Front Cover
 Title Page
 Table of Contents
 Photo: R. A. Carlton
 President's address
 Plant research in the atomic...
 Mediterranean fruit fly eradication...
 Award of honorary memberships
 Injury and loss of citrus trees...
 Effect of phosphate fertilization...
 Starting and maintaining burrowing...
 Preliminary investigations on dieback...
 Possibility of mechanical transmission...
 Transmission of tristeza virus...
 Physiologic races of the burrowing...
 Citrus rootstock selections tolerant...
 New 4-H club program for citrus...
 Field observations of several methods...
 Timing fertilization of citrus...
 Is stem pitting of grapefruit a...
 Seasonal changes in the juice content...
 Effectiveness of different zinc...
 Increased utilization of grapefruit...
 Long range relationships between...
 Notes on the use of systox for...
 Progress report on greasy spot...
 Use of 1,2-dibromo-3-chloropropane...
 Rapid determination of peel oil...
 Effects of finisher pressure on...
 Study of the degrees brix and brix-acid...
 Diacetyl production in orange juice...
 Standardization of Florida citrus...
 Citrus vitamin P
 Vacuum cooling of Florida...
 Quality control of chilled orange...
 Hydrocooling cantaloupes
 Sloughing disease of grapefrui...
 Effect of variety and fresh storage...
 Storage studies on 42 degree brix...
 Purification of naringin
 Sectionizing marsh seedless...
 An effective high pressure cleaning...
 Some studies on the use of sodium...
 Reducing losses in harvesting and...
 Quality of canned grapefruit sections...
 Storage studies on 42 degree brix...
 Effect of thermal treatment and...
 Distribution and handling of frozen...
 Dried citrus pulp insect problem...
 Progress report on cantaloupe...
 Phytotoxicity of fungicides to...
 Irrigation of sebago potatoes at...
 Use of certain herbicides in fields...
 Crop production in soil fumigated...
 Breeding objectives and the establishment...
 Factors influencing consumer preference...
 Outlook for the production of southern...
 Insect problems in the production...
 Influence of nitrogen, phosphorus,...
 Lime-induced manganese deficiency...
 Cucumber fungicides for the west...
 Notes on current development of...
 Evaluation of control methods for...
 Control of diseases in the celery...
 The assay of streptomycin as it...
 Control of pole bean rust with...
 Fungicidal, herbicidal and nematocidal...
 Variety tests of commercial types...
 Results of different seeding and...
 Production of spinach for processing...
 The concept, duties, and operations...
 Notes on tropical fruits in central...
 Marketing of limes and avocados...
 The sub-tropical fruit program...
 Some observations on lime and avocado...
 Future of Florida minor tropical...
 Krome memorial avocado variety...
 Pollination and floral studies...
 Changes in physical characters...
 Further rooting trials of Barbados...
 Research on sub-tropical fruits...
 Some effects of nitrogen, phosphorous...
 A comparison of three clones of...
 Rare fruit council activities...
 Some notes on a weevil attacking...
 Response of lychees to girdlin...
 Some aspects of the lychee as a...
 The effects of longtime avocado...
 Rooting of peach cuttings under...
 Some effects of nitrogen, phosphorus...
 Mist propagation of roses
 Gladiolus botrytis control
 Some notes on philodendron...
 Fertilization of gladiolus
 Studies on the nutritional requirements...
 Virus ring spot of peperomia obtusifolia...
 How to landscape our outdoor space...
 Regional performance of hemerocallis...
 The palm society
 Comparison of 'Happiness' rose...
 Florida nursery law
 Research in the ornamental field...
 The Florida flower and nursery...
 The downward movement of phosphorus...
 Twelve bauhinias for Florida
 Pesticides and plant injury
 The effect of parathion as a corm...
 The genus solandra in Florida
 Studies on chemical weed control...
 Fungicides and plant injury
 The hunting billbug a serious pest...
 List of members
 Back Cover

Group Title: Proceedings of the Annual meeting of the Florida State Horticultural Society.
Title: Annual meeting of the Florida State Horticultural Society
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00053737/00001
 Material Information
Title: Annual meeting of the Florida State Horticultural Society
Alternate Title: Proceedings of the Florida State Horticultural Society for ..
Abbreviated Title: Annu. meet. Fla. State Hort. Soc.
Physical Description: v. : ill., ports. ; 24 cm.
Language: English
Creator: Florida State Horticultural Society -- Meeting
Publisher: The Society
Place of Publication: Florida?
Publication Date: 1951-
Frequency: annual
Subject: Horticulture -- Congresses   ( lcsh )
Gardening -- Congresses -- Florida   ( lcsh )
Gardening -- Congresses   ( lcsh )
Genre: conference publication   ( marcgt )
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
Bibliographic ID: UF00053737
Volume ID: VID00001
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 rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000006221
oclc - 01387526
notis - AAA7465
lccn - 88647898
issn - 0097-1219
 Related Items

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page i
        Page ii
        Page iii
        Page iv
        Page v
        Page vi
    Table of Contents
        Page vii
        Page viii
        Page ix
        Page x
        Page xi
        Page xii
        Page xiii
        Page xiv
        Page xv
    Photo: R. A. Carlton
        Page xvi
    President's address
        Page 1
        Page 2
        Page 3
    Plant research in the atomic age
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Mediterranean fruit fly eradication program in Florida
        Page 12
        Page 13
        Page 14
    Award of honorary memberships
        Page 15
        Page 16
        Page 17
        Page 18
    Injury and loss of citrus trees due to tristeza disease in an Orange county grove
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
    Effect of phosphate fertilization on root grown, soil pH, and chemical constituents
        Page 25
        Page 26
        Page 27
        Page 28
    Starting and maintaining burrowing nematode-infected citrus under greenhouse conditions
        Page 29
        Page 30
    Preliminary investigations on dieback of young transplanted citrus trees
        Page 31
        Page 32
        Page 33
    Possibility of mechanical transmission of nematodes in citrus groves
        Page 34
        Page 35
        Page 36
        Page 37
    Transmission of tristeza virus by aphids in Florida
        Page 38
        Page 39
        Page 40
        Page 41
    Physiologic races of the burrowing nematode in relation to citrus spreading decline
        Page 42
        Page 43
    Citrus rootstock selections tolerant to the burrowing nematode
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
    New 4-H club program for citrus production training
        Page 52
        Page 53
    Field observations of several methods of managing closely set citrus trees
        Page 54
        Page 55
        Page 56
        Page 57
    Timing fertilization of citrus in the Indian River area
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
    Is stem pitting of grapefruit a threat to the Florida grower?
        Page 65
        Page 66
        Page 67
    Seasonal changes in the juice content of pink and red grapefruit during 1955-56
        Page 68
        Page 69
        Page 70
        Page 71
    Effectiveness of different zinc fertilizers on citrus
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
    Increased utilization of grapefruit through improvement in quality of processed products
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
    Long range relationships between weather factors and scale insect populations
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
    Notes on the use of systox for purple mite control of citrus
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
    Progress report on greasy spot and its control
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
    Use of 1,2-dibromo-3-chloropropane on living citrus trees infected with the burrowing nematode
        Page 105
        Page 106
    Rapid determination of peel oil in orange juice for infants
        Page 107
        Page 108
    Effects of finisher pressure on characteristics of valencia orange concentrate
        Page 109
        Page 110
        Page 111
        Page 112
    Study of the degrees brix and brix-acid ratios of grapefruit utilized by Florida citrus processors for the seasons 1952-53 through 1955-56
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
    Diacetyl production in orange juice by organisms grown in a continuous culture system
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
    Standardization of Florida citrus products
        Page 125
        Page 126
        Page 127
    Citrus vitamin P
        Page 128
        Page 129
        Page 130
        Page 131
    Vacuum cooling of Florida vegetables
        Page 132
        Page 133
        Page 134
        Page 135
    Quality control of chilled orange juice from the tree to the consumer
        Page 136
        Page 137
    Hydrocooling cantaloupes
        Page 138
        Page 139
    Sloughing disease of grapefruit
        Page 140
        Page 141
    Effect of variety and fresh storage upon the quality of frozen sweet potatoes
        Page 142
        Page 143
        Page 144
    Storage studies on 42 degree brix concentrated orange juices processed
        Page 145
        Page 146
        Page 147
        Page 148
    Purification of naringin
        Page 149
        Page 150
        Page 151
    Sectionizing marsh seedless grapefruit
        Page 152
        Page 153
    An effective high pressure cleaning system for citrus concentrating plants
        Page 154
        Page 155
        Page 156
        Page 157
        Page 158
    Some studies on the use of sodium nitrate as a corrosion inhibitor in the canning industry
        Page 159
        Page 160
        Page 161
        Page 162
        Page 163
        Page 164
    Reducing losses in harvesting and handling tangerines
        Page 165
        Page 166
        Page 167
        Page 168
        Page 169
    Quality of canned grapefruit sections from plots fertilized with varying amounts of potash
        Page 170
        Page 171
        Page 172
        Page 173
        Page 174
        Page 175
    Storage studies on 42 degree brix concentrated orange juices processed from juices heated at varying folds
        Page 176
        Page 177
        Page 178
        Page 179
        Page 180
    Effect of thermal treatment and concentration on pectinesterase, cloud and pectin in citrus juices using a plant type heat exchanger
        Page 181
        Page 182
        Page 183
        Page 184
    Distribution and handling of frozen fruits, vegetables and juices
        Page 185
        Page 186
        Page 187
        Page 188
        Page 189
        Page 190
    Dried citrus pulp insect problem and its possible solution with insecticide-coated paper bags
        Page 191
        Page 192
        Page 193
        Page 194
    Progress report on cantaloupe varieties
        Page 195
        Page 196
        Page 197
    Phytotoxicity of fungicides to cantaloupes
        Page 198
        Page 199
    Irrigation of sebago potatoes at Hastings, Florida
        Page 200
        Page 201
        Page 202
        Page 203
    Use of certain herbicides in fields of growing tomatoes
        Page 204
        Page 205
        Page 206
    Crop production in soil fumigated with crag mylone as affected by rates, application methods and planting dates
        Page 207
        Page 208
        Page 209
    Breeding objectives and the establishment of new breeding lines of southernpeas
        Page 210
        Page 211
        Page 212
    Factors influencing consumer preference of southern peas
        Page 213
        Page 214
        Page 215
    Outlook for the production of southern field peas for freezing
        Page 216
    Insect problems in the production of southern peas
        Page 217
        Page 218
        Page 219
        Page 220
        Page 221
        Page 222
        Page 223
    Influence of nitrogen, phosphorus, potash and lime on the growth and yield of strawberries
        Page 224
        Page 225
        Page 226
        Page 227
    Lime-induced manganese deficiency of strawberries
        Page 228
        Page 229
    Cucumber fungicides for the west coast of Florida
        Page 230
        Page 231
        Page 232
        Page 233
        Page 234
    Notes on current development of gray mold, botrytis cinerea fr., of tomato and its control
        Page 235
    Evaluation of control methods for blackheart of celery and blossom-end rot of tomatoes
        Page 236
        Page 237
        Page 238
        Page 239
        Page 240
        Page 241
    Control of diseases in the celery seedbed
        Page 242
        Page 243
    The assay of streptomycin as it relates to the control of bacterial spot
        Page 244
        Page 245
        Page 246
    Control of pole bean rust with maneb-sulfur dust
        Page 247
        Page 248
        Page 249
    Fungicidal, herbicidal and nematocidal effects of fumigants applied to vegetable seedbeds on sandy soil
        Page 250
        Page 251
        Page 252
        Page 253
        Page 254
    Variety tests of commercial types and new breeding lines of southernpea
        Page 255
        Page 256
        Page 257
        Page 258
    Results of different seeding and fertilizer rates for potatoes at Hastings
        Page 259
        Page 260
    Production of spinach for processing on muck soils of central Florida
        Page 261
    The concept, duties, and operations of the Florida avocado and lime commission
        Page 262
        Page 263
        Page 264
        Page 265
        Page 266
    Notes on tropical fruits in central America
        Page 267
        Page 268
        Page 269
    Marketing of limes and avocados in Florida
        Page 270
        Page 271
    The sub-tropical fruit program of Dade county
        Page 272
        Page 273
    Some observations on lime and avocado grove cultural and maintenance practices in Dade county
        Page 274
    Future of Florida minor tropical fruit industry in doubt
        Page 275
    Krome memorial avocado variety committee report
        Page 276
    Pollination and floral studies of the Minneola tangelo
        Page 277
        Page 278
        Page 279
        Page 280
        Page 281
    Changes in physical characters and chemical constituents of haden mangos during ripening at 80 degrees Farenheit
        Page 282
        Page 283
        Page 284
    Further rooting trials of Barbados cherry
        Page 285
        Page 286
    Research on sub-tropical fruits as a result of mediterranean fruit fly eradication program
        Page 287
        Page 288
    Some effects of nitrogen, phosphorous and potassium fertilization on the yield and tree growth of avocados
        Page 289
        Page 290
        Page 291
        Page 292
    A comparison of three clones of Barbados cherry and the importance of improved selections for commercial plantings
        Page 293
        Page 294
        Page 295
        Page 296
    Rare fruit council activities 1955-56
        Page 297
        Page 298
        Page 299
        Page 300
        Page 301
        Page 302
    Some notes on a weevil attacking mahogany trees
        Page 303
        Page 304
    Response of lychees to girdling
        Page 305
        Page 306
        Page 307
        Page 308
    Some aspects of the lychee as a commercial crop
        Page 309
        Page 310
        Page 311
        Page 312
    The effects of longtime avocado culture on the composition of sandy soil in Dade county
        Page 313
        Page 314
        Page 315
        Page 316
        Page 317
        Page 318
        Page 319
        Page 320
        Page 321
        Page 322
        Page 323
    Rooting of peach cuttings under mist as affected by media and potassium nutrition
        Page 324
        Page 325
        Page 326
        Page 327
    Some effects of nitrogen, phosphorus and potassium fertilization on the growth, yield and fruit quality of Persian limes
        Page 328
        Page 329
        Page 330
        Page 331
        Page 332
    Mist propagation of roses
        Page 333
        Page 334
        Page 335
        Page 336
    Gladiolus botrytis control
        Page 337
        Page 338
        Page 339
        Page 340
        Page 341
        Page 342
    Some notes on philodendron hybrids
        Page 343
        Page 344
        Page 345
        Page 346
    Fertilization of gladiolus
        Page 347
        Page 348
        Page 349
        Page 350
        Page 351
    Studies on the nutritional requirements of chrysanthemums
        Page 352
        Page 353
        Page 354
        Page 355
        Page 356
    Virus ring spot of peperomia obtusifolia and peperomia obtusifolia var. variegata
        Page 357
        Page 358
        Page 359
    How to landscape our outdoor space for living
        Page 360
        Page 361
        Page 362
    Regional performance of hemerocallis in Florida
        Page 363
        Page 364
        Page 365
    The palm society
        Page 366
        Page 367
    Comparison of 'Happiness' rose production on four rootstocks
        Page 368
        Page 369
    Florida nursery law
        Page 370
        Page 371
        Page 372
        Page 373
        Page 374
        Page 375
        Page 376
        Page 377
        Page 378
    Research in the ornamental field in control of mediterranean fruit fly
        Page 379
    The Florida flower and nursery industry
        Page 380
        Page 381
        Page 382
        Page 383
        Page 384
    The downward movement of phosphorus in potting soils
        Page 385
        Page 386
        Page 387
    Twelve bauhinias for Florida
        Page 388
        Page 389
        Page 390
        Page 391
        Page 392
        Page 393
        Page 394
        Page 395
        Page 396
        Page 397
    Pesticides and plant injury
        Page 398
        Page 399
        Page 400
        Page 401
        Page 402
    The effect of parathion as a corm and soil treatment for gladiolus
        Page 403
        Page 404
    The genus solandra in Florida
        Page 405
        Page 406
    Studies on chemical weed control in plumosus fern
        Page 407
        Page 408
        Page 409
        Page 410
        Page 411
        Page 412
    Fungicides and plant injury
        Page 413
        Page 414
    The hunting billbug a serious pest of Zoysia
        Page 415
        Page 416
        Page 417
        Page 418
        Page 419
        Page 420
        Page 421
        Page 422
    List of members
        Page 423
        Page 424
        Page 425
        Page 426
        Page 427
        Page 428
        Page 429
        Page 430
        Page 431
        Page 432
        Page 433
        Page 434
        Page 435
        Page 436
        Page 437
        Page 438
        Page 439
    Back Cover
        Back Cover
Full Text

of the





Published by the Society


of the



held at
November 7, 8 and 9




Executive Committee


West Palm Beach


Winter Haven


Winter Haven


Winter Garden

South Miami

Louis F. RAUTH
Delray Beach



HOWARD A. THULLBERY, Lake Wales DR. F. S. JAMISON, Gainesville
E. S. REASONER, Bradenton




Executive Committee




Winter Haven


Winter Haven




Ft. Pierce


Plant City

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



Article I-NAME-This organization shall be
known as the Florida State Horticultural So-
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.
BERSHIP-There shall be three classifications
of membership, all of which carry voting
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.
SHIP-Any individual, firm or partnership in-
terested in the development and advancement
of horticulture in Florida shall be eligible for
Article VI-DUES-Dues shall be paid an-
nually according to classification at rate as
prescribed in By-laws.
Society shall hold an annual meeting each year
in accordance with the By-laws unless pre-
vented from doing so by causes beyond its
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.

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.

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.

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

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.


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
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.
Constitution shall become effective immediate-
ly upon approval by a majority vote of the
membership at the annual meeting in October

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

Annual Membership
Sustaining Membership
Patron Membership

$ 4.00
$ 10.00

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.

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


the nomination of Vice President for that sec-
tion. Such nominations by the committee how-
ever shall not preclude nominations from the
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.

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.
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.
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.
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.


(PIOZEC Cdin23

of the


9zJi 'tiauLitwaf SocairQ




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


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


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



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


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


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


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


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


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


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


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


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


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



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


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
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


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
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
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-
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."



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.

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 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
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


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-
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.
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
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.


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
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


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
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.

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
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.


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-
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.


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-
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.


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
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
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
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


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:


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
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
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-


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-
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
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.

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.


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.




State Plant Board of Florida

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
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
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


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


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-
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-


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-
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-
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


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


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-

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
Dr. Camp is an honorary member of the
Kiwanis Club and Gamma Sigma Epsilon,


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.

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
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
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


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.


CftZL<- Section




State Plant Board

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

'/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

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

0 0 000
XO 0
S OX 0 0000
K X X 0
0 X X X XX
X 0 0
X 0 X

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


x x
0 0 X U
0 0 0 0 00 X C
00 0 X
X 0 0 X X 0


X 0 0 X

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

XX X 0 X

X 0
X OXXX X X X 00000

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
1 X
0 00 X
0 000 XX
X X 0 X
OX 0 X00 0
X XO X 0
X X 0





K 0


000 X 0
0 X X

x x

0 00

x x

X 0
x x

OX 0 0
xo XXX oX X oox
XX X X 0
000 OX 0 XXOX

0 X
IX X X 0

)X X
( XO
0 X0


X 0 X

3 X

0 0



0 X
0 0


0 0

X 0

X 0 X

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

X 0 0 OX 0

0 0
X 0 X X 0

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





X 0




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


0 I


1953 11% 155 li56






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

















1511 36.3


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
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
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


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


e 17 131 II 10 Y e 7 C ) 3 I

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A D..A NAUun

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

" '


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?
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).






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

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.
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
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


I LSD 0.05


P 200.




U 1.0

I LSD 9 0.05

IiI Ii l 11 1111


I LSD 0 0.05

K ,

Ill 1111 111ll IIIi

oE"I k~iI LM 0~t OM

I LSD 0.05

II Ill




0 I II111nl.i

illi miii lull

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.




Cu 5

mill loll 11.1---



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.


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
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


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.
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.
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


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.
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.
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,
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.





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


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-

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

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


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.






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


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
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,

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
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


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
I/ Glen Navel orange/Cleopatra mandarin 5/8-in. planted 3/23/56. Data
taken 6/7/56.


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

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.
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
The presence of healthy fibrous roots and
their protection from drying at all times have


proved to be important for vigorous tree
growth, which apparently provides the best
defense against dieback of transplanted citrus
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
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.
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.




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,


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-


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.


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.

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.
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.




Entomology Research Branch
Horticultural Crops Research Branch
Agricultural Research Service
U. S. Department of Agriculture
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.
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

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
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-


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.
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.

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 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


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 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.

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.


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
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
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-
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-
Transmissions of virus by the green citrus
aphid from Meyer lemon produced notably


milder symptom expression on Key limes than
those obtained by tissue transfers to Key
limes from the same Meyer lemon source.
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:
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):
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.





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-


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
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
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


burrowing nematodes from numerous loca-
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.



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.
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-


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
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.


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

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.


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.

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-
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


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-
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


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.
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


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.


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


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.
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
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.
1. Chitwood B. G. and B. A. Oteifa. 1952. Nem-
atodes parasitic on plants. Ann. Rev. Microbiol.
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:
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
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

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 Agricultural Extension Service
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-
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
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-
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


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-
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.
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-
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.)

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.


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.




Florida Agricultural Extension Service
Florida Agricultural Extension Service
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
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.


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-
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-
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-
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
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
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
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


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
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.


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-
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-
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-


fects of crowding and shading found in
most Florida groves 15 years old and older.
a. Increased effectiveness of pest control.
b. Decreased damage to trees and equip-
c. Faster more economical grove opera-
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.
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
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
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.
a. Reduces height of tree.
b. Greatly improves tree vigor.
c. Increases yield and size of fruit.
d. Produces increased cover crop growth.
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.



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
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


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
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
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.
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
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-


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
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
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.


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
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

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

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


Table 3. Summary of fruit characteristics

TREATMENT ABrix Diameter, Avg. Wt.
Brix Acid Acid mm. grams


Feb. and June


May and Oct.


11.73 1.06 11.26



11.70 1.03

11.48 1.09
11.63 1.07

June and Dec. 11.63

Feb., June, and Nov. 11.62





Treatments N.S.

Interaction **



(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


















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-
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.

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-
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-



2 14

o l


F- 61lesO -
a / _..,

Feb Feb May May Oct. June Feb.
June Oct. Dec. June
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-


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
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.

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.
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.




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.


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
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-
One possible explanation is to assume that
the seedling-yellows component is present in


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-
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.


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):
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:
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-



DURING 1955-'561


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-



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.


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


0 R..2.
.S S 5454

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

...... .....

-S.e 7O


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.


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

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)
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)
above 31.7 69.5 81.3 93.6 95.0 90.8 100.0
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.


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

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-


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
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


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.

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:

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.
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.




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
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.


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-
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


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.
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


PH 4



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


3 600-

CL 400-



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.

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.

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


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
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-


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)


mixtures of zinc sulfate and calcium chloride
are being studied further as a possible source
of zinc suitable for soil application to citrus
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.
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-
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:
5. Jamison, Vernon C. 1944. Citrus Nutrition
Studies. Fla. Agr. Exp. Station Annual Report, page
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.
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.




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


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
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

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
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,


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 %
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
Since the 1946-47 season, the pack of
canned grapefruit sections and citrus salad

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 %

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
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
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.


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
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.
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
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-


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
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

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