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 Historic note
 Title Page
 Personnel
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 Reference














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 335
Title: Some symptoms of citrus malnutrition in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00015114/00001
 Material Information
Title: Some symptoms of citrus malnutrition in Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 55 p., 8 leaves of plates : ill. (some col.) ; 23 cm.
Language: English
Creator: Camp, A. F ( Arthur Forrest ), 1896-
Fudge, B. R ( Bonnie Reid )
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1939
 Subjects
Subject: Citrus -- Diseases and pests -- Florida   ( lcsh )
Deficiency diseases in plants   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 45-55.
Statement of Responsibility: by A.F. Camp and B.R. Fudge.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00015114
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924565
oclc - 18214613
notis - AEN5192

Table of Contents
    Historic note
        Historic note
    Title Page
        Page 1
    Personnel
        Page 2
    Main
        Table of Contents
            Page 3
        Introduction
            Page 3
            Page 4
            Page 5
            Page 6
            Page 7
            Page 8
        Copper Deficiency
            Page 9
            Page 10
            Page 11a
            Page 11
            Page 8
            Page 12
            Page 13a
            Page 13
            Page 14
            Page 15
            Page 16
        Zinc deficiency
            Page 17
            Page 18
            Page 19a
            Page 19
            Page 20
            Page 21
            Page 22
            Page 16
        Manganese deficiency
            Page 23
            Page 24
            Page 25a
            Page 25
            Page 26
            Page 27
            Page 22
        Magnesium deficiency
            Page 28
            Page 29
            Page 29
            Page 30
            Page 31
            Page 27
        Nitrogen deficiency
            Page 32
            Page 33
            Page 34
            Page 35
            Page 31
        Iron deficiency
            Page 36
            Page 37a
            Page 37
            Page 35
            Page 38
        Boron deficiency
            Page 39
            Page 40
            Page 41
            Page 38
        Boron toxicity
            Page 41
            Page 42
            Page 43a
            Page 43
        Miscellaneous
            Page 44
    Reference
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida






Bulletin 335


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
WILMON NEWELL, Director








SOME SYMPTOMS OF


CITRUS MALNUTRITION


IN FLORIDA



By

A. F. CAMP and B. R. FUDGE


Single copies will be sent free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


June, 1939









EXECUTIVE STAFF

John J. Tigert, M.A., LL.D., President of
the University
Wilmon Newell, D.Sc., Director
Harold Mowry, M.S.A., Asst. Dir., Research
V. V. Bowman, M.S.A., Asst. to the Director
J. Francis Cooper, M.S.A., Editor
Jefferson Thomas, Assistant Editor
Clyde Beale, A.B.J., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant

MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S.., Agronomist'
W. A. Leukel, Ph.D., Agronomist
G. E. Ritchey, M.S., Associate'
Fred H. Hull, Ph.D., Associate
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant
Roy E. Blaser, M.S., Assistant
ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Animal Husbandman'
R. B. Becker, Ph.D., Dairy Husbandman
L. M. Thurston, Ph.D., Dairy Technologist
W. M. Neal. Ph.D., Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian
N. R. Mehrhof, M.Agr., Poultry Husbandman
O. W. Anderson. M.S., Asst. Poultry Husb.
W. G. Kirk, Ph.D., Asst. An. Husbandman
R. M. Crown, M.S.A., Asst. An. Husbandman
P. T. Dix Arnold, M.S.A., Assistant Dairy
Husbandman
L. L. Rusoff, M.S., Asst. in An. Nutrition'
CHEMISTRY AND SOILS
R. V. Allison. Ph.D.. Chemist'
F. B. Smith, Ph.D., Soils Chemist
C. E. Bell, Ph.D., Associate
R. B. French, Ph.D., Associate
H. W. Winsor, B.S.A., Assistant
J. Russell Henderson, M.S.A., Assistant
L. W. Gaddum, Ph.D., Biochemist
L. H. Rogers, M.A., Spectroscopic Analyst'
Richard A. Carrigan, B.S., Asst. Chemist

ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist'
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant
ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Specialist'
Ruth Overstreet, R.N., Assistant
ENTOMOLOGY
J. R. Watson, A.M., Entomologist'
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist'
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot, M.S.A., Spec. Fumigation Res.
R. D. Dickey, B.S.A., Assistant Horticulturist
J. Carlton Cain, B.S.A., Asst. Horticulturist
Victor F. Nettles, M.S.A., Asst. Hort.
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist'
George F. Weber, Ph. D., Plant Pathologist
R. K. Voorhees, M.S., Assistant'
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Assistant Botanist


BOARD OF CONTROL
R. P. Terry, Chairman, Miami
Thomas W. Bryant, Lakeland
W. M. Palmer, Ocala
H. P. Adair, Jacksonville
Chas. P. Helfenstein, Live Oak
J. T. Diamond, Secretary, Tallahassee

BRANCH STATIONS

NORTH FLORIDA STATION, QUINCY
L. O. Gratz, Ph.D., Plant Path. in Charge
R. R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
Jesse Reeves, Farm Superintendent
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in Charge
John H. Jefferies, Superintendent
Michael Peech, Ph.D., Soils Chemist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Asst. Entomologist
W. W. Lawless, B.S., Asst. Horticulturist
Walter Reuther, B.S., Asst. Horticulturist3
EVERGLADES STATION, BELLE GLADE-
J. R. Neller, Ph.D., Biochemist in Charge
J. W. Wilson, Sc.D., Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane
Physiologist
Jos. R. Beckenbach, Ph.D., Asso. Horticul.
Frederick Boyd, Ph.D., Asst. Agronomist
G. R. Townsend, Ph.D., Asso. Plant Path.
R. W. Kidder, B.S., Asst. Animal Husbandman
W. T. Forsee, Ph.D., Asst. Chemist
B. S. Clayton, B.S.C.E., Drainage Engineer2

SUB-TROPICAL STATION, HOMESTEAD
W. M. Fifield, M.S., Asst. Horticulturist
S. J. Lynch, B.S.A., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Asso. Plant Pathologist
W. CENTRAL FLA. STA., BROOKSVILLE
W. P. Ward, M.S., Asst. An. Husbandman
in Charge2

FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist in
Charge
K. W. Loucks, M.S., Asst. Plant Pathologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
R. N. Lobdell, M.S., Asst. Entomologist
Cocoa
A. S. Rhoads, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist
Monticello
Samuel O. Hill, B.S., Asst. Entomologist'
Bradenton
David G. Kelbert, Asst. Plant Pathologist
Sanford
R. W. Ruprecht, Ph.D., Chemist in Charge,
Celery Investigations
W. B. Shippy, Ph.D., Asso. Plant Pathologist
Lakeland
E. S. Ellison, Meteorologists
B. H. Moore. A.B., Asst. Meteorologist'

'Head of Department.
'In cooperation with U.S.D.A.
'On leave.









SOME SYMPTOMS OF CITRUS MALNUTRITION
IN FLORIDA


By A. F. CAMP and B. R. FUDGE

CONTENTS
PAGE PAGE
COPPER DEFICIENCY ...................................... 8 IRON DEFICIENCY .......................... ............... 35
ZINC DEFICIENCY ....................................... 16/ BORON DEFICIENCY ................. .................. 38
MANGANESE DEFICIENCY ......................... 22 BORON TOXICITY .......................................... 41
M AGNESIUM DEFICIENCY .............................. 27- MISCELLANEOUS ............................................. 44
Y ITROGEN DEFICIENCY .................................. 31 REFERENCES .. ............ ........................ 45

INTRODUCTION
One of the outstanding recent developments in the field of
citrus nutrition has been the utilization of the symptoms found
on leaves, twigs, and fruits as guides in fertilization. Research
which has revealed the specific relationship between nutritional
requirements and certain symptoms exhibited by the citrus tree
has furnished the basis for this development. Thus it has been
found that zinc is a specific remedy for wrenchingg" and copper
for diebackk" and that neither will fill the role of the other.
Likewise, deficiency of either manganese or magnesium will give
rise to certain definite symptoms in the citrus tree, whereas an
excess of boron will produce equally specific symptoms which
are characteristic of the toxic effects of this element. These
symptoms have proved much more specific than at first supposed
and serve as excellent indicators of the tree's nutritional needs.
The idea of using an element as a specific remedy for a particu-
lar set of symptoms is not entirely new, since copper has been
used as a specific for diebackk" for many years.
In Florida nitrogen deficiency has been generally accepted in
the past as the cause of practically all yellowing of citrus leaves
and it is only recently that the various types of yellowing have
been adequately classified with the result that magnesium de-
ficiency is now recognized as the cause of the commonest type of
yellowing. Much of the progress made has resulted from more
detailed and critical observation of the trees themselves; and
the practical utilization of symptoms as a guide in citrus nutri-
tion requires equally careful observation, particularly when
symptoms of several different types are combined in such a way
as to mask partially one or more of them.









SOME SYMPTOMS OF CITRUS MALNUTRITION
IN FLORIDA


By A. F. CAMP and B. R. FUDGE

CONTENTS
PAGE PAGE
COPPER DEFICIENCY ...................................... 8 IRON DEFICIENCY .......................... ............... 35
ZINC DEFICIENCY ....................................... 16/ BORON DEFICIENCY ................. .................. 38
MANGANESE DEFICIENCY ......................... 22 BORON TOXICITY .......................................... 41
M AGNESIUM DEFICIENCY .............................. 27- MISCELLANEOUS ............................................. 44
Y ITROGEN DEFICIENCY .................................. 31 REFERENCES .. ............ ........................ 45

INTRODUCTION
One of the outstanding recent developments in the field of
citrus nutrition has been the utilization of the symptoms found
on leaves, twigs, and fruits as guides in fertilization. Research
which has revealed the specific relationship between nutritional
requirements and certain symptoms exhibited by the citrus tree
has furnished the basis for this development. Thus it has been
found that zinc is a specific remedy for wrenchingg" and copper
for diebackk" and that neither will fill the role of the other.
Likewise, deficiency of either manganese or magnesium will give
rise to certain definite symptoms in the citrus tree, whereas an
excess of boron will produce equally specific symptoms which
are characteristic of the toxic effects of this element. These
symptoms have proved much more specific than at first supposed
and serve as excellent indicators of the tree's nutritional needs.
The idea of using an element as a specific remedy for a particu-
lar set of symptoms is not entirely new, since copper has been
used as a specific for diebackk" for many years.
In Florida nitrogen deficiency has been generally accepted in
the past as the cause of practically all yellowing of citrus leaves
and it is only recently that the various types of yellowing have
been adequately classified with the result that magnesium de-
ficiency is now recognized as the cause of the commonest type of
yellowing. Much of the progress made has resulted from more
detailed and critical observation of the trees themselves; and
the practical utilization of symptoms as a guide in citrus nutri-
tion requires equally careful observation, particularly when
symptoms of several different types are combined in such a way
as to mask partially one or more of them.







Florida Agricultural Experiment Station


In this bulletin will be found illustrations in colorI of the
more common symptoms of malnutrition in citrus as observed
in Florida, together with such information as may be of use
in determining the nutritional requirements of the tree. Since
the field is new the information is not complete nor the con-
clusions final, but an attempt is being made to bring to those
interested, and to growers in particular, the gist of the pertinent
information available at present. Primary attention is given
those symptoms which have been found to be good practical
guides in grove care and those of only academic interest will
be omitted or referred to only briefly. General principles in-
volved in the occurrence and treatment of deficiencies and
toxicities are discussed, but detailed recommendations for treat-
ment are not included since these are being continually changed
through research work and the current recommendations will
be found from year to year in the publications of the Agricul-
tural Experiment Station and other research agencies. In addi-
tion to offering in a single publication descriptions and illustra-
tions which may serve as practical grove guides, this bulletin
is also intended as a reference work on the various symptoms
of malnutrition in citrus and will be referred to from time to
time in the publication of the results of research work now in
progress.
While the symptoms are, in many cases, the most sensitive
and reliable indicators we have, it should be remembered that
the problem is essentially a soil problem in many of its phases.
A tree may receive insufficient quantities of an element for a
number of reasons, most of which involve the soil in one way
or another. An element may become deficient because it is
fixed2 in an unavailable form in the soil, as zinc and manganese
are fixed in marl soils; or it may be leached from the soil,
such leaching frequently being aggravated by too much acidic
material applied to the soil; or it may be "cropped out" when
heavy crops are removed and the element in question is not
LIST OF PLATES
I. Symptoms of copper deficiency on orange twigs.
II. Symptoms of copper deficiency on orange.
III. Symptoms of zinc deficiency on orange leaves and twigs.
IV. Symptoms of manganese deficiency on young orange leaves.
V. Symptoms of magnesium deficiency on grapefruit leaves.
VI. Symptoms of iron deficiency on young orange leaves.
VII. Fruit symptoms characteristic of boron deficiency as described by Morris.
VIII. Symptoms of boron toxicity on grapefruit leaves.
'The term fixed is used in this manuscript to designate a condition of
insolubility or unavailability due to soil conditions; as the unavailability
of manganese in an alkaline soil.







Some Symptoms of Citrus Malnutrition in Florida


added in fertilization. Both leaching and fixation are influenced
to a large degree by soil reaction (pH) and proper soil manage-
ment may greatly reduce such losses, whereas "cropping out"
is primarily due to failure to add the proper materials in the
course of fertilization. Other causes also may be active but
the above are the most important in Florida. The chief in-
fluencing factor outside of the soil is in the tree itself; for
example, the extreme deficiency of one element may so injure
the absorptive system of the tree as to.hinder the absorption
of other elements so that they may in turn become deficient
within the tree although present in adequate amounts in the
soil. Thus the symptoms are primarily a reflection of the con-
dition within the tree itself although the fundamental causes
usually lie directly or indirectly in the soil. Included with the
discussion of each element will be given a brief resume of soil
problems involved, as far as they are understood today, but
this field is relatively new and the conclusions may be subject
to considerable modification in the course of additional research
work.
Since the occurrence of deficiencies is tied up inextricably
with the soil, an understanding of soil problems is a necessity.
While it is not possible to present a discussion of technical soil
problems in this bulletin, it should be remembered that a major
portion of the citrus industry of Florida is located on light
sandy soils of low natural fertility. When such soils are heavily
cropped and are fertilized with only nitrogen, phosphorus, cal-
cium, sulfur, and potassium, other elements necessary to plant
growth rapidly become depleted or "deficient". These sandy
soils present an acute problem because of both their low fer-
tility and the extent to which they are planted to citrus. Other
soil types extensively used for citrus contain large excesses of
carbonates which have a tendency to fix manganese, zinc, iron,
and other elements and render them unavailable to the plant.
It was only after the need for these elements in citrus nutrition
was recognized and they were supplied to trees on such soils
that many of the groves have become productive. Discussions
of Florida citrus soils have been presented by Peech (83, 84)3,
and these publications should be studied in connection with
this bulletin.

3A more comprehensive report on Florida citrus soils has been prepared
by Peech for publication in bulletin form.







Florida Agricultural Experiment Station


Modifications of symptoms are given considerable attention,
particularly with reference to the interrelation of deficiencies,
but modifications based on certain tree conditions should be
called to the attention of the reader. Poorly adapted rootstocks
almost always cause an intensification of deficiency symptoms,
particularly in the case of sour orange stock on light sandy
soils. Extremely.heavy cropping tends to intensify most of the
deficiencies and the outward expression of some of them is asso-
ciated with crop production. Varieties producing seedless or
nearly seedless fruits usually are less affected than seedy vari-
eties. Extreme drought usually intensifies symptoms partly
because of reduced availability of elements in the soil and partly
because of injured root systems. In general, all things which
reduce tree vigor tend to intensify the various deficiencies
through reducing the absorptive power of the root system.
The terms deficiency and toxicity are used to designate certain
tree conditions associated with specific symptoms. "Deficiency"
will be used when an element is indicated as a specific corrective,
although a deficiency may be only relative and not absolute.
The common names will be included, but it is hoped that these
will be eliminated eventually since they are neither specific nor
constant but vary with both locality and crop, i. e., zinc defi-
ciency in citrus is termed frenching in Florida and mottle-leaf
elsewhere, while zinc deficiency in tung trees is termed bronzing.
The term "toxicity" will be used in connection with the symp-
toms arising from the use of an excess of an element which is
toxic. Again it may be argued that this is only relative, but
it serves a useful purpose in indicating those things that are
to be avoided.
The symptoms of the following deficiencies will be discussed
and illustrated: Copper, zinc, manganese, magnesium, nitrogen,
iron, and boron. The terms "minor elements" and "secondary
elements" are not used since they tend to be somewhat mis-
leading. The role of copper is not considered to be essentially
less important than the role of potassium or calcium, and cer-
tainly since its deficiency will result in total crop loss, its role
cannot be a "minor" one or its application of minor importance.
The recognized difference is primarily a difference in the amount
required and from that standpoint a classification of "micro"
and "macro" elements would be justifiable. In this case copper,
zinc, manganese, boron, and iron would fall in the "micro" class
while magnesium would fall in the "macro" class as far as




TABLE 1.-COMPOSITION OF VARIOUS LOTS OF CITRUS LEAVES IN PERCENT OF DRY MATTER.


Variety Source


Valencia and N. S.Wales
Navels
Valencia Solution
Culture
Orange California

Lemon California

Grapefruit California

Wash. Navel California

Valencia California

Valencia Solution
Culture
Valencia California

Parson Brown Florida

Parson Brown Florida

Parson Brown Florida

Parson Brown Florida

Duncan Gft. Florida

Duncan Gft. Florida

Marsh Gft. Florida


SRefer- Ash N' P K
ence |

163 113.05 2.27 0.101 0.717

166 16.82 2.79 6.43

137 -

137 -

137 0.181 -

137 0.186 -

137 0.181 -

167 15.15 2.92 0.230 5.64

169 13.96 1.94 0.141 1.10

4 -

4 -

89 -

89 -

48 115.30 2.17 0.109 2.56

48 14.53 1.71 0.104 3.22

48 113.99 2.23 0.131 2.71
1 1 1 1


Ca Mg


4.36 0.247

1.48 0.190


- I-






1.12 0.150

3.68 0.328

2.78 0.103

2.19 0.029

3.45 0.201

3.17 0.224

4.11 0.156

3.48 0.017

3.59 0.228


0.380 0.420 0.27

0.269 0.202 0.037


U.vuo -

- 0.0028

0.0045

0.032 0.0033

0.041 0.0027

0.018 0.0033


0.0076

0.0097

0.0090


Na S CI


0.196 0.154 0.125

0.270 0.80


Mn Al


0.0012 -


calc:um, r-rre.i :u:l. saIu-., '.;:'ur-, c::;r;:-e, iron, manzaneoO, a:u:~:num and copper.


Cu1





0.00069

0.00131

0.00074

0.00111

0.00128


Notes











Copper-treated






Green leaves

Bronzed leaves

Untreated

Mn-treated

Green leaves

Bronzed leaves

Green leaves


I'T.:co c::::-onts 1a., in or'cr: Nitro-cn, phoophor'u, potas:h,







Florida Agricultural Experiment Station


citrus is concerned. In Table 1 will be found typical analyses
of citrus leaves which show the wide variation in the amount
of individual elements in any given sample. Attention is called,
for instance, to the amounts of calcium, potassium, and nitrogen
as compared with the amounts of manganese and copper, illus-
trating the difference between "macro" and "micro" elements.
As far as citrus fertilization in Florida is concerned it would
probably be better to eliminate classifications and accept all of
the elements required simply as plant nutrients.
Copper and zinc deficiencies are discussed first because they
were the first identified and occur most widely in the citrus
areas of the world; and manganese deficiency is grouped with
them because it is closely related in many ways. All three of
these elements are needed in very small amounts by the tree;
the symptoms of all of them are coincidental with growth and
mature normal foliage or fruit does not develop the symptoms;
soil conditions affect the availability of all three elements in
much the same manner, although in different degrees. Mag-
nesium deficiency is equally important in Florida and is dis-
cussed next but has certain distinct characteristics from the
above three-this element is needed in relatively much larger
amounts, it does not fix in alkaline soils, and the symptoms
show up on mature leaves that were normal during the early
stages of their development. Nitrogen deficiency is briefly dis-
cussed because of its relationships to other deficiencies but will
be the subject of further papers in the future. Finally, iron and
boron deficiencies are included, although neither of them is
satisfactorily worked out as far as symptoms or control is con-
cerned. The discussion of these two is purely tentative and
both will have to be the subject of future reports.

COPPER DEFICIENCY
Copper deficiency is commonly known as diebackk" (Florida),
the name being derived from the dying back of the twigs;
ammoniationn" (Florida), derived from its frequent association
with heavy application of nitrogen (ammonia) ; and "exanthema"
(Florida and California), derived from the Greek and referring
primarily to the excrescences on the surface of the twigs and
fruit. It was first described on oranges in Florida in 1875 by
Fowler (44)4 who considered the 'causal agent to be a fungus.
'Italic figures in parentheses refer to "Literature Cited" near the back
of this bulletin.







Some Symptoms of Citrus Malnutrition in Florida


In 1896 Swingle and Webber (96) described the symptoms in
detail. From 1908 to 1917 Floyd (31, 32, 34, 36, 37, 38, 39,
40, 42) reported a series of extensive studies on the problem
with particular attention being given to the morphology of the
affected tissues. It was first reported in California in 1896 and
is now known to occur in most of the citrus growing areas of
the world (6, 9, 26, 67, 68, 85, 104, 105) and recommended treat-
ments as well as descriptions indicate that it is of common
occurrence in citrus. Cheema (24, 25) and Sahasrabuddhe (90)
have described a condition known as diebackk" in India but the
symptoms reported by them apparently differ from those of
copper deficiency.
Excessive applications of nitrogenous fertilizers have been
considered for years a contributing cause for this trouble while
copper has been used as a corrective for almost as long (40, 42).
More recently it has been shown (19, 45, 46) that copper com-
pounds, whether used as sprays or as soil applications, will serve
as correctives for both vegetative and fruit symptoms, even in
the most acute cases. Chemical analyses *(45, 46) of tissues
from trees exhibiting symptoms of copper deficiency have shown
a much higher nitrogen content than have analyses of compar-
able tissues from trees giving no indications of the deficiency;
and a decline in nitrogen content has been found following the
application of copper treatments to deficient trees. Considering
the work up to the present this condition might be classified -as
either an excess of nitrogen as compared with copperor a'de-
ficiency of copper as compared with nitrogen. Tj'elatter view-
point is the more practical since it is relatively easy to supply'
a deficient element but difficult to remove' an excess ,ofan -'
element. This serves further to illustrate the viewpdint, ex-
pressed in the introduction, that the term 'deIiehcy" is a
relative one. ,
FOLIAGE SYMPTOMS
The first symptom usually looked for as an indicator of ap-
proaching copper deficiency is unusually dark green foliage, the
individual leaves being large and apparently over-vigorous. This
stage may be referred to as incipient copper deficiency, since
gumming and dying back of shoots may not be present. As the
deficiency becomes acute and twigs start to die, some of the
weak twigs will bear very small leaves of yellowish-green color
which drop quickly, leaving the twig denuded. In very acute
cases a peculiarly malformed leaf may develop which shows, in







Florida Agricultural Experiment Station


its developmental stages, a finely netted dark green venation
on a light green background. Mature leaves on affected shoots
may show a very slight reddish sheen due to a finely divided
gummy excrescence.























Fig. 1.-Angular, S-shaped twig growth typical of copper deficiency.

TWIG SYMPTOMS
In the incipient stages of copper deficiency the twigs are
unusually vigorous, long, soft, angular, frequently "S" shaped
and more or less drooping (Fig. 1); in contrast to the short,
round, and compact twig indicative of normal growth. As the
deficiency becomes more acute gum pockets may form between
the wood and bark of the twig near the leaf bases. In severe
cases the leaves are shed from the young twigs and they die
back, often to the point where the new growth originated, giving
rise to the popular name, diebackk" (Plate I). The twig is
covered by a reddish brown gummy excrescence which is typical
of the condition. Associated with the above symptoms, multiple
buds are developed and these produce growth that eventually
dies back in. the manner described (Figs. 2 and 3). The "bushy"
type of growth commonly associated with the above symptoms
is, in reality, due to zinc deficiency although commonly thought






FLORIDA AGRICULTURAL EXPERIMENT STATION


PLATE 1. Symptoms of copper deficiency on orange twig







Some Symptoms of Citrus Malnutrition in Florida


to be a symptom of copper deficiency because it is so often
associated with it.


I


Fig. 2.-Young tree affected by acute copper deficiency


FRUIT SYMPTOMS
Fruit symptoms are most pronounced on oranges. Brown
excrescences of hardened gum on the rind of the fruit (Plate II)
are a commonly recognized symptom of incipient copper defi-
ciency since this symptom, in a mild form, may precede the
appearance of leaf and twig symptoms. These markings, plus
the generally poor quality of the remaining fruit, result in an







Florida Agricultural Experiment Station


citrus is concerned. In Table 1 will be found typical analyses
of citrus leaves which show the wide variation in the amount
of individual elements in any given sample. Attention is called,
for instance, to the amounts of calcium, potassium, and nitrogen
as compared with the amounts of manganese and copper, illus-
trating the difference between "macro" and "micro" elements.
As far as citrus fertilization in Florida is concerned it would
probably be better to eliminate classifications and accept all of
the elements required simply as plant nutrients.
Copper and zinc deficiencies are discussed first because they
were the first identified and occur most widely in the citrus
areas of the world; and manganese deficiency is grouped with
them because it is closely related in many ways. All three of
these elements are needed in very small amounts by the tree;
the symptoms of all of them are coincidental with growth and
mature normal foliage or fruit does not develop the symptoms;
soil conditions affect the availability of all three elements in
much the same manner, although in different degrees. Mag-
nesium deficiency is equally important in Florida and is dis-
cussed next but has certain distinct characteristics from the
above three-this element is needed in relatively much larger
amounts, it does not fix in alkaline soils, and the symptoms
show up on mature leaves that were normal during the early
stages of their development. Nitrogen deficiency is briefly dis-
cussed because of its relationships to other deficiencies but will
be the subject of further papers in the future. Finally, iron and
boron deficiencies are included, although neither of them is
satisfactorily worked out as far as symptoms or control is con-
cerned. The discussion of these two is purely tentative and
both will have to be the subject of future reports.

COPPER DEFICIENCY
Copper deficiency is commonly known as diebackk" (Florida),
the name being derived from the dying back of the twigs;
ammoniationn" (Florida), derived from its frequent association
with heavy application of nitrogen (ammonia) ; and "exanthema"
(Florida and California), derived from the Greek and referring
primarily to the excrescences on the surface of the twigs and
fruit. It was first described on oranges in Florida in 1875 by
Fowler (44)4 who considered the 'causal agent to be a fungus.
'Italic figures in parentheses refer to "Literature Cited" near the back
of this bulletin.






Florida Agricultural Experiment Station


overly large proportion of the crop being thrown into the lower
grades even though the deficiency has not become obviously
acute. Splitting of fruit is common on trees showing mild
symptoms of copper deficiency, with a part of the splitting
starting at the blossom end in the usual way but some of it
taking place across the axis or around the gummy excrescences.
The latter types of splitting are irregular and are associated
with the hardening of the rind in areas covered by the mark-
ings. Such fruits usually show gum pockets in the rind and
around the seed.


IW^


L --;


Fig. 3.-Young tree of same age as that shown in Fig. 2, but treated


with copper sulfate.




FLORIDA AGRICULTURAL EXPERIMENT STATION
o,--

/


PLATE II. Symptoms of copper deficiency on fruit







Some Symptoms of Citrus Malnutrition in Florida


In acute cases the young fruit is light green in color and dis-
figured by light brown markings or excrescences, which darken
and converge as time progresses and may become almost black
by the time the fruit is half grown. Growth of the fruit is
arrested and trees showing pronounced symptoms on both growth
and fruit will have shed most of their fruit before the period
of normal maturity. The few fruits remaining on the tree are
low in acid, high in nitrogen, and low in juice content. Such
trees usually bloom profusely in the spring and set a heavy
crop of fruit which is shed by summer.
Fruit symptoms as described for oranges are not of common
occurrence on grapefruit and are more likely to involve a limited
portion of the fruit surface. This results in lopsided fruits
due to the fact that the area covered by markings does not grow
properly. Such fruits usually show gum pockets in the rind
and occasionally gum around the seeds. When a few fruits are
thus affected the remaining fruits on the tree have a thick,
coarse rind that takes on a yellow color with maturity and the
albedo and pulp are yellowish instead of light colored. Such
fruits frequently develop deep brown pits in the rind while still
on the tree.
MODIFICATIONS OF SYMPTOMS
In the presence of other deficiencies the symptoms of copper
deficiency may be considerably modified. This is particularly
true when copper deficiency is combined with either zinc or
magnesium deficiency. Since both of these effect a restraining
influence on growth, the marked vegetative response that is
characteristic of copper deficiency will be greatly reduced and
the long growth and over-vigorous leaves may not be apparent.
Instead of the long dead twigs so characteristic of copper defi-
ciency there will be dead twigs only an inch or two in length.
Such effects are primarily modifications of the vegetative symp-
toms and trees which are so deficient in magnesium and zinc
as to make the vegetative symptoms of copper deficiency un-
noticeable, except to the experienced eye, will still exhibit the
typical fruit symptoms. As a consequence fruit symptoms are
the most reliable indicator in routine observations.
On very light sandy soils that have been allowed to become
very acid (pH 4.5 to 5.0) acute deficiencies of magnesium, zinc
and manganese, as well as copper, are extremely common, so
that a study of these modifications is important in making diag-
noses. Symptoms of magnesium deficiency may not be readily







Florida Agricultural Experiment Station


apparent if copper deficiency is so acute as to cause the loss
of the crop. Copper applications under such conditions fre-
quently result in heavy cropping followed by acute magnesium
deficiency. (See section on magnesium deficiency.)
VARIETAL SUSCEPTIBILITY
While all kinds of citrus may show symptoms of copper de-.
ficiency occasionally, oranges are much more commonly affected
than grapefruit or tangerines. Pineapple and Valencia oranges
appear to be somewhat more likely to develop symptoms than
other varieties but careful differentiation as to copper require-
ments remains to be made. Young trees of all varieties are more
frequently affected than older trees, probably due to the rela-
tively heavier applications of nitrogen and the fact that such
trees are seldom sprayed with bordeaux.
CAUSATION
A deficiency of copper in sandy soils seems to be brought
on most often by allowing the soil to become too acid, as by
the excessive use of acidic fertilizer materials. Under such
conditions copper is probably leached out of the soil until it
becomes deficient. Factors that promote leaching, as excessive
cultivation, low pH, and lack of cover during the rainy season,
are commonly associated with the occurrence of the deficiency.
Practically, the blame is usually laid to excessive applications
of nitrogen. Since, as mentioned above, the junior author has
shown an apparent relationship between the utilization of nitro-
gen and the presence of copper, this is easily understood. How-
ever, it should be remembered that at very low levels of avail-
able copper the symptoms of copper deficiency can occur without
being associated with an excessive supply of nitrogen. Symp-
toms of copper deficiency occur frequently in groves on marl
soils that are very high in pH and there is some indication
that copper is fixed in such soils when the pH approaches 8.0.
Difficulty in classifying the underlying causes is experienced
because of the common use of bordeaux for disease control which
incidentally supplies the needed copper for nutritional purposes
by absorption through the leaves.
TREATMENT
One of the earliest treatments was to.starve the grove for
nitrogen but some of the earlier workers also reported favor-
able results from the application of large amounts of organic







Some Symptoms of Citrus Malnutrition in Florida


material, even though organic fertilizers were frequently blamed
for the appearance of the symptoms. This apparent anomaly
can probably be explained by the presence of traces of copper
in such materials. Copper was used in the form- of bordeaux,
and copper sulfate crystals were frequently placed under the
bark, but the latter practice has practically died out because
of the excessive gumming and killing of tissues caused by it.
Later workers indicated that copper sulfate applied to the soil
was a satisfactory corrective treatment. fAt present' copper is
commonly applied in spray form -when it is needed also for
disease control, and to the soil when an application of a copper
spray is to be avoided.) In the latter case copper sulfate is.
commonly applied at the rate of one-quarter to two pounds
per tree either as a separate application or combined with the
fertilizer. (Response to the spray is quicker than that to soil
applications, a copper spray applied at blooming time commonly
effecting an almost immediate recovery.)

TABLE 2.-EFFECT OF COPPER AND ZINC TREATMENTS ON PRODUCTION IN
AN ORANGE GROVE ACUTELY AFFECTED BY BOTH COPPER AND ZINC
DEFICIENCIES.

No. Boxes Percent ] Percent Percent
Treatment trees per tree 1's and 2's| 3's Culls
SI l___
Check .........-............. 18 0.7 16.0 80.0 4.0
Zinc spray ..............- .- 46 0.8 25.2 67.2 7.7
Zinc and copper spray 10 2.7 66.7 32.4 0.9
Copper spray ................ 6 2.7 62.7 35.8 1.5
Copper soil treatment .. 5 2.0 80.0 20.0 0.0
Copper and zinc on soll 1 7 1.9 65.4 34.6 0.0

All sprays applied 30 days ahead of bloom and fruit picked 15 months later.

Table 2 contains results of a typical experiment in which
the effects of copper and zinc sprays and soil treatments on
production were studied on trees deficient in both elements.
Sprays applied 30 days before bloom not only increased the
production but also raised the grade; soil applications at the
same time were not quite so effective in production increase;
-and zinc applications were useless in correcting copper deficiency,
although they corrected the symptoms of zinc deficiency. In







16 Florida Agricultural Experiment Station

interpreting this table it should be pointed out that plots re-
ceiving zinc spray applications were interspersed between the
other plots so as to give an over-all picture of the entire area,
and that zinc sprays, while raising the percentage of 1's and 2's
slightly, did not significantly raise the total number of boxes
per tree. Wherever copper was applied, however, either on the
soil or on the tree, there was a marked response with the total
production being somewhat higher where copper was used as
a spray than as a soil treatment. Variations between the last
two items, namely, copper sulfate applied alone to the soil and
copper applied with zinc, are not significant. owing to the small
number of trees, but the difference between these two as a
group and the two copper sprays is significant. Throughout
these experiments zinc sprays gave complete control of french-
ing and zinc soil treatments failed to give any noticeable con-
trol; but as in many other groves, copper deficiency was a con-
trolling factor in production. Only by applying copper could
a crop be retained on the trees.

ZINC DEFICIENCY
Zinc deficiency is commonly known as "frenching" (Florida),
"mottle-leaf" (California and many foreign countries), and "folio-
cellosis" (proposed by Fawcett). It is probably the most wide-
spread deficiency of citrus and the best known, although its
cause and control have been worked out only recently. The use
of zinc as a corrective in California developed from experiments
with iron and zinc sulfates on little-leaf of deciduous fruits
(Chandler, Hoagland and Hibbard (21, 22), Johnston (59, 60,
61, 62), Thomason (100, 101), Parker (74, 75, 76, 77, 78, 79,
80, 81, 82)); and in Florida from work with zinc on bronzing
of tung trees (Mowry and Camp (73), Camp (10, 11, 12, 13,
17, 18) and others (57, 58)). Similar results have been re-
ported from South Africa by Matthews (65) and Matthews
and Powell (66, 87), by Strickland (95) in Australia and num-
erous workers in other citrus growing areas (5, 86, 98, 103).
Subsequent to the discovery of the value of zinc in the field
Chapman, Vanselow and Liebig (23) were able to produce the
symptoms by growing citrus trees in zinc-free culture solutions
and to correct the condition by the addition of zinc. At present
zinc sprays are widely used on citrus in both California and
Florida and are generally accepted as an integral part of the
program of citrus tree nutrition.







Some Symptoms of Citrus Malnutrition in Florida 17

Zinc deficiency symptoms have been associated for many years
with copper deficiency symptoms in Florida, as the two com-
monly occur together. Many earlier workers considered them
symptoms of the same condition. At present the work shows
clearly that they are only associated insofar as soil conditions
may produce a deficiency of both at the same time and that
each may occur independently.

FOLIAGE SYMPTOMS
The very striking leaf symptoms are characterized by irreg-
ular green bands along the midrib and main veins _on a back-
ground of light yellow to almost white Plate II)a The relative
amounts of green and yellow tissue vary from a condition of
mild zinc deficiency in which there are only small yellow splotches
between the larger lateral veins to a condition in which only
a basal portion of the midrib is green and the remainder of
the leaf is light yellow to white. In less acute stages the leaves
are almost normal in size while in very acute cases the leaves
are small, pointed, and abnormally narrow, having not over a
tenth of the area of normal leaves (Fig. 4). KThe tendency
4--_


















Fig. 4.-Leaves showing typical zinc deficiency (left) and similar leaves 30 days after
application of a zinc spray (right).

to produce unusual arrow and pointed leaves is one of the
very distinct ynptoms of zinc deficiency. In the immature
leaves the area between the veins is usually light green, but







Florida Agricultural Experiment Station


this rapidly fades to the characteristic green and yellow pattern.
The pattern is developed coincidental with the development of
the leaf and mature green leaves have not been observed to
become mottled.
TWIG SYMPTOMS
In mild cases zinc deficiency symptoms appear on occasional
weak twigs and particularly on shoots produced at other than
the regular flushes
f of growth and the
remainder of the
foliage seems nor-
-- mal. When more
acute, leaves will
be affected over
Fi -the entire periph-
A ery of the tree,
ig nci ., and the twigs will
be very thin and
short with a
S swmarked tendency
to erect, bushy
growth. This type
Sof growth, com-
: bined with the
Sj erect, narrow leaves
with their char-
acteristic pattern,
- '-gives the tree a
very bushy appear-
ance. The twigs
... ..,.. are weak and die
-~ -.. back rapidly so
That there is al-
ways an excess of
Fig. 5.-Pineapple orange tree showing severe zinc defi-
ciency and typical reduction in top due to dying back of dead wood in the
the twist. tree and the tree
is reduced in size by the pruning that is constantly necessary
(Fig. 5). Coincident with the dying back of the outer twigs,
a profuse development of watersprouts occurs on the limbs and
trunk. These watersprouts commonly produce leaves free of
the pattern, or nearly so, and the tree has a dense growth in
the center in contrast to the dying appearance over its periphery.





FLORIDA AGRICULTURAL EXPERIMENT STATION


PLATE III. Symptoms of zinc deficiency on orange leaves and twigs


~iiDc







Some Symptoms of Citrus Malnutrition in Florida


FRUIT SYMPTOMS
Fruit borne on weak twigs is very small, the rind is smooth
and the color, when ripe, unusually light (Fig. 6). The pulp
of such fruits is woody with a very low juice content and the
taste insipid due to reduced acid content. Fruit borne on the
watersprouts is large, coarse and rather woody; in acute cases
it is mostly either very small or very large culls. While the
production of a very large proportion of culls is a common char-
acteristic, production may cease almost entirely when the
deficiency is unusually acute.



















Fig. 6.-Typical fruit on zinc-deficient trees (left) ani fruit from zinc-deficient tree
one year after treatment with zinc spray (right).

MODIFICATIONS OF SYMPTOMS
In the presence of other deficiencies the symptoms described
above will be little changed except that copper deficiency may
cause all the crop to shed. In the case of deficiencies which
inhibit vegetative growth the response expected from zinc treat-
ments will not be experienced and may be largely limited to
the greening up of the yellow foliage with very little growth;
this is particularly noticeable when magnesium as well as zinc
is deficient. Zinc deficiency symptoms are commonly much
more acute on trees suffering from copper deficiency than on
similar trees that have been treated with copper. This is prob-
ably due to root injury associated with copper deficiency which
reduces the ability of the tree"to absorb zinc and other nutri-







Florida Agricultural Experiment Station


ents. A similar condition is occasionally found where mag-
nesium deficiency is acute and probably for the same reason.

VARIETAL SUSCEPTIBILITY
Zinc deficiency symptoms are most common on oranges, less
common on grapefruit and least common on tangerines, although
they may and do occur on all types and varieties. Pineapple
oranges are commonly most severely affected, with Valencias
and other mid-season and late varieties falling practically in
the same category; early orange varieties are less likely to
show the symptoms under comparable conditions but it is more
a matter of degree rather than a difference between presence
and absence of symptoms. As with other deficiencies unfavor-
able rootstock combinations or anything that weakens the root
system of the tree increase both its incidence and severity.

CAUSATION
Zinc deficiency symptoms were commonly associated in Flor-
ida with over-liming (41, 43) and recent work indicates that
when sandy soils are limed sufficiently to raise the pH above
6.0 zinc deficiency occurs (Camp and Reuther, 18, 19), prob-
ably due to fixation of zinc in an unavailable form. The exact
pH at which fixation occurs has not been determined but for
practical diagnostic purposes a pH of 6.0 can be taken as the
dividing point, since in surveys 80 to 90 percent of the groves
growing on sandy soil with a pH higher than 6.0 which had
not been treated with zinc in any form were affected by zinc
deficiency. Zinc deficiency has been found also on soils con-
taining sufficient marl to raise the pH above 6.0.
When sandy soils are allowed to fall below a pH of 5.25 zinc
deficiency symptoms usually will appear, first in a mild form
and later more pronounced. Whether this is caused by leaching
or fixation of zinc has not been determined definitely but the
former is believed to be the primary cause. Under such condi-
tions zinc deficiency is likely to be associated with manganese,
magnesium, and copper deficiencies. Groves on sandy soils main-
tained within a pH range from 5.5 to 6.0 seldom exhibit zinc
deficiency until the trees become relatively old and in such cases
the deficiency may be due to "cropping out". Tung groves and.
Satsuma orange groves planted on old cotton and corn lands
frequently exhibit zinc deficiency due to "cropping out" but
an analogous situation is, not common in the main portions






Some Symptoms of Citrus Malnutrition in Florida


of the citrus belt. It should be pointed out that the above
remarks refer primarily to groves on soils that have remained
in this pH range (5.5-6.0) for many years. Grove soils that
have been allowed to become very acid and then treated to bring
the pH back to the indicated range do not present an analogous
condition.
Numerous theories have been developed as to the role of zinc
in the plant and the soil or plant mechanism involved in the
occurrence of the deficiency. Since little would be gained in
including such a discussion in a publication of this type the
reader is referred to Chandler (20) for a discussion of the vari-
ous theories that have been advanced.

TREATMENT
Zinc sprayaareagenerally recommended for the treatment of
zinc deficSency. These have been much more effective and
cheaper than have soil treatments even though they may entail
an oil spray for scale control under Florida conditions. This
probably is easily explained, first by the fact that zinc deficiency
commonly occurs on soils that have a high fixing power for
zinc so that large amounts of a relatively expensive material
would be required for correction, and second because the root
system is usually seriously impaired by the deficiency and does
not readily absorb zinc. Applications to the soil have given
very satisfactory results with both citrus and tung trees when
the soil was within a favorable range of pH (5.5 to 6.0) and
the deficiency due in all probability to "cropping out", but such
conditions are rare in commercial citrus in Florida and the de-
ficiency is due primarily to adverse soil conditions. It is prob-"
able, however, that further research work will make it possible
to control the sandy soils in such way as to eliminate the neces-
sity for spray applications.
The sprays used in Florida generally contain zinc sulfate
neutralized with hydrated lime or liquid lime-sulfur. For the
initial correction zinc sulfate is used at the rate of 3 to 5 pounds
per 100 gallons with one-half as much hydrated lime, and for
maintenance at the rate of 1 to 3 pounds per 100 gallons, also
with hydrated lime as above. This spray is commonly combined
with copper or sulfur sprays for pest control. The same type
of spray is used in California, as is also zinc oxide which has
been found to be somewhat hazardous in Florida if applied
on young foliage or fruit. Metallic zinc dust combined with







Florida Agricultural Experiment Station


other dusting materials also is recommended for some condi-
tions in California. ,
Responses to sprays are very rapid and affected leaves turn
green within a maximum of 30 days after the spray is applied
except during the winter months. Leaves on the tree when the
spray is applied will not grow appreciably in size although they
will become green (Fig. 4), but the new foliage will be normal
in size and character if not affected by some other deficiency.
Trees completely out of production for three years due to zinc
deficiency were sprayed in early May and set some June bloom
and almost a full crop the following season, and severely affected
trees that had not died back more than 15 to 20 percent were
returned to production during the current year when sprayed
30 days prior to the spring bloom (Fig. 6).

MANGANESE DEFICIENCY
Manganese deficiency in citrus does not have a definite com-
mon name, although the terms "marl frenching" and "marl
chlorosis" have been applied to the leaf symptoms frequently
exhibited by trees grown on marl soils. These generally are
a mixture of zinc and manganese deficiency symptoms and are
not readily correctible unless both elements are applied. The
terms have, however, been connected with manganese deficiency
in the minds of many growers. First responses to the use of
manganese on citrus in Florida were reported by Skinner and
Bahrt (93), and Skinner, Bahrt and Hughes (94). CThe re-
sponses found were improved growth, the correction oT foliage
chlorosis, increased production, and better fruit colqr and Roy
(89) has reported a greatly increased manganese content in
leaves from trees treated with manganese. Specific symptoms
that could be used diagnostically were identified with the defi-
ciency by Camp and Reuther (19), who described a character-
istic leaf pattern. This symptom was described in more detail
by Camp (13) and by Camp and Peech (16). Skinner, Bahrt
and Hughes (94) had reported responses from manganese appli-
cations on acid as well as on alkaline soils and the leaf symp-
toms associated with the deficiency were found to be widespread
on the light acid sandy soils throughout the citrus growing area.
Failure to identify the symptoms associated with this deficiency
earlier was probably due to the fact that it is commonly asso-
ciated with zinc deficiency and its much more pronounced leaf
symptoms which readily mask the pattern of manganese defi-







16 Florida Agricultural Experiment Station

interpreting this table it should be pointed out that plots re-
ceiving zinc spray applications were interspersed between the
other plots so as to give an over-all picture of the entire area,
and that zinc sprays, while raising the percentage of 1's and 2's
slightly, did not significantly raise the total number of boxes
per tree. Wherever copper was applied, however, either on the
soil or on the tree, there was a marked response with the total
production being somewhat higher where copper was used as
a spray than as a soil treatment. Variations between the last
two items, namely, copper sulfate applied alone to the soil and
copper applied with zinc, are not significant. owing to the small
number of trees, but the difference between these two as a
group and the two copper sprays is significant. Throughout
these experiments zinc sprays gave complete control of french-
ing and zinc soil treatments failed to give any noticeable con-
trol; but as in many other groves, copper deficiency was a con-
trolling factor in production. Only by applying copper could
a crop be retained on the trees.

ZINC DEFICIENCY
Zinc deficiency is commonly known as "frenching" (Florida),
"mottle-leaf" (California and many foreign countries), and "folio-
cellosis" (proposed by Fawcett). It is probably the most wide-
spread deficiency of citrus and the best known, although its
cause and control have been worked out only recently. The use
of zinc as a corrective in California developed from experiments
with iron and zinc sulfates on little-leaf of deciduous fruits
(Chandler, Hoagland and Hibbard (21, 22), Johnston (59, 60,
61, 62), Thomason (100, 101), Parker (74, 75, 76, 77, 78, 79,
80, 81, 82)); and in Florida from work with zinc on bronzing
of tung trees (Mowry and Camp (73), Camp (10, 11, 12, 13,
17, 18) and others (57, 58)). Similar results have been re-
ported from South Africa by Matthews (65) and Matthews
and Powell (66, 87), by Strickland (95) in Australia and num-
erous workers in other citrus growing areas (5, 86, 98, 103).
Subsequent to the discovery of the value of zinc in the field
Chapman, Vanselow and Liebig (23) were able to produce the
symptoms by growing citrus trees in zinc-free culture solutions
and to correct the condition by the addition of zinc. At present
zinc sprays are widely used on citrus in both California and
Florida and are generally accepted as an integral part of the
program of citrus tree nutrition.







Some Symptoms of Citrus Malnutrition in Florida


ciency. As soon as zinc became widely used there was little
difficulty in finding the symptoms of manganese deficiency in
many groves following the correction of zinc deficiency.
The symptoms described in this section apparently are not
exactly the same as those described by Haas (54) in reports
on solution and sand culture work. This is quite probably due
to the fact that manganese deficiency in the field in Florida is
not so acute as that produced by him under controlled condi-
tions and the symptoms are correspondingly modified. The
pattern of fine green veins on a lighter green background as
reported by Haas is found in young leaves but changes rapidly
to the pattern shown in Plate IV. The premature shedding
of young leaves has not been noted but might exist in very
acute cases.
Manganese deficiency of citrus in the field has so far been
reported only from Florida. Since its definite identification
followed only after extensive use of zinc it is entirely possible
that it will be found in other areas where zinc deficiency is
common.
FOLIAGE SYMPTOMS
,Young leaves commonly show a fine pattern of green veins
on a lighter green background.' This pattern is somewhat
similar to that on leaves of the same age affected by zinc defi-
ciency but much less pronounced and definite. KBy the time the
leaves have reached full size the pattern has become somewhat
more distinct as a band of green along the midrib and principal
lateral veins with light green areas between the veins and, in
severe cases, along the edge of the leaf. The yellow to white
areas so typical of zinc deficiency do not develop and the con-
trast is so slight between the two shades of green-as to make
identification difficult in many instances. As the leaves mature
the pattern may disappear if manganese is only slightly deficient
and mature leaves may be entirely green. This presumably
occurs under the conditions of a border-line deficiency in which
the level of manganese supply-is too low to meet the heavy
requirements of vigorous growth but is still sufficiently high
to more than meet the requirements when the tree is not grow-
ing vigorously. When the deficiency is more acute the pattern
will persist throughout the life of the leaf. ~As the leaf matures
its surface becomes dull in marked contrast to the normal shiny
surface of citrus leaves (The light green areas become grayish
and the dark green areas remain a dull, dark green) In some







Florida Agricultural Experiment Station


cases the light green areas may become somewhat bronzed and
for this reason this deficiency is occasionally classified as bronz-
ing, although the term is commonly limited to the symptoms
of magnesium deficiency.
he shape and size of the leaves is normal and the narrow
pointed leaves characteristic of zinc deficiency are not asso-
ciated with manganese deficiency. This is of considerable aid
in diagnosing the symptoms on young leaves when the patterns
might be confused.
TWIG SYMPTOMS
Manganese deficiency is seldom so acute in the field as to cause
pronounced twig symptoms. However, in cases of acute man-
ganese deficiency the growth is reduced nd twigs die, giving
the tree a weak and sparse appearance. The pronounced dying
back on the periphery of the tree is not as apparent as in i
deficiency but is distributed through the entire tree. Such trees
respond )ith vigorous growth when subjected to corrective
treatment
FRUIT SYMPTOMS
Manganese deficiency may greatly reduce the crop; and the
color of the fruit, in the case of oranges and tangerines, may be
poor. Roy (89) has reported an increase in sugar in the juice
when manganese was added to the fertilizer. Skinner and Bahrt
(93) and Skinner, Bahrt and Hughes (94) reported that the
fruit was heavier and firmer following manganese treatment,
and contained an increased amount of manganese. It is prob-
able that as this deficiency is studied further some more distinct
fruit symptoms will be established.

MODIFICATIONS OF SYMPTOMS
Since the deficiency of manganese is frequently associated
with zinc deficiency, combinations of the leaf symptoms of the
two deficiencies are common. "Marl frenching" of grapefruit
characterized by dark green veins with dull whitish green areas
between the veins and with the whole leaf finally taking on a
dull whitish gray cast is typical of this combination (Fig. 7).
On Temple orange foliage the same combination shows a bronze
cast in the lighter portions of the pattern. When such trees
are treated with zinc spray the resulting flush of growth is
typical of manganese deficiency and the whitish cast has dis-







FLORIDA AGRICULTURAL EXPERIMENT STATION
1---<81--- --------------------------------------------------- __


PLATE IV. Symptoms of manganese deficiency on young orange leaves







Some Symptoms of Citrus Malnutrition in Florida


appeared. In such combinations the manganese deficiency is
acute and the zinc deficiency relatively mild, but when the re-
verse occurs the foliage shows the typical symptoms of zinc
deficiency which completely mask the symptoms of manganese
deficiency.


Fig. 7.-Marl chlorosis on grapefruit. This pattern is a combination of the patterns
of zinc and manganese deficiencies, but is primarily the latter.

VARIETAL SUSCEPTIBILITY
Varieties of the mandarin group (tangerines, King oranges,
etc.) are most commonly affected, with grapefruit next, and
finally oranges, although there is little difference between the
latter two. Temple oranges seem to be most commonly and
most severely affected but untreated tangerine groves on light
soils that do not show some symptoms are the exception.







Florida Agricultural Experiment Station


CAUSATION
Manganese deficiency of citrus in Florida was originally asso-
ciated with marl soils which were definitely alkaline. This is
in line with the findings that manganese is fixed in alkaline
soils. Such soils when used for citrus in Florida are usually
ridged to provide proper drainage and the ridge is made up of
a mixture of acid top soil and marl subsoil. The pH varies from
about pH 6.0 when little or no marl is mixed in the ridge to
8.0 if a large amount of marl is included. The pH at which
manganese is fixed has not been accurately determined but ap-
parently it is above the neutral point (pH 7.0). The fixing
power for manganese Ti-such soils is high and Camp and Peech
(16) have shown tha following applications at the rate of ap-
proximately 1,000 pounds of manganese sulfate per acre, less
than one pound per acre of nanganese remained in the exchange-
able form after one year.)
On the acid sands (be ow pH 5.0) the deficiency is probably
brought on by the leaching of manganese. Such soils are con-
sistently very low in exchangeable manganese, usually contain-
ing less than five pounds per acre (16, 83, 84) and both the
low pH and the consequent manganese deficiency can be blamed
on improper fertilizer practices. Manganese deficiency can occur
also on sandy soils when the pH is raised above pH 7.0 by over-
liming, although this is not common.

TREATMENT
Manganese sulfate is used either on the soil or combined with
lime in a spray. Applications to marl soils must be relatively
large, two to 10 pounds per tree of manganous sulfate, and must
be repeated yearly to keep the grove in condition since man-
ganese is rapidly fixed. If applications are to be made to light
sandy soils, one to four pounds per tree is commonly used as an
initial corrective- treatment followed by much smaller amounts
in the fertilizer for maintenance. )It is usually recommended
that acid soils be treated with basic material to bring the pH
up to 6.0, since manganese is leached rapidly from the very
acid sands.
Sprays are much more rapid in correcting the symptoms than
soil treatments, and on marl soils a somewhat more lasting
effect is obtained from a spray than from a moderate soil treat-
ment. Were it not for the fact that the residues from such
sprays cause a build-up of scale (102) manganese sprays would







Some Symptoms of Citrus Malnutrition in Florida 27

be more extensively used. &t present sprays made up of 2 to
4 pounds of manganese sulfate per 100 gallons with half as much
hydrated lime are commonly used as initial correctives and,
when copper sprays are needed for pest control, manganese
sprays are frequently used for maintenance on soils that have
a high fixing power Copper residues are almost certain to make
a subsequent oil spiay necessary and the addition of the man-
ganese does not materially complicate the problem. Manganese
sprays are combined with copper and/or zinc sprays and with
lime-sulfur sprays, and manganous sulfate is sometimes neu-
tralized with liquid lime-sulfur instead of lime in an effort to
reduce the residue.

MAGNESIUM DEFICIENCY
Magnesium deficiency is commonly referred to in Florida as
"bronzing" or "copper leaf", the latter term being largely obsolete
now. These terms are not specific and the term bronzing fre-
quently has been used generically to designate any yellowing or
bronzing of citrus leaves regardless of cause and then sub-
dividing it into various specific types (3, 4). Probably the first
definite report on the value of magnesium in citrus fertilization
was by Averna-Sacca in 1912 (1). Reed and Haas (8) work-
ing with sand cultures described symptoms of magnesium de-
ficiency on citrus in 1924 and Bahrt (2), Bahrt and Hughes (4),
Bryan and DeBusk (8) and Tait (97) reported responses to
the applications of magnesium-bearing materials to citrus trees
in the field and described symptoms associated with the defici-
ency of magnesium. Camp (13) and Fudge (47, 48) described
the leaf symptoms associated with the deficiency in detail and
the latter demonstrated the motivating role of fruit production
in producing the symptoms. The occurrence of magnesium de-
ficiency in Florida is not surprising since magnesium has been
found generally deficient in the Atlantic coastal plain soils and
particularly in the light sands such as are commonly used for
citrus in Florida.
FOLIAGE SYMPTOMS
No symptoms of magnesium deficiency associated with young
leaves have been identified in the field and the symptoms de-
scribed below are those produced on mature leaves following
the removal of magnesium to satisfy fruit requirements. Dur-
ing the summer, when a rapid increase in fruit size occurs, the







Florida Agricultural Experiment Station


other dusting materials also is recommended for some condi-
tions in California. ,
Responses to sprays are very rapid and affected leaves turn
green within a maximum of 30 days after the spray is applied
except during the winter months. Leaves on the tree when the
spray is applied will not grow appreciably in size although they
will become green (Fig. 4), but the new foliage will be normal
in size and character if not affected by some other deficiency.
Trees completely out of production for three years due to zinc
deficiency were sprayed in early May and set some June bloom
and almost a full crop the following season, and severely affected
trees that had not died back more than 15 to 20 percent were
returned to production during the current year when sprayed
30 days prior to the spring bloom (Fig. 6).

MANGANESE DEFICIENCY
Manganese deficiency in citrus does not have a definite com-
mon name, although the terms "marl frenching" and "marl
chlorosis" have been applied to the leaf symptoms frequently
exhibited by trees grown on marl soils. These generally are
a mixture of zinc and manganese deficiency symptoms and are
not readily correctible unless both elements are applied. The
terms have, however, been connected with manganese deficiency
in the minds of many growers. First responses to the use of
manganese on citrus in Florida were reported by Skinner and
Bahrt (93), and Skinner, Bahrt and Hughes (94). CThe re-
sponses found were improved growth, the correction oT foliage
chlorosis, increased production, and better fruit colqr and Roy
(89) has reported a greatly increased manganese content in
leaves from trees treated with manganese. Specific symptoms
that could be used diagnostically were identified with the defi-
ciency by Camp and Reuther (19), who described a character-
istic leaf pattern. This symptom was described in more detail
by Camp (13) and by Camp and Peech (16). Skinner, Bahrt
and Hughes (94) had reported responses from manganese appli-
cations on acid as well as on alkaline soils and the leaf symp-
toms associated with the deficiency were found to be widespread
on the light acid sandy soils throughout the citrus growing area.
Failure to identify the symptoms associated with this deficiency
earlier was probably due to the fact that it is commonly asso-
ciated with zinc deficiency and its much more pronounced leaf
symptoms which readily mask the pattern of manganese defi-







Florida Agricultural Experiment Station


symptoms appear on leaves close to the developing fruit as dis-
connected yellow areas lying along either side of the midrib.
These areas gradually become larger and finally coalesce to
form a large area of yellow tissue surrounding a triangular area
of green tissue at the base of the leaf (Plate V). At this stage
the tip as well as the base of the leaf may be green. The yellow
area may gradually enlarge until the entire leaf becomes yellow
or bronze in color. By October or November, when the fruit
is about mature, leaves in the vicinity of the fruit, and particu-
larly those close to fruit clusters, will present all variations of
the above stages of yellowing while leaves on the portion of the
tree not bearing a crop will be normally green in color. The
appearance in the grove is also irregular, with the amount of


.r4.

t. -*9iaso,


Fig. 8.-De:oliation of magnesium-deficient seedy grapefruit tree induced by a heavy crop.







FLORIDA AGRICULTURAL EXPERIMENT STATION


PLATE V. Symptoms of magnesium deficiency on grapefruit leaves


r '~
.i~-
-.d'-'
re, i







Some Symptoms of Citrus Malnutrition in Florida


yellow foliage on individual trees varying with the size of the
crop.
Leaves that have lost most of their green color drop freely,
frequently leaving heavily laden branches practically defoliated
(Fig. 8). This dropping occurs rather soon in oranges and
heavily cropped orange trees are frequently badly defoliated
by December. Dropping of leaves in grapefruit is slower and
many of the yellow leaves are retained until spring and shed
just prior to spring growth. This droppage is increased by
natural hazards that shock the tree and heavy dropping will
follow cold weather, injurious sprays, or extremely dry periods.

TWIG SYMPTOMS
There are no primary twig symptoms associated as yet with
magnesium deficiency but a secondary effect following defolia-
tion is the death of many twigs due to infection by fungi.
Fruits frequently are seen hanging on completely defoliated
twigs six to 18 inches long and such twigs are naturally weak-
ened and susceptible to infection. Infection may take place
and the twig die before the fruit is picked, allowing the fruit
to drop, or infection may set in following fruit removal. In either
case the twig usually dies back to the point where growth was
initiated and gum is frequently formed at the junction of dead
and live wood, although this is probably indicative of infection.
Not all defoliated twigs die but considerable pruning is always
necessary for the removal of dead wood following crop removal
from magnesium-deficient trees. The potential bearing surface
of the tree is greatly reduced and in severe cases the tree may
actually decrease in size.
FRUIT SYMPTOMS
No striking fruit symptoms are associated with magnesium
deficiency but there is a general decline in production and a
reduction in the average size of individual fruits. This reduc-
tion is the normal result of severe defoliation. Quality of the
fruit is lowered and droppage greatly increased. Considerable
sunburn and wind scarring result from the defoliation and the
presence of many dead twigs.

MODIFICATIONS OF SYMPTOMS
Since magnesium deficiency is associated primarily with fruit
production the principal modification that must be taken into
consideration is the failure of typical symptoms to develop







Florida Agricultural Experiment Station


when there is no crop produced. This may lead to the con-
clusion that the deficiency has disappeared when it is only the
symptoms which are associated with production that have dis-
appeared. Seedy varieties of grapefruit under conditions of
acute magnesium deficiency frequently bear only every other
year and during the alternate years appear to be devoid of
magnesium deficiency. Other factors also may cause loss of
crop and the consequent disappearance of symptoms. Copper
deficiency which is frequently associated with magnesium de-
ficiency on acid sandy soils is a common cause of such crop
loss, and zinc deficiency may produce similar results. Under
such conditions application of the element that is temporarily
limiting production is likely to cause the setting of a heavy
crop and subsequent development of acute magnesium deficiency
symptoms as the crop matures.

VARIETAL SUSCEPTIBILITY
Magnesium deficiency is associated closely with seediness
(47, 48) and varietal differences are usually a reflection of the
seed content of the fruit. Seedy grapefruit varieties are com-
monly and conspicuously affected, due both to their seediness
and to their tendency to cluster production which puts exces-
sive strain on individual branches with the result that portions
of the tree may show a preponderance of yellow leaves while
the remainder of the foliage is green. Pineapple and other
seedy varieties of oranges are acutely affected, whereas Hamlins
and other seedless or nearly seedless varieties are less affected.
Varieties, such as Valencia, which retain their fruit for long
periods are affected somewhat more than their seediness would
seem to justify, probably due to the prolonged drain on the tree.

CAUSATION
The two primary causes of the extensive development of mag-
nesium deficiency are the large magnesium requirement of citrus
and the failure to apply magnesium when fertilizing soils low
in this element. This situation is aggravated by allowing sandy
soils low in magnesium to become too acid, with the resultant
loss of magnesium by leaching. In practice magnesium defici-
ency of citrus is commonly associated with sandy soils having
a pH of less than 5.0. Under such conditions the level of ex-
changeable magnesium will commonly be below 15 pounds per
acre (83, 84) if no magnesium-bearing materials have been ap-







Some Symptoms of Citrus Malnutrition in Florida 31

plied. There is no evidence that magnesium is being fixed to
any extent in an unavailable form in Florida citrus soils. In
fact, the soils highest in exchangeable magnesium are the marl
bearing soils and on these magnesium deficiency symptoms are
rarely seen.
TREATMENT
Dolomitic limestone and magnesium sulfate are commonly
used to correct magnesium deficiency. The former is used on
acid soils both to furnish magnesium and to raise the pH, while
the latter is commonly used on soils above pH 6.0 and also as
a supplement to dolomitic limestone on acid soils. Since the
release of available magnesium from dolomitic limestone is pri-
marily dependent on the reaction between acids in the soil and
carbonates in the limestone, initial correction of magnesium
deficiency on dry sandy soils is likely to be slow when this
material alone is used. Usually it is the second year before
results are apparent. Under such conditions water-soluble mag-
nesium in the form of magnesium sulfate usually is applied
with the dolomitic limestone to furnish immediately available
magnesium. Magnesium sulfate is used also to supplement
dolomitic limestone particularly when the trees are carrying
an unusually heavy crop. High calcium limestone is used to
some extent to correct the soil reaction and is supplemented
with magnesium sulfate. Calcium limestone alone will not cor-
rect magnesium deficiency and may make it more acute by
widening the ratio between calcium and magnesium in the soil.
When calcium limestone is used in conjunction with magnesium
sulfate/the latter corrects the magnesium deficiency while the
former raises the pH so that more of the magnesium will be
retained in the exchangeable form. Calcium limestone is not
extensively used since an over-supply of it will raise the pH
too high and bring on zinc and manganese deficiencies, whereas
dolomitic limestone is much safer in this regard. In addition
to the factor of safety, dolomitic limestone is much more suit-
able for mixing with fertilizer materials since it will not cause
a loss of ammonia from the mixture.

NITROGEN DEFICIENCY
Identification of nitrogen deficiency symptoms is somewhat
involved because a peculiar type of leaf pattern, in which the
tissue along the midrib and the larger veins is distinctly lighter







Some Symptoms of Citrus Malnutrition in Florida 27

be more extensively used. &t present sprays made up of 2 to
4 pounds of manganese sulfate per 100 gallons with half as much
hydrated lime are commonly used as initial correctives and,
when copper sprays are needed for pest control, manganese
sprays are frequently used for maintenance on soils that have
a high fixing power Copper residues are almost certain to make
a subsequent oil spiay necessary and the addition of the man-
ganese does not materially complicate the problem. Manganese
sprays are combined with copper and/or zinc sprays and with
lime-sulfur sprays, and manganous sulfate is sometimes neu-
tralized with liquid lime-sulfur instead of lime in an effort to
reduce the residue.

MAGNESIUM DEFICIENCY
Magnesium deficiency is commonly referred to in Florida as
"bronzing" or "copper leaf", the latter term being largely obsolete
now. These terms are not specific and the term bronzing fre-
quently has been used generically to designate any yellowing or
bronzing of citrus leaves regardless of cause and then sub-
dividing it into various specific types (3, 4). Probably the first
definite report on the value of magnesium in citrus fertilization
was by Averna-Sacca in 1912 (1). Reed and Haas (8) work-
ing with sand cultures described symptoms of magnesium de-
ficiency on citrus in 1924 and Bahrt (2), Bahrt and Hughes (4),
Bryan and DeBusk (8) and Tait (97) reported responses to
the applications of magnesium-bearing materials to citrus trees
in the field and described symptoms associated with the defici-
ency of magnesium. Camp (13) and Fudge (47, 48) described
the leaf symptoms associated with the deficiency in detail and
the latter demonstrated the motivating role of fruit production
in producing the symptoms. The occurrence of magnesium de-
ficiency in Florida is not surprising since magnesium has been
found generally deficient in the Atlantic coastal plain soils and
particularly in the light sands such as are commonly used for
citrus in Florida.
FOLIAGE SYMPTOMS
No symptoms of magnesium deficiency associated with young
leaves have been identified in the field and the symptoms de-
scribed below are those produced on mature leaves following
the removal of magnesium to satisfy fruit requirements. Dur-
ing the summer, when a rapid increase in fruit size occurs, the







Florida Agricultural Experiment Station


in color than the remainder of the leaf, has been classified by
Haas (Fawcett, (28)) as a symptom of nitrogen deficiency and
by Bahrt and Hughes (4) as a symptom of magnesium defi-
ciency, although it is not entirely clear as to whether they were
describing identical conditions, or those described here. Their
descriptions, however, would fit fairly well the pattern here
referred to, although it is associated primarily with girdling of
the twig, limb, or tree in such way as to destroy the food-
conducting tissues without destroying the water-conducting
tissues. When such girdling occurs the leaves become yellow
along the midrib and larger veins while the remainder of the
leaves usually remain a dark dull green color for a time and
then fade slowly to yellow (Fig. 9). Tissue along the midrib
and veins may become extremely light in color, giving rise to
the terms "inverted frenching" and "vein chlorosis". The bleach-
ing is probably caused by the cutting off of normal channels
of food supply without at the same time cutting off entirely the
supply of water. It can hardly be considered a deficiency of
any particular element, particularly since the affected portion
of the tree can be healed only by supplying the missing conduct-
ing tissue, as by inarching. This pattern can be produced
artificially by girdling a twig or branch but is associated in
the field with footrot and gum diseases due to Diplodia and
Phomopsis which destroy the bark or roots, and lightning in-
jury which has girdled the tree.
While leaves affected as above described are likely to have
an abnormal chemical composition and to show deficiencies of
a number of elements, this pattern can hardly be considered a
deficiency in the sense in which this term is used in this bul-
letin. Applications of specific elements are not indicated for
the correction of this pattern but rather the supplying of a
new conducting tissue where this is easily possible. A very
similar pattern to the foregoing appears on older leaves in some
groves following a heavy flush of new growth. The leaves be-
come more deeply colored, however, and then shed. This is
quite probably the leaf symptom described by Bahrt and Hughes
(4) as a form of bronzing.
Deficiency symptoms which respond to applications of nitro-
gen are almost too well known in Florida to merit description
but since they may be confused in some instances, attention is
being called to some of the outstanding characteristics involved.






Some Symptoms of Citrus Malnutrition in Florida


Nitrogen deficiency symptoms fall into two categories, i. e.,
symptoms of trees that are continuously starved for nitrogen
and symptoms brought on by a sharp decline in nitrogen supply.
The second type of nitrogen deficiency is not extremely common
in Florida but does occur occasionally in an acute form when
the nitrogen supply falls during the period of maximum fruit
development. The following descriptions apply strictly to what
may be accurately termed nitrogen deficiency symptoms.


Fig. 9-So-called vein chlorosis which occurs as an after-effect of girdling.


***ft







Florida Agricultural Experiment Station


FOLIAGE SYMPTOMS
Where nitrogen is deficient when growth appears the young
leaves are light yellowish green in color; the veins frequently
are very slightly, but not markedly, lighter in color than the
tissues between. The young leaves are undersized, thin, and
fragile and develop into very light green leaves which may
ultimately become yellow if any fruit is produced. Shedding
of leaves is heavy on such trees and consequently the foliage
is sparse. This type of pattern is common in unfertilized trees.
The second type of pattern may develop when the trees have
sufficient nitrogen during the spring and put on a heavy normal
growth and then become acutely deficient in nitrogen during
the summer and fall when the fruit is maturing and there is
a heavy drain on the tree. Under such conditions the green
leaves slowly bleach to a mottled irregular green and yellow
pattern and ultimately become entirely yellow and shed. In its
final stages this pattern slightly resembles the symptoms of
magnesium deficiency because both are associated with fruit
production. This condition has been observed frequently in
ridged groves that are not sufficiently fertilized in summer to
take care of the crop of fruit. Trees growing on ridged soils
are limited in root space and this is further accentuated by the
waterlogging of part of the ridge during the rainy season.
TWIG SYMPTOMS
While no specific twig or growth symptoms have been identi-
fied, trees that are constantly short of nitrogen are stunted and
irregular in shape and the growth is very short and irregular
on the tree. Such trees seldom die but remain in a permanently
stunted condition until nitrogen is supplied in adequate amounts.
FRUIT SYMPTOMS
Trees deficient in nitrogen frequently produce a good quality
of fruit as far as texture and flavor are concerned but the crop
is very small.
MODIFICATIONS OF SYMPTOMS
While modifications of nitrogen deficiency are not particularly
important, the ability to distinguish between true nitrogen de-
ficiency and the deficiency of other elements is important. As
mentioned under magnesium, the symptoms of the latter defi-
ciency were commonly ascribed to nitrogen deficiency until the
importance of magnesium was established. It must always be







Some Symptoms of Citrus Malnutrition in Florida


remembered that yellow leaves are not necessarily, or in fact
commonly in Florida, an indication of nitrogen deficiency.

CAUSATION
While the causal factor of the first type of nitrogen deficiency
is simply a lack of application, there is some evidence that the
second may be produced either by a failure to time properly the
summer application or to judge accurately the amount of nitro-
gen necessary to mature the crop. There is some indication
that improper nitrification due to waterlogging of the soil
during the summer rainy season may result in a temporary
deficiency of nitrogen which is relieved by dry weather.

TREATMENT
In ordinary cases of nitrogen deficiency the obvious treatment
is to supply nitrogen in the required amounts. In the case of
acute nitrogen deficiency due to fruit production some considera-
tion should be given to the form of nitrogen. The use of nitrates
usually would be indicated, due to their immediate availability.
The subject of nitrogen fertilization is too complex, however,
for discussion in the scope of this bulletin.

IRON DEFICIENCY
The symptoms of iron deficiency have been known generally
as iron chlorosis and the acute stage has been referred to as
decline in some areas. While it has been of-very minor import-)
ance in Florida, it has been a considerable problem in both
Arizona and California. Due to the fact that iron deficiency
has been readily developed in water cultures, the symptoms of
the deficiency in the field were early recognized. In California,
Lipman and Gordon (64), and Thomas and Haas (99) studied
the problem of correcting the deficiency; and recently Moore
(69) has reported on new experiments for its control. Finch,
Albert, and Kinnison (29, 30) reported experimental treatments
of iron deficiency in Arizona on both citrus and Eucalyptus.
There have been no published reports on control in Florida, but
Bahrt has recently reported improvement following soil appli-
cations of ferrous sulfate. No general recommendations have
been made as yet for correction under Florida conditions. This
deficiency is relatively common wherever calcareous soils are
used for citrus, and so far it has been less effectively controlled
than most other deficiencies.







Some Symptoms of Citrus Malnutrition in Florida 31

plied. There is no evidence that magnesium is being fixed to
any extent in an unavailable form in Florida citrus soils. In
fact, the soils highest in exchangeable magnesium are the marl
bearing soils and on these magnesium deficiency symptoms are
rarely seen.
TREATMENT
Dolomitic limestone and magnesium sulfate are commonly
used to correct magnesium deficiency. The former is used on
acid soils both to furnish magnesium and to raise the pH, while
the latter is commonly used on soils above pH 6.0 and also as
a supplement to dolomitic limestone on acid soils. Since the
release of available magnesium from dolomitic limestone is pri-
marily dependent on the reaction between acids in the soil and
carbonates in the limestone, initial correction of magnesium
deficiency on dry sandy soils is likely to be slow when this
material alone is used. Usually it is the second year before
results are apparent. Under such conditions water-soluble mag-
nesium in the form of magnesium sulfate usually is applied
with the dolomitic limestone to furnish immediately available
magnesium. Magnesium sulfate is used also to supplement
dolomitic limestone particularly when the trees are carrying
an unusually heavy crop. High calcium limestone is used to
some extent to correct the soil reaction and is supplemented
with magnesium sulfate. Calcium limestone alone will not cor-
rect magnesium deficiency and may make it more acute by
widening the ratio between calcium and magnesium in the soil.
When calcium limestone is used in conjunction with magnesium
sulfate/the latter corrects the magnesium deficiency while the
former raises the pH so that more of the magnesium will be
retained in the exchangeable form. Calcium limestone is not
extensively used since an over-supply of it will raise the pH
too high and bring on zinc and manganese deficiencies, whereas
dolomitic limestone is much safer in this regard. In addition
to the factor of safety, dolomitic limestone is much more suit-
able for mixing with fertilizer materials since it will not cause
a loss of ammonia from the mixture.

NITROGEN DEFICIENCY
Identification of nitrogen deficiency symptoms is somewhat
involved because a peculiar type of leaf pattern, in which the
tissue along the midrib and the larger veins is distinctly lighter







Florida Agricultural Experiment Station


FOLIAGE SYMPTOMS
The young leaves are very light in color and sometimes almost
white, but with the veins greener than the remainder of the
leaf (Plate VI). Even the small veins are green so that a fine
network of green veins is present on a very light green back-
ground. In acute cases the leaves are tinged with a yellowish
to bronze color which is quite characteristic in oranges. The
leaves are very thin and fragile and shed early. In acute cases
grapefruit leaves may be reduced in size with a pronounced
yellow tinge when young and dark brown markings when older.

TWIG SYMPTOMS
The trees die back severely on the periphery and especially
in the top, so that some trees may have a dead top with the
lower limbs carrying almost normal foliage. Eventually the
trees may be greatly reduced in size and pass out of production.
No particular or peculiar symptoms on the twigs that would
be distinctive have been reported.
FRUIT SYMPTOMS
No definite fruit symptoms have been associated with iron
deficiency beyond the fact that the tree will cease to mature
fruit in acute cases.
VARIETAL SUSCEPTIBILITY
All common varieties of citrus are affected but thin leaves
with very fine dark green venation are more typical of oranges
than grapefruit. In grapefruit there is a tendency to produce
small slightly narrowed leaves that are very light green with
the characteristic venation when the leaves are immature. As
the leaves mature the pattern fades and dark brown markings
appear as raised areas on their surfaces.

CAUSATION
Iron deficiency is attributed mainly to alkalinity of the soil
due to excess carbonates. In Florida it occurs commonly on
alkaline coastal soils that are closely underlaid by lime rock.
In many groves observed there is very little soil above the rock
and the soil consequently dries out excessively during dry
weather. This is probably a contributing factor, since citrus
is grown without observed iron deficiency on marl soils as high
in pH as those in which iron deficiency occurs. The marl soils






FLORIDA AGRICULTURAL EXPERIMENT STATION


PLATE VI. Symptoms of iron deficiency on young orange leaves







Some Symptoms of Citrus Malnutrition in Florida


are much deeper and have a much better regulated moisture
supply. On acid sands similar but less pronounced symptoms
have been noted. Occasional response to iron applications to
the soil in affected groves has been reported and it is probable
that an iron deficiency exists on some such soils, although it
has not been thoroughly worked out as yet.

TREATMENT
Iron sprays and soil applications so far have not offered prac-
tical control of iron deficiency of citrus on alkaline soils. Injec-
tions of iron salts into the trunks of trees have been used to
some extent in both Arizona and California. In making such
applications holes are bored into the trunk or limbs of the tree,
filled with a soluble iron salt such as iron citrate or iron tar-
trate, and then plugged and sealed. Reports on the results


Fig. 10.-Leaves from tree deficient in iron, showing green spots resulting from
the application of an iron spray.







Some Symptoms of Citrus Malnutrition in Florida


remembered that yellow leaves are not necessarily, or in fact
commonly in Florida, an indication of nitrogen deficiency.

CAUSATION
While the causal factor of the first type of nitrogen deficiency
is simply a lack of application, there is some evidence that the
second may be produced either by a failure to time properly the
summer application or to judge accurately the amount of nitro-
gen necessary to mature the crop. There is some indication
that improper nitrification due to waterlogging of the soil
during the summer rainy season may result in a temporary
deficiency of nitrogen which is relieved by dry weather.

TREATMENT
In ordinary cases of nitrogen deficiency the obvious treatment
is to supply nitrogen in the required amounts. In the case of
acute nitrogen deficiency due to fruit production some considera-
tion should be given to the form of nitrogen. The use of nitrates
usually would be indicated, due to their immediate availability.
The subject of nitrogen fertilization is too complex, however,
for discussion in the scope of this bulletin.

IRON DEFICIENCY
The symptoms of iron deficiency have been known generally
as iron chlorosis and the acute stage has been referred to as
decline in some areas. While it has been of-very minor import-)
ance in Florida, it has been a considerable problem in both
Arizona and California. Due to the fact that iron deficiency
has been readily developed in water cultures, the symptoms of
the deficiency in the field were early recognized. In California,
Lipman and Gordon (64), and Thomas and Haas (99) studied
the problem of correcting the deficiency; and recently Moore
(69) has reported on new experiments for its control. Finch,
Albert, and Kinnison (29, 30) reported experimental treatments
of iron deficiency in Arizona on both citrus and Eucalyptus.
There have been no published reports on control in Florida, but
Bahrt has recently reported improvement following soil appli-
cations of ferrous sulfate. No general recommendations have
been made as yet for correction under Florida conditions. This
deficiency is relatively common wherever calcareous soils are
used for citrus, and so far it has been less effectively controlled
than most other deficiencies.







Florida Agricultural Experiment Station


from such treatments have been somewhat conflicting and the
method has not been widely used.
In Florida sprays made up with ferrous sulfate and lime re-
sulted in the development of small green spots on the leaves
similar to those reported by Haas (53). Successive sprayings
did not materially improve the condition of the foliage (Fig. 10).
Soil applications of ferrous sulfate failed to give correction in
a reasonable time, even at high rates of application, probably
due to fixation of the iron. Injections of iron salts into the
trees gave only indifferent results and are not recommended,
on account of both cost and the damage to the wood of the
trees. Partial recovery has been noted when sawdust or other
organic material was used to form an acid layer of decaying
material on top of the original soil but this treatment is too
expensive to use except in the case of a small area which might
otherwise disfigure a grove. Areas in which iron deficiency is
acute are small and except in unusual cases expensive treat-
ments would not be justified even if success were assured. As
mentioned previously there are some indications that iron appli-
cations may prove useful on acid soils, probably due to the lower
fixing capacity of such soils as compared with alkaline ones.

BORON DEFICIENCY
Boron deficiency is known as "hard fruit" in Rhodesia, this
being the only area in which it has been definitely identified
in the field. Field symptoms in Rhodesia were described by
Morris (70, 71, 72), and compare so closely with the symptoms
found in a few groves in Florida that this section has been
included even though response to boron treatment has not yet
been obtained in the Florida conditions. Haas (50, 52) and
Haas and Klotz (55, 56) described certain leaf symptoms asso-
ciated with boron deficiency in water culture and recently Haas
(in press) has reported the production in water cultures of the
symptoms described by Morris as characteristic of the deficiency
in the field. Camp (14) reported on the occasional occurrence
of symptoms in Florida that paralleled those described by Morris
as mentioned above. The present status of the problem in Flor-
ida is as yet unsolved and the descriptions given will be based
on Morris' reports, together with comments on Florida material
that parallels closely the symptoms he described. The final
decision as to whether the Florida symptoms are really those
of boron deficiency will have to be the subject of a later report.







Some Symptoms of Citrus Malnutrition in Florida


FOLIAGE SYMPTOMS
Haas and Klotz (55) reported that enlargement, corking, and
splitting of the upper surface of the veins in the leaves was
characteristic of boron deficiency in water culture. The leaves
were recurved and became brownish-yellow in color. This work
was duplicated in Florida by Camp and Blackmon (15) and
followed up with field experiments with boron compounds in
groves showing this symptom but without results. Morris (72)
reported that the corky veins were not specifically characteristic
of the deficiency symptoms in Rhodesia, but that the !young
leaves showed small water-soaked spots or flecks that became
tiny translucent spots in older leaves.) A spotting or flecking
that resembled his description was found by the writers in
groves in Florida producing the characteristic fruit symptoms.
Associated with this also was a premature shedding of leaves
starting in the tops of the trees and soon leaving the tops almost
completely defoliated. This defoliation is apparently typical of
the symptoms found by Morris.

TWIG SYMPTOMS
Morris described a dying back of the trees and a tendency
to bushy up-right growth, apparently somewhat similar to the
growth condition in acute zinc deficiency. The trees under ob-
servation in Florida had apparently been too lately affected to
show exactly the same condition, although they are dying back
in the tops to some extent. The dying has not been severe so
far and the extreme condition reported by Morris may not have
been reached.
FRUIT SYMPTOMS
Fruit symptoms appear to be the most constant and reliable
for diagnostic purposes. Morris, working with Valencias, re-
ported an unusually heavy shedding of young fruit, with affected
fruits showing a brownish discoloration in the white portion
of the rind (albedo), gum formation and an unusually thick
albedo. Such fruits cut as though they were of a cheesy con-
sistency rather than crisp as is the case with normal fruits.
The peculiar "feel" when cutting was used as a diagnostic
symptom in the field. Older fruits were mis-shapen and had
an unusually thick albedo which frequently contained gum de-
posits; the seed failed to develop and gum deposits were com-
mon around the axis of the fruit. The pulp and peel were







Florida Agricultural Experiment Station


unusually hard and dry and very little if any juice could be
extracted from acutely affected fruits by hand squeezing.
The symptoms fit quite closely the material found in Florida
though they were found most commonly in grapefruit rather
than oranges (Plate VII). The fruits are usually irregular in
shape and frequently lopsided. The irregularity is brought on
by the failure of certain portions of the rind to develop properly
and these areas are hard to the touch and frequently darker
yellow than is ordinarily characteristic of grapefruit peel. These
hard spots contain brown gummy concretions which are apparent
as hard lumps after the fruit has been allowed to shrivel slightly.
Affected fruits may be small, not over three inches in diameter.
The pulp is hard and frequently quite dry and the seeds are not
developed properly; when the fruit is cut only dark seed coats
are found where the seeds should be. In milder cases only a
portion of the seeds may be undeveloped and the remainder
may be of normal size but may have seed coats which are un-
usually dark in color. Gum may be present around the unde-
veloped seed and in a few cases was present in large amounts.
Fruit that is apparently normal is found on the same tree with
affected fruit.
Morris reports a reduced sugar content in affected fruits and
this is in agreement with the work of Haas who has reported
improper translocation of sugars when boron deficiency was
present.
CAUSATION
Morris does not report on the probable reason for the occur-
rence of the deficiency in Rhodesia. In Florida the symptoms
here described have been found associated with alkaline soils
and drouth conditions. In a few severe cases alkaline irriga-
tion water may have been a contributing factor. It seems quite
probable that the combination of alkalinity and extreme drouth
may result in the boron in the soil becoming unavailable to the
plant and this explanation would account for its sporadic oc-
currence.
TREATMENT
Until further work is done no recommendation for treatment
can be made in Florida. Morris reports the successful use of
borax in amounts up to two pounds per tree on oranges without
the occurrence of typical boron toxicity. Such treatments are
usually toxic in Florida, particularly on grapefruit which is
more susceptible to boron toxicity than oranges.







FLORIDA AGRICULTURAL EXPERIMENT STATION







tA~ -


















.
.. .. ,























-7-7
A Nz.:


PLATE VI!. Fruit symptoms characteristic of boron deficiency as described by Morris







Florida Agricultural Experiment Station


from such treatments have been somewhat conflicting and the
method has not been widely used.
In Florida sprays made up with ferrous sulfate and lime re-
sulted in the development of small green spots on the leaves
similar to those reported by Haas (53). Successive sprayings
did not materially improve the condition of the foliage (Fig. 10).
Soil applications of ferrous sulfate failed to give correction in
a reasonable time, even at high rates of application, probably
due to fixation of the iron. Injections of iron salts into the
trees gave only indifferent results and are not recommended,
on account of both cost and the damage to the wood of the
trees. Partial recovery has been noted when sawdust or other
organic material was used to form an acid layer of decaying
material on top of the original soil but this treatment is too
expensive to use except in the case of a small area which might
otherwise disfigure a grove. Areas in which iron deficiency is
acute are small and except in unusual cases expensive treat-
ments would not be justified even if success were assured. As
mentioned previously there are some indications that iron appli-
cations may prove useful on acid soils, probably due to the lower
fixing capacity of such soils as compared with alkaline ones.

BORON DEFICIENCY
Boron deficiency is known as "hard fruit" in Rhodesia, this
being the only area in which it has been definitely identified
in the field. Field symptoms in Rhodesia were described by
Morris (70, 71, 72), and compare so closely with the symptoms
found in a few groves in Florida that this section has been
included even though response to boron treatment has not yet
been obtained in the Florida conditions. Haas (50, 52) and
Haas and Klotz (55, 56) described certain leaf symptoms asso-
ciated with boron deficiency in water culture and recently Haas
(in press) has reported the production in water cultures of the
symptoms described by Morris as characteristic of the deficiency
in the field. Camp (14) reported on the occasional occurrence
of symptoms in Florida that paralleled those described by Morris
as mentioned above. The present status of the problem in Flor-
ida is as yet unsolved and the descriptions given will be based
on Morris' reports, together with comments on Florida material
that parallels closely the symptoms he described. The final
decision as to whether the Florida symptoms are really those
of boron deficiency will have to be the subject of a later report.







Some Symptoms of Citrus Malnutrition in Florida


BORON TOXICITY
Boron toxicity has been known to occur in the field in Cali-
fornia for many years, chiefly due to the presence of boron in
irrigation waters (7, 27, 49, 50, 51, 63, 91, 92). While boron
toxicity symptoms in Florida have been described only recently
(13, 14) many growers and others reported similar symptoms
associated with applications of muriate of potash during the
World War. When the content of borax in this fertilizer
material was reduced by better manufacturing processes the
toxicity disappeared until recent years when it recurred, due
entirely to other causes. At the present time boron toxicity
in Florida is limited to small areas to which borax has been
added inadvertently or experimentally.

FOLIAGE SYMPTOMS
Following application of materials containing boron to a tree,
the first evidence is a pronounced yellowing of the tips of the
leaves which increases in area on the individual leaf until half
or more of the leaf surface is involved. The yellowing extends
down along the edges of the leaf with the green color persist-
ing along the base of the midrib in the form of an inverted
"V". The margin between the yellow and green areas is not
sharp but fades from one condition to the other frequently with
considerable mottling. Dead areas frequently develop along the
edge of the leaf near the tip (Plate VIII). The leaves shed
rapidly at the petiole and if the toxicity is severe the tree may
defoliate quickly and immediately come out with another flush
of growth. In acute cases the new growth may be almost white
with narrow green bands along the midrib and main lateral
veins with the white color rapidly fading to yellow. The leaves
may shed at the petioles and another flush of growth may follow.
When the leaves are young this pattern often resembles the
symptoms of zinc deficiency except for the fact that the leaves
are not narrowed and pointed and, if anything, tend to be
rounder in outline than normal; nor are they brittle and hard
but rather leathery and tough. Several flushes of growth may
follow in succession if moisture conditions are favorable and
the symptoms on succeeding flushes may become either less
pronounced, indicating recovery, or more pronounced and ac-
companied by loss of wood. In the former case the succeeding
flushes of growth are likely to be very vigorous with large







Florida Agricultural Experiment Station


leathery leaves and with less mottling apparent with each suc-
ceeding flush until only small whitish areas occur on the leaf.
These are located between the veins and near the outer margins
of the leaf. These light areas may be typical also of injury
due to very small amounts of borax or other boron salts. If
the tree is too severely injured and particularly if boron
remains in excess in the soil or additional amounts are applied
to the soil the leaves become smaller with successive flushes.
SSuch trees will carry only a small amount of foliage; individual
'-reaves will be about one-third normal size, almost White in color
and with dead areas along their edges near the tips)
In all of the above cases the coloration refers to the top
surface of the leaves. The under surface of the chlorotic areas
while yellow always shows a rough resinous excrescence which
is quite typical and serves as a further means of identification.
On newly affected leaves the excrescence is light yellow to light
brown and appears to be a series of tiny pustules. When af-
fected leaves persist on the tree the excrescences darken and
become almost black.
TWIG SYMPTOMS
No particular twig symptoms have been identified as being
peculiarly typical of boron toxicity but whenever the toxicity
is acute there is considerable loss of small wood and the trees
are gradually reduced mainly to the frame-work of large limbs
which are slow to die. New growth comes out on the large
limbs in the form of short twigs carrying a few affected leaves
and these die off rapidly.

FRUIT SYMPTOMS
No definite fruit symptoms have been identified but the crop
is usually dropped as soon as the tree becomes severely affected
and no new crop is set until the toxicity has been largely elim-
inated.
MODIFICATIONS OF SYMPTOMS
Severe boron toxicity symptoms are too easily identified to
be confused with other symptoms but in the mild form in which
leaves show only whitish areas on the upper surface the pattern
is sometimes confused with injury caused by six-spotted mites,
although the two symptoms are quite different. Lacking other
means of differentiation, an examination of the under side of
the leaf will show the resinous excrescence in the case of boron




FLORIDA AGRICULTURAL EXPERIMENT STATION


1i


PLATE VIII. Symptoms of boron toxicity on grapefruit leaves







Some Symptoms of Citrus Malnutrition in Florida


toxicity and a buff-colored web where the injury is due to
six-spotted mites. In cases of slight toxicity numerous tiny
white spots may develop, giving the leaf
a peculiar speckled appearance (Fig.
11). The back of each light spot shows
the typical pustules.
CAUSATION
Boron toxicity in
Florida results com-
monly from the dump-
ing in the grove of
culls which have been
treated with borax and
not washed, leaving
.field boxes which have
borax on them in the
field during a rain, and
the use of fertilizers
which have had borax
added to them. Us-
ually only a few trees
are affected in any one
grove.
TREATMENT
Attempts to treat
boron toxicity in Flor-
ida are not usually Fig. 11.-Speckled
appearance of leaves
markedly successful, inPP' of mild boron
since the tree has al- toxicity.
ready taken up a great
deal of boron before
the toxicity is discov-
ered. Leaching the soil to remove the excess boron
is sometimes useful in speeding up recovery and
lime is occasionally used to fix the boron in an unavailable
form. Mild cases generally recover about as quickly without
any special treatment if no additional boron is applied, but
the grower who applies some corrective treatment is fre-
quently misled into believing that the recovery is due to the
treatment.







Florida Agricultural Experiment Station


MISCELLANEOUS
A number of other symptoms occur in citrus in Florida which
seem to be due to malnutrition; however, since the causes and
treatments for these have not been determined there seems to
be little point in discussing them in detail. One of these, "yellow
spot", should be mentioned since it causes considerable defolia-
tion occasionally and because it has been extensively discussed
in the literature by Floyd (33, 35, 37). Yellow spot first appears
on young leaves as irregular areas that have a semi-water-soaked
appearance and as the leaf matures yellow spots one-fourth to
.one-half inch in diameter develop on either side of the midrib
and between the lateral veins. The under surfaces of these
spots are covered with a brown resinous excrescence. The leaves
shed soon after the yellow spots become pronounced and the tree
is sometimes severely defoliated as a result. So far it has not
been definitely associated with any nutritional condition. Yellow
spot was apparently quite common from 1908 to 1910 and has
recently recurred in a number of groves.
While the foregoing discussion of citrus deficiency symptoms
is admittedly incomplete, nevertheless, the symptoms illustrated
and discussed are extensively used in grove practice in Florida
and at present constitute some of the most reliable guides avail-
able. It is hoped that this bulletin will make the published
information on the various technical phases of the problems
more easily understood by growers in Florida and possibly aid
workers in other citrus areas in understanding the Florida
problems.
The writers wish to express their appreciation to the various
members of the Staff of the Citrus Experiment Station for their
very generous help in the preparation of the manuscript and
to Dr. Michael Peech in particular for his help on the discussion
of the soil problems involved.








Some Symptoms of Citrus Malnutrition in Florida 45

LITERATURE CITED

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Proc. Fla. State Hort. Soc. 49: 19-22. 1936.








Florida Agricultural Experiment Station


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Some Symptoms of Citrus Malnutrition in Florida


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56. HAAS, A. R. C., and L. J. KLOTZ. Further evidence on the necessity
of boron for health in citrus. Bot. Gaz. 92(1): 94-100. 1931.








Florida Agricultural Experiment Station


57. HAYMAN, W. P. Effects of zinc sulphate on frenched citrus in Polk
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Some Symptoms of Citrus Malnutrition in Florida 49

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