used: (a) broadcast in a concentration of zinc over numerous small band 3 to 4 feet wide, (b) applied in hardenlocal soil zones. The work of Jamison (5) ined chunks made by mixing the zinc sources dicates that this should induce greater total with water and drying, and (c) in small piles movement of zinc down through the soil. In of loose material distributed around the treesthis experiment, application of zinc sulfate in In some treatments, the zinc sources were small piles, either alone or with wettable sulmixed with soda ash (NaCO,) to raise the fur, gave slightly lower zinc levels in the soil pH, wettable sulfur to lower the pH, or leaves than similar amounts applied broadwiha etngaen.Zneslft asas cast or in chunks. However, when five pounds applied in mixtures with calcium, chloride. of zinc sulfate was mixed with five pounds Foliage sprays of zinc sulfate neutralized with of calcium chloride and applied in small piles, hydrated lime were applied for comparison it gave a very striking increase in the zinc with the soil treatments. content of the leaves. The 1956 spring flush In this experiment two zinc chelates (Znleaves contained 170 ppm. of zinc. This is EDTA and ZnEDTA-OH) were tested at a nearly three times as high as that obtained rate much higher than in the first experiment, from a foliage spray at 12 pounds of zinc but were again found to be relatively ineffecsulfate per 100 gallons, and is four, times tive as sources of zinc regardless of the method greater than that obtained from any other of application (Table 4). A small increase in soil treatment. The younger 1956 summer zinc in the spring flush leaves was brought flush leaves contained 82 ppm of zinc, which about by mixtures of chelated zinc and soda is twice as much as the highest level from any ash applied in small piles, when compared other treatment. Several extra samples of with the chelates applied alone. However, leaves were taken and analyzed to verify these none of the chelate treatments brought about unusually high values. In the spring flush they any substantial increase in the zinc content of approach the high leaf zinc levels reported by the summer flush leaves, when compared with Brown (2) for citrus seedlings grown in pots the untreated checks. These results are in of soil in which zinc sulfate had been mixed general agreement with those obtained in the at the rate of 100 pounds per acre. first experiment. It would appear that the high concentraFive pounds of zinc sulfate applied broadtion of soluble calcium supplied by the calcast twice a year showed only a small increase cium chloride replaced most of the zinc fixed in zinc uptake oVer similar application once by the soil in exchangeable form, or by satura year, and the addition of wettable sulfur ating the exchange complex with calcium, preshowed no advantage over zinc sulfate alone vented fixation of zinc in exchangeable form. (Table 5). When applied in chunks, addition This would permit more of the zinc to leach of wettable sulfur gave a small increase over downward into the root zone where it could application of zinc sulfate alone. be taken up by the trees, Zinc sulfate applied as a foliage spray in It was Dot possible to prepare hardened January, 1956 gave a progressive increase in chunks by mixing zinc sulfate and calcium the zinc content of the 1956 spring flush chloride with water even when cement was leaves as the concentration of the spray was added, but satisfactory chunks were made by increased from three to 12 pounds of zinc sulmixing five pounds each of zinc sulfate, cal-

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78 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 cium chloride, and wettable sulfur with water, far below those given by the mixture of zinc Application of these chunks, however, showed sulfate and calcium chloride applied in piles. no advantage over similar chunks containing This may be due to the slow breakdown of only zinc sulfate and wettable sulfur, and the chunks, but it may also be due in part to both of these treatments grave leaf zinc levels lowering of the soil pHby the sulfur. Various 00 Table 5. Effect of amount and method of application of zinc sulfate on the zinc content of Pin*pple orange leaves. Trajgtt 5msn (b) Zinc sulfate Other Material No. of Ga Zno Bo. Spring Sumer LbB/tree Lbe/tree times applied applied Flush Flush appled per tree 2 1 328 Band .-21 2 2 656 "N 32 2 5 W S 1 328 26 28 5 1 820 38 33 5 2 1640 42 35 5 5 W S 1O 82 32 29 5 5 WS 2 1640 33 33 5 1 820 Chunks -30 5 2 1640 35 5 5 W S 1 820 38 35 3 5 W S 2 1640 "40 41 5 5 W S 150 al Ethomeen T-15(0)1 820 "-30 5 5 W S 5 CaC12 1 820 "36 35 5 1 820 Sm. piles 26 28 5 5 W S 1 820 31 26 5 5 CaC2:2 1 820 170 82 3/100 gal* i Ca (00)2/100 gal. 1 -Foliage 31 22 6 " 2 " 1-Spray 44 23 12 " 4 " 1-"60 24+ (riots) Check -None -23 25 (a) Where 2 applications are shown,. they were made about 6 mos. &part, the second one being made in Apr. 1956. (b) 1956 flushes, Bampled August, 1956. (e) Cationic wetting agent (Armour Chemical Division, Armour & Go.)

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WENZEL AND MOORE: GRAPEFRUIT UTILIZATION 79 mixtures of zinc sulfate and calcium chloride creased thle zinc content of the spring flush are being studied further as a possible source Over that obtained with the three-pound rate, of zinc suitable for soil application to citrus but failed to increase the zinc content of the trees. summer flush leaves. A mixture of five pounds SUIXI ABY zinc sulfate and five pounds calcium chloride, A study was made to compare the effectiveapplied in small piles beneath the trees, increasness of soil application of different zinc ed the zinc content of the spring flush leaves to sources to citrus trees growing on acid soil. 170 ppm, and that of the younger summer Zinc sulfate and chelated forms of zinc were flush leaves to 82 ppm. Both figures are untagged with radioactive zinc-65 and leached usually high for mature citrus trees growing through pots of Lakeland soil adjusted to difin the field. ferent pH levels to study their leaching propLITERATURE CITED ertes.Couts adeon he eacate ni1-. Barrows, Harold L., Matthew Drosdoff, and S C -Armm H. Gropp. 1956. Rapid Direct Polarographic cated that ZnEDTA and ZnDCTA (zinc 1, 2 Determination of Zinc in Plant Ash Solutions. Agridiaminocyclohexane tetraacetate) were much 2".trn, J.n W. 1C55. Absorption of Zinc by Citrus more effective in carrying zinc through the soil from Various Soil Types. Thesis, University of Florithan was zinc sulfate. Virtually none of the da .Camp, A. F. 1934. Studies on the Effect of zinc sulfate was leached through the pots. Growtahd of Horticultual Crops. la. Ar. Exp.n Sta. In a field experiment with Pineapple orange Annual Report, page 67. 4. Jamison, Vernon C. 1943. The Effect of Phostrees, zinc sulfate and three zinc chelates were Phates upon the Fixation of Zinc and Copper in Sevabou eqal n icresingthezin cten o eral Florida Soils. Proe. Fla. State Hort. Soc. 56: the leaves when each was applied once a year 5-.Jamison, Vernon C. 1944. Citrus Nutrition at 100 grams of zinc per tree per application. 192 .Fa g.Ep tto nulRprp The highest zinc contents were found in the 1936.Th~eReHactio of Zinc Sulfate with th Soil.Fa leaves from trees that received two pounds of Agr. Exp. Station Bul. 298. 7. Stewart, rvan, C. D. Leonard, and George Edzinc sulfate per tree per application. wards. 1955. Factors Influencing the Absorption of In a second field experiment, a single apZinc by Citrus. Proc. Fla. State Hort. Soc. 68: 82-88. plication of five pounds zinc sulfate per tree, ACKNOwLEDGMIENT applied broadcast in hardened chunks made The authors express their appreciation to the by mixing it with water, or in small piles scatMinute Maid Corporation and to its repretered around the trees gave a slightly higher sentatives for their cooperation and for perzinc content of both spring and summer flush mitting the use of the grove in which the leaves than foliage sprays applied at the rate field experiments reported here were carried of three pounds of zinc sulfate per 100 galout. Appreciation is also expressed to the Dow Ions. Foliage sprays at 6 and 12 pounds of Chemical Company and to Geigy Agricultural zinc sulfate per 100 gallons substantially inChemicals for supplying the zinc chelates used. INCREASED UTILIZATION OF GRAPEFRUIT THROUGH IMPROVEMENT IN QUALITY OF PROCESSED PRODUCTS F. W. WENZEL AND E. L. MOORE mand. The average financial return to grapeFlorida Citrus Experiment Station fruit growers has been small during recent years. During the 1955-56 season 48 percent Lake Alfred of the grapefruit crop used was for processed products, such as canned grapefruit juice, Increased utilization of grapefruit is needed canned grapefruit sections, and frozen conbecause the present supply is in excess of decentrated grapefruit juice. Obviously, large '/Cooperative publication by the Florida Citrus amounts of these products are being bought Experiment Station and Florida Citrus Commission. by consumers, but improvements m the quality Friday Ag4iultural Experiment Station Journal of some of the products packed could and Seie No 564.**.

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80 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 should be made. Better quality in processed have been produced. During the same time grapefruit products should lead to increased production of Florida oranges has increased demand and subsequently to increased utilizafrom 19 million boxes in 1936-37 to over 91 tion of grapefruit. million boxes during the 1955-56 season. It This paper will discuss briefly (a) utilizamay be seen from the figures in Table 1 that tion of Florida grapefruit for processed prodthe utilization of grapefruit by the Florida ucts, (b) factors which affect the quality of citrus processing industry has gradually inprocessed grapefruit products, and (c) past creased over the years. For example, about 38 and current investigations of the Florida Citrus 'percent of the grapefruit used in the 1936-37 Experiment Station and the Florida Citrus season went into processed products comCommission concerning factors upon which pared to 48 percent during 1955-56. The the quality of processed grapefruit products maximum utilization occurred in 1945-46 depends. when 69 percent was processed. The use of UTILIZATION OF FLORIDA GRAPEFRUIT oranges for processing has increased from 3 percent during the 1936-37 season to about There has been a gradual increase in the 37 percent in 1946-47 and to 71 percent in production of Florida grapefruit from about 1955-56. This, it is evident that currently al18 million boxes for the 1936-37 season to a most 50 percent of the grapefruit and over 70 peak production of about 42 million boxes durpercent of the oranges grown in Florida are ing the 1953-54 season; for the past two seabeing used for processed products. This is in sons approximately 35 and 38 million boxes marked contrast to the situation in and prior TAKS I Utilization of Forida Grapefruit -Fresh and Processed l, 2 Fresh fruit Fruit Fresh and sales processed processed Season Processed Thousands Thousands Thousands % Of total of boxes of boxes of boxes 1936-37 11,233 6,759 17,992 37.6 1941-42 8,956 10,443 19,099 53.1 1946-47 10,434 15,866 26,280 6o.4 1951-52 19,172 23,678 32,850 41.6 1952-53 l7,3O5 25,035 32,340 46.5 1953-54 20,451 20,089 4O,54 49.6 1954-55 19,26315,660 34,923 44.8 1955-56 19,925 18,661 38,586 48.4 1 Figures above for boxes for 1953-54 and previous seasons from Florida Citrus Fruit1955 Annual *m=7, prepared by Paul E. Simler and J. C. Townsend, Jr., with the cooperation of Forida Crop and Livestock Reporting Service Orlando, Florida., Florida Citrus Cormission, Lakeland, Florida, Florida Department of Ag;riculture,. Nathan Mayo, Commissioner, and Agricultura2 Marketing Service, U.S. Department of Agriculture. 2 Figures above for boxes for 1954-55 and 1955-56 from Annual Reports, Citrus and Vegetable Inspection Diviaion, Florida Department of Agriculture, Winter Haven,. Florida.

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WENZEL AND MOORE: GRAPEFRUIT UTILIZATION 81 -TABLE 2 Quantity of Florida Grapefruit Used for Packs of Major Processed Products prior to the 1952-53 season 1, 2 Processed 1936-37 1941-42 1946-47 1951-52 grapefruit Boxes % Boxes % Boxes C Boxes % product Canned juice 3,057,179 51.9 5,683,874 58.0 7,5a4,708 49.0 6,812,089 56.3 Canned blinded juice 90,367 1.5 1,123,932 11.5 4,273,355 27.7 2,736,95o 22.7 Canned sections 2,701,714 45.8 2,852,107 29.2 3,453,o27 22.4 2,290,301 19.0 Canned citrus salad 49,205 0.8 122,694 1.3 140,357 0.9 238,054 2.0 Totals 5,898,465 100 9 .0 000 000 12,077,394 100.0 1 Figures above for field boxes furnished by and used through the courtesy of the Florida Canneral Association, Winter Haven, Florida. 2 Fiue bvedo no include utilization of grapefruit for other processed products, such as processed to 1936, when most of the oranges and grapeshould be pointed out, since both seedless and fruit from Florida were sold as fresh fruit. In seedy grapefruit are produced, that during view of these facts, it is time that more emthe 1955-56 season 75 percent of the seedy phasis be placed by growers and processors grapefruit was sent to commercial canneries on the production and use of citrus fruits havbut the corresponding amount of seedless ing internal quality necessary for the producfruit was 32 percent. tion of processed products of good quality. During the last five years utilization of The quantity of grapefruit, used for the prograpefruit (Table 3) for canned juice has duction of the more important processed varied from less than 7 to more than 11 milgrapefruit products is shown in Table 2 for lion boxes, while that for blend has varied some seasons prior to the 1952-53 season. only slightly; these two products in 1955-56 Statistics presented in Table 3 show that the provided an outlet for about 11.8 million four products that have been the best outlets boxes or 66.4 percent of the total grapefruit -for grapefruit during the past five seasons used by processors in the major processed have been canned grapefruit juice, canned products, grapefruit sections, canned blended juice, and Since the 1946-47 season, the pack of frozen grapefruit concentrate. Perhaps it canned grapefruit sections and citrus salad TABLE 3 Quantity of Florida Grapefruit Used for Packs of Major Pro:;essed Products front the 1951-52 Season through the 1955-56 Season 1, 2 Processed -1951-52 1952-53 1953-54 1954-55 1955-56 grapefruit Boxes % Boxes % Boxes % Boxes % BOX03 product Canned juice 6,812,089 50.6 8,338,569 56.2 11,459,550 58.0 8,226,991 53.8 9,585,095 53.8 Canned blended juice 2,736,950 20.4 2,371,543 16.0 2,797,251 14.1 2,074,358 13.6 2,236,437 12.6 Canned sections 2,290,301 17.1 2,553,104 17.2 3,111,999 15.7 3,367,o6i 22.o 3,179,466 17.8 Canned citrus salad 238,054 1.8 289,489 1.9 379,666 1.9 326,857 2.1 295,622 1.7 Frozen concentrate 1,084,986 8.1 1,159,173 7.8 1,682,141 8.5 1,065,480 7.0 2,128,620 12.0 Frozen blended 268,231 2.0 133,785 0.9 358,429 1.8 224,586 1.5 365,110 2.1 concentrate Totals -13,430,611 100.0 14,845,663100.0 19,789,056 100.0 15,285,333 100.0 17,790,350 100.0 1Figures above for field boxes furnished by and used through the courtesy of the Florida Canners' Association, Winter Haven, Florida. 2 Figures above do not include utilization of grapefruit for other processed products, ouch as processed grapefruit concentrate, frozen grapefruit sections, chilled grapefruit sections and salad, or chilled grapefruit juice.

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82 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 has ranged from approximately 4 to 6 million Canned citrus salad and frozen concentrated cases (24/2's). During the 1955-56 season alblended juice together accounted for 3.8 permost 3 million boxes of grapefruit were used cent. The utilization figures given in Tables 2 for canning about 51 million cases of grapeand 3 are only for the more important products fruit sections and salad, which corresponded listed and, therefore, are slightly less than the (Table 3) to 19.5 percent of the total grapeactual total amounts of grapefruit used for fruit used. Through the use of grapefruit of processing. Some fruit also was used for suitable quality and good processing proproducts such as concentrated processed grapecedures, canned sections of excellent quality fruit juice, chilled grapefruit juice, and chilled may be obtained. Such a product has always grapefruit sections and salad. Thus during the met with good consumer acceptance, and it is 1955-56 season, 544,070 boxes and 262,099 believed that the increased sale of canned boxes of grapefruit were used for chilled secgrapefruit sections, both in this country and tions and juice, respectively. in foreign countries, would provide a means QUALITY OF PROCESSED GRAPEFRUIT PRODUCTS for the utilization of some of the excess grapeThmengofteerqaiydpns fruit now available. Since Florida produces Thmengofteerqatydpns over 70 percent of the world crop of grapeupon both the person using the term and the fruit, it would seem that the potential possiproducts to which the term is applied. For exbilities for export of canned grapefruit secample in speaking of fresh grapefruit, growers tions should be very great. It is difficult to and shippers place considerable emphasis on understand why in recent years the grapefruit the external appearance of fruit, provided it section pack continues to be only approximeets maturity standards for internal quality, mately double what it was in the 1930-31 while processors are chiefly concerned with the season. internal characteristics of the fruit. Thus, the concentrator is more interested in the total The largest production o! frozen concensoluble solids in the juice than he is in having trated grapefruit juice occurred during the fruit free of external blemishes. In packing un1955-56 season, when over 2 million gallons sweetened canned .grapefruit juice, the use of were produced from about 238 million boxes of fruit containing juice of low acidity and highfruit. In contrast to this, during the same seaBrix/acid ratio is extremely important, while son over 70 million gallons of frozen confruit with a greater acid content, provided that centrated orange juice were produced. Thus> it is not excessive, may be used for the pro. it is evident that the acceptance and use of duction of sweetened processed grapefruit frozen grapefruit concentrate by consumers products. has been far below that of frozen orange conThe definition of quality for processed citrus centrate. There was a sharp drop in producproducts should be based upon the desires and tion during the 1950-51 season of frozen opinions of consumers, because the demand grapefruit concentrate to only about 188,000 for these products depends to a great extent gallons caused by poor acceptance of the 1.6 upon such desires. Of course, the price that million gallons of this product packed in the consumers have to pay for these products is previous year. The size of the frozen grapeanother factor and perhaps the major one fruit concentrate pack has just in recent seasons which influences total demand; also, today reached and during 1955-56 exceeded what ease of use or convenience is becoming conit was six years ago in its second season. tinually of greater importance to the houseAbout 17% million boxes of grapefruit were wife. Recently, Florida Citrus Mutual has reused in 1955-56, by the processing industry viewed (22) some of the consumer surveys (5, for the production of the major grapefruit 7, 24) which have been made during recent products listed in Table 3. Canned grapefruit years to determine the characteristics of projuice provided an outlet for 53.8 percent of cessed grapefruit products which consumers this fruit and 17.8 percent was used for the considered to be acceptable and of good qualcanning of grapefruit sections. In the producity. The canned grapefruit juices used for one tion of the canned blended juice and frozen of these surveys (4, 5) were packed in the grapefruit concentrate packs, 12.6 and 12.0 pilot plant at the Citrus Experiment Station. percent of fruit were Used, respectively. Other reports on consumer surveys (4, 6) con-

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WENZEL AND MOORE: GRAPEFRUITUTILIZATION 83 corned with this problem have also been pubrecently completed has shown that the dislished. Very briefly and in general, most of coloration or browning of canned grapefruit the results from these surveys have indicated sections during storage is related to the acidity that most consumers prefer grapefruit products in the canned product, which is dependent that have a typical grapefruit flavor, are modupon the acid content of the grapefruit used. erately sweet and not excessively bitter. In general, browning occurred during storage Therefore, these three characteristics may be more frequently in the canned sections with used as an indication of quality in canned the greater acidities. grapefruit juice and other grapefruit products. The effect of cultural practices on the Characteristics other than these also influence quality of canned grapefruit sections has been the quality of such products. For example, subject to investigation during the past three canned grapefruit sections of good quality seasons. Discussion of the data obtained when should also be firm and uniform in size and canned grapefruit sections were processed appearance; discoloration and undesirable flacommercially from fruit grove plots that were vors in sections, caused by poor storage contreated with fertilizer containing various ditions, are not desirable. Likewise frozen amounts of potash has been reported (27). It concentrated grapefruit juice should show no was found, as is generally known, that the tendency to gelation, should reconstitute easitime at which grapefruit are harvested is a ly and then be free from indications of sepafactor affecting the quality of canned seeration or clarification. tions; also that when grapefruit were picked To improve the quality ot processed citrus at the same time from trees which had reproducts, both growers and processors should ceived fertilizer containing 0, 3, and 10 per-consider factual information that has been cent potash, the firmness of the canned secmade available through past research investitions decreased with increase in the amount nations concerning the factors that affect the of potash. A similar study using arsenated and quality of these products. They should also be unarsenated grapefruit will be completed this aware of current research projects, the ultiseason. mate practical object of -which is the profitResearch has been done on various problems able utilization of the entire grapefruit crop concerning the production and storage of frozeither by improvement in the quality of the en concentrated grapefruit juice. .Data on major processed products that are now changes that occur in this product during storpacked, thereby causing better acceptance age, such as gelation, clarification, sugar hyand more demand, or by the development of drate formations and the very slightloss of new processed products or by-products that ascorbic acid have been published in various will provide other outlets for this fruit. Some articles (2, 8, 13, 14, 15, 18, 25). Thermal of these research investigations, that have been stabilization of grapefruit juice for the produccompleted or are in progress, at the Citrus tion of frozen concentrate has been found Experiment Station will be discussed briefly. necessary to prevent the occurrence of gelaPrincipal emphasis concerning processed prodtion and clarification in this product during ucts has been placed on the factors affecting storage and distribution. Atkins, Rouse and the quality of canned grapefruit sections, others (1, 2, 3, 19, 20) have reported results canned grapefruit juice and frozen concen~ obtained from several investigations of this trated grapefruit juice. process for the production of frozen grapeAn investigation on the effect of storage fruit concentrate of good quality. During stortemperature on quality of canned grapefruit age at 0' F. or lower, undesirable flavors may sections was discussed by Huggart, Wenzel develop in frozen grapefruit concentrate, Such and Moore (9). Results indicated that for off-flavors are usually described as being simimaintenance of original good quality in lar to tallow, castor oil, or cardboard. Results canned sections, the products should be held of the study since 1953 of this problem were at 70' F. or lower. Marked changes in color, recently reported (17). Oxidative changes are flavor and firmness that result in lower quality believed to be involved in the development of in this product occurred at storage temperthese off-flavors and it has been found that matures of 80 F. or above. Another study (10) the maintenance of a sufficiently high peel oil

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FLORIDA STATE HORTICULTURAL SOCIETY, 1956 level in grapefruit concentrate helps to preHT)o of sugar and a small amount of peel oil vent either the development or the detection and when this product is mixed with an equal of these undesirable flavors. Two investigavolume of water, a very palatable grapefruit tons were instigated, during the 1955-56 drink is obtained. A clarified grapefruit conseason, at the request of the Quality Advisory centrate of good quality has been prepared Committee of the Florida Canners' Associaand the preparation of either a still or cartion to determine factors that affect the qualboated grapefruit drink from this product is ity of frozen grapefruit concentrate. The first being investigated. Canned blended fruit of these studies was the determination of most juices of various types are being consumed in of the chemical, physical and other characterislarger quantities yearly and, therefore, the use tics of 28 packs of commercial frozen grapeof grapefruit juice in various types of blends fruit concentrate that were collected from 11 may be investigated during this season; sevFlorida plants. The purpose of the second eral packs for storage studies may be prostudy was to obtain data that might indicate cessed. the relationship between the quality of raw From this discussion it should be evident grapefruit juice and that of the frozen grapethat a great amount of research has been and fruit concentrate produced from it. Fruit is being done at the Citrus Experiment Station from different localities were obtained and 11 on problems related to the quality of processed lots were processed in the pilot plant. Data grapefruit products. obtained from these two investigations were Now let us consider what the grower and presented recently (28) and similar studies processor can do to improve the quality of are again planned for this season. The effect processed grapefruit products. One of the of fruit maturity on the quality of frozen major problems that confronts the processor grapefruit concentrate is also being studied in his attempt to make products of uniform intensively. and acceptable quality is the great variation The presence of the bitter glucoside, naringthroughout the entire packing season in the in, is the chief cause of bitterness in processed internal quality of grapefruit that he has to grapefruit products. Kesterson and HendrickSuse Thi wid vaito in frui exst because son (11) found no significant difference in of many factors, such as differences in variethe amount of naringin in juices extracted ties, maturity, cultural practices, rootstock, soil from different varieties of Florida grapefruit and weather conditions. Sites and Camp (21) and also reported that most of the naringin was discussed some of these factors in relation to in the albedo, rag and pulp of the fruit. The the use of citrus fruits, chiefly oranges, for the degree of bitterness in canned grapefruit juice production of frozen citrus concentrates. Wenor frozen concentrate is dependent upon the zel and Moore (26) reported on the characterjuice extracting and finishing procedures used, istics of concentrates made from different since the quantity of pulp, rag, and albedo in varieties of citrus fruits, including grapefruit. the processed product is determined by these In general the flavor of processed products procedures. A method for the estimation of made from seedy grapefruit is better than that naringin was devised by Ting (23) that is in products made from seedless grapefruit. based on the enzymic hydrolysis of it by a Other factors causing wide variations found glycosidase. With further modifications, this in the quality of grapefruit sold for processing laotory proede for pretessiriwgt a are the use of fruit from packing houses which thebray ponrolledure deeo iterne, nd is not suitable for fresh shipments, the fact phrcey graprith prdegc fbttrsss. that only a portion of the grapefruit crop is parsenated, the increased production and use Some work also has been started by Olsen of pink grapefruit, and the tendency for (16) to develop uses for grapefruit in products grapefruit trees to bloom and set fruit at difdifferent from those that have been previously ferent times during the same season. Since discussed, with emphasis on the utilization of such great variation exists in the quality of grapefruit of high acid content. A canned fruit throughout a season, processed products pasteurized grapefruit product has been made of variable quality will result if such fruit is from very sour grapefruit juice by the addiused at random. If products of acceptable,

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"WENZEL AND MOORE: GRAPEFRUIT UTILIZATION 85 uniform, and improved quality are to be portant that growers do not harvest the crop packed, the processor must eliminate the until the fruit has reached its optimum magrapefruit, which he receives from either packturity and a desirable Brix/acid ratio obtained ing houses or groves, that is not suitable for for the specific use for which it is intended. use in the specific type of processed product Since the internal quality of the fruit is one that is being packed. Also for the complete of the major factors that determines the qualutilization of the grapefruit crop, culled fruit ity of processed products, processors should that cannot be either sold as fresh fruit or obtain and use only the kind of grapefruit that used in processed products, will have to be is needed to produce products of good quality. diverted to some other use, such as the proDuring the past season most of the concenduction of citrus by-products as recently sugtrators, who packed frozen grapefruit congested by Kesterson, Hendrickson and Newcentrate, made an effort to obtain fruit of hall in a report (12) to a Grapefruit Study better internal quality than that previously Committee of Florida Citrus Mutual. If such used; this was done following recommendaculled fruit cannot be profitably used for tions of the Quality Advisory Committee of some other purpose, then it will be better to the Florida Canners' Association and surely return it to the grower to be discarded rather was a step in the right direction. than to impose it upon consumers as canned Some incentive to the grower for the prograpefruit juice or frozen grapefruit concenduction of grapefruit of good quality would trate of poor and unacceptable quality. Growbe provided if processors found it economicalers should realize that some of the grapefruit ly possible to pay for grapefruit on the basis that is being produced cannot be made into of its internal quality, as they are now doing canned grapefruit juice, canned sections or for the procurement of oranges of high solids frozen concentrate of good quality. It is sugcontent for frozen orange concentrate. gested that growers find out more about the Prcsigpoeusantchqesde. internal quality of grapefruit that Js needed mieroesong pedes tnd qutynqe deel rby processors for the production of products ,ssed tru sroucseo exetteqal the adeprof good quality; then using information availeed oitrs s. Fn c e ampleth deable about the relation of cultural practices gre foze bcoenessrate mayne grpefrbt juice and other factors to the internal quality, do exractinzend finshngrt mayobeduared. byDuing what they can tQ produce fruit that will be teratngasnd fshng processors. haveing suitable and desirable for the production of theasdth seas rnsmeess orncs ofhaned one or two specific processed products. p sO grapefruit juice and frozen concentrate by Much more information is needed before voluntarily making changes in extracting and such characteristics as flavor or degree of finishing procedures, even though such bitterness in grapefruit may be subject to changes resulted in a decrease in the yield of control by the grower through cultural or other juice. Such efforts are to be commended and practices. However, growers can control to should result in an increased demand for these some extent the acidity in grapefruit by arproducts of better quality. Thermal stabilizasenation; also fertilizer constituents, such as tion of grapefruit juice used in the production potash, have an effect on this characteristic. of frozen concentrate has been found to be Therefore, growers can do something about necessary to prevent gelation and clarification the production of grapefruit with a low acid in this product during distribution and storcontent or high Brix/acid ratio, which is deage. Adjustment of the amount of peel oil in sirable for producing processed products of frozen concentrate is also necessary for degood quality and especially those that will not sizable intensity of flavor and to help prevent be sweetened by the addition of sugar. It is the occurrence or the detection of "oxidized" realized that problems are encountered when off-flavors that may occur during frozen storarsenation is used, but such treatment proage. Unsweetened canned grapefruit juice and vides the principal method for the production unsweetened frozen concentrate should be of less tart or sweeter grapefruit either early made only from fruit that is fully 'mature and in the season or during mid-season. Regardless from juice which has a Brix/acid ratio within of the cultural practices used, it is very imthe range that has been shown by various sur-

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86 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 veys to be acceptable to consumers. When of fresh fruit and processed grapefruit prodsweetened products are packed from low ucts of good quality, together with the diverratio fruit, excessive amounts of sugar should sion to the production of citrus by-products not be added since dilution of the flavor in or other uses of all fruit that cannot be used the product will result. All processed grapefor these purposes because of poor internal fruit products should be stored under condiquality. tions which will minimize changes in flavor that occur if the temperature and time of stor_ LITERATURE CITED age are too great. Storage of canned grape1. Atkins, C. D., and A. H. Rouse. 1953. Timefruit juice and sections at temperatures lower temperatraerelationsips for heat i1nactivation o *etnstrs in ciru jucs Foo Tebnl 7: *O than 80' F., if possible, is advisable and frozen 489-491. S0 2. Atkins, C. D., A. H. Rouse, R. L. Huggart, E. tL. Moore. and F. W. Wenzel. 1953. Gelatin and clarification in concentrated citrus juices. III. Effect It is hoped that this brief discussion will of heat treatment of Valencia orange and Duncan help growers to understand some of the probgaefruit juices prior to concentration. Food Technol. lems involved in the production of processed 3. Atkins, C. D., and A. H. Rouse. 1954. Timegraefui podutsofgod qaltyan -temperature-concentration relationships for heat ingrapfrut poducs o god qulit an to activation of pectinesterase in citrus juices. Food realize that the production of products which Technol8: 498-500.15.Peeecsfrcne 4. Bell Hug P. 1955. Prfrne for canne will be acceptable to most consumers depends grapefruit juices. Proc. Fla. State Hort. Soc. 68: -151-155. to a great extent on the internal quality of 5. Bell, Hugh P. 1955. Preferences for canned e o grapefruit juices. Marketing Research Report No. th gpr S p s108. Agricultural Marketing Service, U. S. Dept. Agriculture, Washington, D. C. SUMMARY 6. Birdsall, Lamont. 1955. Consumer preferences in citrus juices. Proca. State Hort. Soc. 68: 133Statistics presented show that canned grape13. a fruit juice canned blended juice, canned Hall. 1955. Frozen grapefruit sections: Evaluating a new product by retail sales audit and household grapefruit sections, and frozen grapefruit consurvey. Marketing Research Report No. 110. Agriculcentrate are the principal products into which turalM~arketing Service, U. S. Dept. of Agriculture, Wahntn D. C .. Florida fruit are processed. About 48 per8. Huggart, Richard L., Dorothy A. Harman and Edwin L. Moore. 1954. Ascorbic acid retention i cent of the grapefruit crop was used during frozen concentrated citrus juices. Jour. Amer. Dieteti' Assoc. 30: 682-684. 9. Huggart, R .W. Wenzel, and E. L. Moore. cese gapfritprducts 1955. Effect of storage temperature on quality of canned grapefruit sections. Food Technol. 9: 268-270. d th f 10. Huggart, R. L., F. W. Wenzel, and E. L. Moore. S1956. Fla. Agr. Exp. Sta. Unpublished report. tors, such as bitterness, acidity, flavor and 11. Kesterson, J. W., and R. Hendrickson. 1953. Naringi, a bitter principle of grapefruit. Occurrence, stability, that affect the quality of processed Properties, and possible utilization. Fla. Agr. Exp. grapefruit products are briefly discussed. Sta. B 5I,. 12 Ketrsn J.0 W. R. Hedrckon an W. F. *S In order that improvement may be made in Newhall. 1956. Possibilities for the utilization of ..surplus and cull grapefruit as by-products. Fla. processed grapefruit products, it is suggested Agr. Exp. Sta., Citrus Station Mimeo. Report 57-2. 13. Moore, Edwin L., Richard L. Huggart, and that growers produce fruit of such internal Elmer C. Hill. 1950. Storage changes in frozen conualit that most of it can be processed into centrated citrus juices-preliminary report. Proc. Fla. qState Hort. Soc. 63: 165-174. p14. Olsen, R. W., R. L. Huggart, and Dorothy M. -Asbell. 1951. Gelation and clarification in concenStrated citrus juices. .Effect of quantity of pulp sold as fresh fruit should be produced with in concentrate made from seedy varieties of fruit. Food Technol. 5: 530-533. internal ualit suitable for use in one or two 15. Olsen, R. W., and E. L. Moore. 1954. Sugar hydrate formations in frozen citrus concentrates. specific processed products. It is suggested Food Technol. 8: 175-176. that processors use only fruit of such internal 16. Olsen, R. W. 1956. Fla. 'Agr. Exp. Sta. Unpublished report. quality that will result in, the production of 17. Olsen, R. W., E. L. Moore, F. W. Wenzel, and R. L. Huggart. 1957. "Oxidized" flavors i frozen products of good and acceptable quality; that citrus concentrates. Food Technol. 11: processing procedures which affect quality be 18.i' RouseAns H.a1949 Gel formation n frozen carefully controlled and that processed prodProc. Fla. Soc. 62: 170-173. 19. Rouse, A. H., and C. D. Atkis. 1952. Heat ucts be stored at all times under optimum inactivation of pectinesterase in citrus juices. Food conditions for maintenance of their initial good Te 0no -6 .259.Fut 20,. Ros, A. H., an C. D. Atis 193 ute ualit. results from a study on heat inactivation of pectinesterase in citrus juices. Food Technol. 7: 221-223. Com lete utilization of the Florida grape21. Sites, John W., and A. F. Camp. 1955. Producing Florida citrus for frozen concentrate. Food rTechnol. 9: 361-365.

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PRATT: LONG RANGE RELATIONSHIPS 87 22. Steele, Herman F. 1956. Summary of con26. Wenzel, F. W., and E. L. Moore. 1955. Charsumer surveys. Florida Citrus Mutual Mimeo. Reacteristics of concentrates made from different Port Feb. 28. varieties of citrus fruits. Food Technol. 9: 293-296. 23. Ting, S. V. 1955. Application of enzymic hydro27. Wenzel, F. W., R. L. Huggart, E. L. Moore, lysis in the analysis of naringin in grapefru ,it prodJ. W. Sites, E. J. Deszyek, R. W. Barron, R. W. ucts. Fla. Agr. Exp. Sta.. Citrus Station Mimeo. ReOlsen, A. H. Rouse, and C. D. Atkins. 1956. Quality port 56-9. of canned grapefruit sections from plots fertilized wit vayn mut pts. PrV Fla State 24. U. S. Dept. Agriculture. Bureau of Agricultural Hort. Soc. 6:10-175. fpth.ro.F.Ste Economics, Washington, D.C. 1950. Consumers use 28. Wenzel, F. W.. R. W. Olsen, E. L. Moore, R. L. of and opinions about citrus products. Huggart, C. D. Atkins, A. H. Rouse, S. V. Ting, E. C. 25. Wenzel, F. W., E. L. Moore, A. H. Rouse and Hill, E. J. Deszyck, R. Patrick, and R. W. Barron. C. D. Atkins. 1951. Gelatin and clarification in con1956. investigations concerning factors affecting the centrated citrus juices. I introduction and present quality of frozen grapefruit concentrate. Fla. Agr. status. Food Technol. 5: 454-457. Exp. Sta., Citrus Station Mimeo. Report 57-3. LONG RANGE RELATIONSHIPS BETWEEN WEATHER FACTORS AND SCALE INSECT POPULATIONS ROBERT M. PRATT tinuous record is available, there have been two years in which the population was almost Florida Citrus Experiment Station constant at a low level from October through Lake Alfred February. In the other three years, the average infestation has increased sharply in OctoForecasts of scale infestations can be based ber and reached a high level by the middle of in part on annual and seasonal cycles, but to November. Obviously, it is advantageous to forecast the level the population will reach at citrus growers to know as far ahead as possible any given time, it is necessary to know somewhether such a fall red scale outbreak will thing of the factors which cause deviations occur. from the long term average population. It has been known for several years that The abundance of scales and other insects when the red scale activity index (1) inand mites is regulated by many interacting creased to a high level in August, a high popclimatic and biological factors. The total efelation in October and November would folfect of these can be determined only by field low. This observation was used successfully in observations. Methods of determining the forecasting the severe outbreak that occurred populations of scales and other insects and in the fall of 1955. The ecological factors inmites have been described previously (1). A evolved in this pattern were not known. Since continuous record for nearly six years is now the trend was discernible as early as the first available. It is not possible to evaluate all of week in August, obviously, the factors responmany individual factors separately on the basis sible bad to have occurred before this time. A of field records, but some can be isolated in critical examination of a graph showing perthe laboratory, and others are of sufficient imcent of leaves infested showed that in the portance to be recognized even in the presence years when fall outbreaks occurred, a higher of other influences. Certain climatic factors population level occurred as early as mid-July, which have been found to have an influence so the climatological data from the months on the population of Florida red and purple preceding that date were examined. Among scales are discussed here. the factors considered were rainfall (Table 1) and temperatures, as reflected by monthly FLORIDA RED SCALE summation of Heating Degree Days (Table The population of Florida red scale, Chry2). Note that in measuring the amount of cold somphalus aonidium (L.), reaches a peak weather in degree days, a low value indicates sometime in July each year. This is followed warm weather and a high value indicates cold by a declining trend that continues into Sepweather. tember. In the five years for which a conRed scale infestations were computed for Floid Agicltra IExprien Sttin Jural comparison as the maximum infestation in Sri No 563.ur xermn Sain ora October or November, and as the average

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88 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 1 Rainfall 1951-56* Year December Jn=na Fbbraary March April 1950-51 2.6 1.36 2.53 1.68 4.96 1951-52 1.94 .49 5.96 4.7 .84 1952-53 .59 3.51 2.99 3.61 4.90 1953-54 4.10 1.38 1.50 2.23 3.85 195-55 1.39 2.25 1.75 .91 2.67 1955-56 1.08 1.89, .99 .38 2.30 *Ccmpil.ed from Weekly Weather and Crop Sun=7r. percent of leaves infested, August through scale population was for the period, January December (Table 3). through March. Where a substantial differTo seek a basis for comparison, the years ence between the two groups of years was of the record were divided into two groups, found, the coefficient of correlation between one including the three years (1951, 1954, the weather factor and scale population was 1955) in which a fall outbreak occurred, and computed. These comparisons are summarone including two years (1952, 1953) in ized in Table 4. which red scale populations were negligible The correlation between the highest level in the late summer and fall. The climatological of activity in August and the average infestadata for these two groups of years were then tion, August through December, is significant. examined for differences. The months were Thcreatnsbwenheodwahr considered individually and in various comTecorltnsbwenheodwahr binations. Inspection of the population data factor (degree days, January through March) and the climatological records indicated that and both the August activity and fall average the greatest difference in temperature and population is highly significant. rainfall between the two groups of years ocThe negative correlation between the total curred in March, but that the most consistent rainfall, January through March, and August relationship between climatic factors and activity is not significant, but between rain Table 2 Heating Degree Days 1951-56* Year December Jamn=7 February March April 1950-51 253 189 153 68 40 1951-52 71 322 151 45 23 1952-53 207 174 88 18 21 1953-54 145 118 :L2/+ 346 2 195-55 275 242 123 78 4 1955-56 147 309 86 so 15 *Cempated by subtracting-the daly mean temperature frm 650 F. and mming for the period. Data from ggrothermograph stations at ake Alfred,4 Vrritt Island, Tavares, Intz, and Avon Park.

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PRATT: LONG RANGE RELATIONSHIPS 89 FACTORS IN FALL RED SCALE POPULATION IC -'-500..n400 -4. 4.z 7X >4 *0 Fig. 1. Factors in Fall 3 Red Scale Population. 01 .--1 JAN.-MAR. JAN.-MAR. AUGUST OCT-NOV. and fall population, there is significance at lowing a cold, dry winter, or low following a the 19 to I level. warm, wet winter. Factors related to fall outThus there are two climatic factors that are breaks in the last six years are summarized significantly correlated with the red scale in Fig. 1. population in the late summer and fall. UnData for 1956 are not complete. The period, fortunately, there have not been any years in January through March, was both -cold and the period of the record when the critical ,dry, and the index of activity reached a high period was either warm and dry or cold and level in August, so a high population in the wet, so it is difficult to separate the two facfall is to be expected. As of October 24, the tors. While the correlation between degree average infestation was 3.0 percent. days and population is higher, it would be Red scale populations in January and Febmost unsafe to ignore the rainfall factor. It ruary tend to be in proportion to the infestacan only be said that the red scale population tion level in November and December. No can be expected to be high in the fall, folclear basis for forecasting the population trend Table 3 Red Scale:Smllmary of Climatic Factors., Activity, and Population Inches Rain Degree Days Max. Aug. Fall Population Year Jan.-Mar. Jan.-Mar. Activity Average* Max. 1951 5.57 410 3.2 3.0 4.5 1952 11.42 318 3.3-1 1.6 1.6 1953 10.12 280 2.71 1.4 1.5 1954 5.11 388 3.41 2.4 3.1 1955 4.91 443 3.69' 2.9 3.9 1956, 3.26 475 3.41 3.0** *Average percent of leaves infested, August through December. **Preliminary, October 24, 1956.

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90 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 4 Correlations between Red Scale and Weather 1951-55 Correlation Comparison Coefficient Significance* August Activity*/opulation*** .901 19 :1 Degree Deys, Jan.-Har./ gust Activityr .976 99 : 1 Degree Days, Jan.-ar.pulation .968 99 : 1 Rain, Jan.-*Mar. gust Activity .W ns. Rain, Jan.-4ar./ ouation -909 19 :3. *Required for significance at the 19 : 1 l6evel .878. Required for significance at the 99 : I level .959. **"muma activity level during the month. ***Average percent of leaves infested, August through December. from March through June has been found, and time in July, the exact time apparently being there does not appear to be any relationship determined by the time of the onset of the between populations in this period and those rainy season. Following the summer peak of occurring in the fall. infestation, the population declines rapidly PURLE SCALE until mid-September. This reduction has been Purple scale, Lepidosaphes beckii (Newm.), attributed to a disease, Chytridiosis (2, 3). is regarded as the major scale pest of citrus in After September, there is a more or less reguFlorida. An examination of the annual populalar increase in population through the time tion cycles for the last five years reveals that when counts on old leaves are ended in May, there is but little difference from year to year. and until a peak of infestation on new leaves is This suggests that differences in the weather reached again in July. from year to year have less influence on the There is some year-to-year variation in the population level at any given season than is magnitude of the population. Examination of the case for other pests, such as red scale. the population data revealed a small, but conThere is, however, a well defined annual sistent, difference at the end. of December cycle. The population reaches a peak somewhich permitted dividing the record into two Table 5 Purple Scale Infestations in December, May, and July Percent leaves Infested maz. Date of Tear 4th Week-Dec. 4th Week-%aW July July Peak 1951-52 8.5 22.5 10.9 lot Week 1952-53 1. 27.3 14.3 lot Week 1953-54 8.3 29.2 18.3 lot Week 195/o55 12.*8 28.8 17.2 2nd Week 1955-56 .86 23.6 18.8 3rd Week

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PRATT: LONG RANGE RELATIONSHIPS 91 Table 6 Relation Between Degree Days in December and Jamary to Prple Scale Ppulation the following December Degree Days Percent Ieaves Infested in following December Year Dec.+Jan. lot Week 2nd Week 3rd Week 4th Week Av. 1950-51 442 9.2 8.9 8.5 8.5 8.8 1951-52 193 10.8 32-3 31.5 1111 11.2 1952-53 381 8-3 8-3 8.2 8.3 8.3 1953-54 263 12.4 12.3 2. 3.2.8 3.2./ 195/#55 517 7.7 7,6 8.3 8.6 8.1 groups of years. in one group (1951, 1953, that there is anything critical about this par1955), the infestation was between 8 and 9 ticular time. Obviously, there is a very high percent. In the other years (1952, 1954), it correlation between the population in the was over 11 percent, These general relationthird week and in the fourth week. ships persisted until the following July (Table With exceptions noted above, the popula5), with the following exceptions: in May, tions in May and July are proportional to 1954, the population was higher than would those in December, and therefore to the Dehave been expected from the preceding December-January temperature factor. ,cember population, and the July population In 1954, the scale population was low was proportional to that occurring in May. In through March, as expected, but the increase 1956, the July peak was higher than would in population in April and May was rapid and have been expected from the December and a high level was reached. The peak populaMay levels. tion in July was proportionately high. To find climatic factors correlated with the Examination of weather records indicated purple scale population in December, the that the only unusual occurrence was an unrecords were examined in the same way that seasonable cold spell early in March (see was used for red scale. A preliminary exam-Table 2). This was accompanied by a brief ination of the records indicated that there were reduction in scale population and followed by no differences in the summer and fall months an increasing trend. A significant correlation that showed any consistent relationship with (r=.939) was found between the degree days the scale population at the end of the year so in March and the change of scale population attention was given to the records of the prebetween that at the end of December and that vious winter (see Tables I and 2). at the peak of population in July. There was No general relation between rainfall and also a significant correlation (r= --.878) bepopulation was found, but it was determined tween the lowest March weekly mean temthat there was a fairly constant inverse relaperature and the change inscale population tionship between the amount of cold weather from the end of December to the end of May. in December and January and the purple scale In 1956, the scale population at the end population the following December (Table of May was relatively low, and in proportion 6). That is, the warmer this period, the higher to the population at the end of December, but the scale population. the average infestation increased rapidly in With the limited data available, a significant June and July. When the peak was reached correlation (r= -.878: required for 19 : 1. the third week in July, the population was. at -.878) was found only between the temperaa record high level. There are indications thiat, ture factor and the population in the third this was a result of the prolonged drought, but week of December, but it is not considered the evidence is not considered conclusive.

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92 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 There was, however, a significant correlation From the foregoing, it may be concluded (r= -.890) between the rainfall in the perithat the purple population at the end od, January through March, and the ratio beof the calendar year is proportional to the teen the May and July populations. temperatures in the preceding December and In April of 1953, there was a brief decline January (inversely correlated with the number of degree days) and that this general relain purple scale population at a time when a tionship will persist through the peak of instrongly increasing trend was to be expected. festations the following July, but the anticiThis coincided with an extensive rainy period. pated general trend may be modified by subThere was a highly significant negative corresequent weather conditions which have more lation between the amount of rain in March immediate effects (Fig. 2). If there is a late and April (see Table 2) and the population cold spell, the population following will be higher. If there is a wet spring, it will be lower, change in the same period (r== -.993: -.959 but if the spring is exceptionally dry, it will required for significance at 1%). be higher than expected. FACTORS IN PURPLE SCALE POPULATION 30* 26a 24W 500 2C 08 400 160 140 300 0 120 -200 -O DE.-JA .Edof E.Ed fAYApekn W. W. taotos in # 010 0 DEC.-~ JAN En ofDC n fMYA eki

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JOHNSON: SYSTOX USE 93 SUMMARY The purple scale population in May and The population level of red scale in the fall July is proportional to that in December unmonths has been found to be correlated with less there is a spring drought or a late cold the mout o cod wathr i th peiod spell, in which case, the populations will be Jhamr ough Mrc, wathd i egtey perod, higher than idicated, or unless there is abunJaur thog Mach an 66 neaivl cordatsrn an nwihcsteprl related with the rainfall in the same period. dcale spulg ain, will bewher.pr When the index of red scale activity has saeppuainwlbeowr reached a high level in August, a high popuLITERATURE CITED lation in October and November has followed. infestations Fla r we 6920Frcs (11):r21.se T2. Fisher, F. E., W. L. Thompson, and J. T. ber is correlated with the amount of warm eases ofsc1ale insectsssattackingcitrus innFsorida. weather in the previous December and JanF3. Enta 2Martin H. 1955. Factors contributing to nary. the naturalcrol of citrus 8inses2and mites in Flria Jouna Ecn En.4 :4248 NOTES ON THE USE OF SYSTOX FOR PURPLE MITE CONTROL OF CITRUS ROGER&B JOHNSON demeton, is reported to be about as toxic to Florida Citrus Experiment Station warm blooded animals as parathion and is more readily absorbed through the skin. This Lake Alfred means that the same precautions used in handling parathiont must also be employed Systox has been shown to be effective with Systox. against the purple mite, Metatetranychus citri McG., under Florida conditions. Spencer and TIMING OF SYSTOX SPRAYS Selhime (1) reported in 1954 that Systox at jpsne l 3 eosrtdta h dosages of I pint or 1 quart per 100 gallons Jongesn perid ao. (onr) demnstralifdrnhat folcontrolled citrus red mite (purple mite) as longesd aperaiods of ontox durCagiNoveaberl well as oil emulsion, ovotran, aramite or EPN. andweebratuhn application wassoxdrn Nvme Thompson et al. (2) also reported in 1954 ade DnJambery torFug y Thes pp athorws that the average period of control with Systox adsere d thanary oro nebr d toe rease was 6 weeks, but that control for as long as apsogrepsrvedy frat Mchr throgdedteers 13 weeks had been obtained with Systox as Jogrsve an rTompo Mar ) troSepdtatber. compared to only 8 weeks with DN Dry Mix Johnsin Foandermpsed (4)roary toat yn or 3 quarts of an 84 percent oil emulsion. In tr mFrdadresdrmJnaytoM addition, Systox has been used by growers ill but had made no applications prior to January. both ground and air applications with reA grove of thinly-foliated Valencias about portedly satisfactory results at dosages that 8 to 10 feet in height at Haines City, Florida were sometimes very low. Since Systox is an was used for an experiment to determine efexpensive material, it is important that it be fects of date of application. This grove was used efficiently. For this reason, experiments divided into three blocks, each 6 by 20 trees were conducted in 1955-1956 to obtain inin size. Each block or replicate was divided formation on the effect of date of application, into four plots. One plot in each replicate was dosage and thoroughness of application on the sprayed in October, a second inl December, interval of control of purple mite with Systox. a third in February, and the last in April. A Systox is the trade name of an emulsifiable different dosage or material was applied to spray concentrate containing 21.2 percent of each of three subplots of 10 trees each. De0,0-diethyl-0-2 (ethylmercapto) -ethyl thitails of these applications are presented in ophosphate. The active ingredient, known as Table 1. Control following the October application is selorida Aricultural Experiment Stations Journal shown in Fig. 1. Control is considered satisSeis No 52

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94 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 1 Data on the application of sprays in experiment to determine effect of time of application of Systox on purple mite control. Date of Application Spray Dosage Prespray Population Material per 100 per per 100 leaves gallons acre Mites Enos Oct. 27, 1955 Systox: 1/2 pint 2.7 pints 100 80 Systox pint 5.2 pinto 100 so DN Dry Mix 2/3 lb. 2.9 lbs. 100 so Dec. 22 1955 Systox 1/2 pint 2.3 pints 550 690 Systox 1 pint 4.0 pints 550 690 DN Dry Mix 2/3 lb. 2.8 lbs. 550 690 Feb. 16, 1956 Systox 1/2 pint 1.9 pints 650 780 Systox 1 pint 4.9 pints 650 780 Ovotran 1 lb. 6.0 lbs. 650 780 Apr. 4, 1956 Systox 1/2 pint 1.3 pints 1090 540 systox 1 pint 2.9 pints 1090 540 Ovotran 1 lb. 3.3 lbs. 1090 540 factory until the population exceeds 100 mites In Fig. 4 is shown purple mite control with per 100 leaves. Systox at 3 pint per 100 galsprays applied in April, In this application, Ions gave control for a period of 63 to 71 days, Systox at 32 pint controlled purple mite for or about two weeks longer than DN Dry Mix only 20 to 35 days while ovotran as well as I No. 1. Systox gave somewhat better results at pint of Systox both controlled for 35 to 48 the dosage of I pint, but, although both dosdays. ages of Systox were significantly better than The results of this experiment, presented i DN Dry Mix No. 1, there was no significant Figs. I through 4, show that Systox was efdifference between the two Systox treatments. fective against purple mite from late October Control of purple mite with 1/ or I pint of through February, that a dosage of 312 pint of Systox as well as %pound of DN Dry Mix No. Systox per 100 gallons can be superior to DN .P .Dry Mix No. I mn late October and December, I in December sprays is shown in Fig. 2.adtht pnofysxcaeqa1pud Systox at 1/2 pint controlled purple mite for 63 and ota 3int fay. Thscan als spow -to days. T gas o that Systox was relatively ineffective in April. trolforonl 35to 3 das. her wa no Data presented in Table I show that during significant difference between 32 and 1 pint of the interval from October through February Systox, but both dosages were significantly whncnrlasatsatytedsgef bette tha DN ry Mx No 1. pint of Systox per 100 gallons was equivaControl of purple mite with February sprays lent to 2.7 to 1.9 pints per acre. Since the lowis shown in Fig. 3. Systox at 1/2 pint as well as er rate per acre was as effective against a ovotran at I pound controlled purple mite for high mite population as the higher rate against 60 to 74 days. Although mite counts were not a low population, it can be concluded that continued long enough to determine the inabout 2 pints per acre of trees 8 to 10 feet terval of control with I pint of Systox, mite high will give satisfactory results from Octopopulations where this dosage was used reber through February. Larger amounts should gained low even 73 days after application. be needed on larger trees.

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JOHNSON: SYSTOX USE 9 0300 1 99 F* .SIG~ S S S *5 -3 /ON. Dry Mix F .N Dry Mix 0 0 2 MS -*MP5 Systot,1 pj 00-Mew.. 4 P *. S P S IeS -C Syst ta, .Vt. ysteox' pt. ONO -S ---S *o S. S r S b Strn b 471 .*5 4f PopT 9o 10 7. S11 P BtSat fg DAYS AFTER SPRAYING b. ,195 DAYS AFTER SPRAYING A. 42,1955. temn hte-oae fMo to Sys-. Seail fiae Tep6 orng res atHane *oto s6 it Dcme 19, 1 55 we prspa miepp 100 *eavs. Unde ths Scnitos inev-S S S j V. 923 in a gr veo *ae ca at Hans Ciy F5rd .*y ih Mp n f y t x( .tp rar ) Mit pouain.h n sry vere -appie an 12 o1* dy withbot armt S5 egg pe-0 evs ne hs odtos l eid S oS Soto inti tes wer -ent Sytox as welln as DNlyMb.o 1cn dosagef of% P on 2pua in s per ac a eb -ap le pi, % 9 6 Prsp a m/epo ua tr 00 Mith S s d tin 2 yS Sr w 6f 7 or 5 p t DAY SS AFE SPAYN Feb 1615 DAY ATE S PRYN Ap.415 terin whehe doae of 1 or 34 pin oSyhevl foiae Tepl orng trea aie Th ist of ths tet wa state whn uain vrae 8 ie n 550 egg per sp s wer aple Noeme 15 95 to 10 leve. Une thes codtos-nevl in a8pito So (05.5 pitprare,7 o9

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96 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 2 Control of purple mite with 4 dosages of Systox applied to Talencias on November 15, 1955. Haines City, Florida ..... Material ad Live purple mites and eggs per 100 leaves on indicated dates Dosage per 100 gallons.1 (days after application on November 15, 1955.) Nov. 21 Dec. 1 Jan. 3 Feb. 8 Feb. 28 Mar. 21 (4) (+16) (+49) (+85) (+105) (+127) Systox, 1/4 pint Mites t 9 0 23 49 us 171 Eggs 1: 137 9 53 1%6 500 986 Systox, 1/2 pint atm 1 0 0 a 17 120 291 Eggs 1 67 14 34 131 530 1024 systox, 3/4 pint Mites 1 0 0 15 23 82 266 Eggs S 98 21 51 108 332 673 Systox, 1 pint Mites 2 0 0 3 9 44 77 Eggs : 76 18 14 68 1W0 469 DN Dry Mix, 2/3 lb. Mites s 1 1 21 51 182 326 Eggs .92 72 ?2 145 652 129 WBD : MItes (19:1) nod nad nad nod nsd13 (99:1) nod nod nsd nod ned nod 'All sprays included 5 lbs, of wettable sulfur per 100 gallons. 2Average pre-spray mite population -105 mites and 308 eggs per 100 leaves. Table 3 Control of Purple Mite with 4 dosages of Systox applied to Valencia Oranges on April 3, 1956. Haines City, Florida Material and Live purple mites and eggs per 100 leaves n indicated dates Dosage per 100 Gallons (days after application on,April 3, 1956). April 6 April 17 Apri 1 23 May 2 (+3) t+14) (;20) (+29) Systox, 1/8 pint Mites .38 60 32 47 Eggs : 362 50 244 143 systo, 1/4 pint Mites : 24 44 15 215 Eggs 8 482 59 81 114 Systx, 1/2 pint Mites S 17 19. 59 Eggs $ 316 63 31 84 Systax, 1 pint Mites 22 16 2 25 Eggs 3 774 167 64 24 Ovotran, 1 pound Mites 1 36 20 20 39 Eggs : 772 82 76 55 IMD mites (19:B) 152 (99t1) 22t 411 sprays included Ma Z, 2 lbs par 100 gallons; Meutro cop 053", 1.4 lbs, ad vttable sulfur, 5 lbs. 2 Average pro-aprey mite population -205 mites and 890 agge per 100 leaves.

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JOHNSON: SYSTOX USE 97 Table 4. Effect of thoroughness of application on Control of furpoe Mite vith Systox. Iake Alfred, Florida. .Member 1955-March, 1956. Material(s) and Type of lute Number of Mites and Eggs per 100 loaves Dosage / 100 gallons Application Stage DMy Before i=) and After +)Sprayinz Doeebr 8,1955, Z -35 (+32) t+36) (+59) M+83)1 Systax, 1/2 pint Inside Foliage Mites 1 290 298 113 483 731 Eggs 1 7 299 455 1031 1494 Syvtox, 1/A pint Outside Foliage Mites f Y)9 85 0 15 179 Eggs 3 1049 137 33 62 501 Systox, 1/2 pint All Foliage Mites 1 300 177 1 9 90 Eggs & 959 323 29 48 401 DN Dry Mix, 2/3 lb. Outside Foliage Mites 1 310 no A4 88 Soo Eggs 815 448 13D 2%6 1914 Systox lasted only 20 to 29 days. Furthermore, SUMMARY mite populations 29 days after spraying (Table Systox was found to be effective against 3) were significantly higher where these purple mite from late October through Februdosages of Systox were used than where 1 ary, but relatively little value in April. A dospint of Systox or 1 pound of ovotran had been aeo ito ytxpr10gloso used. There was no significant difference bespay was prior Sto pNery M0 x Nalo.s of tween 134 and 32 pint of Systox. spae wassberio nd De Dmbr, Mid Nqa o. Ii The results of these three dosage experipate O t oe ran Dec Fbrary Bqth to xI ments do not prove that dosages of Systox lowdosage wer o ra iven F e feutr ve Bot Apri. er than '/' pint per 100 gallons will give undoae wreeltvyinfcieinA i. satisfactory control of purple mite. They do A dosage of 314 pint of Systox per 100 gallons indicate, however, that control of purple mite applied in October was as effective as 2'3 pound with 0 pint of Systox per 100 gallons may be of DN Dry Mix No. 1. The same dosage, howsatisfactory under some conditions but inever, kas of only slight value when applied in ferior to higher dosages or other acaricides December and April. under other conditions. Brushing-type applications of Systox were Eas effective as full-coverage sprays. Either Etye of Systox application was superior o -~~~~ -* .* One *test was carried out to determine brushing-type DN Dry Mix sprays. whether thorough coverage of all leaf surA faces would give better control of purple mite S than ordinary brushing sprays of the type cides for the citrus red mite purplee mite). Fla. commonly used for rust mite control. The reState o So. roc 67: 194. s sults of this test, presented in Table 4, show sites. The status of the purple mite and its control. .Fla. State Hort. Soc. Proc. 67: 1954. no superiority in purple mite control with a 3. Jeppson, L. R., M. J. Jesser, and J. 0. Comthorough application to all foliage over a in. Seasonal weather influence on efficiency of brushing spray to outside foliage only. Both in uthern California. Jour. Econ. Ent. 47 (3) : 520types of application were superior to a brush4. John'son, R. B. and W. L. Thompson. Progress ing spray with DN Dry Mix No. 1. -ror ores-earch with miticides. Fla. State Hort. Soc 0rc 68 19550.-

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98 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 PROGRESS REPORT ON GREASY SPOT AND ITS CONTROL W. L. TIoImj\s(IxN JON H. Kim; 'sattcr(d IIbo)it oil (itrs liavis. The affected au on thi current veal's 5Tro\\th is at first a N) E. 1. D sz yellow\ I h-brI\ol spot, gradually turning dark Florida Citrus' EXperimcilt Stalioll brown\1 and inl time becoming black. These spots mla\y \-it]-\ from onIe-sixt(eenth to more Lake Alfred thati a tiiarter of all inch in diameter, or may Greasy s p t, a dliseast of ei trus. ha bn be massed over la rger areas. Ill severe cases, present iin Florida for many years ( )l )b ti spots are scattered over the whoi leaf, but sometimes oilk. tlhe d of tile af is Was a minor problem mil -i*bott 1944. Bt e 1950 the d lem w l prevalent m fectcd (Fig. 1). Leaves affected with greasy 1950 til isease \\is pruv;lleIt ill tiI m aIII 'r]Oves in) tile central part of the state, illrill r spot T)l) he folu(I oil aIIV portion of the t .1 tr ee. llt they ale lislalv imore ai)llidalit ill the past -\ears. it his hecone of e Icmio Ijo i ]e urn ortneeiiiallcitus ~(I\I~t~ aeasiithe tree tops. L ees with a Iiiglh peveentage of atim portillc-c inll ll]ctrus (Tn iw ili c r it's ill thc1 state. Ifeeted leaves have a \eilowih east, ani the lesiol)s ma' be coftised with felloww spot, Syp)toms: GrVea5 Spot 5ymp1tom5 art ir a moilbdenlIm dlefiielcy. regular raised, dark spots o. rolps of spots The S\ lopto(is of grcas\ spot may he oI)I-lria A riulturO Experimlwit Stati'ln J111rn11il scr\ d (m t le cl~ic i \cilr s o 'r m ll is citi-I Fi. .eaes afecNdw.h resys.t V' M.S #755 '4^ Fig. 1. Leaves affected with, gr easy spot.

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THOMPSON, ET AL: GREASY SPOT CONTROL 99 as August, but are usually not very noticeable in plots receiving a complete spray program until October. As winter progresses, greasy (10). In later work, Fisher (2) Griffiths (4) spot becomes more severe and reaches a peak and Thompson (8) (10) found that a sumin February or March. In 1954, the severity of mer copper application reduced greasy spot. greasy spot increased about 30 percent beThompson (10) found that 0.75 pound of a tween December 2 and January 25. Experineutral copper (53% metallic copper) was as ments conducted on the east coast during the effective as 1.5 pounds per 100 gallons. It 1955-56 season showed that severity of greasy was also found that two summer applications spot increased 15 percent from October 17 to were more effective than one. Captan and November 29 and 40 percent from October 17 Ziram showed promise, especially with two to March 8. Although a marked reduction of applications (10). it was also found that greasy spot resulted from the fungicidal greasy spot was less abundant where summer sprays, the percentage increase in severity in applications of oil emulsion were made than sprayed plots was comparable to the increase in unsprayed checks (3) (4) (8) (10). in the checks. Timing of the summer copper application Injury: The principal injury caused by has been an important factor in the degree of greasy spot is a premature leaf drop. Somecontrol (3) (4) (10). In 1954, a copper spray times approximately 85 percent of the infected applied on June 10 was effective in one grove, leaves drop during the fall and winter months. but an application on June 15 mn a nearby Heav lef drp i mor comon n yung grove was not effective. All copper sprays apHe v ef d o soe c m n on y u g I d duin July wer efeti e Au us trees, but mature trees may also lose a high Pliddrn uywr fetv.Ags p percentage of leaves. The number of leaves plications were effective in one of four exdropped is proportional to the severity of periments and September applications were of greasy spot. little value i two experiments (10). Purple mites in the fall and winter months Cause: In 1948, Thompson (6) reported were more abundant following copper sprays that greasy spot was more severe in unapplied in September than after earlier applisprayed plots than in plots where rust mite cations. Fall scale infestations were no higher Phyllocoptruta oleivora (Ash.) were kept at following either a summer application of a low level with sulfur sprays. In 1952, Shocopper-oil or copper-parathion than where icki Tanaka and Shunici Yamada (5) reported copper was omitted (10). from Japan that greasy spot was caused by a fungus Mycosphiaerella Horii (Hara.). Fisher In 1954, there was no significant difference (3) also found a fungus associated with in the soluble solids and acid where copper greasy spot. In later work Fisher (2), Grifwas added to summer sprays than where it fiths (4) and Thompson (8) found that was omitted (10). greasy spot was less severe where summer External fruit quality of Hamlin oranges copper sprays and other fungicides had been was affected as a result of a summer copper applied, which further indicated that the inapplication. Winston et al. (11) reported that jury was caused by a fungus. "star melanose" was associated with Bordeaux It has not been determined whether rust mixture sprays. Later, Thompson (7) reported mites and some species of sucking insects are that "star melanose" developed as a result of a contributing factor. Leaves kept free of rust applying sprays containing copper on melanmites with Aramite were less severely affected ose-infected oranges. In general, "star melanby greasy spot than mite-infested leaves (10). ose" on grapefruit has not been as severe as on Areas around purple scale, red scale, and white oranges, but Fisher (2) reported that fruit fly are sometimes discolored. This injury may quality in July and August sprayed plots was -7lso be greasy spot. low due to copper blackening and enlarging melanose lesions already present on the fruit Control: Earlier work showed that greasy when sprayed. The discoloration of blossomspot was more abundant in unsprayed plots end russeting on oranges following a summer and in plots sprayed post-bloom with coppercopper spray was also a factor that lowered oil without subsequent rust mite control than grade.

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100 FLORIDA STATE HORTICULTURAL soCIETY, 1956 EXPERIMENTS IN 1955 ering samples, the fourth leaf from the terminM. ..al was picked. Leaves were classified in the meths: Iecnducte to sitemiar epermi~i laboratory into four grades, based on the mensmr condutrtiod o detpermnectesr to severity of greasy spot. The severity of greasy conro grneasptn tiin of orneeary to spot in each plot was then computed by multiapctonresy of, giies thein eff oe fngtw plying the number of leaves in the light grade cia pays on sungseqdes, te an scal ifnby one, the medium grade by two, and the feaidas span subeueffet oniter and aexmsevere grade by three. Products were added testaltit aliy a the ow nena ofDndexe and then divided by the number of sampled inenal F ulity. Nar yonghed graperuide leaves in each plot, Thus, the higher the rating, grov Cewas Felecrda fo yong, rfted graperit the greater the severity of the disease. grme as seFeor ne these experimet e rpComparison of Materials: In this article, fruits Frore ase sexprented grapaasoonte~ amounts of copper are designated as metallic Erast govwas seeachtexneriWabast, the et copper and applied in the form of a neueatCs. Ierndoed axpermepliathed treet tral copper. In the 1955 experiments, the tmets.Ec plre ranoited repifate threesa amount of copper per 100 gallons was varied tunee Ead pwotrees wanted o All tees-a from 0.16 to 0.53 pound. In the Dundee exD u r prad tw re applibasso. Aus nes periment, applications of 0.39 and 0.53 pound sanrosl Praysonan weale sfr semre of copper per 100 gallons resulted in the contol.Parahio an wetabl sulur ere highest degree of control and were more efcombined with the fungicides in all July sprays festive than 0.16, 0.21 or 0.27 pound (Table except where an oil emulsion was tested for 1). In the Wabasso experiment, all copper control of both scale insects and greasy spot. sprays were about equally effective and sigWhere a second fungicide spray was applied, nificantly reduced the severity of greasy spot. the scalicide was omitted. All sprays were apSome of the lower concentrations of copper plied with high-pressure, hand-gun sprayers. applied in two different sprays at an interval Records of greasy spot severity were obof six weeks were more effective than one tained from samples of fifty leaves from each application of the higher concentr-ations tree. From twigs selected at random in gath(Table 2). For example, at Dundee two apTable 1. Greasy Spot Control with Varying Amounts of Copper. Mean rating of Spraor Dates Pounds ,. Greasy Spot Dundee Wabasso Treatments Per 000 gal, Dundee Wabasso SNo treatment 54.5 2187. July I July 9 Copper 0.16 35.8 14592* S "2 4.7 133 3 " e27 33.8 140.2 0.39 25 2* 102 2** 53 22.3* 142.8 L.S.D. 19:1 25 4 60. 5* L.S.D. 99:1 33.8 80 .9**SAmounts of copper presented as metallic copper.

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-11 .*~.:.: 54 444 -S 43I ,jaddoo~~~~~~ 4'~ms ousa ado o9 ua XX00 ..ec 1:6 4 X1 16 1:61 M 0 M**O .9 090 a 006 *5 1 LO6 0 00*O 00O a4 S 9*.5 009 u00zM Z5 0.6I CO4 00" a 00*TI *C I .019 a 006 a 00*ZC 89.oz 804 u 00~ *1,dv 4 806, *402 v o 00. u -qav a:4 L so 0T 4* 4C0 .u 0T* -444o *O7Y 4x7O a 91*0 aaddo0 5* 0Z 6 lzu9* a0o nE V T xS 0 e T a9* *o 0 xx*dOT .6T IT9* 910 a c osvv aeaa 4sn.a A: 4-OIJ0 j9* 44 -az .1 .1 .55j~~n OA4DJ1 LAI I o UI4 '(z 4 54451 *uDO -a~a S. seq~ 4V. -sol .00 .a ..pnC 4L .6tuq 0 .04 01,11I 0~ 00t gj .ln u. 00l paj~o M10 ..IAO .o puo 9 0 0 .aollpnd L;o *q '*olu oo .ad a oo 0o pu 20 JO wa sio o g a a *s i *.j *1 00n -00 .a uo*~,.i ..51 0o 00o 1S 0:1M 6 sin u .Ifuos snl .j .uaa L-0 0. ..o 4uwa C-SO .apu~ .000? 00 0aado j o 9 0 0sopal 101 ST~IO TOS Avau ri S' No Uscll

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102 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 plication, control was only equal to the July growth, but not enough to depend upon application of 0.16 pound of copper. There where greasy spot is severe. On April 19, 1955, is no explanation why the oil was not effective several different neutral copper compounds in the Wabasso grove, except that it may have were combined with lime-sulfur to determine been applied too early in the summer. Howwhether these mixtures would cause a leaf ever, in both locations, a July application of drop and burn. On December 21, leaf sam0.16 pound of copper combined with oil ples were graded for the severity of greasy emulsion and followed in Augustwith 0.16 spot. Greasy spot was as severe where I galpound of copper plus wettable sulfur resulted Ion of lime-sulfur was used as in the unin a high degree of control. Another very eftreated check, but less severe in three differfective program at Wabasso was a June apent plots where either 3.0 pounds of copper plication of 0.27 pound of copper plus 5 sulfate, 1.0 pound of copper oxide, or 1.5 pounds of wettable sulfur per 100 gallons and pounds of basic copper sulfate was mixed with followed in July with oil emulsion. I gallon of lime-sulfur per 100 gallons. A mixOne application of Captan at 2 pounds per ture of basic copper sulfate and wettable sul100 gallons was as effective at Dundee as One fur was not as effective as any of the limeapplication of 0.16 pound of copper, but not sulfur-copper mixtures. Unfortunately, the as effective as 0.39 pound. At Wabasso, one lime-sulfur-copper combination caused burn application of 2 pounds of Captan per 100 and leaf drop and it is not recommended in gallons was not effective and two applications either a spring or summer spray, but this exwere no more effective than one application periment did demonstrate that, if the copper of 0.16 pound of copper. adheres to the leaves for a long period of time, Ziram applied at 2 pounds per 100 gallons greasy spot will be less severe on the spring was not effective in either experiment, but two flush of growth than on untreated trees. applications at 1 pound was as effective as a Effect on Fruit Quality: In 1955, sumsingle application of 0.39 pound of copper. mer copper sprays were applied on PineNabam applied at 2 quarts plus I pound of apple oranges at the Citrus Experiment Stazinc sulfate per 100 gallons was as effective tion. This grove had received a post-bloom as 0.39 pound of copper at Dundee. At Wabascopper spray and the fruit was not severely so, Ferbam was not effective at 2 pounds per affected with melanose. The amounts of cop100 gallons. per per 100 gallons were 0.16 pound, 0.27 Timing of Sprays: As stated previously, it pound, 0.39 pound and 0.53 pound, respechas been observed that control of greasy spot timely. Dates of application varied between varied in different groves even when the dosJune 28 and August 8. There was very age of copper and time of application were little discoloration where copper was used in similar. In 1955 at the Dundee grove, the amounts between 0.16 pound and 0.39 pound summer flush of growth came out between per 100 gallons. However, where 0.53 pound the July 1 and the August 19 applications. was used, there was a definite discoloration of Where 0.27 pound of copper was used, the melanose lesions. August spray was more effective than one Field observations were made at the Inapplied in July, Where as little as 0.16 pound dian River Field Laboratory where different of copper followed .the July application, there amounts of copper had been applied on Valwas a marked increase in the degree of conencia oranges. The concentrations of copper trol. In another experiment in a 40-year-old sprays were the same as at the Citrus Experigrapefruit grove, various amounts of copper ment Station. Where 0.16 pound per 100 galwere applied between June 21 and September lois was applied, either in one or two ap12. In this grove, there was little or no growth applications, there was no adverse effect. Howafter the spring flush and there was no difever, with 0.27 or 0.39 pound, there was a ference in the degree of greasy spot control, moderate amount of discoloration. When 0.53 regardless of the concentration of copper or pound of copper was used, melanose lesions the timing of the application, were very dark, resulting in a definite grade Some control of greasy spot may be exlowering factor. The timing of sprays was not pected from a post-bloom application on spring a factor since there was as much discoloration

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THOMPSON, ET AL: GREASY SPOT CONTROL 103 following a July 1 spray as there was when tain period. If the second flush develops in the application was made as late as August 8. May or early June, then a July copper spray On grapefruit, a low percentage of melanose of about 0.4 pound per 100 gallons may be lesions had a darker color than normal, but it more effective than an August application. was not a grade-lowering factor. Summer For instance, in 1954, July applications were copper-oil applications darkened corky lesions more effective than August applications in more than the wettable sulfur-copper comthree of four experiments. This does not mean binations, but the grade was not affected that each summer the copper spray should be where fruit was originally free of melanose applied in either July or August, but where lesions. Even though there was a minimum only one summer copper is to be applied, it amount of discoloration of 'lesions and wind should be delayed until after the summer scars in this experiment, a summer copper-oil flush is out. spray is not recommended where the crop is Two low-dosage summer copper sprays can to be sold on the fresh fruit market. be used to advantage where no post-bloom Compared to untreated trees there was no copper is applied. If parathion is used as a significant difference in the amounts of either scalicide and it is necessary to spray in June soluble solids or titratable acid in pink grape. or early July, add the equivalent of 0.16 fruit and Pineapple oranges where summer pound of metallic copper, in the form of a copper sprays bad been applied. neutral copper, per 100 gallons. In four to six Effect On Subsequent Mite and Scale Inweeks follow with 0.2 pound of copper plus festations: Purple mite, Metatetranychus wettable sulfur. If oil is used as a scalicide, citri, was more abundant in September 1953 then follow that application in four to six following an August copper spray than weeks with a low-dosage of copper. The apfollowing earlier applications (10). On Deplication following the scalicide spray is not cember 21, 1955, in the Dundee grove, there necessarily an extra operation because a sulfur was no difference in the percentage of inspray for rust mite control is usually necesfested leaves between plots sprayed with sary following a June or July scalicide spray. copper-wettable sulfur in either July or AuSince oil was not effective at Wabasso in the gust and where the copper was omitted in the one experiment conducted there, it is sugwettable-sulfur spray. In all plots where oil "ested that 0.2 pound of copper be added to was used, alone or in combination with copthe summer oil and followed in four to six per, the mite population was not as high as weeks with the same amount of copper in a where copper-wettable sulfur-parathion had wettable sulfur spray. been used. The oil-copper combination should not be When infestations were low in the spring, applied on oranges to be sold on the fresh scale control has been as satisfactory where fruit market. However, there has been no infungicides have been included in the summer jury other than the effect on corky tissue scalicide sprays as where they were omitted. where wettable sulfur or oil emulsion has been supplemented with neutral copper. The grade DISCUSSION of both oranges and grapefruit was not afTiming of fungicidal applications appears fected when fruit was free of melanose lesions to be one of the most important factors in and blossom-end russeting when the copper greasy spot control and more knowledge is spray was applied. necessary about the life cycle of the fungus The organic fungicides tested have not been before definite recommendations can be made. as effective as copper, especially with one apIn Florida, at the present time, it is not known plication. Even though single, applications of when or how long the leaves are susceptible the organic fungicides Captan and Ziramn to infection. There are usually two to four have not been as effective as copper and are flushes of growth that need protection between more expensive, there may be a place for these February or March and August. If a postmaterials. On oranges, where the crop is bloom copper is applied for melanose congrown for the fresh fruit market, two applitrol, that application will protect the spring cautions of one of these organic fungicides may foliage from greasy spot infection for a cerbe used.

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104 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 SUMMARY Subsequent purple mite infestations were Greasy spot, a disease of citrus, causes a .ohge nDcme weecpe a n premature leaf drop. Symptoms are raised,' cluded in the summer scalicide spray than yellowish-brown to black spots most prevalent where it was omitted. on the undersides of leaves. in 1955, scale infestations were at a low Greasy spot infection was reduced with a level when the scalicides were applied and July or August application of 0.4 pound of the addition of copper to the summer sprays copper per 100 gallons, but two applicationsdid not affect scale infestations by October. one in July at 0.27 pound and a second in LIrT.ATURE CITED August at 0.16 pound-were more effective. 1. Fawcett and Lee. 1926. Citrus diseases and their control. A July oil emulsion spray was as effective in 2. Fisher, Fran. 1i54. Fla. Agri. Expt. Sta. Ann. Central Florida as one copper spray, but was Rept. not ffetiveon he Est oast Vey efee-ge3. Fisher, Fran. 1955. Fla. Agri. Expt. Sta. Ann. not ffetiveon he Est oas. Ver 0feC R*p tive treatments were either July oil followed in 4. Griffiths, J. T. 1955. Greasy spot and factors August with 0.27 pound of copper or June groves. Citrus Industr,nVol. 36 No. 5.lrd ctu copper followed in July with oil. Also effec5. Tanaka, Shoichi and Shunichi Yamada. Studies tive were either two applications of Captan printhfromreBul. No. 1 Horticultural IDivisionitrtionaat 2 pounds, or Ziram at I pound per 100 Tokai-Kinki Agri. Expt. Sta. Okitsu, Japan. 6. Thompson, W. L. 1948. Greasy spot on citrus gallons. leaves. Citrus Industry, Vol. 29 No. 4. Summer copper sprays did not affect soluble 7. Thompson, W. L. 1949. The relationship, of tim...ing post-bloom sprays to certain fruit blemishes on solids or acid in the puice of Pineapple oranges oranges. Citrus Industry, Vol. 30 No. 4. or red grapefruit. Melanose lesions were 8. Thompson, W. L. 1954. Fla. Agri. Expt. Sta. noticeably darkened and enlarged where 0.4 9"." Thomnpson, W. L. 1955. Fla. Agri. Expt. Sta. pound of copper per 100 gallons was applied Ann. Rept. on oranges, but there was very little adverse C10.u~ Thomsonr W'. L3. 15. Greasy Spot Control, Ciru Inuty Vol 36 No .-. 5.effect following either one or two applica11. Winston, J. R., John Bowman and Walter J. tionsof 016 pund o coper.ch. 1927. Citrus melanose and its control. U.S.D.A. tin of 0.1 pon of copr -* 44

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FELDMESSER AND FEDER: NEMAGON USE 105 USE OF 1,2-DIBROMO-3-CHLOROPROPANE ON. LIVING CITRUS TREES INFECTED WITH THE BURROWING NEMATODE JUL*s FELDMESSER AND WILLIAM A. FEDER surface at the rate of one gallon, two gallons, and four gallons of Nemagon per acre, reNematology Section and Fruit spectively. and Nut Crops Section Each of three plots of twenty trees each, numbers 3, 4, and 5, was drenched with 1,000 Horticultural Crops Research Branch gallons of water which contained the 50% .emulsifiable concentrate adjusted so that each Agricultural Research IService plot received amounts equivalent to one galUnited States Department of Agriculture lon, two gallons, and four gallons of 1,2-diOrlandobromo-3-chloropropane per acre, respectively. OrlandoThe plots were then harrowed with a disk Part of an eight-year-old grove planted to barrow and an additional 1,000 gallons of Valencia orange on Rough lemon rootstock water was added to each plot. heavily infected with the burrowing nematode, In four plots, numbers 9, 10, 11, and 12, Radopholus similis (Cobb) Thorne,' reported areas twenty by thirty feet around single trees to be the causative agent of spreading decline were treated with band injection apparatus. of citrus (2), was made available to the auThe 50% emulsifiable concentrate was applied thors for fumigation experiments in May 1955'. on twelve-inch centers, ten inches deep. Single It was decided to use 1,2-dibromo-3-chloropro_ trees in two plots were treated with amounts pane in this grove since this is readily availequivalent to 13.8 gallons of 1,2-,dibromo-3able commercially and has been reported to be chloropropane per acre (roughly equal to 10 non-toxic to citrus in nematocidal applications p.p.m. by volume in the soil four feet deep) (1). All treatments were made with an emul_ and single trees in the other two plots were sifiable concentrate containing 50% by weight treated with amounts equivalent to 27.6 galof this chemical'. loans of 1,2-dibromo-3-chloropropane per acre (roughly equivalent to 20 p.p.m.). METHODS Two plots, numbers 2 and 8 (twenty trees Pre-treatment root samples were taken and each), were set aside as untreate d controls. ten plots were set up and fumigated in the RESULTS first week of June 1955.. During this time, maximum air temperatures averaged 95' F. Pre-treatment root samples were collected and the soil temperature at the six-inch leve June 4, 1955, and post-treatment root samples was 82' F. Relative soil moisture was 1.86% were collected September 29, 1955, November at the six-inch level. 21, 1955, March 9, 1956, and June 6, 1956 Three plots of twenty trees each, numbers (Tab ile 1). Each sample consisted of approxi1, 6, and 7, were treated with a tractor-drawn mately 100 grams of root material. Samples pressure applicator delivering a continuous were incubated according to the technique deflow of fumigant through nine injection points vised by Young (3), and nematode counts ten inches apart and ten inches beneath the were made over a period of several weeks after collection. On each of the sampling dates, ob'/The authors wish to express their thanks to Mr. servations were made on the condition of owner Eosftheanrove, for theirs wholehearte coperatreated trees: amount of new growth, chlorosis tion; and to Dr. A. F. Camp, Vice-Director-in-Charge or the lack of it wilt symptoms, etc. and to Dr. R. F. Suit, Pathologist, Citrus Experiment Station, Lake Alfred, for their interest in this At no time during the one-year observation pro and for their help in securing the experii 2/ 1, 2-dibromo-3-chloropropane was made available to treatment in trees in plots 1, 3, 4, 5, 6, and by the Shell Chemical Company under the name "I that caused them to differ in any way from S -.0..

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106 -FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 1. Numbers of IRadopholus similis individuals occurring in one set of pre-treatment root samples and four sets of post-treatment root samples taken over a one-year period from a planting of Valencia on Rough lemon rootstock treated with 50% emulsifiable concentrate 1,2-dibromo-3chloroproparie Post Treatment Plots and Treatments Pr-treatment Sept. 29 -Nov. 21 -Mar. 9-19 June 6 -Jul. 9 (June 4,195) Oct. 17,1955 Dec. 19,195 1956 1956 1.1 gal./ acre, pressure rig 11 24 18 148 32 2. Control 146 125 766 252 25 3. 1 gal./acre, drench 4 68 117 84 35 4. 2 gal./acre, drench 48 2 252 128 24 5. 4 gal/acre, drench 31 17 1 188 53 6. 2 gal./acre, pressure rig 5 14 0 492 80 7. 4 gal./acre, pressure rig 17 26 0 66 28 8. Control 3 139 429 96 37 9. 13.8 gal./acre, hand injected n5 0 0 0 27 10. 27.6 gal./acre, hand injected 272 0 0 0 28 U. 27.6 gal./acre, hand injected 19 7 0 16 12. 13.8 gal./acre, hand injected 449 0 0 0 40 *No roots encountered the trees in check plots 2 and 8. Nematode er significant reductions of burrowing nemacounts indicate that no significant differences tode populations nor favorable growth reexisted between the check plots and the sponses, and that the higher dosage rates that treatment plots. The trees in both the check do approach the levels at which nematode and treatment plots showed slight symptoms eradication might be expected are not tolerated of chlorosis and wilt throughout the observaby living citrus trees. Intermediate rates of aption period. New growth was sporadic and plication will be tried in other experiments. was observed in trees in all of these plots. The trees in plots 9, 10, 11, and 12 began to LITERATURE CITED show signs of chemical injury such as defolia1. McBeth, C. W., and G. B. Bergeson. 1955. 1,2tion and branch and root die-back by Sentemdibromo-3-chloropropane-a new nematocide. Plant rDis. Reptr. 39(3) : 223-225. ber 1955 and were judged to be dead or dy2. Suit, R. F., and E. P. DuCharme. 1953. The ing by March 1956. burrowing nematode and other parasitic nematodes The data indicate that the three lower dosR~ptre. 37(7): 379-38d3. n o itu. lntDs age rates of 1,2-dibromo-3-chloropropane that 3. Young. T. W. 1954. An inoculation method for are tolerated by living citrus trees cause neith,lecting miratory endo-parasitic nematodes. Plant *is Rpr 3810 794-795. 0 0

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KILBURN AND PETROS: PEEL OIL 107 RAPID DETERMINATION OF, PEEL OIL IN ORANGE JUICE FOR INFANTS R. W. KILBURN AND L. W. PETOS Figure I LIGHT TRANMISSIO$ foi NFIXWM OF S7E10 DISTILLE Florida Citrus Canners Cooperative ,D ONE OI. IN WT -SOLmr s 4m Lake Wales GO eon Mechanically extracted orange juice contains a moderate amount of essential oil from 10% Ae,,n the peel of the fruit. The characteristic flavor of orange juice is due in part to this essential !24 oil. Excessive peel oil is removed from the 10% Iwprpnl 5% Actn juice by vacuum distillation or centrifuging during the processing of canned orange juice. The deoiling process is controlled to leave a 20 desirable amount of oil in the juice. 003 .0 The amount of oil in canned orange juice IOLB OLEI ITA produced for infants is considerably lower transmission was reached at oil concentrations than the level considered desirable in regular too high to be useful. canned juice. Removal of almost all of the oil Wolford, Patton and McNary (3) enimproves digestibility, justifying t he sacrifice countered the same difficulty with the turof aroma. bidimetric method during their studies of The concentration of peel oil in citrus juice citrus waste disposal. Their modified procedis measured by the modified Clevenger method ure substituted ethyl alcohol for acetone as (2) by inspectors of the Department of Agrithe organic solvent. This modification was reculture for determining grade. More rapid ported to give satisfactory results at concenmethods of analysis have been developed by trations below .005%. various workers. The turbidimetric method of The high excise tax on ethyl alcohol makes Burdick and Allen (1) has been extensively it desirable to use other organic solvents if used. This method was tested and found to give unsatisfactory results for the low oil in Figure 2 orange juice for babies. The solubility of oilCOPRSNFCLVGEAD UIDMTC in the aetone distillate, noted by Burdick and FROL IE U 0S Allen as being of no consequence at the levels CeegrMto normally encountered in canned juice, was .bdmrcMto....... the cause of difficulty. A study was made of modification of the -O turbidimetric method at low oil concentration. 00 .IN --5-. Attempts were made to minimize the effect t of oil solubility by decreasing the acetone con.S centration in the distillate. Turbidimetric measurements of oil in several acetone-water *1 2 4 5 6 -. 9 -0 4 efxtrereas ed in Fge .a .4ut y 0 efec 0erasd 0dlt aceonebu 10%~4 T4ME g HOUR

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108 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 possible. The turbidity of peel oil in 10% in the boiling flask and distilled according to isopropanol was tested with the result shown the procedure. The light transmission of the in Fig. 1. The sensitivity is higher with this distillate was plotted against the volume of solvent than is the case with acetone; also the oil added to the flask (the same value as the limiting solubility is lower. The preliminary re% "recoverable" oil by volume). A series of sults looked satisfactory so the distillation proruns established the relationship over the cedure was set up to give 10% isopropanol in range .002% to .03% oil by volume. This meththe diluted distillate. A distillation ratio of od of standardization automatically corrects two to one was also used to improve accuracy for incomplete recovery by distillation. at low oil levels. The graph of the data on semi-log paper EXPEIMENAL ROCEUBEwas a straight line, indicating a uniform reEXPEIMENAL ROCEUREcovery by distillation, as well as conformity Apparatus. The distillation apparatus conto Beer's law, over the selected range. Comsists of a 500 ml. boiling flask, a Kjeldahl trap parison of this graph with the dilution graph and a West type condenser in the vertical posishown in Fig. 1, indicates an 84% recovery of I P tion for convenience. Light transmission of the oil by distillation. This checks with the value turbid distillate is measured on a B&L Monoobtained by Burdick and Scott (. chromatic photoelectric colorimeter with a 435 Comparison with the Clevenger Method. mu filter. U.S.P. isopropanol is used. A 750 The modified turbidimetric method was used wvatt electric beater was found to be the most for routine testing, of canned orange juice for convenient heat source. babies. Samples were checked for oil every Procedure. 100 ml. of juice and 5 ml. of thirty minutes without difficulty because the isopropanol are added to the flask. The trap entire determination takes, about seven minand condenser are connected and 20 ml. disutes. The USDA inspectors also ran oil by the tilled into a 50 nil. graduate. The distillate is Clevenger method on composites of samples mixed, made up to 50 ml. by addition of taken over a period of several hours. The water then mixed again. The turbid solution data obtained, permits an indirect comparison is poured into a tube and the light transmisof the two methods. Results of the two methsion measured against a distilled water blank. ods for a typical day of operation is shown in The transmission reading is converted to oil Fig. 2. Results throughout the season exhibit concentration from a standardization curve. similar agreement. The Clevenger method genA 10% solution of isopropanol should be erally gives slightly lower results. checked for turbidity occasionally. Presence of -SUMMARY turbidity indicates an unsatisfactory purity of alcohol. A modified turbidimetric method for estimation of peel oil in orange juice, based on DISCUSSION distillation with isopropanol, gives satisfactory Standardization of the procedure. The proresults on juice with low oil content. cedure was standardized by a method selected LITERATURE CITED* as most likely to give good correlation with 1. Burdick, E. M., and Allen, J. S. Analytical the Clevenger method. A series of dilutions of Chemistry 20, 539-41 (1948). steam distilled orange oil in isopropanol was 2.i U. S. DepartmeC~ne of grculture',c U.Prtdprepared. 5 ml. of solution, containing a known Marketing Aministration.amount of oil, was added to 100 ml. of water .WoFdrd, R.n y. Patton, V. Pad McNary, *. R Foo Teholg 6. 418-21 (1952).

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BISSETT AND VELDHUIS: VALE\CIA CONCENTRATE 109 EFFECTS OF FINISHER PRESSURE ON CHARACTERISTICS OF VALENCIA ORANGE CONCENTRATE .W. BISSETT AND.M. K. VELDHUIS sure and heat treatment temperature in the preparation of Valencia orange juice for conU. S. Citrus Products Station' centration. Winter Haven EXPERIMENTAL In 0o r .Equipment In pocesin cirusjuies th laoraory A standard Brown Citrus Machinery Corpilot plant a screw type finisher was modified oration. extractor using the same settings as so that it could be more precisely controlled Pncmeca rciewsue ncneto and adjusted, and its operation Imade more. ith comeil pctc hasusder finishnertmodn uniform over reasonable variations in rate of ithe as Mdes Cbedsbelmw.yThis finisher hasda juice feed and pulp content. Tests were made horizontal screw operating in a cylindrical on Valencia orange juice to determine the ef~ screen 5 inches in diameter and 9 inches in fect of different finisher settings on juice length. The pulp passes out through a conical yield, pectmnesterase activity, pectin, flavon-anur rfehaigaleanenray oids, and cloud stability of unheated and fixed by an adjustment at the end of the heated concentrates. screw shaft. With a fixed orifice, the relationWhile it would not be possible to adapt ship between juice and pulp produced dethe settings directly to other finishers, the repends to a large extent on the rate of feed. sults illustrate some of the effects that could This particular finisher was modified by rebe expected with variations in fishing pracplacing the screw adjustment with an air tices. Extracting and finishing equipment actuated diaphragm, and air at constant presmust act together and the method of operasure was supplied to one side of the diation of one will markedly affect the method of phragm. This maintained a constant pressure operation of the other. However, certain prinon the end of the shaft, but left it free to move ciples will apply to all units. horizontally and vary the size of the orifice in accord with the rate of feed and the amount Olsen, Huggart, and Asbell (8) extracted of pulp present. The effective diameter of the Pineapple orange juice at low and high presdiaphragm was about 5 inches, so air pressure. Pulpy cutback juice and 55' Brix concensures of 5, 6, 7, and 8psig. gave loadings on trates were prepared from each and subsethe end of the shaft of about 100, 120, 140, quently blended in various proportions in and 160 pounds. A new drive was installed preparation of 42' Brix products. An increasing which reduced the speed of the screw to 200 tendency toward gelation was observed with RPM from a previous 262.5 RPM. This modihigh pressure extraction over that of low presfied finisher duplicated the operation of comsure and with increased concentration of coarse mercial finishers very well. It was noted that pulp in the cutback juice. Rouse (9) reported the pulp from this finisher Contained fewer increasing pectinesterase (PE) activity with particles of coarse pulp than that from larger increasing pulp content in Valencia orange machines used in processing plants. juice. Rouse and Atkins (10) found that PE Peaaino ape was completely inactivated in a shorter time Peaaino ape in an orange juice of 5% pulp content than in1 Fifty boxes of Valencia oranges were deone of 10% pulp content. livered to the laboratory immediately after picking. The fruit was mechanically randomIt was the purpose, of this investigation to ized into four lots of 1100 to 1200 pounds study the effect of varying the finisher presand stored at 40' F. until processed. The juice '/One of thelaboratories of the Southern Utiliza2/The mention of trade products does not imply tion Research Branch, Agricultural Research Service, that they are preferred by the Department of AgriU. S. Department of Agriculture. culture over similar products not mentioned.

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110 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 of the four lots was extracted separately using of a Stormer instrument using a 26-gram acfinisher settings of 5, 6, 7, and 8 psig, diativating weight. Brix was measured by both phragm pressures respectively. The juice from spindle and refractometer; acid (as anhydrous each lot of fruit was divided into four porcitric) was titrated with standard alkali; and tions consisting of controls and portions suspended solids were determined by the heat treated to 150", 1700, and 190" F. The method used by the U. S. Department of juice was heated in a small tube beat exchangAgriculture in grading canned grapefruit er in 6 seconds, held at the temperature for 5 juice. seconds and cooled to 60" F. in 3 seconds in an annular ice water cooler. Each portion was EXPERtIMENTAL RESULTS AND DISCUSSION concentrated to 55' Brix at 75* F. in a falling Yields from each lot of fruit are shown in film evaporator, cut back to 42' Brix with unTable 1. As the extractor settings remained heated juice, canned, and frozen at O" F. constant, the yield of peel remained practically Analytical Methods the same for all four lots. The percentage of PE ws dterinedby moifie mehod finisher wastes (pulp and rag) decreased, and peiwus described by aiset modified methd the juice yields increased with increases in Reusy des1ibe byta Becisseytt, hs ofndc finisher settings. The yields of juice increased reasyin (co(); tolual pectin byatoMfrom 51.7% to 53.3% which isg equivalent to an Creay an Mcomb 7);solule ecti by increase from 5.3 to 5.45 gallons per 90that of McComb and McCready (6); flavonpound box of fruit. oids by the Davis method (2); cloud both inThaayssotesigetrgtjue itially and after storage at 40* F. by the methTrhm nalyset of ruthae prngeste ngt Tabe od of Loeffler (5); and visual cloud stability Thomeac at dof frt nae pretdinable 2er bysothes eetd decrded by Guyer ner of4) ences in Brix, acid, initial cloud, peel oil, total scostds ered reorded0sithe reuberos pectin, or flavonoids of the juices processed secods equied or 10 sindl reolutons at the four finisher settings. Small increases were observed in the suspended solids, PE, Table 1. Materials balance during extraction and finishing and soluble pectin with increased finisher pressure. Finisher Peel Finisher Juice Total The analyses of the 42* Brix products are settings -waste waste yield recovery presented in Table 3. The PE data follow the Psig %%expected trend of reduced activity with in6 49.8 7.1 53.2 100.1 creased treatment temperature, but do not in7 39. 6. 25 9. dicate a change with increased finisher pres8 39.4 6.4 53.3 99.1 sure. There was a slight increase in soluble Table 2. Analyses of single strength juice Finisher Brix at 20* C. Acid Suspended Initial Oil PEu./ml. Pectin Flavonolds settings Spindle Refracsolids cloud x 104 total soluble tometer psig. 0 % % %light % ppm ppm ppm transmission 5 12.90 13.05 1.10 14 24.0 0.066 43.8 1138 165 380 6 13.20 13.00 1.07 15 24.5 0.064 38.3 1100 165 37T 7 13.35 13.3 0 0 15 22.0 0.050 49.6 1200 185 405 8 13.30 13.10 1.09 16 23.5 0.056 47.3 1025 18 388

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BISSETT AND VELDHUIS: VALENCIA CONCENTRATE ill Table 3. Analyses of 42" Brix concentrates values with increased finisher pressure, or Finisher Treatment PlEu./ml. Soluble Flavonoids Viscosity Weeks heat treatment. Increases in viscosities of the settings temp. xJ04 per pectin in 120*Brix sec./100 stable concentrates with increased finisher pressures 120 Brix ,,. o,40.F are pronounced while the use of heat treatU"' ments did not influence the viscosities of the F PP"' PM products. Visual evaluation for cloud stability 5 control 45.8 666 363 82.1 5 week. Of these, the product of 6-pound fin6 control 40.7 662 380 87.9 the product of 5and 6-pound settings and 190 5.836 373 96.8 >5 190" F. heat treatment remained stable for five 7 control 42A4 701 375 139.3 < I weeks. 150 23. 834 383 1422 < 1 170 6.9 890 329 132.7 < I The loss of cloud during 40" F. storage, as 190 5.2 835 358 124.2
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STENSTROM AND WESTBROOK: BRIX-ACID RATIOS 113 A STUDY OF THE DEGREES BRIX AND BRIXACID RATIOS OF GRAPEFRUIT UTILIZED BY FLORIDA CITRUS PROCESSORS FOR THE SEASONS 1952-53 THROUGH 1955-56 E. C. STENSTROM AND G. F. WESTBROOK 10.0 to 10.49, 10.5 to 10.99, and 11.0 degrees and higher; and ratios-6.0 to 6.49 to 1, 6.5 Citrus & Vegetable Inspection Division to 6.99 to 1, 7.0 to 7.49 to 1, 7.5 to 7.99 to 1, State Department of Agriculture 8.0 to 8.49 to 1, 8.5 to 8.99 to 1, and 9.0 to I and higher. Each month was tabulated indiWinter Haven vidually, and the percentages of loads falling In February, of 1956, our Division was into each of the categories for that period were asked by the citrus industry, through the calculated, The tabulations were drawn up so Quality Advisory Committee of the Florida as to represent fruit received by all major proCanners' Association, to supply such tabucessors, with each day's receipts for the late data as we bad available on the permonths of October, November and June being centages of grapefruit utilized by citrus procompletely covered, and with each alternate cessors which would meet various Brix and day'Is receipts being tabulated for the heavy ratio levels. The purpose of these data was to six months of the processing season. In all, furnish additional information to the Advisory more than 137,000 individual loads were tabCommittee on the availability of grapefruit ulated. Since this constitutes more than half for processing into a frozen concentrate which of all grapefruit received by all processing would be of a superior quality as compared to Plants during these seasons, statistical sample that previously produced from fruit meeting variation is not a complicating factor. only basic maturity levels. At the time of the The results of the tabulation of the 1952-53 request, we were able to tabulate only a through 1955-56 seasons are shown in Tables limited amount of data, taken entirely from I through 4. The tabulation was to have inthe months of February and March for the eluded the previous five seasons, but records past several seasons. This information was for 1951-52 had been partially destroyed, and made available to the industry without delay, data were available for only the months of and was considered during the drafting of a February and March. Table 5 is a partial sumFlorida Citrus Commission regulation last mary of Tables 1 through 4, showing the perMarch, setting up minimum requirements for centages of loads received at Iprocessing grapefruit to be used in the production of plants which met certain selected -minimums. frozen concentrated grapefruit juice, which In addition to these especia ly compiled data were optional until September 1, 1956 (1). which indicate the Percentages meeting variDuring the summer of 1956, we tabulated ous Brix and ratio levels, our Division routinethis same type information for each month of ly tabulates and distributes seasonal sumn* 6 the past four seasons. All information was ob-maries of percent citric acid and degrees Brix tained from our inspectors' work-sheets, which :bf week-endings, including volume of moveare standard forms used for recording analyses ment, for all fruit received at processing of loads of fruit received at processing plants. plants (2). This information is available to all For reasons of simplicity, loads rather than segments of the citrus industry, and the tabboxes were used as the basic unit in this tabulated data will not be repeated here. Howulation. The analyses of the individual loads ever, these data have been averaged monthly were extracted and grouped in respective for the past five seasons and are graphically Brix and ratio brackets as follows: Degrees illustrated in Fig. 1. This information is hence Brix-less than 9.0, 9.0 to 9.49, 9.5 to 9.99, a part of the present study, and it is from these II

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114 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Figure 1. 12.012.0 1955-56 1954-55 .............. 1953-54 _Degrees Brix 1952-53 11.0 1951-52 _11.0 10.0 ..----...10.0 Brix-acid ratio 8.0.-8.o 7.0 17.0 423 1,324 1,966 29,3h 2.7177 3,259 1,693 1,275 728 (One thousand boxes, 5 year average) Oct. NOT. Dec. Jan. Feb. Mar. April may June data that we can determine what time of the weather conditions will be no more unusual season the grapefruit utilized reaches its highthan those of the past five years. Hurricanes, est Brix level, together with appropriate rafreezes, and droughts may seriously affect the tios. quality and movement of the grapefruit crop. A further bit of information is included (2) That cultural practices will remain eshere, also. As a result of the optional comsentially the same. Certain spray and other pliance provision of the regulation previously cultural practices may cause additional varimentioned, close records were maintained on ables. (3) That fruit will be harvested at the fruit received for concentrating during the about the same periods as in the past. Changes period March 18 to July 1, 1956. Some 3700 in fruit utilization intervals would be most loads were processed under this plan, and only significant. a negligible portion failed to meet the miniAs can be seen from the tables, there is mum Brix of 9.5 degrees. However, some 20%6 an ample supply of fruit meeting 9.5 degrees were below the specified 7.5 to I ratio level, Brix with a minimum of 7.5 to 1 ratio any principally because of inadequate screening month from February through June. Since evaby fruit procurement departments. Nevertheporation facilities are relatively idle during less, the average ratio of the unsweetened .February and March, it is convenient for prograpefruit concentrate packed during this cessors to concentrate grapefruit juice durperiod was more than 9.0 to 1, as evidenced ing these two months. However, those desiring by our inspection records (3). to pack unsweetened juice will find it much In attempting to evaluate the factual inless difficult if they can delay their operations formation we have presented here; it is necesuntil April or May, for the percentage of 9.0 sary to make several assumptions: (1) That to I ratio fruit has risen sharply by that time, ~ S I

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116 FLORIDA STATE HORTICULTURAL SOCIE-TY, 1956 0 O 1 c A, m ''1 omm 0 n eos NCOOe .VsN .9~sNa e O oON HNNHW "sHH N H 99 44 (; c '4 l -m 00 a' M o m -rd -c --1 10c n 10 r0 Z; c; (3 8M C1r4 A -O 4 C ol Hw*N H H H ll 0 -f lH 0 H H'1 Hi s smH 0 El O H H H ii 00 N O O O r-4 ......e. ....1! 9. ..... 0 Cm m n --jm rr -: c (,54 04 A cl alNEE O cEM NcoN" Hl 10 IN m N c H c r; A r4 r4 4 0 l0 0I e .. ee .. E5 ..1%. ...Tl. .lic e9 VN ~r -InrV 0 -: O 'Nc m .Codd N5 0' r-l~ Hi M ~o o A m m CIN w~~l ..9 .............. 14 0* 0C* W rl o N 1-1 C -4 -: u r-Cl _zy m ND ~ d r O m O cl 0~M~d 0 O1 H a, 3 00 -1 C o r\C r' C 0 Ad"C 0d C\ D H 'I -:Iso ................. ..... .H "r A m -Ac 14 A al H0" HM r-1r 1A 8w 'i C! ID D rM 4, m -"0 0 "Co o' 'o .r0, H AH oC 1 c A 14 A 8 ,, OOH : m H l0 H OOO01,NH OOHHH V\ CI o 1 OC moase -0 sc o.stO 0 1-4 ......... O Hm~si r-iO O rd m OsE. a ti r H O O D ~ cc v A ~ o O m9 NOO .,e n < e .1 --.\ -O E .... .-.

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18 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 MVODI 0 'jZNa 8 1 -OT W. 8 0 ..clj w 18,clMO LAAa, 8 8 N ..0 0 ..o .\... -2 0o s O~ Cn~ al -r+ 0 0-A s-t 8 A \ 16 u I c l wl H w 0 0 0 0C OVO (M 0 L an 4 0 0o oO + A j4Z o ol -co o 'o o 14w 1 CZ Or a 14 C Cl I Ll lu Ca -I rz 0 1H 0l% 01c l ciH00 C_ Ic L c 0 c t; 7 L' -(It;c t9cl9 ' pE "o 0-----t o P----l 0 \ 0o .-0 Ncl 00 co 31 0 0 0 K\mm o o d NdN L'w w i-i91'' 4"; -14t ZN' a, N -0 t-f5 01 0 0 0 K\ G\ 0 0m 0 0 0 tN 160 i'% qiR t 0 owc m m8 tDN 0 0 coc wI .~ ~ ~ l N N CV M O L OOOO

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120 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 largely on purchased fruit will have to insist 2. Citrus & Vegetable inspection Division. Averag aci an soiscnet y weo ri e on very rigid requirements as to acceptable ceived at processing cplants, 1949-50 tkhrougu 195 lots. In either case, field men will have to 56. (Mimeographed reports) know within very close limits the actual Brix 4.bAnshed Reports,9561949-50 and ratio that may be expected before picking through 1955-56. crews move into a block for harvesting .chan in For5ia rap efrui. USDA Tech se 86 REFERENCES April 1945. 1. Florida Citrus Commission. Amendment No. 5, Regulation No. 19, March 7, 1956. DIACETYL PRODUCTION IN ORANGE JUICE BY ORGANISMS GROWN IN A CONTINUOUS CULTURE SYSTEM LLoyD D. WITTER growth and. metabolic product formation and ..s. the latter carmot bestudied separately. Meta Dosto, Rsearh &Devlopent In the continuous culture system the vessel Department or fermentor in -which the test organisms are growing and forming metabolic products is Continental Can Company, Inc. supplied with fresh sterile medium at a conChicago, Illinois .stant rate. A constant volume is maintained in the fermentor by having an overflow rate that is constant as well as equal to the input rate INTRODUCTION of the fresh medium. By appropriate adjustThe development of an off-flavor and odor ment of the: flow rate through the fermentor, during the manufacture of frozen orange juice a constant microbial population density of acconcentrate has resulted in severe economic tively growing organisms can be maintained. losses to a number of citrus concentrate packAt this constant population the rate of product ers. This off-flavor is reminiscent of "butterformation can be studied without being afmilk" and is a result of the accumulation of fected by variations in thenumber of ordiacetyl, a metabolic product of certain bacganisms. teria. Other than the work by Kilburn and THEORY oF PR1OUCT FoRM ATION IN A Tuthill (11), former studies on the growth CONTINUOUS CUIrURE SYSTEM characteristics of these organisms and their To assist the reader, the following nomenproduction of diacetyl in orange juice has been clature will be used in the development of limited to static batchwise cultures. Kilburn equations: and Tuthill (11) used the continuous culture a =diacetyl concentration at, time It (in method to show the relationship between data p.p.M. obtained by plate count, microsopic count, and a.= diacetyl concentration at zero time (in diacetyl analysis, and thereby Validated the p.p.m.) use of the latter analysis as a quality control k = growth rate constant (in reciprocal tool in the citrus industry. hours) It was considered appropriate to supplek'=reaction rate constant for diacetyl forment this applied investigation with a more mation (in p~p.m. formed per hour by basic approach to the characteristics involved one million organisms per ml or a in the formation of diacetyl in orange juice in population density of one,) a continuous culture system. This technique R =medium flow rate (in ml per hour) manages a unique separation of the rate of t = time (in hours) diacetyl production by a given organism from V= capacity of the, fermentor (in ml) that organism's rate of growth. Batchwise inx= bacterial population density at time t vestigations tare necessarily a summation of (in million organisms per ml),

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WITTER: DIACETYL IN ORANGE JUICE 121 x"= bacterial population density at zero tration in the overflow from the fermentor was time representative of the instantaneous product Equations applicable to the behavior of a concentration within the fermentor, which population density with time in a continuous from a practical standpoint, as shown by Macculture system were derived by Monod (14) Donald and Pire t (12), was not too difficult using a differential material balance of the to realize. With these assumptions, a differensystem. By a slightly different approach,' Golle tial material balance of the fermentor gives (8) arrived at the same basic equation of the following expression: kx -f k I xdt -dt dt V Equation (1) states that the rate of change In equation (3) the terms, R, V, and k' are of bacterial population in the fermentor with constants, but the population density, x, in a time is equal to the rate of bacterial density general solution is a variable with time. Howincrease less the rate at which the bacteria ever, the variation of the population density are being washed from the fermentor. Intewith time is described by the exponential form gration of equation (1) yields. of equation (2). Hence, substituting for x in I equation (3) from equation (2) and rear: k -xe(k-R/)t ranging gives the basic expression da R (k-R/)t Hence, when the rate of medium flow (R) dtVA a kfxoe divided by the capacity (V) of the fermentor This differential equation is first order and is equal to growth rate constant (k), the IIinear with respect to a, and has the solution: population density of the bacteria in the fermentor will remain constant. Monod (14) pre60R dt scented a rigorous proof of this fact. Under e t these conditions the bacteria were being washed from the fermentor in the overflow at which upon integration and simplification bea rate commensurate with their rate of recomes production in the fermentor. a k .kxg (k-R/V)t -At/v Although the characteristics of a bacterial population in a continuous culture system, as When t=0, then a a. and the constant of discussed above, have received a good deal of integration becomes attention (6, 16), only a limited descriptiGn of product formation by bacteria in this sysC aklxo tem has been made. Maxon (13) in his micro0 biological process report on continuous ferk mentation presented a detailed treatment of Substituting into equation (6) for the constant product formation in cases where the subof integration, C, as given in equation (7), strate concentration was rate-limiting. Howthe final expression obtained is: ever, in this investigation of the rate of diacetyl production in orange juice, as in many a .kxpe -Rt/ (,kt -. ) ag e -Rt/V other fermentation where the substrate conk 0 centration might be excessive, the rate-limiting When equation (8) was used in the calcufactor in the system would be the enzyme conlation of experimental results the unknown centration or bacterial population density. was the reaction rate constant for diacetyl In attempting to develop an expression for formation, k'. Implicit in this constant are the the product concentration and rate of product experimental conditions such as temperature, formation in a continuous culture system, it medium, etc., but most important, the organwas assumed that the rate of product formaism being tested. A comparison of the k' tion was proportional to the bacterial populavalues of two different organisms tested under tion density and that this was rate-limiting. essentially the same conditions was a comFurther, it was assumed that product concenprison of their ability to produce diacetyl

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122 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 under these conditions. Further, if the k' value ly 0.01 ml) of stain solution (consisting of 1 of an organism was known, the level of diaceml 10% tannic acid, 2 0 0 0.001% aqueous tyl concentration for any bacterial population methylene blue, and 1 drop of acid alcohol) density in the continuous culture system could was placed over the fixed smear and examined be estimated. through a coverslip which is sealed to the Determination of k': Under experimental slide with wax. This wax seal prevents the conditions the population density was held esevaporation of the stain solution. The medium sentially constant with x. equal to x. Also dark contrast oil immersion objective of a under these conditions the diacetyl concenphase microscope and 15X oculars were used tration is constant and a. is equal to> a. To obi onig h clr otie rdo tain constant x and a values, conditions were which a field corresponding to 1/400th of a adjusted such that k is equal to R/V. Hence, sq. mm. on the smear was ruled off by previsubstituting into equation (8) for x., ao, and k ously viewing a haemocytorneter under the gives same conditions. The dilution factor for countk I xe Rt/Ving was 4 x 10'. a : kx eRt/ --1) + -Rt/V From the number of different methods available in the literature for the quantitative which simplified and-solved for k' gives determination of diacetyl (5, 17, 19), several aR of which were specifically used for the deteck' 1.1 tion of diacety] in orange juice (3, 10), the XV procedure of Westerfeld (20) was finally chosen and used without modification. To preThe units of k' are expressed as p.p.m. of pare the sample of orange juice for the diacediacetyl formed per hour by a population dentyl test, a distillation was perfoi-med. Distillasity of one (a million organisms per ml). tion was not carried out for the purpose of EXPEIRIMENTAL METHODS concentration as done by Hill, Wenzel and Barreto (10) and by Byer (3), but to physiThe. continuous culture system employed cally separate the diacetyl from the orange did not vary appreciably in general set-up juice. The single strength juice used for this from those already described in the literature study contained an unknown substance which (2, 4, 6, 7, 15), except for possible simplifiinhibited the development of the diacetyl test. cation. The fermentor consisted of a 500 ml It was shown by a series of experiments that flask with a side arm overflow. Both the ferthis inhibition was not due to the juice maskmentor and a sterile medium supply flask were ing the color of the test, to the presence of immersed in a 30* C. constant temperature an unknown constituent in the juice competing bath and equipped with magnetic stirrers to with diacetyl for the guanidinyl groups of insure adequate agitation. The flow rate of creatine, or to the juice having sufficient bufsterile orange juice was controlled by a Sigmafering capacity to prevent obtaining the remotor pump which delivered by positive disquired alkalinity. An attempt to remove the placement as low as 4.7 ml per hour. inhibiting factor by treatment with Norite Growth in the fermentor was followed by charcoal was unsuccessful, hence, distillation plate counts and direct counts. A number of was employed. direct counting methods have been developed A standard curve relating diacetyl concenspecifically for the determination of organtration and optical density readings was conisms in orange juice (9, 18, 21) and these structed using known amounts of purified along with some 25 other staining procedures diacetyl. were examined for possible use. The procedure finally adopted was as follows: With the use The two organisms used in this investigaof a standard loop, 0.01 ml of the sample to tion, Lactobacillus No. 802 and Lactobacillus be counted was evenly spread over an area No. 805, were both originally isolated from of I sq. cm. that had previously been ruled off orange juice and for neither organism was the on a clean slide. The smear was air dried and species established. Both organisms were capalightly fixed with heat, A drop (approximateble of growth in orange juice with the produc-

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WITTER: DIACETYL IN ORANGE JUICE 123 tion of a typical "buttermilk" off-odor and off-tration was experienced. Both the population flavor. density and the diacetyl concentration Under conditions of slightly changed flow rate would To start a continuous culture system exper-I ..seek new equilibrium concentrations and reiment, the fermentor was inoculated with an mi osata hs e eesa oga actively growing culture of the organism to be tested. This culture was allowed to grow thneflwrewakptcsat.Isebatchwise in the fermentor for five to eight ing this new level the diacetyl concentration hours before starting to add fresh sterile single paralleled the population density as was obS served by Kilburn and Tuthill (11) in their strngt orne ce h frs y0e wa added continuously and at a constant rate to investigation. Adams and Hungate (1) disthe fermentor, although the rate was sometimes cussed this leveling off phenomenon at some purposely changed during the course of an length and devised a system of predicting the experiment to some other constant value, leveling off population density at different While a run was in progress, direct counts, flow rates. plate counts, and diacetyl tests were made. In Fig. I over the course of the experiment The overflow of juice was collected and the the flow rate .gradually increased until at volume measured at various times to deterabout 50 hours the flow rate had increased mine the flow rate, R. When the run was completed-generally from 50 to 80 hours after the start-the population density and diacetyl 2F-GROWTH AND DIACETYL FORMATION BY concentration were plotted against time to 'ACTOBACILLUS 44805 U .ECONT NUOUS give a graphical picture of the experiment. 20 1\ The rate of diacetyl production was also calculated. Each experiment differed slightly in DICETYL 2 detail, but all of them followed the general pattern described.zI *0 80 0 to -0~~8 * RESULTS AND DiscussION o / POPULATION Three representat ive graphs of three typicalDEST 4 experiments are given in Figs. 1, 2, and 3. In these three experiments, as well as in all other I 0 2 40 6O 1405 experiments performed during the course of TIME I N HOURS this investigation, when the rate of delivery "f2 U I TUMUTM#W* of fresh juice was altered, an alteration in the n1 ai5. ,. .n .6 population density and the diacetyl concen50 25' GROWTH AND DIACETYL FORMATION .5 GROWTH AN D DIACETYL FORMATION BY ~2.5 BY LACTOBACILLUS 4116802 IN A LACTOBACILLUS 9*802 IN A CONTINUOUS CONTINUOUS CULTURE SYSTEM. CULTURE SYSTEM. 20. -4-2.0 POPULATION DEN SITY -0 *J3 --15 -OUATO 4 .5 .. --.-POPULAR N DENSITY ACETYL \ -.T O ~ ICEY -z. ICEY O 0 0 0 0 -1. TL .E 1N H -ME -.N .Q 10 0 30 406300t TIEI HOURS IME IN.S r HOURS

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124 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 sufficiently to dilute the organisms from the SUMMARY fermentor at a rate greater than they were Two organisms previously implicated in the being reproduced and both the population spoilage of orange juice were grown in the density and the diacetyl concentration dropped. continuous culture system and their rates of However, it is important to note that these diacetyl production were determined. One of variables were kept constant for something the test organisms, Lactobaciffits No. 802, proover 30 hours. In Figs. 2 and 3, the flow rate ducked diacetyl at the rate of 0.015 p.p.m. per was purposely changed and the curves rehour, per on'e million organisms per ml. The sponded as would be expected. other test organism, Lactobacillus No. 805, proFor those portions of these experiments duced diacetyl at a rate 167 times as great as where the population density and the diacetyl the first, or 2.5 p.p.m. of diacetyl per hour, concentration remained constant, values of k' per one million organisms per ml. were calculated using equation (10). Using The relationship of product formation to all of the data available, k' values were calcupopulation density in a continuous culture lated and averaged for both test organisms. system was mathematically defined and a The average k' value for Lactobaciffits No. 805 method for calculating the diacetyl concenwas 2.5 and that of Lactobacillus No. 802 was tration and rate of diacetyl formation was 0.010. The reaction rate constant k' is the derived. proportionality factor which relates the rate of ACKNOWLEDGMENT diacetyl production by a given organism to its The author wishes to thank V. S. Troy, J. population density, while the constant ratio of M. Berry, and J. F. Folinazzo for their ask'/k relates the concentration of diacetyl to sistance and helpful suggestions and other the population density under equilibrium conmembers of the research staff who reviewed ditions. The average k' values given merely this manuscript and assisted in its preparation express an order of magnitude of diacetyl for publication. formation, since at the high population densitisusde ermnt0 th vau ofk vaiS SERTR CITED t1. Adams, S L. and R. E. Hungate. Continuous slightly with the population density, as disfermentation cycle times: prediction from growth curve cussed by Adams and Hungate (1). Since k ana s. Ind En Chm 42 181518 8(t9k0) 2. Bifod H. R. R. E. SSW .StradP was considered a constant in the integration J. Kolachov. Alcoholic fermentation of molasses: rapid ...ontinuous fermentation process. Ind. Eng. Chem., 34, of equation (4), a true variation mn k in turn c406-1410 (1942). caused a pseudo variation in k', although the 3.i Bme'ye ..isual detection cofneihera dacetyl or magnitude of the error was not great. At the juice. Food Technol., 8, 173-174 (1954). ..4. Elsworth. R. and L. R. P. Meakin. Laboratory and lower population densities that would be met Pilot plant equipment for the continuous culture of in commercial operations (less than one mil927,a muly 24 1. md, lion organisms per ml), both k and k' would 5-.Englis. D. T., E. J. Fisch, and S. L. Bash. Determination of diacetyl. Anal. Chem., 25, 1373-1375 be constant. Experimentally, however, it was (1953). very difficult to adequately balance the conmics ofna coinuous ProEagaon fo micoorgnisms tinuous culture system at these lower levels. J. Ag. & Food Chem., 2, 66-69 (1954). 7. Gerhardt, P. Brucella suis in aerated broth culThe ~ ~ ~ ~ ~ ~ ~ ~ ~~ue rstsfthsexemesagnecontinuouss culture studies. J. Bact., 52, 283-292 Th rst of teeeprmnsinm(196) phasize the lack of validity in using either 8. Golle, H. A. Microorganisms production: theoretical considerations of a continuous culture system. J. plate or direct counts as the sole criterion for Ag. & Food Chem., 1, 789-793 (1953). predicting potential off-flavor in concentrated parison ofE various methodsz forandetectio aro. mco.orange juice. Organism No. 805 produced diaorganisms which produce off-flavors in orange con6 3 centrate. Third Annual Citrus Processors Meeting, cetyl at about 167 times the rate of organism Citrus Experiment Station, Lake Alfred, Florida. OctoNo. 802, while growing at a rate that is roughb1,0. Hill, E. C., F. W. Wenzel, and A. Barreto. ly 67% the rate of the latter. Disregarding diluColorimetric method for detection of microbial spoilo age in citrus juice. Food Technol., 8, 168-171 (1954). tion, ten thousand No. 805 organisms per ml 11. Kilburn, R. W. and P. Tuthill. Plant sanitation and microbiological control methods. Presented at the would produce 0.1 p.p.m. diacetyl (an unaC14th Annual I.F.T. meeting, June, 1954. ceptable level) in four hours while it would 12. MacDonald, R. W. and E. P. Piret. Continuous flow stirred tank reactor systems: agitation requirerequire one million No. 802 organisms per mi ments. Chem. Engrg. Progr., 47, 363-369 (1951). a period of eight hours to produce this same continu~ous fnrment ir-a discusin of issprincipes level of diacetyl concentration. a implications. Applied Microbiology, 3, 110-122 (1 5 )

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POBJECKY: FLORIDA CITRUS STANDARDIZATION 125 14. Monod, J. La technique de culture continue, 18. Stevens, J. W. and T. C. Manchester.. Methods theorie et applications. Ann. Inst. Pasteur, 79, 390-410 for direct count of microorganisms in citrus products. (1950). J. Assoc. Off. Agr. Chem., 27:2, 302-307 (1944). 15. Moyer, H. V. A continuous method for culturing 19. Stotz, E. and J. Raborg. A colorimetric deterbacteria for chemical study. J. Bact., 18, 59-67 (1929). mination of acetoin and diacetyl. J. Biol. Chem., 150, 16. Novick. A. and L. Szilard. Experiments with the 25-31 (1943). chemostat on spontaneous mutations of bacteria. Proc. 20. Westerfeld. W. W. A colorimetric determination Nat'l Acad. Sci., 36, 708-719 (1950). of blood acetoin. J. Biol. Chem., 161, 495-502 (1945). 17. Roe, H. R. and J. Mitchell. Determination of 21. Wolford, E. R. A direct microscopic method small concentrations of carbonyl compounds by a modified for estimation of microorganisms in California differential pH method. Anal. Chem., 23, 1758-1760 frozen citrus concentrate. Bur. of Agr. and Ind. Chem. (1951). Bulletin, AIC-365; U. S. D. A. (1953). STANDARDIZATION OF FLORIDA CITRUS PRODUCTS ARTHUR R. POBJECKY To put our taxpayers at ease, this inspection was not a handout; the canner reimbursed the Southern Fruit Distributors, Inc. government for all Inspectors' salaries and exOrlando penses for the services rendered. Memer ad rind o te loid S. t The War Department made full use of the Horticultural Society, I will present my topic Fed.ra tanydarrd durng there a t rhasfol in the hope that it will not only benefit our boe.Te are n hi atprhsn great citrus industry but also the ultimate conprogram by paying for all processed citrus on sumers of our products. Because standardizaa rd ai. .ttecoeoftewr h tion has been such an important factor in the majority of Florida citrus canners were having deelpen ndgrwh fou poese all of their products inspected. To the credit citrus industry a brief history of its standards .f .u inusr thswsbig oeetrl is in order. on a voluntary basis with the canners payin g the cost of inspection. The depression brought on the first need for standards. The United States Department In 1948, I realized that the existing Federal of Agriculture was petitioned to issue a FedStandards needed some drastic changes. At an eral standard for Canned Grapefruit sections. industry meeting I suggested that the indusThis standard enabled a canner to have his try incorporate Brix-acid ratios into the standwarehouse stocks graded and certified by Fedards to eliminate the extremely tart juice that eral Inspectors. Banks used these. certificates was canned in some seasons. For example, to establish a fair loan value. As other citrus canned grapefruit juice with a Brix of 9.5" products were introduced Federal Standards and an acid of 2.00% was in the Fancy Grade, were issued on them. even though the Brix-acid ratio was below 5 With the rapid expansion of canned citrus, to 1. Canned orange juice with ratios below 8 many buyers changed from the early practice to I also fell into Fancy Grade. The Florida of buying on samples and started to buy on a Citrus Industry, gave my suggestion unanigrade basis. In 1940, another use was made of mous backing. However, the Federal Governthe standards. Several Florida Canners rement was not able to make these revisions quested the U. S. Department.of Agriculture without the approval of the other citrus proto furnish inspectors to their plants on a conducing areas. During this delay, another segtinuous basis. These Federal Inspectors would ment of the industry was heard from. Frozen' observe the fruit used, the entire processing of orange concentrate bad been introduced and the product and the overall sanitation of the the concentrators wanted the new found entire operation. With this added information,' "Cinderella" protected at any cost. This comthey were able to do a much better job of bination of events coupled with Fuller Wargra'ding the finished product. The Canner was ren's ambition to be governor, climaxed in Mr. then allowed to indicate on his label that his Warren realizing his life's ambition and in the product was packed under Federal Inspection birth of "The Florida Citrus Code of 1949." along with the official grade assigned the This Law is unique in many ways. It not product. This was the start of Grade Labeling. only requires that all fresh fruit meet the ma-

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126 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 turity laws in the code, but also all citrus prodcome a longr way in improving our canned nets processed in Florida must meet its regrapefruit juice from the high acid product quirements or be labeled SUBSTANDARD. of the past. But I feel that to move forward The code also authorized the Florida Citrus we must have an examination of conscience. Commission to establish State Grades on all Our maturity laws are based on Brix-acid processed citrus. The Commissioner of Agriratios. This allows some crops of fruit to be culture has the responsibility of Inspection and harvested as early as September and October. Compliance with the law. The inspection is The native Floridian or Florida cracker doesn't being carried out at present by Federal Ineat grapefruit until a much later date. So we spectors under a joint agreement with the live under two sets of maturity standards, a Florida Department of Agriculture. The Citrus brix-acid ratio for the "Yankees" and a taste Commission has adopted the Federal Standtest for ourselves. The unfortunate part is that yards as State Standards. Here I wish to emonly a very small part of our crop is picked phasize that whereas in other citrus producing during this early period; statistics will hear me areas the use of these standards is voluntary out on this. The only argument that can be in Florida because of its laws they are comadvanced for this early harvest is that it helps pulsory. the market on fresh fruit by extending the shipStandards can be classified into three parts. ping season. Most growers will, bear me out if a product is to be properly labeled, it must that for many years, they haven't realized any be described, this is a "Standard of Identity." of this better market price. It is my honest To protect the consumer the containers must opinion that if the grapefruit season was postbe properly filled, this is a "Standard of Fill." poned until November it would not only elimOnce established, these two are seldom inate some of the undesirable fresh fruit going changed so we will concern ourselves with the to market and to canneries but it would also third part-that is, -"Standards of Quality." create a better economical return to the growThe standard for Canned Grapefruit has er and processors httefw rp o e b est stood d th e test o f tim e .F an cy G rap efru it ig p e d lar iy wh at t a e e t r nf t eections se notne o n change in ps thert mained on the trees longer. This would enycourage more consumers to eat grapefruit in near future. Because of the high labor cost fresh form thus helping the fresh market. By involved, canners try only to pack Fancy eliminating the very small percentage of early quality. However, some fruit due to its nagrapefruit being canned in September and ture, does not hold up as well during process October the overall quality of canned sweetand consequently some of the segments beened grapefruit juice would be improved. Our come broken and soft. This is graded as best quality unsweetened grapefruit juice is Choice instead of Fancy. Since both of these canned in the late spring when grapefruit grades have the same nutritive value, conreaches its optimum sweetness. Canners sumer should choose based on the use intendwould be encouraged to carry over large ined for the canned grapefruit. purchased. ventories of premium quality unsweetened The Standard for Canned Grapefruit Juice juice if they knew that they did not have to has had many revisions. There are separate recompete with the low price now created by quirements for the two styles; that is sweetthe canning of the early packing house elimened and unsweetened. The sweetened style inations. Buyers would also remain more active requires a minimum Brix of 11.5 and a through September and October with this minimum Brix-acid ratio of 9 to 1. The unadded confidence in our market. I am cersweetened style a minimum Brix of 9.0" and tain that all of this would add up to improved sliding scale of ratios starting at 8 to 1 at quality in both fresh grapefruits and canned a Brix of 9.0' down, to a ratio of 7 to I at grapefruit juice, with a better economical re" Brix level of 10.5 or higher. We all agree turn to all segments of the industry. that a 7 to I Brix-acid ratio is too tart and The Standard for Canned Orange juice has so it would seem advisable to raise this level -also had many revisions. Sweetened Orange and at the same time simplify the standard by juice requires a minimum Brix of, 10.5* and a doing away with the sliding scale. We have minimum Brix-acid ratio of 12 to 1. Unsweet-

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POBJECKY: FLORIDA CITRUS STANDARDIZATION 127 ened orange juice a minimum Brix of 10.5' uct. The code prohibits the addition of sugar and a sliding ratio scale of 10 to 1 if the to Florida Orange Concentrate-this protects Brix is less than 11.5 and down to 9 to I if the consumer from any possible adulteration the Brix is above 11.5. Here again we all that might arise by the substitution of sugar agree that the 9 to I ratio at any Brix level is for natural fruit solids. The code establishes a too tart and so it should be raised and the minimum fruit solids value in the finished consliding scale, which only serves to confuse centrate which assures the consumer that after our production personnel, be done away with. the addition of three parts water the reconAgain we can help the quality of both fresh stituted orange juice is of the same strength oranges and canned orange juice by holding as the freshly extracted orange juice. The back slightly on our picking schedule. minimum Brix-acid ratio of 12 to 1 is much There is one other important factor in higher than the minimum of 8 to 1 allowed orange juice that I must dwell on. This factor in fresh fruit and the present 9 to I allowed is color. Many of our northern friends associate in canned orange juice. And here I wish to the word orange with the orange color. The clinch my previous arguments against the deep orange color of synthetic beverages to early harvesting of Florida citrus. In spite of which artificial color has been added, strengththe rigid controls the concentrators have imens this delusion. The color of Florida orange posed on themselves. They were able to projuice varies from yellow to yellow-orange in duce seventy million gallons of frozen orange color. This variation in color'depends on the concentrate during the past season. To do this, variety of orange and to a lesser degree on the they utilized fifty million boxes of oranges out growing season. Consumers should be inof a ninety-two million box crop. This entire formed that this lack of orange color in no production was accomplished during a four way detracts from the health-giving qualities months production period, in most plants, and of Florida orange juice--actually in many inthe growers enjoyed the best returns on record. stances the vitamin level on the pale colored Consumers may now ask this question: If early varieties is even higher than the later your industry is so highly standardized why varieties. the variations in quality? There are many reaThe suggestions I have made on Canned sons. Primarily the differences in the varieties Grapefruit juice and Orange juice would of of fruit we grow; differences in the processing course also benefit the quality of canned and blending of fruit; and differences in the blended juice. packers as well. Standards will never change Canned tangerine juice can be improved by these, but standards can and must assure you changes in the methods of process and stora satisfactory product. Many of our quality age. Some in the industry would like to reproblems arise after our products leave our classify tangerines and call them oranges. I warehouses. Prolonged storage at high temwish to remain old-fashioned in this respect. peratures will alter the quality of all canned To me those zipper-skinned fruit mother put citrus products. Many handlers and consumers in our stockings at Christmas are still tangerstill fail to realize that frozen orange concenines. trate is a perishable product and must be Our latest product, orange juice in carhandled as such. tons, still is in search of an official name. BeIn conclusion any industry that has enjoyed cause of the varied methods 'of production it the tremendous growth of ours has a right to had been very difficult to establish a Standard be proud of the products it produces. Howof Identity. However, steps have been taken ever, to continue forward we must not rest to have the Federal Food and Drug Adminon past performances. It is with this thought istration issue a Standard of Identity and this that I wish to re-emphasize that the only should enable packers to properly label this real important change we can make to further item. improve our products is 'to change our maI have saved Frozen Orange Concentrate turity laws. To do this the standards must be for the very last. My reason is, that the Florida rigid enough to delay the picking of fruit until citrus code and Federal Standards have done November or such time that we ourselves are much to promote the popularity of this prodsatisfied with the flavor of the fruit we harvest.

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128 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 CITRUS VITAMIN 'P' (Citrus Bio-Flavonoids) BORIS SOKOLOFF, M.D., ISIDOR CHAMELIN, SC.D, cept of Szent-Gyorgyi and to work with vitaMORTN BIKIN, M.., ILLIM C MARINmin P as a flavonoid complex. We chose the MORTN BIKIN, M.., ILLIM C MARINsecond approach and decided to work and to M.D., CLARENCE SAELHOF, ,M.D., PHD., SHIRO investigate the flavonoid compound we exKATO, M.D., HUGO EsPINAL, M.D., WITH TECHtracted from citrus wastes. This compound, NICA ASSSTACE O TAEYUN Kim Al composed of the flavonoids naturally present NICA ASISTNCE F TEKYNG KM, AX-both in grapefruits and oranges, we called WELL SIMPSON, NORMAN ANDREE citrus vitamin P, or C.V.P. It is water soluble, AND'GORGEBENNNGERand it contains several flavonoids, apparently AND EORG RENINGR -forming one or two complex flavonoid mole-' Southern Bio-Research Laboratory cules, as flavonoids tend to do so easily. it Swas this compound that we have been invesFlorda Suthen Colegetigating experimentally and clinically for the Lakeland last nine years. Twenty years ago in 1936, Dr. Albert THE BIO-ASSAY FOR VITAMIN P Szent-Gyorgyi announced the discovery of a The chemical tests on flavonoids are of a Capillary Permeability factor, vitamin P, isolimited significance. The boro-citrate test, the late by him and his associates from red pepLawrence test and others give an indication per and lemon. At first be believed that vitaof the chemical nature of a flavonoid but they min P was a single chemical substance. Howdo not disclose the biological activity of the ever, several months after his announcement' compound. Thus, our second problem was to he rectified his statement admitting that vitawork out a reliable bio-assay. Ambrose and min P is a compound of several flavonoids. DeEds offered a method of testing capillary Immediately after the discovery of vitamin permeability by applying chloroform to the P, the California Fruit Growers Exchange emskin of rabbits and injecting trypan blue dye. barked on an extensive investigation of vitaAlthough this method has some merit, it is min P. The California scientists isolated sevnot sufficiently exact for any quantitative test. eral flavonoids present in citrus fruit and Gradually we elaborated a bio-assay technique synthesized some, like methyl-chalcone heswhich we believe is accurate and dependable. peridin. The results of the clinical trials with This method is based on the discovery of Dr. their flavonoid compounds weren't very enM. J. Shear of the National Health Institutes couraging, and somewhat disappointing. that the polysaccharide isolated from Serratia By 1946-47, the whole problem of vitamin marcescens induces an extensive hemorrhage P reached a critical state. The work of Szentin the tumors of animals. (1) Gyorgyi seemed to be discredited and conThe bacterial polysaccharide preparation troversial. The vitamin nature of vitamin P supplied to us by Dr. Shear and labeled P-25 was denied by some workers, its therapeutic is well standardized. A dose of 0.5 mg. invalue questioned, and some workers even jected in a rat, 150 grams weight and bearer claimed that vitamin P or flavonoids are of a tumor two inches in diameter, kills the neither absorbed nor assimilated by the oranimal in 6-7 hours. Death is caused by a proganism (Clark). It was under these highly fuse capillary bleeding and a destruction of unfavorable conditions that the Southern BiOnumerous capillaries of the tumor. Research Laboratory in 1947 began the inOur tests with citrus vitamin P have demonvestigation on citrus vitamin P. strated its biological activity. Table I gives We visualized two possible roads of attackthe data pertaining to one of our tests, ing this problem. One, to follow the steps of California and to try isolating various citrus When 3 mg. of the citrus vitamin P comflavonoids, or to return to the original conpound were injected one hour before the in-

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SOKOLOFF, ET AL: CITRUS VITAMIN P 129 jection of bacterial polysaccharide, the animals however, the dose of vitamin P was increased lived an average of 20 hours instead of an to 10 mg., 66% of the animals survived and average of 7 hours without vitamin P. When, 33% lived an average of 45 hours. (2) TABLE I TFE PROTECTIVE ACTION OF CITRUS VITAMIN P AGAINST THE HEMORREAGE-INDUCING ACTIVITY OF BACTERIAL POLYSACCHARIDE, P-25() TREATMIENIT Rat Nos. Citrus Result: P-25 Vitamin P Desth or survival 171-A, m. 005 mg. 3 mg. Death in 17 hrea 171-B,* fo 005 inG. 3 mgo Death in 22 hrs. 25 ninno 171-C 0 M O.5 mg. 3 wg Death in 18 hrs. 171-D, m. 0.5 mg a 3 rg. Death in 19 hrs a 10 mine 171-E, m. 005 =g. 3 mg. Death in 20 hrs. 40 min. 174-Aa, fo..5 ng. 3 mg. Death in 19 hAra 174-B, rao 0945 mg 3 mg. De ath in 24 hrs o 30 min. 174-4 M 0.5 M90 10 mgo Death in 36 hrs 174-D, mo 0.5 mg. 10 mgo Survived 174-E, M. Oo5 mga 10 mg. Death in 52 hrso 174-F, mo 0.5 g. 10 mg. Survived 177-L, f. 0*5 Mgo 10 mg. Survived 177iB m 0.5 mgo 10 mg. Death in 66 hrs 177-C, f 0.5 mg. 10 mg. Survived 177-D, m. 0.4 mg. 10 mg. Survived 177E, me 0o45 mg 10 mg Survived 177-F, m. 0.5 mg. 10 mg. Survived 177-H, m. 05 mg. 10 mg. Death in 26 h". 173-A, m. 0.5 mg. 10 mg. Survived Controls 178B,~ m. 0.5 mg. None Death in 6 hrso 25 min. 178-C, f. O5 mg. None Death in 7 hrs. 35 min. 178-D, M 005 mge None Death in 9 hrs. 178~*, f. -05 mg. None Death in 7 hrs 30 min. 178-F, f 0.5 mg. None Death in 8 hrs. 20 min. 176-H, 4. 005 mg. None Death in 7 hr. 15 mn P-25 is a preparation of Shar bacterial polysaceharideo

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130 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Rechecking -our results, we found that a THE PHYSIOLOGY OF THE CAPILLARY SYSTEM dose of 12 mg. gave a complete protection to all animals receiving the deadly dose of 0.5 The medical profession fully realizes the mg. of bacterial polysaccharide. Thus this dose important role which capillary dysfunction served us during all our further investigations plays in many diseases. Stefanini and Dameas the basis of our bio-assays. shek (3) in their recent book on hemorrhagic disorders point out capillary fragility as the During the following years, we had the cause of abnormal bleedings. One must clearopportunity to test various citrus flavonoids ly visualize that the essential exchange of body isolated by us or produced by Californians or fluids takes place in the capillaries and that some other companies. We found that waterthe role of the large blood vessels is actually insoluble hesperidin gave no protection against limited to transporting blood to the capillaries. capillary hemorrhage tested by this method, The peculiar paradox of the human organism even when given in a dose ten times larger is that the capillaries are easily injured by than our protective dose of 12 mg. Taking the numerous bacterial and chemical agents or by index 1.0 (corresponding to 12 mg.) as a demetabolic disturbances, parting point for the tests of other flavonoids, we found that methyl-chalcone hesperidin We know by now that increased capillary showed a very mild capillary activity with an fragility is a common phenomenon, much index of 0.1. The synthetic phosphorylated more so than we thought ten or fifteen year's hesperidin exerted an activity about 0.15. Ruago. The work of Griffith (4), Beardwood (5), tin gave an index of 0.2. On the other band, Greenblatt (6) and many others indicate that the lemon infusion prepared by the California the capillaries are abnormally fragile, and Fruit Growers Exchange has a relatively high therefore might bleed easily in numerous diindex of 0.3, or approximately three times less seases such as arteriosclerosis, hypertension, capillary activity than our Florida citrus vitaand particularly so in diabetes (7). When a min P compound. (Table II) stroke (apoplexy) occurs, this means that some capillaries of the brain tissue became over-fragile and broke down causing bleeding, often fatal. In many bacterial infections AGAINST MRHG-RDCIvG BACTEI PCLYA INNM and in almost all virus infections, capillary fragility, localized or generalized, is present. Th Mina dom of flavoIndex of (8, 9, 10). The inflammation of the mucous CoMpounds foi d eh by05M.o eio ial membrane itself, when one has a sore throat, -Batr. olysochaideor swollen gums, or pneumonia, or any other "irsol viav .i .infectious disease is closely associated with Water-insolubla the injury to the capillary system. Even in hesperidi 120 F 0 heart failure, with sudden death or coronary 0 eserin 12U a 0. thrombosis, one might blame capillary injury Phosphorylated has. for the tragic accident. For in such cases, the peridin, X.D.C. So 1w* 0.15 so-called intimal capillary, which is located in nenaifornia 5 Mg. 0. the wall of the larger coronary vessels is abRutin 60 Mg. 0.2 normally fragile and might suddenly break down and bleed. If the bleeding is profuse, ()Rats, British bread, average weight 1o gia., man dies at once. When the bleeding is very dameter r small, a blood clot is formed and coronary occlusion, known as coronary thrombosis, takes Having asserted and proved to our own place. (11, 12, 13, 14). Older people rore satisfaction that the Florida citrus vitamin P frequently have increased capillary fragility compound is biologically superior to the ones than younger ones, and the danger to their produced by Californians, we embarked on lives from capillary bleeding is higher. (15, the clinical investigations with this compound. 16, 17).

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SOKOLOFF, ET AL: CITRUS VITAMIN P 131 CLINICAL INVESTIGATIONS B.: Obst. & Gynee., 2: 530-534, November 1953. (7) Loewe. Walter H.; Eye, Ear, Nose & Throat Monthly, 34:108, 1955. (8) Biskind, M. S. and Martin, W. C.: The clincal investigations, in which inetyAm. J. Dig. Dis., 21:177, 1954. (9) Biskind, M. S. and two physicians associated with various hospiMari*nW.oC: A J22:41-45, 1955. (10) Sooof Bois Am. J-. S** *.. Dig Di 221 195 (11 tals took part, and the results of which were wartman, W. B.: Am. Heart J., 15: 459, 1938. (12) .'. .Winternitz, M., Thomas, B., and LeCompte, P.: The reported. in sixty-three papers published im Biology of Arteriosclerosis, Springfield, Charles Thommedial nd sienifi ourals hav deonas, 1938. (13) Paterson, J. C.: Arch. Path., 29: 345, medcalandscintiioras aedmn 1940. (14) Sokoloff, B., Martin, W. C., Saelhof, C. C.: strated the therapeutic value of the Florida J. Am. Geriatr. Soc. (in press). (15) Ibid. (16) Martin, W. C.: Intern. Record of Med. & Gen. Prac. Clincitrus vitamin P compound, isolated by us ics. Vol. 168, No. 2, February 1955. (17) Perry, D. J. fromcitus ast, i thefolowig cndiion and Linden, L.: Science Newsletter, April, 1953. (18) fr~mcitrS Watein te folowng cnditons Arons, I., Freedman, J., and Weintraub, S.: Brit. J. where increased capillary fragility or capillary of Radiology, 27:696-98, 1954. (19) Sokoloff, B., and Eddy, W. H.: Capillary Fragility & Stress, Mono. FSC bleeding was evidenced. 3:33-65, 1952. (20) Martin, William P. Proc. Meet., Raditio eryhem (1819,20)Buffalo Gen. Hospital, May. 1952. (21) Jones, Leland Radatin eythma 1,1,2) W. and Croce, Pietro: Capil. Frag. & Stress, 3:19-21, Tuberculous hemoptysis (21, 22) 19,52. (22) Sokoloff, B., and Eddy, W. H. Bio-Flavonoids i Capillary Fragility, Mono. 2, FSC, 1952. (23) Habitual. Abortion (23, 24, 25, 26, 27, 28) Papers of the Royal Committee on Population, Vol. IV Reproductive Wastage: Abortion, Stillbirth, and InErythroblastosis Fetalis (29, 30) fant Mortality. London, 1950. His Majesty's Stat. Off. Bleeding Gastric and Duodenal Ulcers (31, pp. 3-52. (24 Moore, Robert Allan: Pathologic Anato32,33) ical Manifestations of Disease. Saunders Co., 1952. (25) Greenblatt, R. B., and Suran, R. R.: Am. J. Obst. Cerebral Hemorrhage: Stroke (34, 35) & Gynec., 57:294, 1949. (26) Taylor, Finis A.: West. Retinitis (36, 37, 38) J. of Surg., Obst., and Gynec., Vol. 64, pp. 280-283, '. May 1956. (27) iskind. Leonard: Journal-Lancet, Dental Diseases and Surgery (39, 40) __Vol. 75, No. 6, p. 272, Minneapolis, June 1955. (28) Javert, Carl T.: Obst. & Gynee., Vol. 3, No. 4, April Hemorrhagic Cystitis (41) 1954. (29) Rogers, George C., and Fleming, John M.: Hemorrhagic Diathesis (3, 42, 43) West. J. Surg., Obstet., and Gynee., 63:586, 1955. (30) Jacobs, Warren M.: Surg., Gynec., & Obstet., August Increased Capillary Fragility (44, 45) 1956, Vol. 102, 233-236, 1956. (31) Gray, H. K., Shands, W. C. M., and Thuringer, C.: Ann. Surg., 139: Altogether about 9,000 case histories were 731, 1954. (32) Ivy, A. C., Grossman, M. I., and collected during the last seven years. Bacharach, W. H.: Peptic Ulcer, New York, Blakiston Co., 1950. (33) Weiss. S. and Weiss, B.: Bull. Int. To conclude: The experimental and clinical C Ong. of. Gastroenterology, London, July 1956. (34) P Alvarez, Walter C.: J.A.M.A., 157:1199, 1955. (35) studies on Florida citrus vitamin P compound Sokoloff, B., Biskind, M., Martin, W. C. and Chamelin, r.: Trav. XXth Intern. Congress Physioextracted from citrus waste, have supplied the logy, August 1, 1956, Brussels. (36) Shepardson, evidence of its therapeutic value in increased H. C.. and Crawford. J. W.: Calif. & West. Med., 35: 111, 1931. (37) Wagener, H. P...Proc. Am. Diabetes capillary fragility and capillary bleeding. InAsso., 5:203, 1945. (38) Loewe, Walter R.: Eye, Ear, Nose & Throat Monthly, Vol. 34, No. 2, Februdirectly, the data so collected confirms the ary 1955. (39) Puckett, John B.: Dental Digest, GJune 1956. (40) Wellensiek, Ellen K.: Texas Dental original findngs of Szent-Gyorgyi and his asJournal, June 1956. (41) Saelhof, Clarence C.: Am. sociates concerning vitamin P. J. Dig. Dis., 22:204-6, July 1955. (42) Sokoloff, Boris and Eddy, Walter H.: Capillary Frag. & Stress, Mono. FSC. 3:14-16, 1952. (43) Sokoloff, B. and REFERENCES Eddy, W. H.: Capillary Frag. & Stress, Mono. FSC, 1952. (44) Martin, W. C.: Intern. Record of Med. & (1) Shear, M. J. et al, J. Nat. Inst., 44:4, 81, 1943, Gen. Prae. Clinics, Vol. 168, No. 2, February 1955. (2) Sokoloff, B. Eddy, W. H., and Redd, J. B.: J. (45) Sokoloff, B., Biskind, M. S., Martin, W. C. and Clin. Inv., 30:395, 1951. (3) Stefanini, M. and DameSaelhof, C. C.: Clin. Med., Vol. 2, No. 8, pp. 787-792, shek. W.: The Hemorrhagic Disorders, Grune & StratAugust 1955. (46) Biskind, M. S. and Martin, W. C.: ton, 1955, New York. (4) Griffith, J. W., Jr., and LinAm. J. Dig. Dis., 22:41--45, 19551 (47) Biskind, M. S. dauer, M. A.: Am. Heart J., 28:758, 1944. (5) Beardand Martin, W. C.: Am. J. Dig. Dis., 21-177, 1954. wood, J. T., Roberts, E., and Trueman, R.: Proc. Amer. (48) Finch, Frederick L.: Tri-State Medical Journal, Diabetes Assoc., 8:241, 1948. (6) Greenblatt, Robert Feb. 1956, Vol. III, No. 12.

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132 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 VACUUM COOLING OF FLORIDA VEGETABLES R. K. SHOWALTER AND B. D. THomPSON sure over water is reduced to 0.18 inches Florda gricltual EpermentStaion (vacuum of 29.82 inches) the water boils at 32' F. The water which "boils" or evaporates Gainesville from the vegetables cools them to a temperature corresponding to the temperature of The first Florida shipments of vacuum the water. To secure the reduced pressure, cooled lettuce were made from Oneco during vegetables are placed in a chamber and the the 1955-56 season. Although the vacuum required ,acuum is obtained by a pump or cooling of lettuce has developed rapidly in a steam jet. The cooling of the vegetable is California and Arizona since the first commeasured with a recording thermometer and mercial shipments in 1948, the method has the vacuum is released when the desired not been widely adapted in other areas. Floritemperature is reached. Since vacuum cooling da growers and shippers have shown considdepends upon evaporation of water, one enable interest in vacuum cooling. The remight think that considerable weight loss ported advantages are the maintenance of occurs. However, wilting is not severe and better quality by more rapid precooling and Friedman and Radspinner (4) reported the reduction in packing and shipping costs weight losses of only I to 4.7 percent. through cheaper containers and the elimination 'The lettuce vacuum cooled in fiberboard of package and top ice. Lettuce has not been cartons at Oneco was either packed dry in grown in sufficient volume in concentrated the field or washed and packed in the packareas in Florida to justify the cost of establishinghouse. The vacuum tube (22 ft. long x ing a permanently located vacuum cooler. The 7,12 ft. in diameter) was loaded with 240 carunit at Oneco was semi-portable and when tons each containing D-6 or 2 dozen heads of the lettuce season ended in Manatee County lettuce. The vacuum pump, powered by a it was moved to lettuce production areas in diesel engine, pulled the air from the tube other states. The results presented here were containing the lettuce through a second tube obtained from preliminary vacuum cooling of equal size containing blocks of ice. The studies with several vegetables to determine tube of ice condensed the evaporated moisprimarily the effects of the vacuum treatment ture before it reached the vacuum pump. on quality. Studies were made in a laboratory model Vacuum cooling has been studied by sevvacuum cooler at Belle Glade in May and eral investigators. Friedman (3) found that June 1956. The vacuum chamber, with a almost any fruit or vegetable can be vacuum capacity of about 4 cartons, was evacuated by cooled to some extent, but there was a rapid an .electric powered pump. The evaporated temperature decrease only in vegetables with moisture was condensed by mechanical rea large ratio of surface area to volume. Vac. frigeration. uum cooling was found effective for prepackaged spinach, coleslaw, and salad mixVcu CLNGFLETE after the bags were packed in master conData were obtained on the weight loss, tainers (2). cooling rate, and quality of wet and dry lettuce. Wetting the lettuce before vacuum VACUUM COOLING PROCESS cooling did not affect the cooling rate. Little The process by which the rapid chilling difference in weight loss was found among 50 occurs is based on evaporative cooling. At cartons of wet and dry lettuce from five difnormal atmospheric pressure of approximateferent lots as shown in Table 1. When the ly 30 inches, water boils at 212* F. If the presindividual heads were weighed in one test, those with added water lost only 1.9 percent 'Th rauthsrsowis. th express aprkciationto th compared with 2.3 percent weight loss of the Prine and Griffin farms for making the eq uipment dry heads. availab le f r these studies. They also wish to thank the growers and shippers who furnished vegetables Vacuum cooling had no apparent detritests.th opne h upidcnanr o h mental effects upon the quality of the lettuce.

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SHOWALTER AND THOMPSON: COOLING VEGETABLES 133 Table 1. -Average Temperatures and Weight Losses of Wet and Dry Lettuce Vacuum Cooled in Commercial Unit at Oneco, Florida Dry Units Tested Time in : Vegetable Temp. -Weight or Vacuum Before After Loss Wet Number Type :. in. 0 OF Lettuce Wet 10 Fiberboard Cartons 45 65 36 2.6 Wet 10 " 36 71 38 3.5 Wet '10 " 40 76 38 3.1 Dry 10 "t "t 36 75 38 3.1 Dry 10 "t "t 57 74 42 .3.2 Wet 32 Single Heads 45 65 36 1.9 Dry 30 Single Heads 45 65 36 2.3 When held in storage at 370-40' for 8 days cooled to 38' at the base of the stalks, conthe quality was still good. The dry lettuce siderable freezing injury of the leaves ocshowed moderate wilting after 8 days and a curred. Weight loss of 4.1 percent compared with Although the vegetables were vacuum slight wilting and a loss of 1.4 percent for coe nfl as iebadcros ml the wet lettuce. After 16 days storage the baskets and wirebound crates, the containers outer leaves of both wet and dry lettuce were wr o l oprdi h aetss I weentalcmae ntesm et. considerably wilted. Another lot hydrocooled Fiberboard cartons and wirebound crates of and top-iced for 16 days was very crisp. sweet corn were vacuum cooled at the same However, the top-iced heads developed more time in one test (Test No. 3, Table 3), and reddish discoloration than the vacuum cooled there was little difference in rate of cooling heads. and no difference in appearance of the corn. VEGETABLES IN VARIOUS CONTAINERS In another test bunched radishes in wooden During March 1956, small quantities of baskets were vacuum cooled with topped prevegetables were cooled in the commercial packaged radishes (Table 2). Some of the vacuum unit along with the loads of lettuce. tops on the bunched radishes were severely Prepackaged broccoli, spinach, radishes, salad wilted, but there was no change in appearmix, and coleslaw cooled at different rates. ance of the prepackaged lot. The weight loss The temperature of the broccoli decreased of the bunched radishes averaged 7 percent only 15' in the same period that the spinach compared with 4 percent for the prepackaged and salad mix cooled 30-33* (Table 2). In ones. the commercial vacuum unit celery cooled PREwVETTING OF SWEET CORN from 61 to 45 at the slowest rate for the vegetables in bulk containers. Since succulence or moisture content is In the laboratory vacuum unit two tests one of the important quality factors of sweet of similar cartons of celery cooled from 80" corn, attempts were made to reduce the to 38' in 30 minutes and from 80* to 44' in moisture loss during cooling by previously 20 minutes. Friedman and Radspinner (4) wetting the ears in water. The results in Test found that the initial temperature of celery 5, Table 3, showed that in one' test in the had a marked effect on the final temperature, laboratory cooler the weight loss was rewhile the initial temperature of lettuce had duced one-half by wetting. In Test 6 the dry little effect on its final temperature. They ears lost 6.1 percent compared with no loss attributed the difference to the smaller surfor the wet ears. Ears from the same lot face area-volume ratio of celery. In the celery gained 13.7 percent in weight during hydro-

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134 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 cooling. Dewey (1) also reduced the weight slightly. The hydrocooled ears maintained loss of sweet corn by adding water immedithe most succulence and the freshest husks. ately prior to the vacuum treatment. He reThe husks in all treatments remained green. duced the weight loss from 3.2 percent for Slight denting of kernels was found only in dry broccoli to almost Done for wet broccoli. the dry vacuum lot after 6 and 7 days' storage. EFFECT OF VACUUM COOLING ON QUALITY Small quantities of vacuum cooled and Qualty valatios o th dryandwet hydrocooled vegetables were stored at 37*vacuumtyooleduatdons of theedryweed cor 40. and at 65*-70' for comparisons of quality. wereumaded a nd hav ytadroafted swee 6. n After 6 days at 65* 70' the celery leaves and were' stoae at 35res and 90ft ercn 6,a stems of lioth vacuum and hydrocooled lots day' sorae a 35and90-5 prcet rla~were considerably yellowed. After 11 days tive humidity. The vacuum cooled ears were at3"4"teqaIofheeerfrmbh packd. n fierbard artns ad te hyro~ lots was good, only "a few leaves were slightcooled ears in wirebound crates. The succuw t lence as measured by the shear press, was weight loss averaged.2 ounces per stalk in lower after vacuum cooling dry than at harboth lots. vest, and remained lower than the other treatments at all storage periods (Table 4). The The vacuum cooled packages of salad mix kernels vacuum cooled wet were still more developed decay in cold storage faster than succulent after 7 days' cold storage than at the hydrocooled packages. The quality of harvest, although the husks had wilted very the vacuum cooled and hydrocooled escarole Table 2. --Average Temperatures and Weight Losses of Vegetables in Various Containers Vacuum Cooled in Commercial unit at Oneco, Florida V t C Number of : Vegetable Temperature :Initial Weight :eeale .Cntie nits Tested Before After Decrease Weight :loss F FOF oz/unit % Broccoli Cellophane Bag 12 Bags 64 49 15 11.5 1.8 Coleslaw Cellophane Bag" 12 Bags 7.4 49 .25 10.5 4.8 Salad k:ix Cellophane Bag 12 Bags 79 46 33 8.9 3.8 Spinach Cellophane Bag 12 Bags 78 48 30 11.9 2. I i 78 48 30 11.3 2.6 Radishes Polyethylene Bag 15 Bags 70 11 29 G.1 5.5 itit to 15 It 0.1 2.6 Radishes Wooden Basket 15 Bunches 62 44 18 7.3 7.3 i" 15 -7.7 6.9 Cauliflower Fiberboard Carton 8 Heads 77 50 27 50.0 4.0 Endive Wooden Basket 7 Heads 75 53 22 14.6 3.0 Escarole Wooden Basket 4 Heads 71 53 18 33.2 3.4 Sweet Corn Fiberboard Carton 59 Ears 64 44 20 9.7 1.8 "1 if of .4 "o 64 41 23 10.2 1.2 Celery Fiberboard Carton 12 Stalks 61 45 16 35.5 2.3 " 12 61 45 16 34.1 2.3 t i 12 I so 38 42 --It It 12 It 80 44 36---Cooled in laboratory unit at Belle Glade, Florida

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SHOWALTER AND THOMPSON: COOLING VEGETABLES 135 Table 3. -Average Temp~eratures and Weight Losses of .1'et and Dry Sweet Corn Vacuum Cooled in Laboratory Unit at Belle 7,lade, Florida. Test Dxr Units Containers Tim,.e in Corn Temperature Cob) Weight ...Vacm efore After. Decrease Loss 'let :..:Ears .i.. O *40 OF OF *. 1 Dry 2 Fiberboard Cartons 18 78 38 40-2 Dry 2 30 84 38 46 3 Dry 1 W Jirebound Crate 25 83 40 43 3 Dry 1 Fiberboard Carton 25 84 36 48 4 Wet 1 Wirebound Crate 40 82 33 494 Dry 1 "40 84 32 52-5 "let ( o Ears 40 81 .35 46 2.7 5 Dry 60 Ears 40 90 34 56 5.5 6 *et 36 Ears 40 84 38 46 0 6 Dry 36 Ears 40 86 38 .48 6.1 and endive was about the same after 11 days cess. The vacuum method did not result in cold storage. objectionable wilting except for radish tops. SUMIMARY Weight loss of sweet corn was reduced by Setting before vacuum cooling. Vacuum cooled lettuce originated from the semicooled vegetables retained their freshness portable installation at Oneco. A number of ?eldrng s bra vegetables were vacuum cooled in the Spring LTRTR IE of 1956 with the commercial lettuce cooling LTRTR IE equipment and a laboratory model at Belle 1. Dewey, D. H. Evaporative Cooling of FruitT; and .Vegetables. Refrig. Engin. 60: 1281-1283. 1952. Glade. The vegetables with a large ratio of 2. Friedman, B. A. Vacuum Cooling of Prepackaged surface area to volume cooled most rapidly Spinach, ,Coleslaw, and Mixed Salad. Proc. Amer. Soc. SHort. Sci. 58: 279-287. 1951. but sweet corn and celery also cooled satis3. ............-....--.............-----Vacuum Cooling Upheld fact~ilU.in Tests. Western Grower and Shipper 23 (8): 21-24, -. i. 00 5.31. 1952. The bulk and prepackaged vegetable con4 ......................................... and W. A. Radspinner. tainrs estd dd nt afectthecooing roVacuum Cooling Fresh Vegetables and Fruits. U.S.D.A. taierstesed id otaffct he oolngpro Agr. Marketing Service Report No. 107. 1956. Table 4. -Changes in Quality of Florida Sweet Corn After Dry and W4et Vacuum Cooling and Hydrocooling.. 1.ethod of *At Harvest 'I2 Days Cold Storape 6 Days Cold Storare 7 Days Cold Storage: Precooling SuclneSucculence liusks K* nl Suclnce: Husks Kernels: Succulence :Husks :Kernels MI. Juice :ml. Juice Condition: Denting: RL. Juice Condition: Denting: ml. Juice :Condition :Dentin, Dry Vacuum Cooled 11.4 11.2 Slight None 11.2 Slight Slight on 10.2 Slight Slight on Wilting tiltingg 25% ears Wilting 50 ears Wet Vacuum Cooled.11.4 15.7 Fresh None 11.0 Not None 13.0 Very None Crisp Slight Hydrocooled 11.4 18.6 Fresh None 18'.4 Fresh None --.---det Cold store temperature 350 F. and relative humidity 90--95 percent.

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136 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 THE QUALITY CONTROL OF CHILLED ORANGE JUICE FROM THE TREE TO THE CONSUMER LEO J LiSTER of soluble solids to the acid content, since it Halco Products, Inc. has been found that when certain ratios of Fairvillasugars to acids are found in the fruit, the Fairvillajuice will also have best flavor, color, cloud, AND RTHR C.FAYvitamin C, and all the other desirable qualiANATUCFties. H. P. Hood & Sons Once the particular crops are selected for Boston, Mass. picking, the steps from the groves to the processing plant, the storage and extraction For a number of years, due to the cornsages are very similar to that which is perpatability of citrus juice and milk, the citrus formed in other types. of citrus juice plants. and dairy farmers looked for a suitable means Extreme care is exercised in properly grading of processing and packaging citrus jicee for the fruit to be certain that no undesirable distribution by dairy route trucks. With the fruit enters the line for extraction into the advent of chilled orange juice, this was acjuice. accomplished. The juice flows into a stainless steel trough, Cartoned, or chilled orange puice as it is which is connected to each extractor, and commonly called, is a single strength orange thence into a paddle type prefinisher. The juice, ma rketed in a waxed fiberboard carton. overflow from the prefinisher passes into the The juice is extracted and treated in such a screw type finisher. The type and amount of manner as to retain most of the desirable pulp or juice sacks in the finished product is flavoy and aromas ghicjiassociate d h governed by thep si ofthe openng ied jhe perishable in nature, and must be stored or flows into a surge tank where it is pumped to transported under adequate refrigeration in the blend tanks as pulpy juice is desired. order to reach the consumer in a palatable state. During the past season (1955-56) more The juice from the finisher surge tank is than 3,000,000 boxes of Florida oranges were also pumped to the blend tanks. From this used in production of this product. It is antiline a sample is taken every fifteen minutes cipated that during the current 1956-57 seaand checked for brix-acid ratio and rapid peel son, an excess of 5,000,000 boxes will be utiloil determination (Burdick Method). Through ized. It is the goal of the product control in this method of checks, a constant ratio can the Chilled Orange juice industry to present be maintained by either increasing or reducto the customer-the housewife, the instituing the flow of fruit in the bins. From the tional dietician, or the restaurateur-orange blend tanks, the juice is pumped through a juice of such quality, to have more uniformity plate type heat exchange for stabilization of in flavor and aroma, than juice extracted from enzymic and microbiologicalaction. Procesfresh oranges themselves. sing time and temperature are carefully conThe selection of the fruit to be extracted trolled so that no significant change in flavor is the first and a very important step in qualwill occur. After stabilization, the juice is ity control of chilled juice. This is accomnrapidly cooled to 32' F. and pumped to a polished in the groves, where the fruit is tested cold wall or refrigerated holding tank. The and tasted at regular intervals for maturity juice flows by gravity to a milk type filling by trained technicians and buyers. When the machine where milk type cartons are filled, fruit in the groves reaches its peak of ma-, sealed, and hand packed in cases. The cases, turity, it is then selected for its quality. The closed by an automatic sealer, are then conmaturity of the fruit is based for all practical veyed to the cold room for storage and ultipurposes on the relationship of the per cent mnate loading onto a refrigerated truck.

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LISTER AND FAY: QUALITY CONTROL OF ORANGE JUICE 137 Samples are taken at regular intervals from shipment is analyzed for Vitamin C content. the production line by a U.S. Department of If flavor criticisms indicate a strong peel oil Agriculture Inspector. These samples are flavor, determination is made for the pertested for brix-acid ratio, carton fill temperacentage of peel oil, otherwise this test is ture, and peel oil content. At present, there omitted. are no U.S.D.A. grade standards for chilled Standards of satisfactory. performance with orange juice, only those regulations set by plus or minus tolerances for each of these the Florida Citrus Commission and inforced measurements have been mutually agreed to by the U.S.D.A. Inspector. by the parties concerned, and close contact Plant Sanitation is the most important part is maintained by phone between the Florida of quality control. Through laboratory tests and New England laboratories if results indisuch as mold counts, microscopic examinacate an unfavorable trend in compliance with tions, insect counts, and platting, the cleanlithe standards. Deviations from standards call ness of the equipment can be determined. for prompt correction and not necessarily reAfter each day's operation, floors, walls, tanks, jection unless it is believed the deviation will extractors, and all pipelines are thoroughly result in unfavorable customer reaction. cleaned with a strong detergent and sanitized DISTRIBUTrION CHANNELS with hot water and chlorine solution. When a shipment arrives at the New EngIn less than twenty minutes from the time land plant, it is transferred directly to specialthe orange rolls from the bins, it has been ly refrigerated chests maintained at 30' F., juiced, placed in a carton, eased, and in the providing the temperature and flavor at the cold room ready for shipment. time of unloading are found to be satisfacThe advent of mechanically refrigerated intory. The temperatures normally maintained sulated trucks has played an important part for refrigeration of dairy products are not rein expanding the geographical limits of the garded as adequate for the handling of market for chilled orange juice. Fast trucks chilled orange juice. Each shipment is kept equipped with sleeping accommodations for sufficiently isolated in the storage chest, and the relief driver or the use of exchange drivrecords k~pt of the disposition of each shipers at designated points enroute enable dement into the various channels of distribulIvyfrmFrdatNwEgan mrks tion so that it could be promptly located and in approximately 36 hours. Control of temwithdrawn from the market if subsequent perature is so important that spot checks are tests and especially the progressive flavor demade, unknown to the drivers, by inserting a velopment in the shelf life samples indicate specially designed thermograph in one of the ta vnasih hnewl etknwt cases after removing two of the quart packcustomer satisfaction. Great care must be exages. ercised to avoid excessive inventories, and to SAMPLING PROCEDURE insure systematic turnover of the loads in the Upon arrival at the destination, spot checks order of their receipt. Close contact between of the temperature of the product in differthe laboratory and distribution is absolutely ent parts of the load are made; the thermoessential. Special icing of each case of orange graph is sent to the laboratory together with juice on milk routes is necessary to maintain six quart packages, two each are taken from temperatures well below those normally rea case in the rear, middle, and front of the garded as satisfactory in handling dairy prodload. One of each pair of samples is set aside nets. Route men have learned to pay critical for shelf life determination at 45' F. and is attention to the termination date on the packflavored each day for four days, then at less age and refuse to accept a product which is frequent intervals until the termination date so near its termination date that the customer stamped on the top of each package., The will not have time to use it. Routemen have three other paired samples are each subjected learned the hard way that. the distribution of to the following tests, net weight of contents, one bad lot of orange juice can result in a microbiological counts for bacteria, yeasts greater drop in sales than they can build back and molds, pH, brix-acid ratio, and flavor in three or four months. criticisms by two or more experienced perThe successful distribution of orange juice sons. One of the three samples from each depends upon rigid control of four things:

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138 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 (1) careful selection and skillful blending of the market any product which will jeopardize fruit, (2) precision in processing, (3) absouninterrupted customer satisfaction. lute control of temperatures below 35" F. from Florida to the customer's doorstep, and The distribution of orange puice on milk (4) thorough laboratory checking at the proroutes is a natural; it can be done if we face cessing and distribution end, coupled with up to the problems of complete control from unyielding determination to withdraw from the tree to the customer's doorstep. HYDROCOOLING CANTALOUPES K. E. FORD the rate of heat removal. Bulbs of the therAssoiateA riultral conoistmometers were placed in the flesh at the stem AsoiaeAgiulualEonms end, in the cavity, and in the flesh at the blosGeorgia Experiment Station som end. Results given are from the readings of the thermometers inserted in the flesh, Experiment, Georgia which were practically identical for both posiThe growth and prosperity of cantaloupe tions. production in the Southeast depend on placing Full slip and full ripe cantaloupes were high quality melons on the market. Hydroused for the 1956 tests. Information was obcooling tests were conducted during June and tained on the effect of hydrocooling on the July of 1955 and 1956 by workers of the quality of cantaloupes in addition to the rates Georgia Experiment Statio'n in cooperation of heat removal. Crates of cantaloupes at each with the Georgia Coastal Plain Experiment stage of maturity were hydrocooled and held Station at Tifton, Georgia. The purpose of the in storage at 38" F. for eight days. Check tests was to determine the effect on the crates were placed in the same storage withmarketability of cantaloupes of higher quality. out hydrocooling. At the end of the storage Information on the rate of heat removal is essential to determine the possibility of hydroRATE OF HEAT REMOVA cooling cantaloupes. A pilot plant model of a BY STAGE OF MATURITY hydrocooler was obtained from a local manPMR G S ufacturer. This equipment was limited to processing two jumbo crates of cantaloupes at T E MPE RA TURE (*F) the time. The process involved was practically identical to that of the commercial models 80\ sold by this and other manufacturers to hydrocool peaches at rates ranging up to 600 crates or bushels per hour. Hydrocooling is known to slow the ripening % process in other products, and if immature%% cantaloupes are so treated, they might not%% have the desired quality. Consequently, canta60 -% FULL SLIP) loupes for the 1955 tests were picked at three stages of maturity, namely: full slip, showing% good color, and full ripe. Tests were made by size of melon and included sizes 36s, 27s, and 50FULL RIPE jumbos. In these preliminary tests three thermometers were inserted into the cantaloupes at different positions and readings were recorded at 49 two minute intervals for one hour to obtain 0 5 3 56 r 3. 4, G E Jora Seie No 303 Geri xeietSain TM MNTSATRSAT

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FORD: HYDROCOOLING CANTALOUPES19 period, refractometer readings were made of down to 50* F. (see chart). Cantaloupes used the cantaloupe juice. Such readings are closely for tests to prepare this chart were size 27s. A correlated with quality as rated by taste. The slightly shorter length of time was necessary Zeiss band refractometer reads percentage of to reduce the temperature to 50' F. in size 36s sucrose directly but the readings are more and the time for jumbos was about the same correctly percentages of total soluble solids. as for 27s, Cantaloupes of the PMR No. 45 variety While additional testing is essential, perwere used for most of the tests. This is the haps the most significant single finding in the variety currently grown in practically every 1956 tests was the relationship between hydroarea from which cantaloupes are shipped in cooling and soluble solids in the cantaloupe crates. juice after eight days in storage. The soluble Since the temperature in refrigerated rail solids content was higher at the end of the cars and trucks is about 50' F. at the time of storage period for cantaloupes which had been loading, this was considered to be the maxihydrocooled than for those which were not Mila temperature at which the cantaloupes h'ydrocooled prior to storage (see tables). The should be removed from the hydrocooler. Low analysis of variance indicates that stage of maer temperatures would probably be desirable turity was non-significant as a source of variabecause of the possibility of a rise between tion in the soluble solids in the cantaloupe the hydrocooler and the refrigerated carrier. juice; however, treatment and maturity by Considering the initial temperatures of the treatment interaction were highly significant. cantaloupes, there was little difference in the The temperature of the hydrocooled cantarate of heat removal when maturity was the loupes was reduced to 40' F. within an hour. source of variation. Between 35 and 40 minA much longer time was required for those utes were required to bring the temperature cantaloupes placed in cold storage without PERCENT SOLUBLE SOLIDS IN PMR # 45 CANTALOUPES AFTER EIGHT DAYS IN STORAGE, BY STAGE OF MATURITY AT HARVEST AND BY TREATMENT BEFORE STORAGE MATURITY AND AVERAGE STANDARD COEFFICIENT TREATMENT DEVIATION OF VARIATION FULL SLIP HYDROCOOLED 8.42 0.533 6.33 NOT HYDROCOOLED 7.82 -1.474 18.84 FULL RIPE HYDROCOOLED 8.81 0.727 8.26 NOT HYDROCOOLED 6.96 1 1.415 2033 ANALYSIS OF VARIANCE OF SOLUBLE SOLIDS IN PMR # 45 CANTALOUPES AFTER STORAGE SOUCE F V RIAIONDEGREES OF SUM OF MEAN SOUCEOFVARATONFREEDOM SQUARES SQUARE REPLICATES 19 36.657 MATURITY 1 1.128 1.128 TREATMENT 0 29.890 29.890** MATURITY BY TREATMENT INTERACTION 1. 7.750 7.750" RESIDUAL 57 63.084 1.107 TOTAL 79 138.509 SIGNIFICANT AT THE 0.01 LEVEL.

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140 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 hy~dr~o(ooling,_. III thw lAttr treatment. the( hhrco ld eor stonitgey. 11dollbtedly. the res11pinittion pnoc( ss, dorin" \\fit(-] thr sugars res itiol IrMC-Cs, hild bWIL-1 "reatly R'duced conitinuew to breall dtown, occurred for it lmnwr Iy Hte timlw the( canitaloupcs w\crc remlovcd I1criod thian ill the ctiittlolIpl.t \ which \\ wx It I I 11 tI Ih I drocoolr I nd i I(I Il eI i I sto rail14 THE SLOUGHING DISEASE OF GRAPEFRUIT W. GM'11()(N \\I) Holl ii rIx .KL 2 1d :( slhlw the prorless of the Ilorida Cilrl!. Ex.prlflilit StatdII I w. I xxis tiktil IMx ix\ till fliCK1i12 i Zt \\ Im 11 timli itbolit fivc 1wrvellt of thc Ltke -\lfltd fruit in this picki wxere Jffected ). ( )i most of thI rulit" slowughingo shows oly as it disIni 1955, Gricirson aod Neu hll] ( I ) reportedly colored iarea Cwept for oil( Irilit onl whIidh that it distinctive mid pcculimu pcel breakdo\\ii the Icsiolns are( fitr enlolugh advitilecd that the ld I)eC iltIed Oil retd dlid J)iitk 14E111tfirit foilecrlotie tissiies (dlill be slll1dwd off b\ threc coliscelitiv( sel isolis ilild hild t d letiiidr frlssurt So eii I t( it c\;sionlill s ver I losses ill trI nsit. This dise1s111 1l4 .,S i te mef i( of te fruits ds ott I~hl s9.-6iw llliik tliotisc fifthi tlemsiiix tolSli l \\is hi l till, Illm li d Slol ( l illt lwci ilts fi II )(eiI\ lou sHill ill hx tlhl t ts I lk 1 til distil tive )r linti il \\I lich I dl I ( [Ii tIll disea d tis s1' iiitiiIitt tromi thw liLc lth tik'lle below. thos colrr cspolldiloexactly to thw dictio are dh0initiol of lo 1hlilw Il its I i-l (.;I sclisc. TIi c e Io.to l tIl e iof slol litwi ll ) toF .gR Gt g956 marks feda fifth consecutive sa sesoqe ito which this disiise hi(s ben observd. It h es beeI fomid in fid coutiics i Lkj Polk, 1l ih dS. ra, imd PinlLaS ;i a d 11n1c(onI irmi'ed reports iixxicSti that it exi tt( Ix presltit il othr d i ict. Th -total ItiiItit f lilost 1)1 h I ar is I I t dI If xxjti ii. i wml ri si I c slo (T lil5 ocll lirs o il\ (il l] ill th siilsoll w h1 l t prices iarie high, the losti of i sitlliee carload ifi trieeet calI cthse i dispropol tiollitleI severI itgt5i loss toi g r pr str xii e the illsiFig. 1. Sloughing of Ruby Red Grapefruit, photographed five days from picking and subsequent to O~s(:nPTH)Ndegreening. Iloxx .csioriiis t its\ ter\ ailit disco r iitiolls thit xltim ite l I d tla seitill t brtwo i. 2 show tfo stlit 1 fr it At se1 (litys color. This ijiii fury it It i p c 11l ill th it is di from picking r, the 4 o lxx s i s i it)ow quitt m1 oist c-olored peelA docs Tot dr1 up w1 \ith a helb t iand ilr-( 1)",inminog to slip of catsil Illder becomlis soft anld mloist il. Ht. discilse; I)](fingr pro sl Ire. (r'sses. The discilstd lissluc dous nlot (,xtend) Fi(,. :1 talken tcii days from picking, shows deeper thanl the( albedo anid ill the( advanlced the extremely stagr of slollghing( ill which coilstag~es slight fing(er pressure \\ill cause the ill siderabhle ;treas of the Pcul ilre realdiky separable jurfed portions to siollgh off fthe solund fHeshj 1r0om thc solund Ilesh below\. Thec clit sections belowN. A cuiriouis chaitracterist ic is that fruits show\ hlow thc Icsionis do Ilot p'lictratte beyond alfflictcd \\411 slow.Thing~ scldoml succumb to thw illbcdo. Penlicillillm (biluc zind Ire n olds I or to Fi('. I. shiows" a vcr\ adkaniced (.as( of st(.m1-cid r.(), dllughilophotwographicd twen.1t\-oni da\.s troill Ipi( kill,-. ThI It(,oc otic \i\su u r sciparatced S~ v "'""'" 7" ""61"." froml the heailthy\ 11lls bm fillocr precssilre allonc.

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GRIERSON AND PATRICK: GRAPEFRUIT SLOUGIIING 141 h onllha' hi a I o C-oll e fromi ilxcstigiltioli of losses i(r))ot((l In commercial packinglhollses. (ultil-cs lilvc bell llade of the various A1iaiisinls follnd ill the liecrotic lesions. Most oftese irTe flormlal (rOVe Olgallisins, blit aliv that seemi at all iiioisual have i0eei used to illo illitte litalt li grajpefrulit il an effort to reproduc( the disease. This is COmplicated by the fact that tie fruit seems to be susceptible [oi ollkf a vc]\ shol-t period ilt thie begilillingl of the seilsou. () ie organism at present beilgo stiid slo\\s oime promise ill this rtegrd. Fig. 2. The same fruit as in Fig. 1, photographed two days later. The albedo antid iVtdo \\-ere redlleed to a s mniiLS. Despite this thc flesh reiaiiield pluimp health ai(d with tilrg(id juice vesicles. Ex i'lil.IMENTAL Since s511ull}hiim does not appeal tilitil lol to tell days after piCkinl( it is never apparent inl the grovc, is seei! oiil occasionally it tilepackinghouse anld is lisiialk elloliCtcllteie-d as a tran sit or market disease. Sile it is nlot possible to predict W\luj sloollghing \\ill occur, it has not been possib e to set up sysxStemiatie expci melts to stilf this disease All inforlailFig. 4. A very advanced case of sloughing. This red grapefruit was held at room temperature until twenty-one days from picking. OBSEM ATl()NS Hatlier dct it led ease histories are heii takenl Woeil\er new instances of slouthini are eIColliteled. Silce this disease scemis to be definitely\ associated with soie grO'ves and not others the qilestiolls involved inclined heavil towards Cultural practices, age of trees, weatl (1' 1cltitioi is etc. Thie hollowiu ig, points halve beeni noted: 1. Confirmed cases are jolifiiled to red1 alld Iiok grapefruit. Ucoufirmed reports have b eIn received of SuiuluhiliT on other varieties, !it it has not becl possible to obtain amy such fruit for cXainillatioll. 2. It is confined to very early pickings, not hllaig becii uicouillntered ltter tall October. Fig. 3. The same fruit as in Figs. 1 and 2, photoIf these same groves aTre piCked agai later, graphed ten days from picking. (Held at room temt r i perature). l( icici i owraplelt

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142 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 3. It appears to be associated with fruit 8. The most promising line of approach at from young trees (but that is almost inevitable present seems to lie in the investigation of any with a comparatively new variety such as Ruby possible correlations with other grove diseases. Red grapefruit). For this reason the observations of production 4. Sloughing is checked or controlled by managers are of great interest. cold storage. Oin two separate occasions,' part Corrective Measures. of an affected picking has been held in cold storage. Only very minor evidence of slough_ So little is known of the causes of this ing was found in the cold stored fruit even disease that it is not possible to recommend when it was subsequently held at room tema remedial program Two suggestions, howperature. When a single crop has been shipped ever, may_ help to minimize losses from as a split load, half in cartons and half in wiresloughing. If a grove is known to have probound boxes, sloughing appeared only in the duced fruit with sloughing in a previous seafruit in the cartons. It is felt that this is probson it could be checked by picking samples in ably a reflection of the difficulty of cooling the period before the grove is expected to pass fruit in cartons quickly. the maturity tests. Such samples should be 5. Since it is usually discovered after packdegreened, and held at room temperature, and ing it is generally attributed to some packingchecked for any signs of incipient sloughing. house problem such as over-heated degreening .Since sloughing is checked by refrigeration rooms, rough handling or (on Western shipit is to be expected that prompt and effective ments) cyanide fumigation. The evidence so pre-cooling, followed by the best ava ,ilable infar available indicates very strongly that transit refrigeration would minimize such sloughing 'riginates in the grove. This is parlosses, ticularly apparent when fruit from several The best corrective measure, in the long groves is handled in the packinghouse at the run, is probably to help investigate the cause same time. of the disease by reporting known instances 6. Sloughing tends to re-occur in frulit from of sloughing as promptly and fully as possible. certain groves. One of theprincipal reasons for giving these 7. Except in the fall of 1955, sloughing ocreports is to encourage shippers to contact curred only during a period of high rainfall. these authors when sloughing is encountered. In 1955 there was little rainfall during the LITERATURE CITED sloughing season. However, it has been pointed out (2) that in the case of brown rot, heavy .-,Griersow W. and W. F. dewhrll. r1955 "Sloughdew can be as damaging as actual rainfall, So rndust 36 10) : J Octobed. 2. Knrr L. C. H.J et0n .J enls moisture conditions cannot be eliminated as 1956. Occurrence and control of brown rot of citrus a pertinent factor. oin the tree a diseaseewmbto Florida. Citrus MagaEFFECT OF VARIETY AND FRESH STORAGE UPON THE QUALITY OF FROZEN SWEET POTATOES MAURICE W. HOOVER AND VI TOR F. NETTLES' be produced by freezing (1) (4). Normally Florida Agricultural Experiment Station better results are obtained when sweet potatoes are canned immediately after they are Gainesville harvested without. going through a curing Sweet potatoes are usually processed by process and extended storage (2). Best recanning.; however, an excellent product can sults are obtained with frozen sweet potatoes which are cured after: harvesting (1). The '/Department of Food Technology and Nutrition purpose of this investigation was to determine culturl*Expement Station. the effect of fresh storage and variety upon Seriesrd uou.a Exeimn43.inJora the quality of the frozen product. The effect

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HOOVER AND NETTLES: SWEET POTATOES 143 of cooking method upon the carotene conSpectronic 20 Colorimeter set at a wavelength tent, in preparing the potato for freezing, was of 450 mu. The carotene content of the potaalso studied. toes was determined by comparing with a ATERIALS AND 'ETHODS standard curve made with pure carotene conStaining 90 percent beta and 10 percent alpha. tdywerie te ofseertoo eri Rsedti The effect of cooking methods on the carostud wee th HertogldGeoria edtene content was studied. In this phase of the Goldrush, Unit No. 1 Porto Rico, and Earlystudy the potatoes were cooked (1) by baking port. As soon as the potatoes were harvested, in an oven for about one hour at 350" F.; (2) they were graded and cured at 85 F. for 10s daysfor 30 minutes; and (3) with free steam for After the sweet potatoes were cured, sam40 minutes. ples were placed in storage at 60" F. PotatoesREUT NDSSIO for freezing were taken from storage at intervals of three weeks over a period of 105 There was a wide variation in the quality days (0, 21. 42, 63, 84, and 105 days). After of frozen sweet potatoes among the different removing the potatoes from storage, they were varieties. The Georgia Red variety received ,baked for about an hour at 350" F., cooled and the highest rating for color, texture, and flavor frozen at zero degrees F. Approximately three (Table 1). It was also preferred by the panel weeks after the potatoes were frozen, they over the other four varieties tested. Even were removed from the freezer, heated for though this variety was lowest in carotene conabout 20 minutes and evaluated subjectively tent, its color was rated highest by the taste for color, texture, and flavor. Scores ranged panel. It was bright yellow in comparison with from one for those that were unacceptable to the darker or duller orange color of the Heartosix for excellent. Each taste panel member gave gold and Goldrush varieties. Although caroa preference rating and, in this instance the tene is the primary factor contributing to the lowest number represented first preference. color of frozen sweet potatoes, it does not For carotene analysis the potatoes were cut seem to be the only thing affecting their color. longitudinally and a quarter of each potato was There did not appear to be any difference dried at 65" F. after which they were ground in the quality of potatoes that could be atthrough a 20 mesh screen. One gram of the tribute to time in storage. Evidently, thereoven dried sweet potato was boiled in 25 ml. fore, sweet potatoes may be cured and stored of distilled water for five minutes. One hunfor at least 105 days at 60" F without any dried ml. of 95 percent ethyl alcohol were appreciable decline in quality. This statement added to the boiled material, and the contents refers only to, the potatoes that are sound and ground in a Hamilton Beach Blender for five free from disease at the end of the Storage minutes. The blended material was filtered period. and the filtrate was transferred to a separatory funnel containing about 100 mle.o Tae1 -Sube val o s Distilled water was added to facilitate the Coo etr lvr Peeec transfer of the carotene from the alcohol frac-6 6 6 tion into the N-hexane. The alcohol-water "ertgld 4. *4 4. fraction was drawn off and the funnel stem Gerg**d 44.2 1 dried by inserting a strip of gauze into the Goldr"sh 4. 43'. lower part of the funnel. Preliminary work inP*r* Ri** 3 4. .2 dictated that there was little, if any, advantage to running the material through a separation column. The carotene solution was transferred Significant differences were found in the into a 250 ml. volumetric flask and made to carotene content of different varieties (Table volume. About 25 ml. of the extract was fil2). The Goldrush and Heartogold varieties tered into a 100 ml. erlenmeyer flask containcontained the largest amounts. The former coning anhydrous sodium sulfate and the percent tainted 43.3 mg. per 100 grams of dry potatoes of light transmission through the carotene soand the latter contained 28.8 mg. The Porto lution was obtained with a Bausch and Lomb Rico, Earlyport, and Georgia Red varieties

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144 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Table 2. -Carotene content (mg. per 100 grams of dry potatoes) of frozen sweet potatoes stored fresh at 60OF for different periods of time prior to freezing. Days in Storage Variety Mean 0 21 42 63 84 105 Heartogold 25.9 30.0 32.2 32.9 24.3 28,0 28.8 Georgia Red 13.8 19.3 14.5 16.6 15.8 15.9 16.0 Goldr-sh 38.6 49.4 42.7 46.1 41.7 41.6 43.3 Porto Rico 16.3 18.2 16.1 21.0 16.6 19.8 18.0 Earlyport 15.3 15.9 17.1 19.2 17.9 17.8 17.2 Mean 21.9 26.5 24.5 27.1 23.3 24.6 L.S.D. for variety at -.05 level = 4.80 L.S.D. for varietyt at .01 level = 6.02 possessed 18.0, 17.2, and 16.0 mg., respectivethat is consistent with maintaining good texly, carotene per 100 grams of dry potatoes. ture, appearance, and flavor. This point should There appeared to be a significant increase in also be considered when preparing sweet potathe carotene content of the potatoes during to samples for carotene analysis. the first three weeks of storage; however, It has been reported that it is not necessary there was considerable variation from one into cook sweet potatoes in preparation for makterval to the next which lessens the probability ing carotene analyses (3). This is true whereor hypothesis that a true increase in carotene fresh tissue is used rather than oven dried madid occur in storage. trial. Evidence obtained in this study indiA greater loss of carotene resulted when cates, however, that the tissue should be potatoes were cooked by baking than occurred cooked if the potatoes are to 'be dried prior to when they were cooked with steam under making the carotene determinations. When the pressure or with free steam (Table 3). 'Potasweet potatoes were cooked, there was no sigtoes baked in dry heat alone lost 11.9 percent nificant difference in carotene content between of the carotene, on dry weight basis. Those those with freshly cooked tissue and the ones cooked with free steam lost 4.4 percent, and that were dried in an oven at 65" C. the ones cooked under steam pressure lost only SUMMARY AND CONCLUSIONS 0.75 percent. Thus, it is evident that the use of dry heat in the preparation of sweet pota-. A study was made to determine the effect. toes for freezing should be held to a minimum of variety and fresh storage upon the quality of frozen sweet potatoes. The influence of Table 3. -Effect of cooking methods upon the carotene content of sweet cooking methods upon the carotene content potatoes of the Goldrush variety, on a dry weight basis.wa aso tde .Sw tp ta es ffie ar rethod of cooking r me) Percent loss ties were cured at 85' F. for 10 days followed Control (ra ) 47.86 by fresh storage at 60" F. for periods of time Steam (10 Ibs. pressure) 47.50 0.75 ranging from zero to 105 days before freezing. Free Steam 45.75 4.39 The frozen potatoes were reheated and graded 3aked (350*F) 42.17 11.89 by the taste panel for color, texture, and flavor. The carotene content was also deter**.D fo aoea .0 1 lee -2.1 mined

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ROUSE, ET AL: ORANGE JUICE STUDIES 145 Sweet potatoes of the Georgia Red variety carotene from the potatoes when they were were preferred over the other varieties as a cooked with dry heat than occurred when frozen product. However, a good frozen prodsteam was used. uct was produced with potatoes of the GoldLITERATURE CITED rush, Porto Rico, and Heartogold varieties. 1. Hoover. Maurice W. and G. J. Stout. 1956. Fresh storage up to 105 days did not seem Food rechnot10: 250253.s to affect the quality of frozen potatoes when 2. Huffington si M. 06 E .tR. Mto vrn land good sound potatoes were used. The method canning: Influence of storage on quality. Proc. Amer. Hort. Soc. 67: 504-513. of cooking the potatoes in preparation for 3. Mitchell, H. L. 1949. Determination of carotene freezing had a significant effect upon their "4" Woodroff, J. G. and-Atkinson Ida S. 1944. Precarotene content. There was a greater loss of servin swee3"Zt potatoes by freezing. Ga. Expt. Sta. Bu. o 23 ., STORAGE STUDIES ON 42 BRIX CONCENTRATED ORANGE JUICES PROCESSED FROM JUICES HEATED AT VARYING FOLDS. II. CHEMICAL CHANGES WITH PARTICULAR REFERENCE TO PECTIN' A. H. ROUSE, C. D. ATKINS AND E. L. MOORE into three equal volumes and one of these was Florda itrs EperientStaionused as an unheated control; the other two Florda itrs EperientStaionvolumes were heated in a tubular pasteurizer Lake Alfred to 150" and 175" F., respectively, in 6 seconds and cooled in 14 seconds. All products were The purpose of this investigation was to further concentrated in the pilot plant Model determine some of the chemical changes, and B evaporator (2) to 55 Brix, cut-back to 42 especially the loss of pectin, that would occur Brix with unheated juice, sealed in 6-oz. cans, in frozen orange concentrates during storage and stored at -8* F. until the beginning of the at 40* F. It was also desirable that similar in40 F. storage period. Further detailed inforformation be obtained on heat-treated conmation on the preparation of these 42" Brix centrates when the thermal treatment is apfrozen orange concentrates is described in the plied either prior to concentration or at diffirst paper in this series (6). ferent stages of the concentration process. A At the beginning of the 40' F. storage total of 24 experimental packs of frozen conperiod, the 24 experimental packs were thawed centrated .orange juices, prepared from Pinefor I hour in a Thermo-Rotor type thawer apple and Valencia oranges, were used in this with rolls submerged in water at 40"'F.,,The study. speed of rotation of the rolls was 60 r.p.m. The EXPERIMENTAL PROCEDURES thawed samples were placed directly in storPreparation and Storage of Samples. -In age at 40* F. and analyzed at periodic interpreparing the 24 packs of concentrates, singlevals until an extreme degree of clarification destrength juice was used as the 1-fold product veloped in each sample, and concentrates were removed from the pilot Methods of Analyses. -Samples of 42 Brix plant Model A thermocompressor type evaconcentrates were examined for gelation, (7), orator (1) at concentrations of 2-, 3-, and 4. both prior to and after 40" F. storage, and fold. Each of these four products was divided then reconstituted with three volumes of dis'/Cooperative research by the Florida Citrus Extilled water. After three minutes of stirring, periment Station and Florida Citrus Commission. the juices were centrifuged for 15 minutes at i Agricultural Experiment Station Journal 0 0eres No 052 070 rm in an Inentoa .etiue

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146 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Size 1, Type SB and the percentage pulp by EXPERIMENTAL RESULTS AND DISCUSSION volume noted. Subsequently, centrifuge juice will be referred to as serum. Other analyses were determined on either the reconstituted apple and Valencia orange concentrates, prior juices or serums. to storage at 400 F., are presented in Tables I and 2, respectively. Control or unheated samPectinesterase activity (8) is expressed by ples varied very little in activity (14.6 to 17.1 the symbol (PE.u)g. which represents the units), while the activity of the heat-treated milliequiValents of ester hydrolyzed per minute samples fluctuated (4.9 to 11.2 units) accordper gram of soluble solids (" Brix). This is ing to thermal treatment and quantity of pulp multiplied by 1000 for easy interpretation. in unheated cut-back juices added. ApproxiHesperidin (3), the principal glycoside of mately 50 percent of the activity shown for orange, was determined initially and after the the 42* Brix concentrates, which were stabilconcentrates showed extreme clarification. ized at 150* F., and 80 percent or more of that These analyses were made on the reconstituted in the products stabilized at 175" F. was from juices. Light transmittance (5), index of cloud, the unheated cut-back juices. was determined on the serum by using a LumeThe total glycosides, expressed as hesperitron colorimeter, Model No. 402-E; clarificadin, in the Pineapple and Valencia orange contion was considered to be extreme when values centrates, prior to storage, ranged from 28 to were 85 percent or greater. Pectin, as anhydro37 mg./100 ml. of reconstituted juice. After galacturonic acid, was measured by the rapid the development of extreme clarification in the colorimetric method of Dische (4) as applied samples at 40' F. storage, the amount of to citrus juices by Rouse and Atkins (8) with glycosides remained the same. the modifications that the samples of reconPulp (Tables I and 2), indicative of instituted juices were not comminuted prior to soluble solids, varied from 5.0 to 7.0 percent centrifugation and that the sample used for and 4.5 to 5.5 percent for the Pineapple and analysis was 15 grams of serum. Previous tests Valencia orange concentrates, respectively. had shown that the amount of pectin, exAfter extreme clarification, the corresponding pressed as milligrams peir 100 grams of serum, pulp levels increased, varying from 7.5 to 8.5 was approximately the same as the waterpercent and from 8.0 to 9.5 percent. Although the size of pulp particles influences the persoluble pectic substances in the reconstituted centage of pulp, as determined by the centrijuice and is a major factor that determines the fugal method, it is of interest to know that amount of cloud or turbidity in the juice. the water-insoluble solids in the products also TABLE I Summary of Chemical Properties in 420 Brix Pineapple orange Woncentrates Stored at 400F. Samples prior to storage Samples after extreme clarification Concentration Thermal (PE.U.)g. Pulp by Pectin Time Pulp by pectin when treatment soluble solids volume in serum required volume in serum stabilized a?. X 1000 % mg./100g. days % mg./l00g. control 15.8 6.o 9.4 1.5 8.0 4.3 1-fold 1500 10.9 5.0 10.3 10.0 8.0 5.0 1750 7.9 5.0 10.3 9.5 S.0 6.3 control 14.6 6.o 8.6 1.0 8.0 3.9 2-fold 1500 9.6 5.0 21.3 7.0 8.0 5.3 }750 7.0 5.0 11.3 9.0 7.5 5.2 control 15.9 6.o 8.4 0.5 8.0 3.3 3-fold 150* 9.4 5.0 10.7 6.5 8.0 4.9 1750 6.9 5.0 11.2 7.0 8.0 6.o Watrol 15.2 7.0 7.0 0.5 8.5 3.2 4-fold 150 3.1.2 6.0 10.4 4.0 8.5 4.0 1750 6.1 5.5 .1.1 6.5 S.0 5.0 1 Anlye on reconstituted juices

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ROUSE, ET AL: ORANGE JUICE STUDIES 147 TAWL 2 &=ary of Chemical Properties in 420 Brix Valencia Orange WnC&ntratea Stored at 40aF. Samples prior to storage Samples after extreme clarification Concentration Thermal (FE.U.)g. Pulp by Pectin Time Pulp by Pectin when treatment soluble solids volume in serum required Volume in serum stabilized OF. X 1000 % ./-00g. days % mg./l00g. Control 16.6 5.5 12.1 4.0 8.5 5.1 1-fold 1500 10.5 5.0 12.8 i6.x 9_.0 4.9 1750 6.3 5.0 12.3 34.0 8.5 4.8 control 17.1 5.0 12.3 2.0 8.0 5.2 2-fold 1500 7.5 4.5 13.5 13.5 9.5 4.6 175* 5.3 4.5 13.6 27.0 8.5 4.5 Control 15.0 5.5 12.1 2.0 8.0 5.3 3-fold 150* 8.3 5.0 14.2 12.0 8.5 5.5 1750 5.9 4.5 13.9 16.5 9.0 5.3 Control 14.7 5.0 2.6 1.5 8.3 4.9 4-fold 1500 8.8 5.0 13.8 7.0 9.0 4.6 1750 4.9 4.5 14.2 9.5 9.5 5.0 1 Analyses an reconstituted juices. increased as did the apparent pulp content cative of slight gelation, when stored at 40" F. during storage. For example, the average Data in Tables 1 and 2 show that during storwater-insoluble solids found in the Pineapple age of the concentrates at 40' F., the pectin and Valencia orange concentrates prior to decreased 50 percent or more with subsestorage were 61 to 52 mg./100 g. of reconquent increase in clarification. The gradual stituted juices, respectively, whereas, after exloss of pectin during storage and its relationtreme clarification had occurred, these average ship to clarification, index of cloud, for the values for the corresponding juices increased controls and heat-treated 1-, 2-, 3-, and 4-fold to 80 and 74 mg./100 g. products is presented graphically in Figs. 1, Timereqire fo th'24samlesof on2, 3, and 4. As the pectin in the serum det r ed s or t e ds ree of concreased during storage of the products at 40" centate tosho anextemedegee f cars F. the apparent pulp content and the waterfication varied from 0.5 to 34 days, depending o on the variety of fruit from which it was protioned. Formation of degraded pectic comcessed, thermal treatment, and fold at which pounds, such as insoluble pectinates and peeit was stabilized (Tables 1 and 2). As .extates, through the action of pectinesterase on pected under similar conditions of processing, the water-soluble pectin, is the cause of these Valencia orange concentrates were more stable increases. The longer storage life at 40' F. of at 40" F. storage than the Pineapple orange the Valencia packs was probably due to the products; also the packs heated at Iand 2greater amount of pectin found initially in the fold were more stable than those heated at 3serum and to a higher degree of polymerizaand 4-fold. tion of the pectin molecule; the latter was inThe amount of pectin in the heat-treated dicated by a slower rate of change in viscosity packs was greater than in the control packs as previously reported (9). because of the partial inactivation of pectinesterase, thereby preventing the destruction of No significant differences in flavor were obpectin during concentration; also the quanserved by the authors between the controls tity of pectin was greater in the Valencia and the heat-treated samples; neither were orange products (12.1 to 14.2 mg./100 g.) flavor differences found when juices were than in the Pineapple orange products (7.O to heated at these different folds. However, a 11.2 mg./100 g.). There were not sufficient slight lowering of flavor quality was observed quantities of pectin in any of the products to in both the Pineapple and Valencia orange cause semi-or solid gels during storage; howpacks after storage at 40' F. for 10 and 24 ever, all samples developed No. 2 gels, indidays, respectively.

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148 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 12 -None 1 -None 9 ~~Slight 9 -\Sih Definite Definite 150* F. 70 0 1.506F. control Extreme 0 7*. xrm E3 < E3 PINEPPW PINEAPPLE ORANGE JUICES W ORANGE JUICES 0 L) O None None W 2 12 W ~Slight a Slight W 175*F. Definite .Definite Control ---.. 1_5Y*F. Extreme Coto 150* F. Extreme 3 .3 VALENCIA VALENCIA ORANGE JUICES ORANGE JUICES 0 5 10 15 20 25 30 5 10 15 20 25 30 TIME -DAYS TIME -DAYS Fig. 1. Relationship of pectin to clarification durFig. 2. Relationship of pectin to clarification during 400 F. storage of 42V Brix orange concentrates ing 400 F. storage of 420 Brix orange concentrates when juices to evaporator were heat treated at Iwhen juices to evaporator were heat treated at 2-fold. fold. 12 None None None 9 -\Slight \Slight Definite Definite -6 .175*F 6 -. 0 .50*F 0-1750F. Extreme cjO'F E xtremo z .CotroE 3 Control PIANEAPPLE 2 RPINEAPPLE W2 ORNG -UCSOAG UCS -2 -Slght Sliht0 3~Nn ; CNom .Cnto VALENIA VAENC0 ORANG JulES ORNGE ~iOr 0 5 0 15 20 5 300 5 0 1 20 5Or TiME-DYS TME -DAY Fig S.Rltonhpo pgi o hrfct dCr FW 4.R0tosi fpci ocaiiaindr ng~~~L 4ligh W.soaeo 2 rxoag ocnrts ig40F trg f40Bi rnecnetae when~sfn, jcsteprtrweeeatradat-fd. wejuestevprtrwrhetreeDefnte4fod

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HENDRICKSON AND KESTERSON: NARINGIN 149 SUMMARY centration of citrus juices. Proc. Fla. State Hort. Soc., 64: 188-191. Storage of 42' Brix Pineapple and Valencia 3. Davis W.B 947 Determination offlavanones orange concentrates at 40" F. resulted in in4. Dische, A. 1947. A new specific color reaction of hexuronic acids. Jour. Biol. Chem. 167: 189-198. creased gelatin, clarification, and apparent 5. Huggart, R. L., E. L. Moore, and F. W. Wenpulp content, whereas pectin decreased. Total 2e1. 1951. The measurement of clarification in conScentrated citrus juices. Proc. Fla. State Hort. Soc. glycosides, as hesperidin, remained constant in 64: 185-188. 6. Moore, .E. L., A. H. Rouse, and C. D. Atkins. these products during storage. The experi1956. Storage studies on 42' Brix concentr-ated mental nacks heated at Iand 2-fold were orange juices processed from juices heated at varying r folds. I. Physical changes and retention of cloud. more stable than those heated at 3and 4Proa. State Hort. Soc. 69: 176-181. 7. Olsen, R. W., R. L. Huggart, and -D. M. Asbell. fold; also all of the Valencia concentrates, 1951. Gelation and clarification in concentrated citrus control and heat-treated, were more stable juices. II. Effect of quantity of pulp in concentrate made from seedy varieties of fruit. Food Technol., than the Pineapple packs. s: 530-533. 8. Rouse, A. H. and C. D. Atkins. 1955. PectinLITERTURE ITEDesterase and pectin in commercial citrus juices as LITERTURE ITEDdetermined by methods used at the Citrus Experi1. Atkins, C. D., F. W. Wenzel. and E. L. Moore. meant Station .Agr. Exp. Sta. Tech. Bul. 570. 1950. Report on new technical strides in design of 9. Rouse, A. H., C. D. Atkins, and E. L. Moore. FCC evaporator. Food Inds. 22: 1353, 1466, 1467. 1955. Chemical changes in processed citrus juices 2. Atkins, C. D., F. W. Wenzel, and E. L. Moore. and concentrates during storage at 40' F. Univ. of 1951. An evaporator of improved design for the conFlorida Citrus Exp. Sta. Mimeo Rept. 56-3, October4. PURIFICATION OF NARINGIN R. HENDRICKSON AND J. W. KESTERSON utes and the clear extract concentrated to apFlorda itrs EperientStaion proximately one-ninth the original volume. The concentrated extract is allowed to crystalLake Alfred lize for two days in a cool place and then filtered. The isolated naringin crystals are then The pharmaceutical usefulness and physiopurified by the following technique. First dislogical importance of naringin has long been solved in a small amount of hot water containoverlooked, even though its characteristic biting 20 percent alcohol, impurities are precipiterness is a nostalgic reminder of early medistated by adding an excess of neutral lead aceeines. Prime interest has been centered on tate with the excess lead eliminated by passing the tasteless glucoside of sweet oranges, heshydrogen sulfide through the solution. After peridin, which has been closely associated with filtering, naringin is crystallized by concenall vitamin P investigations. Circumstantial trating the solution and allowing it to stand in evidence has pointed to the fact that naringin a cool place. The naringin is further purified may have an even greater pharmacological bv dissolving it in small amounts of hot water, activity as previously shown by Armentano from which it will recrystallize upon cooling. (1) and recent work on antiviral activity (4). The pronounced solubility of naringin in water Sufficient evidence has been accumulated to above 50* C. has been shown by Pulley (8) encourage the pharmaceutical industry to obwho plotted its solubility at numerous temjectively re-evaluate naringin. An investigation peratures. The simplicity of recrystallizing nawas therefore undertaken to find an improved ringin from water can readily be seen from naringin purification procedure for preparing his plotted solubility curve which shows narina high purity product. gin to be more than 10 percent soluble at As with many products, naringin has a much 75' C. and less than 0.02 percent soluble at higher solubility in hot water than in cold 6"C. This decreased solubility of naringin at and is the basis for an extraction and purificalow temperatures may at times cause the pretion technique reported by Poore (7). Accipitation of this substance in canned grapecording to this method, crude naringin is exfruit sections and juice. tracted from chopped grapefruit peel by adding four parts of water and beating to 90' C. Naringin may also be recrystallized from The water extract is filtered off after five milwater by adding an alkali, which greatly inFlorda griultral, EperientStaionJounal creases its solubility followed by acidification, Series No r524 rlExeietSato ora and is the basis of another extraction technique

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150 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 (3). The addition of acid forces the recrystalover a longer period of time, and washing the lization of naringin, but the compound thus final product with more isopropyl alcohol, even obtained is yellow. It was found difficult to better results were obtained. Recovery was imremove this color even when activated carbon proved to 89 percent; the final product was is used. exceedingly white and analyzed as being a 100 The need for an even better method of puripercent pure product by the Davis test. fying naringin became evident in the over all E ffect of Recycling Alcohol. -In repeated investigation on the recovery of citrus gluco~ trials where attempts were made to conserve sides. Some of the results have been reported alcohol and improve the over-all recovery by previously by the authors (6), but the optire-using the filtrate of one run as the solvent mum methods of purifying crude naringin refor the second, the following results were obquired further study. tainted. Initial recovery was 88 percent with EXTRACTION TECHNIQUE AND DiscussioN the product being 99.5 percent pure; the following trial using the previous filtrate imIn the following investigation three differproved the recovery to 9apercent with purity ent samples of crude naringin were employed. of the product dropping to 98 percent, ReTwo samples used were purchased and anausing the filtrate a second time decreased the lyzed 81 and 86 percent pure by the Davis recovery to 91 percent and the product purity test (5) while the third sample was only 29 to 95 percent. The concentration of naringin in percent pure. This last sample was typical of the filtrates continually increased to 2.4 perthe crude naringin obtained in the alkaline excent and failed to crystallize further during an traction of grapefruit peel by the Baier process extended holding time. (3). About 50 percent of the impurities in this Effect of Concentration. -The possibility product is a filter-aid which is added to fa-ofartiacnetrinraiofsvntt llta he gin ampe axrc~ n. xrcswr naringin in this purification procedure was anale byini teDsmpest an( etr)t.wr then investigated. Crude naringin of 86 peranalzed y te Dais est 5)-cent purity was dissolved in boiling isopropyl The first hopeful sign of a new method to alcohol at four concentration levels; 30 g. purify naringin occurred when an attempt was per 600 ml., 30 g. per 300 ml., 30 g. per 150 made to dissolve and filter a hot, highly conmi., and 30 g. per 100 ml. These levels of concentrated solution of naringin in 99 percent centration are respectively equivalent to 4.3 isopropyl alcohol. Before the filtration was 8.6, 17.2 and 25.8 g. of pure naringin per 100 more than one-third complete the entire mass ml. of isopropyl alcohol. Each sample was had become granular, stiff, and finally solidistirred for two minutes, filtered, and the filfied. The product was crystalline, with the trate heated to its boiling point to initiate minute crystals being needle-shaped. crystallization. As soon as each sample began Upon stirring 30 g. of a purchased naringin to crystallize, it was allowed to cool and was sample (86 percent pure) in 150 ml. of boilfiltered subsequently and washed. The saming isopropyl alcohol, a solution was obtained ple with the lowest naringin concentration was that filtered readily leaving a residue of 2.5 g. an exception in that it failed to crystallize of which 0.5 g. was found to be naringin. promptly and was allowed to cool to room The clear filtrate, when boiled, quickly seeded temperature and stand overnight. By the next itself and within five minutes had crystallized day the sample appeared to have crystallized into a solid mass. After diluting with 150 ml. as well as the others. Isolated similarly, it was more of isopropyl alcohol and stirring to a thin found to be the equal of the other three trials, slurry, the naringin was filtered and dried at each of which yielded an 89-90 percent re85* C. There was an 87 percent recovery of a covery of naringin having 98-99.5 percent very white product which analyzed as being purity. The trial having a concentration of 95 percent naringin. The filtrate was found to 8.6 g. of naringin per 100 ml. of isopropyl have 1.0 percent naringin still in solution, alcohol appeared to be the more suitable for When this trial was repeated with a few modia large scale operation. At higher concentrafications, such as stirring the initial solution tons, it is conceivable that recrystallization longer, permitting the naringin to crystallize could begin before the initial filtration was

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HENDRICKSON AND KESTERSON: NARINGIN 151 complete. There is the further disadvantage at mentioned, since the naringin can be dried higher concentrations that the voluminous more readily and a't higher temperatures. The character of the recrystallized naringin will so octa-hydrate product must be carefully dried stiffen the mixture as to make handling too at approximately 60' C., after which the temdifficult. At lower concentrations, the higher perature can be raised slowly to over 100' C., cost of solvent and longer time required for whereupon an equivalent dihydrate product recrystallization would preclude, its industrial will be obtained. use. In preparing a highly purified product, it is In a trial where crude naringin of 29 peralso important to consider the hygroscopic cent purity was purified by this procedure usproperty of naringin. An exceedingly dry sammng a ten to one solvent to naringin ratio, a ple of naringin dihydrate, dried at 105-1100 C. product of 98 percent purity was obtained. for two hours, was found to increase approxiThe recovery of available naringin was not mately six percent in weight in less than two as efficient as with samples of higher initial hours when exposed to average room temperpurity, being only 60 percent. The filtrate and nature conditions. The uptake of water is exwashings contained 26 percent of unrecoverceedingly rapid initially, and especially so able naringin and constituted the greatest loss. with a small sample having a large surface The 14 percent naringin remaining in the exexposed. tracted crude residue could be recovered with Thsouityf ang niopplamore efficient washing of this residue. A betTohol isiluencty gfrartngy by waso rpystalter recovery of purified naringin is possible lihzatisn nfdexneou grater bywTe ocrtawhen the crude naringin samples have a highdiatfo f n raneous waet. th 0 pc-y e r in itia l p u rity .It is q u ite p o ssib le in th is c a se s ol ue ir o m r ci l s r9 p e rc e nt sopr-6 that the crude naringin recovered by the saolbleile thme ircae (9s peruet opryoBaier process (3) could be isolated using tahe wextenthe dpprydrate 0.s sperbeny Te smaller quantities of filter-aid which would solubixten of thpproxmaey t.2 prnt. Thleimprove the purity of the crude product. sculsiny watese jstm twe revrsegthemoieUpon using purchased naringin of 86 percent clsmwtri uttervre h iy purity under similar conditions, there was a infrmatbing the mosoluble.ne of tdhis 92 percent recovery of a 99.5 percent pure nfratin, the spolblt was insiamgmt deproduct. Only 5.5 percent naringin was lost dtemine thsprfpctof extaos wesated tixdin the filtrate and washings, with another 1.9 trn the alfho.eAsee of xtanos waer m percent lost in the extracted residue. anW s other trial with 'a purchased product of 81 ples were made in which the water content percent purity, 85 percent was recovered with was as follows: less than 1 percent, 2 percent, 11.4 percent naringin being lost in the filtrate 3 percent, and 4 percent. After shaking each and 3 percent in the residue. sample with an excess of naringin for 14 hours at 27' C., the solubility of the dihydrate in Critical Effect of Water. -Another imporeach was respectively as follows: 0.15, 0.28, tant consideration in the purification of naringin 0.40, and 0.50 percent. When each of the four is water. For example, naringin will crystallize isopropano samples was refluxed for 15 minfrom water as an octa-hydrate molecule having utes at approximately 82' C. with an excess of eight waters of crystallization, which product naringin., the dihydrate crystals had the folmelts at 83' C. (2). When crystallized from lowing solubility: 0.65, 1.1, 1.6, and 2.5 percertain other solvents, such as isopropyl alcocent respectively. Relating this information hol, naringin has two waters of crystallization back to the isopropanol purification procedure, and melts at 171* C. (2). The physical apit can be shown that maximum yield of puripearance of the products under the microfield naringin is obtained by cooling the crysscope is very similar, crystallizing as needles tallized naringin as close to room temperature which. are usually found agglomerated in a as possible before filtering and by making rosette pattern. The drying of purified naringin every effort to keep the isopropanol as anhyis considerably simplified when the dihydrate drous as possible. In a number of repeated exmolecule is formed and is a distinct advantraction trials, naringin recovery was improved tage of this process over the others previously one to three percent by thoroughly drying

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152 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 crude naringin samples just prior to extraction process as anhydrous as possible was shown. and keeping the isopropanol well enclosed at It was found that solvent costs can be reduced all times possible. by recycling the extraction alcohol in subseSUMMfARY quent purifications, but its effect was reflected Commercial purification of crude naringin in the final product purity. Solubility of narinwas shown to be possible by the following gin in isopropyl alcohol and mixtures of it and method: Sufficient well dried' crude naringin water were measured at two temperatures. is slurried for five to ten minutes with boiling LITERATURE CITED hot anhydrous (or 99 percent) isopropanol' .Amnao .Teefeto lvn yso to yeldan 85 t 10 ercnt nrinin sluton-blood pressure. Feit. ges. Experimentelle Medizin The dissolved naringin is filtered quickly from 102 219. 1939.,n .nus.nte aann the insolubles and heated further or seeded to -glucosides IV. Naringin and hesperidin. J. Pharm. initiate crystallization of the naringin dihy_ So. Jaan 49; 123-34 1929. drate. The crystallized naringin and solution U. S. Patent No 2,4103 Ma 2, 1947d .M is allowed to cool to room temperature, wheresushima. Antiviral chemotherapy VI. Parental and upon it is filtered and the pure naringin furthothe eAffe5cts of flavanoids. Stanford Med. Bull. 11: er washed with isopropyl alcohol. The crystals 45.' Da C. .etermnation6 of fanones in are dried at 85' C., yielding a final product of c6. Hendrickson, R. and J. W. Kesterson. Recovery of citrus glucosides. Proc. Fla. Hort. Soc. 67: 19998 to 100 percent purity. 203. 1954. In establishing a new purification procedure, 7. Pore, H. D. Reoey of narn and petin the effects of naringin concentration were 1934.PlyGN.Subitofnrnnin ae. measured and the necessity of keeping the Ind. Eng. Chem. Anal. Ed. 8: 360. 1936. SECTIONIZING MARSH SEEDLESS GRAPEFRUIT GIIAY SINGLETON Lye peeled sections are usually not of as high quality as were those produced by hand Shirriff-Horsey Corporation, Ltd. peeling. At times the lye is too cool or too PlantCityweak and fragments of membrane are not rePlat Ctymoved. Frequently, the lye is too hot or too In the early days of grapefruit sectionizing strong and "cuts" into the sections making the peeling was done with knives. Girls sliced them soft and of poor appearance and texture. off the stem and stylar ends of the fruit, then During the period when hand peeling was the lateral peel was removed by strokes of the in vogue, the marsh seedless variety of grapeknife, from top to bottom. In peeling, a con.. fruit was preferred. .The sections were more siderable slice was cut from each segment. uniform because no ragged pits were left where seed were removed. About 1929 the first canners started using When lye peeling came in, marsh seedless lye to remove the carpellary membranes after fruit went out. Seeded fruit became the standthe albedo had been stripped by hand. This ard for sections. This change was caused by saved that part of the fruit which bad previthe fact that seeded fruit has a solid core, ously been lost in hand peeling, while marsh seedless has-a hollow core. Lye When lye peeling was started, there was a gets into this hollow core and destroys the great protest from the "green peel" canners membranes which bind the carpels together. who said that the lye would poison~those who When the sectionizing girls pick up a marsh ate lye peel sections. But, when they found seedless fruit that has been lye peeled, the that lye peeling increased,,the yield about 30 segments fall apart in hand and she 'throws per cent and decreased the cost of operation them on the garbage belt. The fruit must be considerably, they decided that their fears firm if good sections are to be produced. about the toxicity of lye peeled fruit were The shift from marsh to seeded fruit inunfounded, which, in fact, they were. volved about four million boxes each year and

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SINGLETON: GRAPEFRUIT SECTIONIZING 153 was a serious blow to the marsh. Fruit for We next tried separating the carpels and sectionizing brings a premium over fruit for dropping them on a LaPorte mat which carjuice. ried them through the lye and rinse and disSome years ago we decided that we could charged onto a wide rubber belt, from which sell more sections if we could again get the the sections were packed. This worked well smooth, firm sections that were produced except that too many of the peeled sections when we used the band peeling of marsh instuck in the meshes of the LaPorte mat and stead of the lye peeling of the seeded variewere mashed. ties. The results of our investigation were pubThe next step was to pass the separated carlished in the magazine Citrus Industry, May, pels through the lye on a wire mesh belt and 1953. The present paper is given to report discharge into a flume of cold water which certain refinements in the process that have served as a rinse. The flume carried the secbeen made since the first work was done. tions to the packing room where they were In the laboratory work, marsh seedless fruit discharged onto another wire mesh belt from was dipped in water at 190 degrees, Fahrenwhich they were packed. The flume was used heit, for from seven to nine minutes. The because we had gotten so much better results time required to soften the albedo varies with in the laboratory, where the sections were the size of the fruit and the thickness of the dipped into cold water, than we had been peel. When the peel was soft, the fruit was able to get by the usual cooling sprays. The cooled in water and the albedo removed by -flume method worked much better than we hand. This is the standard procedure in prehad expected. It is well known to all who have parig gapefuitforlye eelng.worked with sections that when the fruit comes parig gapefuitforlye eelng.to the sectionizers, fresh from the lye bath and In the usual lye peel method the whole rinse, it is soft and difficult to handle without fruit is run through the lye bath and rinse ecsiebekg.We h y eldsc water sprays in stainless steel baskets. This reteon xcae brakage Whe they weed sec-an moves that part of the carpellary membrane tsd wate beomte flxue thaey werehadrmver whic isexpoed.Insead f ding his we been able to get in any other way. Even late separated the carpels so that all of the memin the season the flumed sections were firm. brane would be exposed to the action of the lye. This separation is easily and quickly done We. do not attempt to explain the improveby unskilled labor. It is naturally slow for a ment in texture, yield and appearance of these few days, but good speed is attained within flumed sections except to offer the following a week. comments: In the laboratory we placed the separated 1. The water used in the flume was from carpels in wire baskets and dipped them in a a deep well and contained considerable calcisolution of canner's alkali having a strength of urn in solution. 2 per cent and a temperature of 190 degrees, 2. Using a 0.17 per cent solution of calcium Fahrenheit. The membrane wvas dissolved in chloride in distilled water we got results simia few seconds and the baskets were dipped in lar to those given in the flume. cold water to cool the sections and rinse off 3. Soluble calcium in the flume water probthe dissolved membrane. The sections were ably precipitated insoluble calcium pectate in then clean and ready to pack. In this laborathe outer layer of cells in the sections. tory work we had no broken sections. This 4. Lye peeled whole fruit, when passed method worked equally well with marsh through the flume, showed little or no firming, grapefruit, seeded grapefruit and Valencia probably because relatively few eells-were exoranges. The product was of better appearposed to the water. ance than that produced by the old hand The development of chilled sections in glass peeling or the regular lye peel process. makes it imperative that we produce sections The next step was to place the separated having better appearance than those we are carpels in wire baskets and send them through now packing in tin. Hand peeling is one anthe regular lye sprays and cold water rinse. swer, but at a heavy loss in yield. The process This worked well but was too slow for comoutlined here may be a better answer-in both mercial production. glass and tin.

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154 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 AN EFFECTIVE HIGH PRESSURE CLEANING SYSTEM FOR CITRUS. CONCENTRATING PLANTS D. I. MURDOCK which is enough volume to operate one GunStaff Bacteriologist jet. The unit, which costs approximately $250., may be mounted on wheels for portable C. H. BRoKAw .use. It is ideally suited for small cleaning Chie, Qaliy Cntro Deartentoperations, and for high-pressure cleaning of Chie, Qaliy Cntro Deartentextractors was found to be more effective Minute Maid Corporation than any of the other methods investigated. aFor example, an In-line extractor (manufacrtured by Food Machinery & Cherical CorIn the citrus juice concentrating industry, as poration) could be cleaned approximately 5 with other food processors, there has been a minutes faster with a GunJet than with a considerable lag in improving cleaning methsteam gun in one study where both methods ods compared to technological advances in of cleaning were compared.' (Table I, Fig. 2 processing. Recently, however, with the steady and 3). High pressure cleaning using a GunJet, decrease in profit margins, there has been 'a besides saving time, has numerous other adgrowing impetus to improve cleaning practices. vantages; namely, This change has emphasized reducing the 1. Not hazardous(Eliminates burns obamount of production time lost when the plant tained from the steam guns.) is shut down for clean-up. In the citrus con.. 2. Reduces humidity and resulting mold centrating industry this clean-up period usualgrowth. ly occurs two or more times per week and it 3. Can see what you are doing. may require, depending upon the size of the 4. Results in better and more thorough plant, 4 or more hours. The biggest bottleclean-up than can be obtained by other standneck in cleaning Minute Maid Corporation ard methods. plants has been in the juice extraction room 5. Makes cleaning job easier. where fiber brushes and steam guns were 6. Separate adjustment of handle of gun formerly used to clean the juice extractors controls the type of spray needed for cleaning and the finishers. The use of fiber brushes was job. time consuming, and the steam gun was cum7. Not bulky-easy to handle. Readily rebersome besides having the tendency to "bake" moves material from cracks and crevices difcitrus solids on the surfaces being cleaned. ficult to clean by other methods. Steam guns also produce a considerable 8. Eliminates tedious hand dressing. amount of vapor, especially during cold weathThe small portable high pressure system er when it is not uncommon for the whole proved to be so successful that a more permajuice room to be completely fogged, making it nent installation was investigated. Heretofore, impossible to see what has, or has not, been the detergent solution for steam guns was precleaned. pared by adding the material to make-up vesTo alleviate this condition, Minute Maid insels from 5-gallon buckets which were usually vestigated the possibilities of high-pressure either 934 full or completely filled. Such prepaequipment for cleaning the extractors. A small ration of the solution, which was heated in a portable insecticide spray rig, shown in Fig. 1, tank by manually opening and closing a steam was obtained which consisted of a John Bean valve, required one man's attention and reModel 33-K pumping unit, a 55-gallon drum, sulted in a variation of detergent concentrahigh-pressure hose, and a heavy-duty adjusttion, and of temperature for each batch. able GunJet spray gun, a type commonly used To eliminate this situation, the Engineering to spray citrus trees. The pump delivers 3 Department of Minute Maid Corporation degallons per minute at 300 pounds .pressure, veloped an automatic detergent mixing system.

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MURDOCK AND BROKAW: CLEANING SYSTEM 155 FIGURE I 7 -G .-a -l -j -I S S-7C6 S --0SS7. --40 G0JS E-OMAY G~rK Tam Ienough for heating, ie, 200-500 gallons. Detergent tanks used in one installation are shown MIS e W)FDVC"I.4.C. MMMR""W in Fig. 5.) The stock solution which for convenience, may be prepared one or mdre days M.W. cleed Seh etc" in advance of plant clean-up, is made up at the Ste. rate of 1 pound of detergent per gallon of .a water. The stock solution in the concentrate St.. tank is diluted 16 to I with water by means 2 .t10 9of a flow control valve as it is pumped by a centrifugal pump into the mixing tank. The diluted solution in the mixing tank, which is The unit which is shown in Fig. 4 can be built used for cleaning purposes, is maintained at for approximately $2,000. It consists, essena constant level by an electrode limit switch. tially, of a 500-gallon stock detergent solution A steam jet heater, illustrated in Fig. 4, for tank, a similar size mixing tank, high pressure heating the solution in the mixing tank can pump, high pressure hoses, and GunJets. (Caalso be used for pre-heating the stock solupacities of solution tanks are dependent upon tion in the concentrate tank. In this installathe number of gallons of detergent required tinteearisdsgdtorseheefor cleaning. For efficient operation, the conperature of the stock solution in the concencentrate solution tank should provide stock solution for one or more clean-ups. The mixing trate tank to 212' F. within 30 minutes, and tank, on the other hand, need only be large that in the mixing tank from 70' F. to 140' F.

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156 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 itt t Iitt 1 150 'i ( )1 ill >, p VII li i IIt '. II fit' i ii i s i i l s. \\I Ii it cill1 m P ()\ d(I ili other tfillip ert i ni'' (i tilt di I it tid iollitl Iii< (. t H I -> (ts uIf ti w p> ll it ti i t') o il \'itri )lls titi ks, tC. t roI I~c )\ I t direct ilctillig turilipciatilic co11i1erittilre. A liiili-pi'ssilrt P)llml1) is l(5td to rtt'lild li\oitli llitltids of Cleimilli-r. A CciI)IIIIII) HIL' dtieTergllt sollitioll dilrowlli p~il)(lille's trifilotal p>ump1[ (Icsiogited to dclivcr 155 (rallo is to vtilAiolts 2(ittiolls ill fiv ilicu 'FOll). -liriil10 t'iiititte at i 55 p>ounds irssrc, is i5so iusld )rcssulre hosc.", \\'ili Gull.IHeS lttaiLd. itIV \\ithl dw S\' "Will fol "h~itlI-filusil)Y" filw exco1J25ected to tie \jitscii.l', dNjirclt olltlct .tlttors \\ I it d iter ellt slltioalt \'lteirt ( \iii t \\os iii i, i*( liiS d otvt ch il It (d illik-\ i sili H is Hii p i)is [>itog <> i Ct e MIlli trnictoill it) I(l ill) to 5 n115 ilit\ 1we iiswd \\-ithl 1o lliti()11 hack thloll ll i c jie liiec lillc ZIld 11 tll(, s\ still. \\ hil il Sll)p[)('s det Lrellit ,olutjoill ilit() tjiw cxtliwtor, .T hlis p1.oC-(dtlr-e is o'clilu lk itt tl(t rittc of "a g ldoll's p~er ll1lilitte. TIlw (Tuns elill> o\ (d ill clcil iiig F \M .C. cxtrtc-tors oni\ ill( 0 >CrTated tl it p-)ll ip pic1 s."linIec\\ ('('? 20)0 iiwu t w Brl ( )-\\ i i e(-xhiwtori,, timmullfacttired h to 300 ) oilllids p(,I. S([Iltt-( illchl, \\'itl it deteTBlro\\ I I Citills Mlitchl ie \ Corp-orattionl, 1sc i yelit so litioll tellip~eli"A lli oI it pproximiith-k\ bulilt-ill cIcilililly s\vstclil for tis Iml-po'sc.) 125 F. 0l disclissioll so fillhils dealt it il ciu In ild iti l to ek'ilillo t l(, (,Xtit ors, the il" f ic qep iw l et11310 1 \-wi llc l(l p ll is sh t 00111.ct il( 1e Us d \cr\ (1cO \l l [ do\\11 lor tli, pil-p sc thS itt is -% elo-'lld o '...''....' 'n1 Fig. 2. In-lire juice extractor installation. Covers (A) are removed during cleaning process. (Photograph courtesy of Food Machinery & Chemical Corporation).

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lIU !))CiK AND BROKAW: CLEANING SYSTEM 157 i id (v k t\ p c (lc a ii-iilp TI n l j( p let io tim ( { i ) p Ilcltill Ill p li ts is AFs( clcalwd Iii ftl thI I( st of (tII' plt1it is still ill \\it 11 C1hl( il KIt('(I \\A t (i if)f)1.()NiAMtr Pinlirer 1.C20,0 In A cI.\ 25 p.I>.i i. t f I t I I( p I i it mer \icc \\ Atc supply, 11ut i 58 1 I\ t I fuoi i i fresrlt: icrts exreileu as tie avwrape tnzber p (, Sc: .t. frrc tM, telt rxafl. sur s st 1i1. ihis f p .1! Uit i l I P ( HI l mIr &le 15 to 20 iniiiiit .(mp1(lle i \d ic tlit-r m Ilot til fillislill scrvl I> chi il(811 d Chlo ii h-d('( \atci hitck-fllsill i sit i t \(,I\ mnillifiliz<' ilhe tillic wre lilvr d, pn<>p r coolrdill'ffective ilwauis of controlling~ btc-tcriial cm)AtiOnl id( triiing (d all indikidiuals involved famintioi. )11(li S[11(d\ \dhwic (dmle \\its ieear.01w0 Itimo flactol Ipolisiblc juliceC werc phitcd prior to iand( j11t ;Ifter this for this inwfficiecc ill cellinl is Hte scasonltyp c a minir, *: ridictioln in totitl iaibl al latlu' ()f th citrii is n(fdustr \\hich r1e)Slllts, cFugts 3. i:'5in to ", cor wt (btiet( oit a, |e il Iof m fo tso ill aludst a clplet ebaied of p~mdlictioll pelsoillicl A t (e rilill of ( iwh In <)k cer\ iw l c liiiiiii i u cd h)\ (Iir Imck. \\it01 lk t w k(,\ (,m plo\(wi bwimr I(,t it \\as y l tt e de tkat ill mrd(r t 'ltilwd Irom \car to (.Zar Fig. 3. Cleaning extractor with GunJet. Note absence of foor mist around sLurtaCes being Clejaned.

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-9 o V elooo "D xa'o-AZ', 2l~laj lqlA&JILP .0 t .00t' S1 gw*UJoqo =U 04@.I uosmi 0n 0 o 0 so 0 l S=! M0 *D0 earO.g;go o ow : o l 0.I ale. s~umo pusnqppjn 0 ma01 pa miu aq .lq 0s i .0jpu $Um 09. C -.OTJ s.o s. ui 0uo aon 0q .rl laqs .UMOE* 0 0.Utj 0q ..0lad .~q .i 0a "J 0.00 0 -xa0 .u J0041 u q~~l~omuj *F M .0 II mi. 00s 4 2ivj 4oLo 00 0o .0p 0 suq ~ .pu 'oo -~ a.TJUq UO 3O aq ~ ~ OU~u 0.u I'~ojn~u o oall *~~~41c u u...0. 0 0. -anfo ui 0as .aun V .p9usi .t 0io *4,% 4u w ib 0. .oi lo 02 ) 0 ..oel x 0 .0o i 0q o0 0lt,) -( 0.~od w m o *It. 0..4 0is a a i 4 u .a Id i, osi, si uo l np i aq .0jn .0a .. o40.u u Luals~~~~~~~~~~s ~ ainsai -~t aq -glqs !'i~vl arfOSUoda sq on unauu a 00 ycrov -&O Jw 17W 0w 0 '74 -pa774a V -' 0 a -a a 0 W C. V 'U

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MARSHALL: CORROSION INHII3TOR 159 Fig. 6. High pressure system can also be used for cleaning Brown extractors. (Photograph courtesy of Brown Citrus Machinery Corporation). tion w ith hih pressure system \\'its found to be a very effective cleaning tool. Several of its advaitages over other methods of cleaning are given. The importance of intermittent cleaning of the extractors with chlorinated Fig. 5. Installation of high pressure cleaning syswater is discussed along with the need of emtem showing mixing tank-left, and concentrate stock solution tank right. High pressure pump is ploviiig trailled personnel to reduce cleaning located on floor with steam and water control valves mounted above tanks. SOME STUDIES ON THE USE OF SODIUM NITRITE AS A CORROSION INHIBITOR IN THE CANNING INDUSTRY J. 1. MnARsHALL' fot many items b\ extenisive liboratorv tests and sll)seqlent industry experience. Where it has been necessary to maintaiii the internal till coatingy wight at a hir level, the exterior INTRODUCTION I"vl~h ihe e iti coiatirng wei ght has been reduced, in many As the cained food industry and the can iistaices, to the niiuim by the use of (fmanufacturing industry have advanced techniferential electroplating. It is generally accepted call, there has been a trend toward reduced that inder good handlinig and storage condlitin coating weights on al[ containers. Such tions, the lightest external tin coating performs reduction has resulted in millions of dollars satisfactorily v; whereas, under improper condiill savill(gs to the canning industry and to the tions, the heaviest tin coating weights are not consuming 1 public. It also has set upi a safesufficient to prevent olltside rusting. (1) guard against drastic cutbacks in tin plate availability in times of national emergency. The presence of rust ol the outside of a The use of electrolytic plate bearilly ollj a can of fOod detracts from its sales value. This small percentage of the tii ised on the
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160 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 generally the most attractive container as well. Since there is always the Another reason for rust prevention is that specipossibility of contamination of the product, fications for canned foods purchased by the any additive used should be nontoxic. This government, armed forces, and other agencies stipulation narrowed the field and made exstipulate that the cans shall be free from rust. perimentation with sodium nitrite attractive. The successful use of lighter electrolytic tin In order to better understand the function coatings on cans for civilian trade has led the of sodium nitrite as a corrosion inhibitor, we military services to make exhaustive tests on would like to cover briefly some of the factors the exterior rust resistance of such containers. contributing to the external corrosion of metal Their tests included CTS, No. 25, No. 50 and containers. 1.25 lb. plates. Two types of organic coatings CAUSE OF RUST were employed: that applied to the flat sheet Each corrosion problem may vary because of plate prior to can fabrication and that apof the nature of the materials and process inplied to the filled container after processing. volved, but the basic chemical reactions have The cans were stored under Temperate, much in common. External rusting of cans Desert, Arctic and Tropic climatic conditions. may be considered a part of the general subThe test results indicated again that the exject of corrosion of ferrous metals. ternal protection afforded the steel base is not Although many factors are involved in the influenced in direct proportion to the tin coatcorrosion of metals, only a few (oxygen, moising used. The postcoating and the precoating ture, temperature, and presence of acids or of the plate with organic materials respectivesalts) are of particular interest in connection ly gave the best protection against rusting. with external corrosion of tin plate containers. There was little difference in the degree of Effective prevention of external rusting is simrusting among the various tin coating weights ply the control of one or more of these primary in either the coated variables or the plain factors through taking reasonable precautions variables. (2) to protect the cans during processing, cooling, Normally, the lighter tin coating weights and storage. used to replace the heavier coatings can be Many theories have been advanced regardexpected to perform satisfactorily if good can ing the exact nature of the corrosion of iron. handling and processing procedures are folOne explanation is given by Hildebrand (6) lowed. These processing techniques include who indicates that the initial step in the formathe use of non-corrosive processing and cooltion of rust is the production of ferrous ions. ing waters, the use of recommended processing These ions combine with oxygen to form ferric and cooling practices, the casing of dry clean oxide. The production of ferrous ions is recans which are warm enough to evaporate any tarded on pure iron by the polarization effect traces of moisture, and clean, dry storage conof hydrogen; however, their production is ditions with uniform temperatures. Because of catalyzed by the presence of impurities, varithe economic advantages of lighter tin coatous salts and hydrogen ions. ings, it is to the advantage of the packer to Although, as stated above, many ideas have use all precautions to assure satisfactory perbeen advanced to explain corrosion, it has been formance of the container. At best, however, established that metallic corrosion in a solusome packing procedures are too corrosive to tion capable of conducting electricity is of an allow the satisfactory use of reduced tin coatelectrochemical nature. (5). Two dissimilar ings without special precautions. metals in electrical contact and wetted by a In working with the various canners, it was conducting solution, form an electrolytic cell. found that grapefruit sections and pimientos, The less noble of the two metals becomes the both boiling water process items, required anode and corrodes; whereas, the other metal special handling precautions if the industry becomes the cathode and is protected. Actualwas to enjoy the advantage of the lighter tin ly, when the exterior of a tinplate container is coatings. Since the problem was mainly one exposed to certain atmospheric conditions or of exterior can corrosion, the experimental to corrosive water in the presence of oxygen, work was directed toward an additive for the corrosion takes place at minute points where process or cooling water which would help the iron is exposed. Small electrolytic cells are

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MARSHALL: CORROSION INHIBITOR 161 established at these exposed points. UJd the Diurim th( past few ears, considerable corrosion of iron occurs preferential to that work has beci done to develop a protective of the tin. The tin coatingy or an overcoating of oxide film oi iron similar to that which ocelnaml retards rustic b protecting the iron rs naturally oit almi tase .It t s found that froii pia p sical contact with the corrosive water a film could be formed o ferous minetal ill or atmosphere conditios. This situation is the absence of excessive dissolved ox ygen with quite different front that existing oil the inside oxidizing laterials such a sodii nitrite and of the container where, in most cases, as thc chromate. (2) (.3) Pryor and Cohen (9) conresult of the presence of little or no oxygen th chided that the protective action of the above till is anodic to the iron and thcrb provides anIdic inhibitors is ecsed oni the formation of sacrificial prot-c-tionl anld suifficienlt shelf hife protective films of 2 gammna Fe.0, maintained for satisfactory merlchandisin)g. ill constaint r-epair. The protective film iii aerated solutions is formed primarily 'by) reaction It has beel Shlow\I that the formation of ferwith dissolved oxygeni; however, in deaerated rotis ion either by electroebemical action or solutions the inhibitors, dlue to their oxidizingy through soluitionl by wNeak acids. is ani essential character, react directly with iron to formn prostep in the formation of rust. If means for tectivefiis. stopping this part of the reaction are estahExPEILMENTAL PROCEDUHE lished. theii rustiiT.g could he retarded or perIn this work. the use of a longY-kilownui rust haps prexenlted. inhibitor \wa> applied to the CanniT indciustry. 300 m 0 00 Fig. 1. Tihplate strips immersed in Sodium Nitrite solution of indicated concentrations for period of 4 weeks at room temperature.

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162 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 To determine the desired concentration of Coke ends and No. 100-25 bodies. This plant sodium nitrite for the semi-commercial tests, employs two Draper type. cookers operating strips Of tiniplate were immersed in solutions with hot water several degrees below the boilof sodium nitrite at concentrations of 0, 100, ,ing point. Water at below boiling temperatures 200, 300, 400, 500 and 1000 ppm. The nitrite contains appreciable dissolved oxygen which solutions and tinplate strips were placed in when combined with the elevated temperature 500 ml. beakers and stored at room temperaand the possible presence of corrosive salts ture. One strip was completely submerged and creates conditions very conducive to rapid coranother was partially submerged and partially rosion of the can exterior. The sodium nitrite out of the water in each case. Above 200 ppm. was added to one cooker in the recommended no rust was encountered on the strips during amounts, and none was added to the other a period of four weeks. Slight rust was obcooker. The pH of the water was 7.5. Apserved on the strips of tinplate in the unapproximately 100,000 cans were used in the treated water in about 24 hours. Fig. (1) is a test run. The cans from the cooker with sodium photograph of the results of this experiment. nitrite added were practically rust free when In the semi-commercial tests, sodium nitrite they reached the casing operation. The cans was added to the process water to a concenfrom the cooker with no nitrite treatment had traction of 400 to 600 ppm. Periodically sodium appreciable rust at points of exposure of the nitrite was added to maintain the concentrabase steel. The addition of nitrite to this cooker tion. Both continuous type cookers and batch provided a practical means of controlling type retorts were used in studying the effectroublesome rusting. tiveness of sodium nitrite. The use of sodium In Plant B, the operation was slightly difnitrite in cooling water was not considered ferent than Plant A in that the conveyors carbecause the expense of such treatment would rying the cans to the grapefruit section packmake it non-commercial, unless the water was ers ran continuously, and as the cans traveled recirculated which would bring in many techon these lines there was considerable abrasion nical problems. Our experience indicates that of the body of the can by the guide rails. the protective film formed during processing A trial run of 65,000 303 x 406 cans fabrigave adequate protection during cooling and coated from outside plain Common Coke ends normal storage. and No. 100-25 bodies was made using no It has been reported that sodium nitrite in chemical rust inhibitor. The cans were conconcentrations below 200 ppm. has caused sidered commercially acceptable at the end pitting of ferrous metals. (7) Since the sodium of the process. However, at the end of one nitrite concentration is being continually diweek's storage in the 'anner's warehouse, luted in the cooker by the condensation of about 40% of the cans had a slight yellow steam and the replacement of water carried stain of rust at the abrasions caused by the out on the cans, the method shown in the cans rubbing on the guide rails. The test was appendix was developed for accurately deterrepeated using 300-400 ppm. sodium nitrite mining its concentration. Because excessive in the cooker. At the end of one week's storamounts of sodium nitrite do not give signiage in the same warehouse as the first samficantly better results, careful control of its ples, these cans were free from rust at the concentration in the water will mean savings abrasion marks on the can body. Representaas well as preventing ineffectively low contive samples stored in the laboratory for two centration from occurring. years remained rust free It was quite obvious Sodium nitrite cannot be used in solutions that the protective film formed by the sodium having a pH lower than 6.5 because it decomnitrite 0ad prevented rust formation during poses chemically. In our tests, all water was the warehousing of the product. found to be in the pH range of 6.5 -7.5 and Similar tests were run at other citrus plants no pH adjustments were necessary. Water with and in all instances, the amount of outside rust excessively high pH should be treated because on the cans was greatly reduced by the use of it will cause severe detinning of the cans. nitrite. In Plant A, tests were run using, 303,x.406 In the packing of grapefruit sections there cans fabricated from plain outside Common is a tendency for free grapefruit juice cells to

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MARSHALL: CORROSION INHIBITOR 163 adhere to the outside of the containers. If the and spangling problem has practically been sacs stay in contact with the can for an apeliminated. preciable length, of time, the tin is dissolved During the 1955 pimiento season, test runs to the tin-iron alloy layer, producing an un of 401 x 411 cans fabricated from outside lacsightly black mark. We have noted that plants quered No. 25 ends and outside plain No. which allow cans of broken sections to accum100-25 bodies were made at two different late for a period of time before closing and pimiento plants. At Plant C they were filled processing usually have a large amount of exin the normal manner, and given a normal eternal container marking. During our observaprocess in boiling water containing 400 ppm. tions, however, we have failed to find any rust nitrite. After processing and cooling, the cans at these marks, and since the bodies were were examined and no corrosion was observed. usually covered by paper labels the condition Samples of the pack were placed in different was less offensive. For government sales these warehouse locations which were conducive to detinned areas might be considered objectionsweat rusting. These cans were examined after able. ten months' storage and no rust was observed Since these tests were instigated, several on the cans. million cans fabricated from outside plain No. At Plant D, part of the same lot of cans 100-25 bodies have been packed with citrus were packed with pimientos and given a simisections without incident. In all cases, the lar process. This packer did not use sodium packers felt that with their particular operanitrite in the processing water. The cans were tons sodium nitrite was necessary and added slightly rusty when examined after the process it to their cookers. Besides protecting the cans, and appreciably rusty after storage for ten it was felt that the material probably would months in a commercial warehouse. However, extend the service life of the equipment. Howother cans of pimientos processed in water conever, to evaluate this point fully, a separate taining sodium nitrite arid stored in the same study would be required and was considered warehouse had not developed any apparent beyond the scope of our investigation. degree of rust. Two pimiento packers encountered rusting Fig. 2 shows a comparison of the condition and severe spangling of the cans during the of the cans packed by the two canners. This processing of 401 x 411 cans. Spangling is the experiment was not designed initially to demetching of the tin coating so that the crystal onstrate the effectiveness of sodium nitrite, pattern of the tin is visible. The process for and it is possible that other factors exerted 401 x 411 'cans of pimientos is approximately some influence. Neveretheless, the results cer. 100 minutes in boiling water (212' F.). Even tainly indicate that the use of sodium nitrite in if the water is only slightly corrosive during a the process water showed beneficial effects. cook of such duration, the effects are very Many cans fabricated from plate having reobvious. These canners were using cans fabriducked tin coating weights are steam processed. cated from outside plain Common Coke bodies It would be desirable to give these cans addiand No. 50 ends. tonal protection through the use of a rust inIt was believed that the use of sodium nitrite hibitor. Since there is no liquid contact period would retard the rust formation, but how it in a steam process to produce the protective would affect the spangling was unknown. Apcoating of the base steel by oxidation with approximately 400 ppm. was added to the retorts. sodium trite, the cans would have to be imThe cans were stacked in retort crates, and mersed for a short period of time in a conthree of the retort baskets were placed in centrated solution of sodium nitrite prior to vertical retorts. After the cans were cooked processing. and cooled, they were examined. No rust or Solutions of sodium nitrite containing 0, spangling of the tin was observed. The actual 500, 1000 and 1500 ppm. and 1%, 1-3%, 2% mechanism by which the nitrite eliminated the and 21/% were prepared. Strips of tinplate were spangling of the tinplate was not determined immersed in the solution at a temperature at this time. The nitrite has been used comof 180* F. for 30 second intervals ranging mercially for two seasons and the corrosion from 0 to 22 minutes. After the immersion, the

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164 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 sailples \wcre plaCed ill sliallo\ poreclail not toxic ill th(l (lanltities used. As with all trays containing i' of distilltd water. chemicals, lhowtver, its storage an(d use should Ihe results of this test irdicatecd that there he followed judiciously hy responsible plamt was sOMe protection gi vi the tilplate, part ipersollnel il order to avoid iisapplicatioi. cularlv when the plate \a.s treated at the higiAn attempt to uise sodium nitrite as a rust cr eoncentrations and lol iger time intervals. inhibitOr for stemiii processed itemis Iby a short -Iowever, the degree of riist protectioll givell timie higlTI colicenltration (lip niletiod did tiot b. the treatmelnt varied collsiderably. prove suiccessfil. However, further work will Sa mlples of the platc froimn the above (xbe dOne to (eterinin e if a suitable nieans cal perimelnit were placed il ail aiutoclave and probe developed to give additional protection to messed one hour at 250 F. The excess nitrite Cans which are steam processed. Ci iseld co-isiderable 1spotti g of the plate wMlic-11 (Tive it illi objectiolliable appcillalluc,ACNwEGE s \xhjli aveit n ojc-tiniahe apeiraict. The author aeknowlecdlyes the hielpful stigaiitd it (lid not apprecial)k retard rustiiln. w s To date experiments lisilig a sodium nitrite gestions tf Mr. I. ILovt and Mr. K. E. Leins dip to prevent corrosioI (lii ring steam proof the Solvav Division of Allied Chemical and cessi g have in)t Iee i ie iii rti ig.i H owevr, e Corporttion ainid Stokely-Van Camp, Inc., the experiments have beeii very cutrso\ ald for the method for determining nitrite concern a mort1 exhaustive study will be made. iatiOi. REFERENCES CoNC-slo~s 1. American Can Co.Iiiletin-The External RustIn coiicllision, this \ork ioidiciates that sodiinof Food CansOI-tober 1949. A. Beatli and E. Cassady---Preventinv Corrosion 1im iitrite \which has bcci lised sucessfully ill -f Exterior t ns-linformation Lelter. National o th e r in d u strike s a s a r iu t i hll ib ito r c a ll e ( ) i .T-e M akiri n g. 195 5. IM.c Carol Hii (. ii. Franicis. rhe Maiking, value to mali of tht caill-rs ising a hot \water Shaping and Treatinv of steel-6th Edition-Pubished by United States Steel Co. proCcss, ill potec-tilig proctsslig c(Illlp)llt .M. DarrienCorrosion Inhibitions with Chrofrtom co-rtosion aind ill retardill the formatioli ntites-The Oil and Gas Journal--January and Februmry 1949. of i-list oli the exterior of tlic call durilig pro5. H. Gratas inhibition Of Metallic Corrosion in .I" A iiteous Media-Corroion--National Association of messing and subsepic-iit storage. The efficCtrrosion Eininvers, January 1956. tiveliess 1iiider actual coiditiOiis of lise shotuild G. Hildebrand. --Principles of Chenistry---MacMillan Pliblishing Co. 1912. be clicked I\ each packer for his particular E. Leins-corrosion Inhibition with Sodium Ni.file-Sokvay Process Jliiision, Allied Chemical and product, cquipmelnt antd process. Sodium 1liti'Ne cororationIr rliwihdned Paper. rite is a ielati eL ii xp( si ve Illaterll a lld is M ntell. C. L. Tii Published by the Cheicial Fig. 2. 401 x 411 cans of Pimentos processed with and without Sodium Nitrite in Cooker water.

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GRIERSON: TANGERINE HARVESTING 165 9. Pryor, M. J. and Cohen, M.-,Journa ElectroApparatuschemical Society 100, 203-1953. Graduate-1 -100 ml. 10. Uhlig, H.--Corrosion Control in Water Systems 1 -25 ml. -Industrial & Engineering Chemistry--July 1952. Pipette -1 -10 ml. Mohr Type 11. Wachter, A.-Sodium Nitrite as Corrosion InFlask 250 ml. Erlenmeyer hibitor for Water--Industrial & Engineering Chemistry-Vol. 37, No. 8 (1945). MethodAPPENDIX Measure 25 ml. permanganate solution into 250 The determination of Sodium Nitrite: ml Erlenbeyer flask, ake s f crystals of Potassium Permanganate Solution, 1065 g. per t .i atefroth 10 m nptte wh bhe sampl g) tabletreiardistilledd ssterngan gae to.0 until the permanganate solution is decolorized. ml. Tablets dissolve very slowly and if possible, (tIn browniprecipitae frafms, sttis an indicasolution should be prepared ahead of use. The cto h cdcnetaini o o. tablets can be crushed by using a stirring rod, Results-being careful not to lose any material. Sodium Bisulfate Crystals (Sani-Flush or Bowlene is a 177x100=PMNNO good source). ml. Nitrite so]. REDUCING LOSSES IN HARVESTING AND HANDLING TANGERINES W. GRIERSON vided into two lots, each consisting of 100 fruit. One lot was held in the degreening room Florida Citrus Experiment Station as long as the greenest fruit (Group "C") were Lake Alfred in there, which is what happens in commercial practice. The duplicate lots within the Previous studies (3, 4) on the handling of "A" and "B" categories were removed from tangerines have shown that ethylene degreenthe degreening room as soon as they were coning tended to increase stem-end rot and also sidered to be degreened to an extent equivasensitized the tangerines towards certain types lent to commercial practice. After degreening, of mechanical injury. In order to study these the various samples were washed, polished, effects more closely, tangerines were separated tae n trda 0 .frdcysuis after picking into several categories according They were examined at one, two and three to color, each category being handled separateweeks from date of picking, separate records ly through the Experiment Station packing being kept of stem-end rot, blue and green house. The next logical step was to spot-pick molds and peel injuries. into the various color categories. This was done A further study was carried out which (exin 1954-55. It was found that decay was least cept for the first two replications) used these in tangerines picked full color and not desame pickings of tangerines. Since it had been greened. Decay was excessive in tangerines found previously that degreening sensitized picked without a good color break and heavily tangerines to handling injury, particularly by degreened. Severe peel injury occurred to the polisher brushes (4), additional samples fully colored tangerines when they were subwere picked to provide further information on jected to the ethylene degreening process, as this point. These additional samples were would normally be the case when mixtures of washed and polished before degreening. Algreen and naturally colored fruit are handled thghntdvatdfrcm riaprtc, together. this provided a comparison with the samples METHODS receiving the normal treatment of washing Seven pickings were made between Novemand polishing after degreening. All samples ber 4 and November 29, 1955. At each pickwere waxed prior to storage at 70* F. Since ing the tangerines were separated by the pickthe prior washing and polishing impedes deers into three color categories: e.g. "A",' good greening, these samples were removed from orange color break; "B", yellow color break; the ethylene treatment at the same time as "C", little or no color break. The fruit from the regular samples, regardless of their color. each of the "A" and "B" categories were di-' The color of samples was determined by use of the visual comparison colorimeter as develFidaio 5Aricultural Experiment Stations Journal oped by Rouse and Bowers (8) from an origSerie No 66.

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166 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 inal design by Baier and Ramsey (1). In this RESULTS apparatus the reflected light from the surface of the sample is focused on a ground glass Color at Picking and Subsequent Decay -plate for comparison with Munsell color plates Table 1 shows the total losses from all causes (7). presented as the averages of the seven repliTable 1: Total losses (all causes) in tangerines spot, picked for color between Nov. 4-29, 1955 and held after degreening at 700 F. STotal Dercent losses (averages of 7 pickings) Treatment Holding Bes posible Medium to Little or no period color brk (A) Door color (B) color break Wc I week 6 6 Mininm degreening period 2 weeks 14 24-3 weeks 26 40 0 I week 3 6 6 Full degreening period 2 weeks 11 26 24 59 w e e k s 3 0 5 0 5 0 All times are from date of picking. Table 2t Total losses (at two weeks from oicking) In tangerines Piced in three color categories, all of which were given the same degreening period. Degreening considered to be equivalent to that used in commercial practice. Date (al1 Good orange color Yellow color Full 5re.en Degreening 1955) break (A) break (B) (C) Period (hours) Percent Percent Percent Nov. 4 2 2 10 72 Nov. 7 6 8 6 70 Nov. 9 10 -19 12 68 Nov. 14 3-1 23 38 66 Nov. :L5 13 45 25 91 Nov .21 13 35 27 46 Nov. 29 20 48 48 76 Averages 10.7% 25.7% 23.7% 69.3 hours L. S. D. (5% Level) ----14.71 Analysis of Variance ."F" values Foclrcaeris67* For picking dates 6.59 Significant at the 5% level.

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GRIERSON: TANGERINE HARVESTING 169 to "color up" to the extent needed for a No. danced. This decrease in keeping quality was 1 pack. During the month of November, No. 2 not related to the length of the degreening tangerines could not be shipped (2) and the period, nor to rainfall. Since the two seasons' cannery price for "eliminations" was 35 to 40c pickings terminated on December 13, 1954 per box. Taking the cost of growing tangerines and November 29th, 1955, respectively, it is as 85c per box (9), picking. and hauling as not considered that the increased losses were :75c (10) and estimating the cost of degreendue to "over-maturity" in any normal use of ing and handling through the packinghouse as the term. loc, then the out-of-pocket expenses on these The studies on the relationship between eliminations was $1.70. Thus almost every ethylene treatment and the "zebra skin" peel box of green tangerines picked throughout the injury indicates that the previously observed course of this experiment would have represensitizing of the fruit due to ethylene degreensented a loss of $1.30-$1.35. If these fruit bad ing is a genuine phenomenon but is in some been left on the tree they would have been way linked to rainfall, since the effect was saleable fruit. Many of them were possibly offfound only in those samples picked within five bloom and if harvested later would have been days of the last heavy rain. Commercially it is available for a premium market. A double not possible to avoid this damage by washing spot-picking of early tangerines for size and and polishing prior to degreening as such accolor would involve a higher than normal picktion drastically slows up ethylene degreening ing cost, but this would be cheaper than pick(5). It is however suggested that such losses ing green tangerines for a $1.30 loss. might be minimized by curtailing degreening Decay studies showed that, in two succesas much as possible in the periods after heavy sive years, decay increased as the season adrain. 0 RAINFALL 17 29 7 k0 26 2 PEEL INJURY 4540Degreened after w0shingand polishing 3 -Degreened before washing and polishing c' 25 -' 200 W 14 5 5 .0 -0 0 OCTOBER NOVEMBER Fig. 1. Peel injury of tangerines (at one week from picking) as related to timing of ethylene degreening and to rainfall.

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170 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 SUMMARY gerines were polished subsequent to ethylene degreening. A spot-picking program was carried out for It is recommended that early tangerines be tangerines throughout the month of November closely spot-picked for color-break, as well as 1955. The tangerines were separated into for size. three color categories which were handled separately throughout the experiments. LITERATURE CITED, It was found that decay in tangerines picked 1. Baier, W. E., Ramsey, H. et al. 1932. Colorwith a good orange color break was about hall ing citrus fruit. Bulletin, California Fruit Growers that in tangerines picked with a poor color 2.Daily Market Bulletin Nov. 29, 1955, No. 41. break or no color break at all. Florida Citrus Mutual, Lakeland, Florida. 3. Grierson, W. and W. F. Newhall. 1955. TolerFinal color in tangerines picked too green ance toethylne of variou types of citrus fruit. Pr* Am S00 c.. H. Si. 654-5, e and degreened with ethylene was so poor that 4. and 1956. Reducing it is unlikely that they could have packed A" Soc. Hor00 6 e 236-3, une e enough No. I fruit to pay for cost of handling. 5. and .F 195 egreeni of ciru fris Ann R .Fl. Ag.Ep.Sn I The balance of this fruit would have had to press). be sent to the cannery or abandoned, the loss g4 poeure E t d ucton of ks de4 a A n in either case being at least $1.30 per standard citru fruit. Fla. Agr xt. Stn. Bull.C450.o nc box of "packinghouse eliminations." 10 East Franklin St., Baltimore 2, Maryland. S .Rue.H.adJ C. Bwr. 15. Pakig A distinctive form of peel injury, often ho se Researc. la. Cit us BE .Stn .L a An known to the trade as "zebra skin" occurred Prog. aRae, .jet 7. Poialns foag in three pickings that were harvested three to Temples and tangerines, 1945-50. Citrus Magazinel.5 0~~() 1617 Dec0.4 3.. five days after heavy rain. This form of in40. D .A. H. 1956. Costs of picking and jury was greatly aggravated when such tanhau"i"gFlidca citrus fruits 1954-55 season. Univ. of QUALITY OF CANNED GRAPEFRUIT SECTIONS FROM PLOTS FERTILIZED WITH VARYING AMOUNTS OF POTASH' F.W. WENZEL, R. L. HUGGART, E. L.MOORE, the quality of the fresh fruit utilized, which in J. W. SITES, E. J. DESZYCK, R. W. BARRON, turn depends on the many factors affecting S. the internal quality of fruit. S.The quality of citrus fruits is affected by Florida Citrus Experiment Station many factors, such as fertilizer and spray practices, root stock, variety, soil and weather conLake Alfred ditions. Various investigations have been made The Florida pack of canned grapefruit sec_ (1, 3, 4, 5, 6, 7, 8, 10, 12, 13) concerning the tions has averaged about 43% million cases influence of variable potash fertilization on the (24/2's) each year during the last 5 seasons. quality and composition of citrus fruits, inDuring the 1955-56 season almost 3132 million cluding grapefruit, oranges and limes. Sites boxes of grapefruit were used for canning (12) reported on the effect of using different about 5/2 million cases of grapefruit sections amounts of potash in fertilizing on the quality and citrus salad; this corresponded to approxiof Duncan grapefruit, as indicated by changes mately 20 percent of the crop of seedy grapein soluble solids, acidity, vitamin C and yield fruit. The quality of canned grapefruit sections, of ince. which is one factor that determines acceptaInformation is not available concerning the bility and future demand, is dependent upon importance of fertilizer practices in influencing /Cooperative research by the Florida Citrus Exthe quality of canned grapefruit sections. The periment Station and Florida Citrus Commission. purpose of this report is to present data that Floida NAgricultural Experiment Station Journal wrebtnddrnghre irssass Series,' No 560 wer obae dungtrecrssaos

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WENZEL, ET AL: GRAPEFRUIT QUALITY STUDIES17 concerning the quality of canned grapefruit on January 14, 1956 from February 6 to Febsections, prepared with fruit from grove plots ruary 10, 1956, Samples of the 1955 and 1956 fertilized with varying amounts of potash, so packs were also inspected and graded (14) at that such information will be available to both the plant immediately after packing and again processors and growers. after 2 weeks by Mr. Walter D. Pond, U.S. D.A., -Agricultural Marketing Service, Winter EXPERIMENrAL PROCEDURE Haven, Florida. Grade A or U.S. Fancy comSource of fruit.-Duncan grapefruit was obmercial packs obtained from the commercial tainted from plots in Block V at the Citrus Explants in 1954, 1955, and 1956 were also experiment Station; these plots have been deammned for comparative purposes. scribed by Ruprecht (11) and Sites (12). Methods of examining and grading, used The fertilizer applied since 1939 contained the at the Station, were more critical and differequivalent of 3 percent N, 6 percent P20s, 3 ent from those used by the AMS (14) and percent MgO, 1 percent MnO, 12 percent Coo, therefore will be described. All of the sections together with various amounts of K2. After from about one-half of the total number of picking, all of the lots of fruit were held for 3 cans in each pack were examined individually; to 4 days before processing. The size of the the number of size 303 cans used from each fruit used varied considerably because it was pack is listed in Tables 1 and 2. The sections not possible to obtain sufficient amounts of from each can were drained on either a 10 or fruit of any one size. During the 1953-54 sea16 mesh screen for 2 minutes. Each section son fruit from plots treated with fertilizers was then examined by the senior author to having the equivalent of 0, 3 and 10 percent see whether the main vascular bundle or K20 was processed on February 12, 1954; fruit "thread" was present on the section and to picked the following season from the same divide the sections into three groups on the plots was packed on February 26, 1955, and basis of firmness; namely, whole sections, secduring the third season on January 14, 1956. tions that broke on handling and soft sections. All of the trees from these plots were removed The sections in each of the three groups were recently to make land available for new plant.. weighed to obtain the total drained weight. wings. The drained syrup from the cans in each pack Canning of Grapefruit Sections. -Usual was mixed together and the acid, soluble solids commercial procedures for the peeling, secand pH in this syrup were determined. Finaltionizing and processing of grapefruit sections ly, the quality of each pack was rated as either were used. The sections canned in 1954 were good, fair or poor chiefly on the basis of the packed at the Tampa plant of the Florida Difirmness of the sections, The flavor, color and vision, California Packing Corporation those general appearance or character were also for the next two seasons were canned at the noted. Winter Haven plant of Bordo Products ComThe whole, broken and soft grapefruit secpany. Yield-data are not presented since the tions from the pack of January 14, 1956 were individual lots of fruit used, approximately 5 analyzed for pectic substances using the rapid boxes, were very small. It was also decided colorimetric method of Dische (2) as dethat only the packs of whole sections would scribed by Rouse and Atkins (9) for citrus be examined and so the cans of broken secconcentrates. Water-soluble, oxalate-soluble, tions, which were a small percentage of the and sodium hydroxide-soluble pectic subcans in each pack, were discarded. Packs of stances were determined and results reported the canned whole grapefruit sections were on a wet basis as milligrams per 100 grams. stored at 80* F. at the Citrus Experiment Station until examined., EXPERIMENTAL ]RESULTS AND DiSCUSSION Examination of Canned Grapefruit Sections. Results from the examination of the nine --All of the products packed on February 12, experimental packs of canned grapefruit see1954 were examined at the Station during the tons are shown in Tables 1, 2 and 30 Informaperiod March 30 to April 5, 1954; those tion on three commercial packs of canned seepacked on February 26, 1955 were examined tions of good quality are also included in from May 25 to Juine 1, 1955; those packed Tables I and 2 for comparative purposes..

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172 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Data in Table 1 show that the rating of side of the segment. Since each of the juice canned sections, based on firmness, decreased sacs is attached to this "thread," perhaps a in the 1954 packs as the amount of potash in section having the "thread" would not break the fertilizer used was increased; the number apart as easily as one without the "thread." of whole sections in these packs was 68, 48 This information was obtained since the quesand 28 percent and the number of soft sections tion was raised as to the possibility of the dewas 6, 19 and 42 percent of the total number creased occurrence of this "thread" on canned of sections when the K20 level was 0, 3 and 10 sections because of cultural practices. The perpercent, respectively. In the 1955 packs precentage of sections from both the 1955 and pared from fruit from the same plots, this 1956 packs that had a "thread" was greater trend was not evident. All of the sections in than that in the 1954 packs. It should be noted these three packs were of poor quality bethat the "thread" occurred less frequently on cause of softness, which possibly resulted from sections in the 1954 and 1956 packs from the the fact that the fruit was picked too late in 10 percent potash plot. Since the "thread" was the season. If grapefruit is allowed to remain present on most of the sections in the nine on the tree too long, canned sections of good packs and since variations in procedures used quality will not be obtained from this fruit for lyp peeling could cause destruction of this regardless of the cultural practices used. Re"thread," it is doubtful that the composition of sults obtained from the examination of the the fertilizer is related to either the presence 1956 packs showed that when the K20 level or absence of the "thread." was 0, 3 and 10 percent the number of whole Analytical results from the examination of sections in these packs was 60, 50 and 30 perthe syrups drained from the sections in each cent and the number of soft sections was 11, of the nine experimental packs showed a range 36 and 51 percent, respectively, these results in pH from 3.2 to 3.4. The acidity in the bein siila tothoe fond or he 954 syrups from the sections showed (Table 1) packs. the usual trends found in grapefruit, as reThe percentage of the grapefruit sections ported by Sites (12) when the amount of from the various packs which had a "thread" potash in the fertilizer used is varied. Acidity is indicated in Table 1. The "thread" is the increases as the potash content of the fertilizer main vascular bundle traversing the dorsal is increased. Differences in the acidity of the TABLE I Effect of Variable Potash fertilization on the Firmness of Canned Grapefruit Sections Variation No. of No. of "Thread" firmness -t Final Total acid, as of potash 303 cans sections present Whole Broke on Soft rating anhydrous citric, in fertilizer examined examined handling in drained syrup% Packed February 12, 1954 K20 -0% 83 1190 79 68 26 6 Good 0.82 S% 107 1659 78 48 33 19 Fair 1.07 "-1cf, 95 1594 64 28 30 42 Poor 1.25 Packed February 26.-955 K20 -0% 64 1147 86 47 17 36 Poor 1.00 -% 66 1227 86 47 21 32 Poor 1.08 -10% 62 1204 83 39 16 45 Poor 122 Packed Januar 14, 1956 K20 -0 -47 769 95 60 29 11 Good 0.87 -% 734 90 50 14 36 Poor 1.19 -14 41 729 85 30 19 51 Poor 1.21. Commercial packs -For comparison Season packed 1953-54 36 652 57 51 48 1 Good 0.94 S954-55 48 876 89 42 51 7 Good 1.01 1955-56 16 286 92 75 21 4 Good 1.05 1These sections were whole when removed from cans to screens, but they broke into two pieces upon further handling during examination.

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WENZEL, ET AL: GRAPEFRUIT QUALITY STUDIES 173 grapefruit caused differences in the Brix/acid noticeable loss of liquid from the sections or ratio of the drained syrups, which ranged from "bleeding" when they were allowed to stand. 15.8 to 23.2 in the nine packs. Perhaps it also should be pointed out that it Swas not the purpose of this study to pack Th oalgyoids s aigni h Grade A or U.S. Fancy canned sections, but drained syrups from the 1954 packs were 68, to process the grapefruit at a time when dif46 and 4 mg./100 g., when the potash levels ferences in quality of the canned product were 0, 3 and 10 percent, respectively. The would possibly result. 1955 canned sections were not analyzed for total glycosides, but that in the 1956 packs Data concerning the effect of varying potash was determined, as naringin, by Dr. S. V. Ting. fertilization on the pectic substances in canned The substances ranged from 100 to 41 mg./ grapefruit sections were obtained by analyzing 100 g. in the sections and from 86 to 36 whole, broken and soft sections from the 1956 mg./100 g. in the drained syrup .These results are presented i Table 3. the amount of potash in the fertilizer seemed The 1954 and 1955 products were not anato cause a decrease of the total glycosides. lyzed for pectic substances. However, since the sample from the low potPectic substances occur in citrus fruits in ash plots had a greater amount of membrane the middle lamellae, which are the layers befrom the segments attached to the canned sectween each of the adjacent cellulose walls of tions and since there was a significant correcells. During ripening of the fruit, protopectmn lation between the total glycosides and the (the sodium hydroxide-soluble fraction) is variable amount of membrane attached to the converted by hydrolysis into water-soluble sections, the effect of different potash levels pectin and then by demethylation this waterwas not determinable. soluble pectin is changed to low-methoxyl pectin; this and pectin degraded by other The final ratings for the 1955 and 1956 means form insoluble salts with calcium and packs, based upon the examination at the magnesium that are soluble in ammonium Station, as well as the final AMS grades (14) oxalate solution. The amounts and types of and information on drained weight are given pectic substances in grapefruit, when picked, in Table 2. The color and flavor of the grapeshould be related to the firmness of canned fruit sections from the nine experimental packs grapefruit sections; also sections may become were acceptable. In the packs containing a less firm during processing if further changes large percentage of soft sections, there was a in the pectic substances occur. TABLE 2 Effect of Variable Potash Fertilization on the Quality of Canned Grapefruit Sections Variation No. of 303 cans Drained weight Wholeness Final Final of potash examined per can -oz, % $core rating grade in fertilizer Station AMS Station AMS Station 2 AMS Station AMS Packed February 26, 195 K20 -C6 64 6 9.3 10.1 64 18 Poor B -U.S. Choice 0 -3% 66 6 8.9 9.8 68 18 Poor B -" 0 -10% 62 6 8.6 9.6 55 18 Poor B -" S Packed January 1956 K20 -0% 47 9 9.8 10.3 89 19 Good A.U.S. Fancy "30 44 8 8.9 9.8 64 18 Poor A -" "-10% 41 a 8.5 9.8 49 18 Poor B -" Choice Comercial pack -For comparison Season packed 1955-56 16 6 10.2 n.2 96 19 Good A -U.S. Fancy 1Graded 2 week's after packing by Walter D. Pond, U.S.D.A., Agricultural Marketing Service, Winter Haven, Florida. 2 Includes both whole sections and those that broke on subsequent handling as indicated in Table 1.

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174 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 Data obtained from the examination of the 41.4 percent less than at the 0 percent potash 1956 packs (Table 3) show that the waterlevel; at the 10 percent level for the corressoluble pectin in the three kinds of grapefruit ponding sections, the percentages were resections was greater at the 10 percent potash spectively, 28.6, 44.1, and 43.0 percent less level than when no potash was applied in the than at the 0 percent potash level. More data fertilizer; whereas, the oxalate-soluble pectin are needed to determine the exact relation bedecreased with increased levels of potash. teen the types of pectic substances and the When calculated from data in Table 3, the softening of grapefruit sections. percentage of total pectic substances at the 3 Finally, it should be pointed out again that percent potash level for whole, broken, and the only purpose of this study was to detersoft sections were respectively, 35.8, 32.4, mine the effect on the quality of canned and 32.7 percent less than at the 0 percent grapefruit sections of using fruit from trees potash level; at the 10 percent potash level that had been treated with fertilizer containfor the corresponding grapefruit sections, the ing various amounts of potash. The determinpercentages were respectively, 34.3, 35.9, and ation of what the best level of potash in fertil36.1 percent less than at the 0 percent potash izer should be for the production of citrus level. The quantities of both the water-soluble depends upon many factors. Results indicated and total pectin were greater in the soft secthat as the potash level in the fertilizer intions than in the whole or broken sections, creased, the quality of the canned grapefruit The whole, broken, and soft sections were sections packed deteriorated because of a deanalyzed also for pectinesterase activity' and crease in firmness. It is realized that large water-insoluble solids. A residual pectinesterfruit are desirable for sectionizing and that the as6 activity ranging from 0.3 to 2.0 X 10' size of the fruit increases as the amount of units, representing the milliequivalents of potash in the fertilizer is increased; also that ester hydrolyzed per minute per gram of comwhen fertilizer containing low amounts of potminuted products, was found in these grapeash are used, then decreased production and fruit packs. Results also showed that the permore pre-harvest drop occur. Therefore, it centages of water-insoluble solids at the 3 is suggested that if a fertilizer containing a percent potash level for whole, broken, and large amount of potash is used in producing soft sections were respectively, 25.5, 39.8, and grapefruit for sectionizing, then the grower TABLE 3 Effect of Variable Potash Fertilization on the Pectic Substances in Canned Grapefruit Sections Whole sections Broken sections Soft sections Total pack Variation % of Pectic % of Pectic % of Pectic Pectic of Potash 1956 substances 1956 substances 1956 substances substances in fertilizer pack mg./100 g. pack mg./100 g. pack mg. /100 g. mg./100 g. Water-soluble Pectic substances *20 -0% 60 so 29 90 11 109 6 -3 50 80 14 95 36 104 90 -10% 30 87 19 102 51 129 111 Ammonium oxalate-soluble Pectic substances E20 -0% 60 257 29 262 11 272 26o -3 50 141 14 146 36 160 149 -10 30 131 19 121 51 126 127 Sodium hydroxide-soluble Pectic substances K20 -0 S 6o 158 29 163 11 170 16 6 -3 .50 97 14 107 36 107 102 If -10% 30 107 19 107 51 97 102 Total pectic substances 20 -0 60 495 29 515 11 551 -507 -% -50 318 14 348 36 371 341 "-10% 30 325 19 330 51 352 340 1 Calculated value based on the percentage of whole, broken and soft sections in each pack.

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WENZEL, ET AL: GRAPEFRUIT QUALITY STUDIES 175 or processor should see that the fruit is harMr. C. E. Lucas and Mr. J. D. Tidwell, and vested soon enough in the season so that their assistance was appreciated. Packs were softening of the canned sections will not regraded by Mr. Walter D. Pond, U.S.D.A., sult. Agricultural Marketing Service, Winter Haven, SUMAINIY Florida and his help is hereby acknowledged. Fruit from grove plots treated with 0, 3, or 10 percent potash in the fertilizer was used LITERATURE CITED for packing of canned grapefruit sections dur1. Bahrt, George M., and Wallace R. Roy. 1940. ing three citrus seasons. Progress report of the effects of no potassium and & -various sources and amounts of potassium on citrus. Data obtained from examination of the nine Proc. Fla. State Hort. Soc. 53: 26-34. S 2. Dische, Z. 1947. A new specific color reaction packs idicate that the time at which the fruit of hexuronic acids. Jour. Biol. Chem. 167: 189-198. 3. Embleton, T. W., W. W. Jones and J. D. KirkSg y patrick .Influence of applications of dolomite, canned grapefruit sections. If fruit is allowed potash, and phosphate on quality, grade, and composition of Valencia orange fruit. Proc. Amer. Soc. to remain on the tree too long, then canned Hort. Sci. 67: 191-201. 4. Fuge B. R., adGB.Fheln 14. Som sections of good quality cannot be packed, reeffe-ctd o. so ., and Fetiie mnritg composition. gardless of the cultural practice used. Proc. Fla. State Hort. Sec. 53: 38-46. 5. Hilgeman, R. H., C. 'W. Van Horn, and W. E. When grapefruit was picked at the same Martin. 1937. A preliminary report on the effects time from trees which had received fertilizer of frtilizng pactices upona maturity and quality of Mrhgafuti Azona Po. Amer S *ot containing 0 3 and 10 percent potash, the Sci. 35: 352-355. 6. Jones, Winston W., and E. R. Parker. 1949. firmness and quality of the canned grapefruit Effects of nitrogen, phosphorus, and potassium fertisections decreased with increase in the am mount o a sh an g Nanie maner i ce. on me o c. of potash Hort. Sci. 53: 91-102. 7. Lynch, S. John, Seymour Goldweber, and ClarThe greatest amounts of total pectm and fence Rich. 1953. Some effects of nitrogen, phosphorus -and potassium fertilization on the constituents of water-insoluble solids were found in the Persian lime fruits. ProA. Fla. State Hort. Soc. 66: canned grapefruit sections when there was no 224-227.tewatran Pu F Smt 19. 8 .thr Watr an PalF mih 92 potash in the fertilizer used; as the potash level Relation of nitrogen, potassium, and magnesium fertilization to some fruit qualities of Valencia increased to 10 percent, the total pectin genorange. Proe. Amer. Soc. Hort. Sci. 59: 1-12. rally decreased in the whole broken and soft 9. Rouse, A. H. and C. D. Atkins. 1955. Pectinesterase and pectin in commercial citrus juices as sections. The water-soluble pectin was greatest determined by methods used at the Citrus Experient Station. Fla .Exp. Sta. Tech. Bul. 570. in the soft sections and least im the whole see10. Roy, Wallace 1R.-1946. Effect of potassium detions at the three potash levels. ficiency and of potassium derived, from different sources on the composition of the juice of Valencia oranges. Jour. Agr. Res. 70 (5): 143-169. ACKNOWLEDGMENTS 11. Ruprecht, R. W. 1922-1936. Effect of potash Than