Front Cover
 Title Page
 Table of Contents
 Literature cited

Group Title: Bulletin
Title: Malnutrition symptoms of citrus with practical methods of treatment
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00014965/00001
 Material Information
Title: Malnutrition symptoms of citrus with practical methods of treatment
Series Title: Bulletin
Physical Description: 64 p. : ill. (some col.) ; 23 cm.
Language: English
Creator: Bryan, O. C ( Ollie Clifton ), b. 1894
Publisher: State of Florida, Dept. of Agriculture
Place of Publication: Tallahassee
Publication Date: 1957
Subject: Citrus fruits -- Florida   ( lcsh )
Citrus -- Diseases and pests -- Florida   ( lcsh )
Deficiency diseases in plants -- Florida   ( lcsh )
Citrus -- Nutrition   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by O.C. Bryan.
Bibliography: Includes bibliographical references (p. 63-64).
General Note: "March, 1957."
 Record Information
Bibliographic ID: UF00014965
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA3213
ltuf - AMT3474
oclc - 47034107
alephbibnum - 002567187

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page 1
        Page 2
        Page 3
    Table of Contents
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    Literature cited
        Page 63
        Page 64
Full Text

Malnutrition Symptoms of



Early Stage

Advanced Stage

NATHAN MAYO, Commissioner



Malnutrition Symptoms of


with Practical Methods

of Treatment


NATHAN MAYO, Commissioner


This bulletin was originally sponsored by!
the Florida Citrus Growers, Incorporated, and
its publication and free distribution were made
possible through the generositil of the State
Department of Agriculture at Tallahassee.

The supphl of the second printing of this
bulletin has been exhausted, and the demand
justified another reprinting. The State Depart-
ment of Agriculture is glad to make available
to citrus growers a third printing of the bulle-
tin which has been revised and brought up to

COVER-Deficiency symptoms of nitrogen in orange leaves.
Early stage (A) indicated by pale green color. Advanced stage
(B) indicated by yellow color. (See page 8 for description.)


Commercial plant food-fertilizers-is not only one of the
essentials for citrus production in Florida, but one of the most
expensive factors. The wide range of inherent properties of
plant nutrients greatly complicates soil fertility problems.
That some nutrients are required only in trace amounts and
some in large amounts is a deep mystery to both practical and
technical workers. Variations in individual nutrient properties
account for the wide range in soil reaction (pH). Further-
more, some nutrients are attracted to the soil particles and
others are not. Some leach rather readily while others ac-
cumulate with fertilizer practices. Successful management of
soil fertility problems necessitates a working knowledge of
the behavior of nutrients in the soil. When a nutrient is defi-
cient, crops are abnormal, diseased and unproductive.
The discovery that each nutrient performs individual func-
tions in a plant, a deficiency of which causes specific deficiency
patterns, was a milestone in the progress of agriculture. This
has enabled growers to pinpoint many nutrition problems and
place their endeavors on a scientific basis. To recognize and
identify deficiency symptom patterns in citrus is a worthy ac-
complishment. Yet, it is equally important for the grower to
know the reasons for the abnormality, whether they are due to
actual shortage in the soil, or to unbalanced nutrients caused
by unscientific practices. For that reason some representative
data dealing with nutrient needs, fertilizer materials, and re-
action of nutrients with typical citrus soils are presented for
study along with the deficiency symptom patterns.
To correct malnutrition problems involves either supple-
menting the soil for actual shortage, or counteracting excesses
and adjusting unbalanced nutrients. These have been repeat-
edly demonstrated since the original printing of this bulletin
in 1940, and again in 1950. Several new discoveries have
been made since the last printing. For these reasons, the
bulletin has been revised and brought up to date, adding new
data and illustrations as deemed advisable.





Synopsis of Malnutrition Symptoms of Citrus, Soil Relations,
Treatments, Excesses, Historical Use of the following Nutrients:

N itrog en . .. ....... .. ...... .

P hosphoru s ..... ........... . .... .... .

Potassium (Potash)

Magnesium .... ..

C a lciu m .. ... .. ..... ..................

B o r o n ... ..... ............ .... ..

Copper ...



Zinc ......

...... .. ... . ..... 2 7

.......... .......... 3 1

. .. ...... ... 3 4

. .................. ..... 3 7

M olybdenum .......... ...........



FERTILIZER EFFICIENCY .... ............ ...............

L E A C H IN G L O SSE S ..... ........... ........... .......... ................. ......

SOIL ACCUMULATIONS AND SOIL REACTION. ..........................


TIM E OF APPLICATION .. ............ .............................................


SU M M A R Y .. ... .. ......... .... .. .......... .. .......

A CK N O W LED GM EN TS .... .......... .... .....................................

LITERA TU RE CITED ....... .... ....... .. .. .......... ............




.... 22

CONTENTS (Continued)


Plates: Page

1. Deficiency Symptoms of Nitrogen in Orange Leaves.... ........ Cover

2. Deficiency Symptoms of Magnesium in Grapefruit Leaves............ 17

3. Deficiency Symptoms of Copper in Pineapple Oranges................ 29

4. Deficiency Symptoms of Manganese in Grapefruit Leaves......... 33

5. Deficiency Symptoms of Iron in Orange Leaves.. ............... 35

6. Deficiency Symptoms of Zinc in Orange Leaves .................. 39


1. Phosphorus Deficiency Symptoms in the Leaves and Fruit
of O rang es .. . ................................... ....... 11

2. Symptoms of Zinc Deficiency (Foliage) and Copper (Fruit)
in Pineapple Oranges ................. ........ ...................... .. ... 13

;. Deficiency Symptoms of Potassium in Common Grapefruit......... 15

4. Deficiency Symptoms of Magnesium in Grapefruit..................... 19

5. Deficiency Symptoms of Calcium in Grapefruit Leaves and Trees 21

6. Leaf Symptoms of Boron Deficiency.............................. ............ 23

7. Symptoms of Boron Deficiency in Citrus Leaves and Fruit......... 25

8. Mild Case of Boron Toxicity in Grapefruit Leaves........................ 26

9. Molybdenum Deficiency in Orange Leaves .............. .............. 41

10. Perchlorate Chlorosis in Grapefruit Leaves............................. 43

11. Biuret Chlorosis of Citrus....................... ....... ................ ............ 44

12. Arsenic Toxicity of Grapefruit Leaves................................ 45


CONTENTS (Continued)

Tables: Page
1. Nutrient Content of Citrus as Related to Fertilizer Needs
on San dy S oils............. ............... ..... . ............. ............. ........... 4 7

2. Composition of the Principal Fertilizer Materials ................. 48

3. The Efficiency of Different Sources of Nitrogen on the Produc-
tion of Pineapple Oranges With and Without Copper................ 50

4. Total Amount of Drainage During the Year (1924) and the
P lant F ood L eached........................................................ ............... 53

5. Relative Leaching Losses of the Major Fertilizer Nutrients
from Some Typical Florida Soils ............................ ........... 55

6. Available Plant Nutrients in the Soil as Affected by
Different Fertilizer Treatments............................ .................. 56



The purpose of this bulletin is to bring before the Florida
grower, in a brief practical and scientific manner, the known
information regarding the malnutrition problems of citrus,
pointing out the deficiency symptoms of various nutrients, as
well as the symptoms of excesses. By so doing and suggesting
economical methods of treatment, it is hoped that the grower
will understand production problems sufficiently well to elim-
inate wasteful practices and increase the efficiency of produc-
tion. The increased demand for fruit of high internal quality
necessitates more attention to those production factors which
favorably affect quality.
Of all the production factors confronting Florida growers,
that of commercial plant food is one of the most expensive,
the most confusing and the least understood. Unless the
grower has dependable scientific methods rather than guess-
work, he will not be able to avoid wasteful practices in deal-
ing with malnutrition problems.
No attempt is made to cite all the literature dealing with
this subject. Some of direct concern will be mentioned.
In order to discuss this subject, using a minimum of techni-
cal terms, it will be necessary for the grower to accept the
generally established facts: That many chemical elements,
such as nitrogen, phosphoric acid and potash as well as boron,
copper, zinc, manganese, magnesium and others, are required
for growth and production of all crops. When any one of
these is lacking in the soil or exists in unbalanced form, it
must be supplied or adjustments made to permit a good utili-
zation of the other nutrients. The exact role played by the
different nutrients in the growth of plants is not definitely
known, but the external effects or deficiency symptoms have
been scientifically correlated for most nutrients, enabling the
grower to understand and use them intelligently.
Years of study have shown that each of the required nutri-
ent elements has a specific function to perform in the plant,
and that no one element can substitute entirely for another.
Therefore, when an element is present in insufficient amounts

Technical Director, Soil Science Foundation, Lakeland, Florida.

Department of Agriculture

to perform its "Specific Function" and/or has antagonistic in-
fluences from other elements, a very definite abnormality
develops in the leaves, branches and fruit. Since the leaf is
the seat of almost all synthesis and growth it is the place
where most deficiency symptoms develop. Because of this
condition, a good portion of this bulletin will deal with defi-
ciency leaf symptom patterns shown in color as well as black
and white half tones. Any characteristic deficiency symptoms
in other parts of the plant will also be pointed out.

Frequently, two or more deficiency symptom patterns occur
on the same leaf, thus producing a combination pattern which
may confuse, the casual observer. For that reason, it is neces-
sary to study the range of identification characteristics of each
nutrient pattern separately. By so doing, the combination
patterns can usually be recognized. A brief description of
the deficiency symptom patterns of the different nutrients is
presented, together with the soil relations, treatments, symp-
toms of excesses, and historical usage. In addition, some pat-
terns of leaf chlorosis and toxicities are presented to give the
grower a more complete understanding of the abnormal leaf
discolorations observed in Florida.

The reader is urged to study the illustrations in detail along
with the description, because the plates and figures contain
pattern differences that are difficult to describe in words. In
each case typical representative illustrations have been chosen,
and along with each illustration the important differentiating
characteristics and treatments are included.


Deficiency Symptoms: Since nitrogen has a marked influ-
ence on plant growth in general, its deficiency symptoms are
easily recognized by most growers. A deficiency of nitrogen
in citrus is first characterized by a uniform loss of chlorophyll
over the entire leaf, with occasional discoloration of veins in
early stages, resulting in a pale yellowish-green color in early
stages, to old ivory color in the advanced stages. The off-color
"hungry" appearance is usually recognized by most growers.
The colors of young and old leaves are given on the cover.
The deficiency extends over the entire plant, with the greatest
severity on fruiting branches, the leaves of which may show a
slight mottling effect in acute cases. Severely affected trees

Malnutrition Symptoms of Citrus

show stunted condition, sparse foliage, dead wood, as well as
reduction in size and amount of fruit. Other than size and
amount, the quality of fruit is not adversely affected.
Nitrogen deficiency should not be confused with yellowing
of leaves and vein chlorosis brought about by girdling, dis-
ease, root-pruning, or any condition which interferes with the
normal flow of sap in the tree. One of the symptoms of
early boron deficiency is characterized by bronzed off-colored
leaves and vein chlorosis. See Figure 6.

Soil Relations: Deficiency symptoms of nitrogen may occur
on any mineral soil, but as a rule they are most commonly
found on the thinner sandy types and in neglected groves.
Nitrogen fluctuates in the soil more than any other nutrient
and shows the least tendency to accumulate, regardless of
the amounts applied. Records indicate that liberal amounts
of available nitrogen in soil prior to and during the bloom
period and spring growth, with lesser amounts during summer
and fall, favor production and maturity of fruit. If the soil
reaction is favorable, (approximately pH 6.0) the efficiency
of nitrogen is improved.
Treatment: The treatment for nitrogen deficiency is too
well known to warrant discussion here. Severe deficiencies
should receive soluble nitrogen, preferably nitrate nitrogen
because it penetrates more quickly into the root zone. The
comparative value of different sources of nitrogen will be dis-
cussed later. If soil moisture is low, it will be difficult for
the trees to absorb any form of nitrogen.

Nitrogen Excess: An excess of nitrogen produces a rank
evergreen succulent growth. The leaves are abnormally green,
large and coarse, and the branches are succulent and angular.
Excess nitrogen in late summer and fall may produce tender
rind fruit, and with favorable moisture and warm weather,
such fruit tend to crease and split. The vigorous growth re-
sulting from excess nitrogen utilizes other elements rapidly,
and may show the characteristic dieback and ammoniationn"
symptoms, unless copper is present. An over-dose of any solu-
ble salt, including nitrates and sulphates, will cause a prema-
ture droppage of foliage, and even burning of the leaves.
Historical Use: Nitrogen has been used in one form or an-
other as long as citrus growing in Florida has been an indus-
try. Its usage is so commonly known that a discussion here
would not be justified.

Department of Agriculture


Deficiency Symptoms: The importance of phosphorus for
all crops is well recognized. However, no distinct phosphorus
deficiency symptom pattern develops in citrus leaves under
Florida conditions such as the characteristic leaf patterns of
magnesium, zinc and iron deficiencies. A slow stunted growth
with small, lusterless leaves and reduction in crop appears to
be the dominant effects produced by a deficiency of phos-
phorus in citrus under Florida conditions.

According to Young and Forsee (45) of Florida, a phos-
phorus deficiency of citrus on organic soils produces small,
thick-rind fruit which drop prematurely. Figure 1, lower
right). They report no leaf burns due to phosphorus defici-
ency. Haas (19) of California reports that a deficiency of
phosphorus in citrus is characterized by small, lusterless,
brownish-green leaves, which in advanced cases show irregu-
lar burning effects, as illustrated in Figure 1, upper. More-
over, a phosphorus shortage produces a marked absence of
shoots or new branches. These symptoms occur under con-
trolled as well as under field conditions.

Soil Relations: The problem of phosphates in sands is not
as serious as it is in clay soils, because iron and aluminum
compounds in the clays render the phosphate unavailable.
This is especially true in humid regions where the soils are
acid and the reserves of calcium have been depleted.

It is generally known that phosphates do not leach even on
sandy lands as rapidly as nitrogen. See Tables 4 and 5. For
that reason, continuous application over and above that of
crop removals result in an accumulation of this nutrient.
Where the soils are relatively low in fixing agents as it is the
case with many Florida soils, a good portion of the accumu-
lated phosphates appears available for plant use. Therefore,
this nutrient is more efficient on sandy lands void of extreme
relationships than most other nutrients.

Treatment: Although there are a number of sources of
phosphates available as fertilizer, most of them center around
acidulated or treated phosphate rock. This is considered the
standard phosphate fertilizer. Where this nutrient appears
to be deficient, the treated and more soluble forms are the
most effective materials available. Where phosphates tend
to accumulate, other sources may be used satisfactorily.

Phosphorus Excess: Due to the high fixing power of clay and

Malnutrition Symptoms of Citrus


Figure 3. Deficiency Symptoms of Potassium in Common Grapefruit.
UPPER: Drooping of branches, showing lack of rigidity.
LOWER: Advanced case deficiency in the leaves. Left, normal, center yellow
area; right leaf tissue disintegrated necrosis.

A *



Department of Agriculture

Historical Use: Potash has been used for citrus in Florida
almost as long as the industry has exited. The early sources
consisted of hardwood ashes, kainit and natural materials.
Other citrus growing areas do not use as much potash as does
Florida, largely due to differences in soil. Before 1940, it was
thought that potash reduced fruit size. But Chapman and co-
workers (8) in California, and Reuther and Smith (31) in
Florida, have shown experimentally that high levels of potash
increase fruit size and coarseness.


Deficiency Symptoms: Magnesium deficiency in citrus is
characterized by a type of leaf chlorosis commonly known in
Florida as bronzing. This discoloration or loss of chlorophyll
occurs only on mature leaves, and is more prevalent on
heavily fruiting trees and branches, and is more noticeable in
late summer and fall, but may be seen any season where the
nutrient is deficient.

Although there is a variety of leaf symptoms associated
with this deficiency, the typical cases develop yellow chloro-
tic areas in the initial stage on each side of the mid-rib. Later
these areas enlarge often at an angle to the mid-rib and
usually coalesce to form a yellow zone surrounding a wedge-
shaped green area at the leaf base. As the deficiency ad-
vances, the entire leaf becomes yellow or bronze-like, hence
the name. This advanced condition might be confused with
an advanced case of nitrogen deficiency, but intermediate
stages can always be found to serve for differentiation. The
range of these color patterns is illustrated in Plate 2. The
patterns are usually more pronounced in grapefruit than
Magnesium deficiency is closely associated with seediness of
fruit and size of crop. Ample magnesium enables citrus trees
to markedly tolerate cold. In a large measure magnesium de-
ficiency is responsible for the alternate bearing habits of the
common seedy grapefruit and pineapple oranges. Affected
leaves appear to drop earlier from the orange than the grape-
fruit trees, producing a somewhat sparse foilage during the
fall and winter, but in severe cases all varieties drop their
affected leaves freely, often leaving completely defoliated
twigs, many of which die and become diseased. Figure 4
(lower) shows a grapefruit tree severely defoliated as a re-
sult of magnesium deficiency, and the range of the deficiency
in the individual leaves (upper).


Department of Agriculture

There appears to be no marked fruit symptoms with this
deficiency except reduced crop yields and alternate bearing
qualities. The deadwood and twigs resulting from the defi-
ciency may increase the disease hazard of the fruit. The de-
ficiency is often associated with copper and zinc deficiencies,
in which case combination symptoms result.

Soil Relations: Magnesium deficiency occurs more generally
on the thin, sandy types of soil, but may be found on heavier
types and even marls; it rarely occurs on muck and peat soils.
Soil acids as well as excessive amounts of potash and other
bases tend to deplete the soil magnesium. This was markedly
true in Florida back in the late twenties and thirties. The ac-
tual leaching losses of magnesium are much greater than crop
removal in comparison with those of phosphates. This means
that magnesium must be added in some form to maintain soil
Treatment: Severe cases of magnesium deficiency should
have soluble magnesium at the rate of 75 to 150 pounds per
acre, depending upon tree size. However, in most cases, as
well as for maintenance supplies, dolomite in sufficient
amounts to hold the soil reaction to about pH 6.0 will supply
the needed magnesium, provided the other nutrients are not
in excess. It may be necessary to use soluble forms on marls,
but even here the magnesium in dolomite can be used.
Magnesium Excess: Due to the marked tendency for soluble
magnesium salts to leach and the slow, availability of carbon-
ates and phosphates, it is doubtful that a rational practice
would cause crop injury. Excessive applications of dolomite
rarely produce a soil reaction of pH 7.0 or above, and no ill
effects have been reported even where excessive rates of dolo-
mite have been made. But excessive amounts of a magnesium
sulphate will deplete the soil of other bases and result in an
unbalanced nutrient ratio. This may delay normal fruit col-
Historical Use: Although Averna-Saca (*) reported the
value of magnesium in correcting certain chlorosis of citrus on
ferruginous soils in 1912, the leaf symptoms of magnesium de-
ficiency were first described by Reed and Haas (30) in Cali-
fornia in 1924. Later Bryan and DeBusk (4) reported that
the widespread trouble in Florida known as Citrus Bronze was
due to magnesium deficiency, and Tait (43) further demon-
strated the value of different sources of magnesium. Bahrt
(1, 2) and co-worker reported that, lime, manganese, magne-

(*) Bol. Agr. (Sao Paulo) 13, Ser. 1912 (2); 129-150. 1912.

Figure 4. Deficiency Symptoms of Magnesium in Grapefruit.
UPPER: Range of magnesium deficiency symptoms in grapefruit leaves, show-
ing early stages on left and progressive stages on right.
LOWER: Severe case of magnesium deficiency in grapefruit tree.

Department of Agriculture

sium and potash salts were beneficial on bronze groves as
early as 1934, but failed to associate the bronze with magne-
sium deficiency until 1937. In the later year, workers in Aus-
tralia (y) reported the beneficial effects of dolomitic lime-
stone (started in 1932) in correcting a leaf chlorosis of citrus,
which proved to be a magnesium deficiency. Several investi-
gators have shown that chlorotic and bronze leaves of citrus
contain less magnesium than healthy leaves.

The records show that Florida citrus industry was suffering
severely under the strain of magnesium shortage in the early
thirties and that they were aggravated by high levels of potash
and phosphoric acid in the fertilizer. A rational use of mag-
nesium during the past 20 years has been of invaluable help
to the industry. Since citrus needs liberal calcium and favor-
able soil pH, dolomite has served a three fold purpose.


Deficiency Symptoms: Only in rare cases has a deficiency
symptom of calcium been reported under field conditions of
any crop, and none for citrus. Under controlled conditions,
however, calcium deficiency symptom patterns have been de-
scribed for citrus by Reed and Haas (30), and Bryan (5).
These symptoms are characterized by a marked stunted and
hard condition of the tree, with small leaves. The flushes of
growth are short, with a tendency for the terminal branches
to die back. In severe cases the leaves become chlorotic at the
margins and tips, which progresses toward the leaf center and
base (Figure 5). In some ways this deficiency resembles a
mild case of boron toxicity. But close examination reveals
that the undersurface of the leaves with the boron pattern
has gum excretions. (See Figures 5 and 8.) The calcium defi-
ciency pattern may be confused with an advanced case of
Biuret toxicity. The differences consist of smaller leaves with
calcium deficiency, and the chlorosis following the leaf mar-
gins, whereas the Biuret toxicity is somewhat patchy in early
stages, beginning in the tip of the leaf and spreading inward
with severe cases to include most, if not all, of the leaf. The
tips of calcium deficient leaves are often blunt and sometimes
incompletely developed.
Soil Relations: Of all the nutrients, calcium seems to have
the greatest controlling or balancing effect in the soil. It con-
stitutes over 50 % of the active bases in productive soils, being

(y) Agr. Gaz. N.S. Wales 48 (9) 501-504, 1937.

Malnutrition Symptoms of Citrus

Figure 5. Deficiency Symptoms of Calcium in Grapefruit Leaves and Trees.
(Controlled Cultures.)
UPPER: Leaves showing loss of chlorophyll in tips and edges of leaves.
LOWER: Normal tree on right contrasted with calcium deficient tree on left.
held largely in a replaceable form by the soil colloids (clays
and humus). This in a measure represents the available cal-
cium present. Soil acids tend to dissolve the calcium, thereby
increasing the intensity of leaching losses, with a resultant
lowered fertility. In humid regions the calcium losses from
leaching alone are greater than that of any other nutrient,
varying from 200 to 600 pounds or more per acre annually. It
is highly desirable to maintain the needed calcium to destroy
acids as well as.to serve as a balancing agent for biological
processes. A rational use of lime is the secret of soil fertility
in most areas, including Florida.
Treatment: Only under unusual conditions does the soil re-
quire calcium for nutritional purposes to a greater degree

__ -_ I '

Department of Agriculture

than lime for neutralizing soil acids. Although a soil reaction
of approximately pH 6.0 is to be desired, it should be distinct-
ly understood that pH alone is not enough, and dependence
on it may lead to trouble. Records show that rain water has
a favorable pH, but no calcium and magnesium. Ample cal-
cium should be the objective, rather than a pH of 6.0 or other-
wise. Sands and sandy soils should have as much as 700 to
1000 pounds of calcium per acre 12 inches of soil. This may
be supplied from lime, slag, oyster shells, or dolomite. Heavy
soils and soils high in organic matter should have 50 to 100
per cent more calcium than that required by sandy soils.
Dolomite has done more to improve groves, per unit cost, than
any other single commodity. It supplies both calcium and
magnesium without the risk of too high pH values.

Calcium Excess: An excess of calcium in the soil solution
rarely occurs, since the sulphate and phosphate of calcium
have a low solubility in soil water. But an excess of calcium
carbonate or hydrate on sands produces high pH values which
in turn reduce the availability of manganese, zinc and iron.
Many of the unproductive groves in Florida, in the twenties,
were due to excessive amounts of hydrated and carbonated
lime (15). Fortunately an excess of dolomite does not produce
unfavorable pH values and consequently does not produce the
locking effect on the secondary nutrients.

Historical Use: Calcium in the form of lime, shells, ashes,
bonemeal, and as a carrier of phosphates in the fertilizer, has
been used for many decades. But the use of lime on Florida
soils came into ill-repute about 1918 following excessive ap-
plications to groves. The use of high calcium lime is still a
doubtful practice among some Florida growers, but where the
secondary elements are applied, its ill effects can be correct-
ed. With a rational use of trace elements the objection to
lime is fading. It is interesting to note that since 1933, dolo-
mitic limestone has been used on Florida soils with marked
success. Its greatest value lies in the magnesium content and
non-injurious effect on the soil reaction, regardless of amounts.


Deficiency Symptoms: Boron deficiency in citrus foliage is
characterized by a marked tendency of the leaves to wilt,
curl and pucker. They have a dull brownish-green color with
the absence of luster.

Figure 6. Leaf Symptoms of Boron Deficiency as described by Smith and Reuther for Valencia Orange. Proc. Fla. State Hart. Soc. 62, 1949.
Left: Early symptoms of curling and yellowing along midrib and lateral veins.
RIGHT: Later stage showing pronounced veinal chlorosis, enlarged veins and defoliation.

Department of Agriculture

Young leaves shed prematurely and the stems show gum
formations and often die in irregular areas. The midrib and
lateral veins of young leaves are chlorotic and are usually en-
larged with some splitting. The young branches may have
multiple buds with a rosette appearance somewhat like that
of copper deficiency. The old leaves are often thick, brittle
with bronze color, somewhat like magnesium deficiency, and
may develop split veins (Figure 7, center and upper).
Boron deficient fruit is characterized by small, misshapen,
hard fruit which frequently contain brown gummy discolora-
tion in the albedo layer of the rind (Figure 7, lower). The
fruit is often lopsided. Gum may be found anywhere in the
fruit, which often shows dark spots, dark seed coat, undevel-
oped seed and marked dryness. Sour rootstock seems to be
more sensitive to shortage of boron than lemon root.

Soil Relation: Observations indicate that acid soils in hu-
mid regions often show distinct boron shortage, frequently
containing less than one part per million of water soluble
boron. Like other nutrients, the availability of boron is de-
pendent on the soil reaction as well as other nutrients pres-
ent. Boron deficiency symptoms are more evident during pro-
longed periods of drought than during normal seasons and
where excess lime is used on light soil. But boron deficiency
may occur on any soil type.
Treatment: Soil application of borax has usually been the
specific treatment for this deficiency with most annual crops.
This is also true for citrus. In addition, borax has been suc-
cessfully applied to citrus in a spray, at the rate of 1 pound
per 100 gallons. Soil applications range from 10 to 15 pounds
borax per acre on light sands to as high as 50 pounds per
acre on marls and heavy soils. Equivalent amounts of boric
acid, fertilizer borate or other boron sources are being suc-
cessfully used. A Fritted Borate-ground glass-like material
-is comparatively recent in usage. Because of its slow solu-
bility there is less risk involved on acid soils than the water
soluble forms.

Boron Excess: Like copper, boron is poisonous and quickly
shows evidence of excess, especially on acid sands. Yet, there
is an optimum range for its usage. Soil applications of soluble
boron rarely produce toxicity on neutral and marl soils. Be-
cause of the extremely sensitive nature of citrus to excess
boron, growers have heard more about toxicity resulting from
excess than about boron deficiencies.
Boron toxicity is usually a result of excess boron irrigation

Figure 7. Corking of veins and curling of terminal leaves of Grapefruit "A",
puckering of leaves with corking and splitting of veins "B" and "C", accompa-
nied by leathery and brittle conditions with bronze colorations are symptoms
of Boron deficiency as reported by Haas.
LOWER: Dry discolorations, abortive seed on left and hard "rind" with gum
formations, right, are Boron deficiency symptoms of fruit as reported by Morris.

Department of Agriculture

water in alkali regions. In Florida only limited cases of boron
toxicity have been reported. These have been associated with
borax treated crates left in the grove. In some instances in
Florida and California, evidence of excess boron in the ferti-
lizer and spray has been reported.

The first evidence of boron toxicity is a marked yellowing
of leaf tips. This yellowing often extends down the edges or
sides of leaves nearest the tips, and the yellow and green por-
tions frequently blend showing a somewhat mottled effect.
Figure 8 shows a typical case of boron toxicity in grapefruit,
which is more sensitive than the orange. Affected leaves fre-
quently show dead areas at tips and leaf margins. In severe
cases the leaves shed quickly, depending on the severity of
the toxicity. With severe cases the successive flushes are al-
most white and the twigs frequently die. The under surface
of the chlorotic areas shows a rough, resinous excrescence in
the form of tiny brown to yellow pustules, which serves to

Figure 8. A mild case of Boron Toxicity in Grapefruit leaves, showing yellowing
of leaves at tips and margins. Gum excretion on the undersurface of leaves
serves to identify boron toxicity.

Malnutrition Symptoms of Citrus

help identify the symptoms. These excrescences turn black
with age. This resinous excrescence on the under side of
leaves differentiates boron toxicity from fluoride toxicity. In
light cases of toxicity, small whitish areas occur between the
veins and near the leaf margins. These areas are sometimes
confused with injury from the six-spotted mites.

Since many boron compounds are soluble in water, their
injurious effect in the soil is usually alleviated by flooding
and rain. Calcium renders boron insoluble and this can be
utilized to overcome the excess in most instances by working
400 to 800 pounds hydrated lime per acre into the soil and
watering down. This, of course, applies to the sandier types
where the toxicity is most commonly found. Larger amounts
would be required on heavier types.

Historical Use: Haas (18) and co-workers in California
pointed out the symptoms of boron deficiency in the vegeta-
tive parts of citrus grown in water cultures (1927, 1930).
Later Morris (24) of Rhodesia reported symptoms of boron
deficiency in fruit. Observations in recent years indicate that
both leaf and fruit symptoms occur in Florida, and experi-
mental records confirm these observations (38). Boron is now
used in either sprays or in fertilizers as a general practice
for citrus groves in Florida.


Deficiency Symptoms: A deficiency of copper in citrus is
much more frequently noted in the fruit than in the foliage
and twigs. The first foliage symptoms to develop are deep
green, over-sized coarse leaves accompanied by long, vigor-
ous, pliant and often "S" shaped shoots, giving the appear-
ance of excessive nitrogen fertilization. For this reason the
early workers concluded that diebackk" or exanthema (now
known to be copper deficiency) was due to excessive nitrogen
fertilization. In the early stages of the deficiency, young
twigs often develop small, blister-like gum pockets between
the bark and wood at or near the buds. With the progress of
the disease the terminal twigs usually develop brown staining
and dieback at the ends, and reddish-brown, rigid eruptions
develop from the bark on the older twigs, giving rise to the
term "Red Rust", frequently applied to this disease by the
grower. As the deficiency symptoms become acute, multiple
buds frequently develop in the axis of the leaves. In aggra-
vated cases the production of new shoots and dieback of

Department of Agriculture

older ones result in a bushy rosette type of growth. These
symptoms are illustrated in Plate 3.
The fruit usually develops symptoms of copper deficiency
before the branches are affected, and in mild cases of the de-
ficiency, the symptoms may be confined entirely to the fruit.
These are characterized by dark brown, gum-soaked erup-
tions, varying from numerous, minute, scattered specks to
spots one-eighth inch in diameter. These eruptions may occur
as irregular blotches, frequently covering large areas of the
fruit and turning black as the fruit matures. Fruit blemished
as a result of diebackk" or exanthema are termed "ammon-
iated" by the growers and have no commercial value. This
deficiency may occur on various kinds of citrus but is more
prevalent on oranges than grapefruit and tangerines.
Since copper deficiency has a more marked effect on the
fruit and twigs of citrus, a deficiency of other elements may
mask these symptoms. This is particularly true with a de-
ficiency of zinc and magnesium, and even manganese at times.
A shortage of these elements retards appearance of copper
deficiency. But as a rule, the symptoms are specific and the
differences are merely a matter of degree and not of kind. In
severe cases, fruit symptoms are the most reliable guides for
copper deficiency. With acute deficiency of one or more ele-
ments, the less pronounced deficiencies may not be apparent
until the acute case is alleviated.
Copper deficiency is common with young trees on new
land. This is due to the low copper content of virgin soils,
and the tendency of active organic matter to render copper
unavailable. Heavy fertilizer without copper usually causes
ammoniation or copper deficiency in young trees.
Soil Relations: Although copper deficiency is known to oc-
cur on most any soil type, it is more prevalent on new land
and soils with clean cultural practices. Any treatment or
practice which induces rapid growth of trees may bring about
a copper deficiency where no copper is added in the spray or
fertilizer program. A rapid growth necessitates proportional
amounts of copper to avoid a deficiency of this nutrient. Ex-
perimental records (45) by a number of workers show that
high amounts of available phosphates cause a copper defici-
ency. The records indicate that high phosphates hinder the
intake of copper by the plants. Copper compounds in the soil
are less soluble than compounds of nitrogen and potash. Be-
cause of this fact, repeated copper applications result in cop-
per cumulation in soil.



danced Stage

Department of Agriculture

Treatment: Copper sulphate, either in the form of a spray
or as a soil application, has been the usual treatment for this
deficiency. The spray produces much more rapid corrective
results, but is often objectionable because of the possible
scale infestation following its usage. If the soil is free of
other nutrients which cause antagonistic effects, the amounts
of copper required to supply needs are relatively small. Pos-
sibly 1/100 to 1/50 that of nitrogen will suffice. Organic soils
and soils with high reserves of phosphates will need more.
Within recent years, copper oxide, hydroxide and even finely
ground metallic copper have been used satisfactorily as a soil
or spray amendment.

Copper Excess: Very small amounts of copper are neces-
sary for tree and fruit needs, and excessive rates (3 to 8
pounds per tree) will cause injury, even on marls, resulting
in the splitting of bark, gumming, defoliation and possible
death of tree. Many growers have applied liberal amounts
of copper in the fertilizer (sometimes as much as 1/4 that of
nitrogen) in addition to copper spray for a number of years,
especially during the 40's. Since copper does not leach from
the soil to any extent this has resulted in a marked accumu-
lation of copper in some soils amounting to 800 pounds or
more of copper oxide per acre. This has become a serious
problem in many groves, especially on acid sandy soils. The
excess copper is toxic to tree roots, causing unthrifty and
markedly stunted trees. It is antagonistic to iron and accounts
for the widespread problem of iron deficiency in many Florida
groves. Liberal amounts of lime and/or soil amendments suf-
ficient to raise the soil reaction to pH 6.0 or above will reduce
the severity of the problem of excess copper. Iron salts, in-
cluding Chelated iron, may be needed to correct the iron de-
ficiencies. Liberal phosphates are known to retard copper

Historical Use: The symptoms of citrus diebackk" or ex-
anthema were first described in 1875 by Fowler (12) from
Florida, where the trouble was known to have occurred as
early as 1864 (32). It was first investigated in 1896 by Swin-
gle and Webber (42) who concluded that it was a malnutri-
tional disease, and subsequently by Floyd and others. Rec-
ords by Frotcher (xx) show that Bordeaux spray successfully
controlled diebackk" as early as 1897, but little attention was
given to this treatment. Floyd (13, 14) reported similar re-
sults in 1908 and 1913, as have other workers in this and

(xx) Proc. Fla. State Hort. Soc. 1897.

Malnutrition Symptoms of Citrus 31

varied countries (10). Along with the use of copper, either
in Bordeaux spray or soil treatments for diebackk" or exan-
thema, it was observed for some years that Bordeaux fre-
quently exerted a stimulating effect on the tree. In the middle
thirties, Fudge of the Florida Citrus Experiment Station show-
ed experimentally that copper regulated the absorption of
nitrogen and served in a nutritional manner for citrus. While
some still classify diebackk" or exanthema of citrus as a phy-
siological disease, it is in reality a deficiency. Like many other
agricultural problems, the practice in the use of copper to
correct abnormalities preceded the theory regarding its func-
tion. Furthermore, if small amounts produced good results,
more were often used, resulting in excesses.


Deficiency Symptoms: The symptoms of manganese defici-
ency in citrus are usually less distinct than those of magne-
sium and zinc. This is due to the small contrast of the leaf
color in the deficiency pattern, and the limited areas showing
this deficiency. Nevertheless, the manganese pattern is speci-
fic and well defined, and can be easily recognized once it is

The symptoms occur on both young and mature leaves,
without affecting leaf size, whereas zinc deficiency has a
marked reduction on size of leaves, and magnesium deficien-
cy pattern is characterized by green veins on a light green
background, and may be confused with iron deficiencies.
(Compare Plates 4 and 5.) As the leaves become more ma-
ture, the pattern develops bands of green along the main and
lateral veins with light green tissue. The color contrasts are
less vivid than in the case of zinc deficiency. Plate 5 shows
the range of the manganese deficiency in grapefruit leaves.
The light green area extends to the leaf margin in severe
cases; and the advanced cases are somewhat similar to the
early stages of zinc deficiency, although the color contrasts
are never as great. If the deficiency of manganese is severe,
the pattern persists with normal size leaves and the light
green colors may develop a gray to slight bronze effect, which
might be confused with magnesium deficiency. Manganese
deficiency is often found on marl soils, hence the term "Marl

The deficiency is seldom severe enough to cause twig symp-
toms. With acute cases, however, the twigs may die, asso-
ciated with a marked reduction in growth. The symptoms of
dying twigs is not as severe as in the case of zinc deficiency,

32 Department of Agriculture

nor do the trees show the rosette or bushy appearance. Man-
ganese deficiency was for a long time confused with french-
ing or zinc deficiency. From systematic studies of zinc and
manganese treatments, the pattern differences have been
identified (6).
Manganese has a favorable effect on the quality of oranges
and tangerines, according to Skinner and Bahrt (37).
In contrast with copper and zinc, manganese deficiency
does not affect oranges and grapefruit as readily as it does
tangerines, temples and king oranges.
Soil Relations: Manganese deficiency appears more often
on marl and over-limed soils than on the neutral and acid
soils. This is due to the insolubility of manganese in alkaline
media. Marl and over-limed soils are generally slightly un-
available. In some cases acid soils show manganese deficiency
as a result of soil depletion and fixation. Where crop yields
are heavy, the soil may become depleted of available manga-
nese, but in most cases the deficiency results from unbalanced
soil conditions as much as from actual shortage of the soil.

Treatment: Manganese sulphate and oxide are commonly
used as the corrective for manganese deficiency, applied in
soil treatments at the rate of 1/ to 2 pounds per tree, the
amount depending on tree size, severity of case and type of
soil. Manganese sulphate may be applied in spray form,
using solution of about the same concentration as copper sul-
phate in Bordeaux, or in conjunction with Bordeaux and
lime sulphur sprays. Like copper and zinc spray, the manga-
nese may increase the scale hazard, thus necessitating an oily
spray to follow later. Unless the deficiency is severe, soil
treatments are generally used, except on marl soils. The
spray treatment gives quicker results, but the effects are not
as long lasting. In soil treatment, mulching, or use of heavy
cover crops with applications of manganese, will usually
Manganese Excess: No known symptoms of manganese ex-
cess have been reported in Florida, though the rates of appli-
cation have been high in places. As with other nutrients, ex-
cessive amounts of manganese will hinder the utilization of
other nutrients, and may even be toxic.

Historical Use: Manganese has become of general use in
agriculture within recent years. Its use on citrus in Florida
was suggested by the stimulating effects produced in truck
crops growing on marly soil, first reported by Schriener and
Dawson (36). Following these results, Florida citrus growers


. A B C

? S Early Intermediate Advanced Stage c

a.3 -t
4 _

a o


. a

Department of Agriculture

used manganese with success on marly soils. Skinner and his
co-workers (37) later reported that manganese on acid soils
had a marked improvement on the quality of fruit, while
Camp and Peech (6) correlated manganese deficiency in
citrus with soil analysis. Manganese is widely used in Florida
and California on citrus and other crops, especially on alka-
line soils and soils low in available manganese.


Deficiency Symptoms: Iron deficiency in citrus has been
commonly referred to as iron or marl chlorosis. The latter
term, however, is a general one applied with equal frequency
to manganese deficiency, also of widespread occurrence on
marl soils. Within recent years, iron deficiency in citrus has
markedly increased on acid sandy soils due to the accumula-
tion of copper.

Iron deficiency is characterized by a general chlorotic con-
dition of the leaves, particular the younger ones, with the
midrib and smaller veins retaining their chlorophyll longer
than the leaf tissue, resulting in a green network on a yellow-
ish-green or light green background. The range of these
colors and veinations is illustrated in Plate 5. In severe cases
the young leaves are small and yellowish to old ivory in color
and may be almost free of veination. Such leaves usually
shed early, leaving a defoliated effect. In light cases, the leaf
tissue may become green as the leaves mature and the netted
effect disappears entirely. This is not unusual on sandy soils,
but severe and chronic cases are usually associated with
marly or over-limed soils.

In acute cases, the twigs die back severely in the tree tops
and extremes of the branches, showing a marked decrease in
tree size. Such trees produce little or no fruit but other than
size of crop no characteristic fruit symptoms have been asso-
ciated with iron deficiency. Although no varieties of citrus
are susceptible, oranges seem to be the most severely affected.

It is quite common to find other deficiencies associated with
iron deficiency in citrus. This is particularly true with man-
ganese and zinc. Under such conditions there is definite
blending of the individual pattern'. Careful examination,
however, shows that the specific patterns persist and can be
recognized in the presence of others.



un .


* 4'

W 0 docd tg

0yia tg

Department of Agriculture

Soil Relations: There are three soil conditions conducive to
iron deficiency in citrus, namely: (1) marl and alkaline soils,
(2) sands with white sandy subsoil and (3) sands which have
a high amount of cumulated copper. Marl and alkaline soils
usually induce iron deficiency. Here the soil reaction has a
positive and controlling effect on the availability of a nutrient.
An alkaline reaction reduces the availability of iron, thereby
producing an iron chlorosis. An excess of carbonates on sand
produces an alkaline reaction and accounts for much of the
iron chlorosis in sandy annual crops as well as citrus. This is
greatly aggravated in soils with a low content of organic

Light sands with white subsoil are often deficient in iron.
This is aggravated by unfavorable soil reaction or excess of
other nutrients, particularly copper and heavy metals. Ex-
cesses of copper seriously aggravate iron deficiency on acid
soils and hinder production. Records by many growers indi-
cate that iron improves fruit color, especially on the light
Treatment: No entirely satisfactory treatment for iron de-
ficiency has been developed for citrus on all alkaline soils.
But some of the new Chelated materials offer promise. The
Chelate known as "Verson-ol" is successful for some marl
soils. There is good reason to feel that satisfactory chelates
will be perfected for all alkaline soils. A practical method of
treating this deficiency on such soils involves the use of heavy
mulching with organic matter and acid fertilizers. The acidu-
lated effect resulting from the fertilizer and organic matter
will usually bring enough iron into solution to alleviate the
trouble, except where the marl extends to the surface.

Spraying for iron deficiency has not been as satisfactory
with citrus as it has with pineapple and other crops. Some
reports indicate that with appropriate spreaders, iron salts
may be successfully used as a spray. In some of the Western
states, (33) injection of soluble iron salts, such a iron citrate
or tartrate, directly into the trees has been known to give
beneficial results. This treatment usually has to be repeated
at somewhat frequent intervals, and is objectionable because
of the damage to the wood.
On thin, sandy soils of acid or neutral reaction, iron sul-
phate applied at the rate of 1 to 3 pounds per tree has given
beneficial results. Even here the use of mulches proves help-
ful. Chelated iron is much faster and more desirable than
the sulphate in severe cases. But the amount of iron applied
in the Chelates is very small and the treatment has to be

Malnutrition Symptoms of Citrus

repeated almost each year. Observations and limited experi-
mental data indicate that liberal amounts of insoluble iron
ores will alleviate iron deficiency problems if the soil pH is
favorable. Where copper is excessive, adjusting soil pH to
6.0 or above is necessary to avoid severe toxicity.
Iron Excess: The soluble iron salts such as sulphates and
chlorides are acidic in nature, and will burn the moist foliage
and fruit if allowed to come into contact with them. All the
common iron salts become insoluble soon after being incor-
porated into the soil due to the tendency of iron to form
insoluble compounds with other soil constituents and nutri-
ents. For this reason excess iron reduces the availability of
phosphates. In practice, it is doubtful that difficulty will be
experienced from excess iron except under rather special and
very acid conditions. The chelates are more acid than the
common salts, and will burn foliage and fruit if not used with
Historical Use: Iron deficiency in citrus as well as other
crops has been a serious problem in some regions for many
decades. This is particularly true in alkaline soils. (9), (11),
(33). Many investigators have studied this problem with va-
ried degrees of success. The use of chelated iron was first
studied in California. Leonard and Stewart of Florida Citrus
Experiment Station showed that it was a ready and quick
method of combatting iron deficiency of citrus in Florida.
This has proven to be very valuable for severe cases of iron


Deficiency Symptoms: Like magnesium, zinc deficiency
symptoms are characterized by specific leaf discolorations
commonly known in Florida as "Frenching", and in Cali-
fornia as "Foliocellosis" and "Mottle leaf". The initial stages
of the deficiency appear as irregular chlorotic areas in the
leaf tissue, between the main and lateral veins. The tissue
immediately adjoining the veins remains green, while the
chlorophyll disappears (or fails to develop in the leaf tissue).
This results in an irregular, mottled or variegated mixture of
vivid green and white to yellow colors. These colors and
range of leaf patterns are illustrated in Plate 6. These pat-
terns will serve to identify the zinc deficiency more correctly
than word descriptions.
In the early stages of the deficiency, the characteristic leaf

Department of Agriculture

pattern may occur on apparently normal sized leaves, but as
the deficiency becomes more acute, the new leaves are small,
narrow and pointed, with a greater loss of chlorophyll as il-
lustrated in Plate 4 (B). Small, pointed leaves are one of the
distinctive zinc deficiency symptoms in citrus.

Associated with the deficiency symptoms, there are marked
tendencies for twigs to be small, short and bushy. These
twigs are weak and die back rapidly, leaving an abundance
of dead wood and partly defoliated branches so commonly
associated with zinc deficiency in the acute stages. This ad-
vanced deficiency is often associated with dense interior
growth of water sprouts.

Although zinc deficiencies may occur on all varieties of
citrus, it is most severe on oranges and least severe on tan-
gerines. Pineapples and Valencias are more susceptible than
the early varieties of oranges. The deficiency is commonly
associated with copper and magnesium deficiencies and may
appear more severe in combinations than when alone, be-
cause of the increased weakness of the trees. But the indi-
vidual leaf patterns remain almost unchanged.

Fruit produced on zinc deficient trees is usually small, off-
size, and of poor quality. In severe cases, it is very small with
woody pulp and insipid taste, except when borne on water
sprouts (so common with zinc deficiency). Here it is large,
coarse and of poor quality.

Soil Relations: Although zinc deficiency in citrus may oc-
cur on almost any soil type, it is most commonly found on
marls, over-limed or strongly acid soils. Excesses of lime, ni-
trogen, phosphates, potash and other nutrients tend to retard
the availability of zinc. A pH of about 6.0 appears to be the
optimum reaction for the availability of zinc under the soil
conditions in Florida. The necessity for a well-balanced fer-
tilizer is more important on sandy lands than on heavier
types. Zinc is more sensitive to unbalanced nutrients and soil
reaction than most other nutrients.

Treatment: Zinc sulphate spray was the common treat-
ment for this deficiency in the early years of its usage. Cali-
fornia growers were the first to use zinc oxide as a successful
treatment for this deficiency. Zinc oxide and carbonate are
now being successfully used in many cases. But the scale prob-
lem is usually worse following sprays. Within recent years
many growers have successfully used soil applications of zinc,
where the soil reaction and phosphates can be modified.









Typical Stage Advanced Stage

Department of Agriculture

The most general treatment for zinc deficiency consist of
two to four pounds of the zinc sulphate per one hundred gal-
lons of lime sulphur or Bordeaux spray. These rates are for
corrective measures. One-half these amounts will suffice for
a maintenance treatment. The treatments are usually most
effective when applied just prior to new growth. The spray
treatments may be required once or twice a year for control,
but the need for soil treatments is much less frequent. Soil
applications at the rate of 1/3 to 2/3 pound of the sulphate
or the equivalent per tree annually will furnish ample zinc
for citrus, except in unbalanced soil conditions.
Zinc Excess: Excess zinc in the spray may aggravate the
scale problem and over-green the fruit, especially if applied
as a spray late in season. Due to the tendency for insoluble
zinc compounds to form in the soil, an excess of zinc would
not likely occur, except with large amounts on rather light
soils. Zinc is not as toxic as copper, but excess rates would
likely cause a burning and loss of leaves.

Historical Use: The use of zinc as a corrective for french-
ing in citrus developed first in California about 1932 (11, 26),
(32), (33). Its specific usage on citrus resulted from a series
of studies dealing with the influence of secondary elements
on little leaf of deciduous fruit (11). Within recent years,
investigators in many citrus growing areas have shown the
specific needs of zinc for citrus. It is now widely used and
accepted as a regular part of citrus production program.


Deficiency Symptoms: The symptom of molybdenum defi-
ciency appears first as water soaked areas in the spring flush,
later developing into interveinal circular chlorotic areas. It
is more noticeable during the summer and early fall months.
Figure 9 gives a typical circular spot pattern. In this figure
the green and yellow chlorotic areas are contrasted in black
and white. This yellow circular spotting is a positive identi-
fication of molybdenum deficiency. With advanced cases the
yellow tissue becomes necrotic and often disappears, leaving
holes in the leaves. Severly affected trees may become de-
foliated and the fruit show marked breakdown of the rind.
The deficiency has been reported in all kinds of fruit, but
trees on grapefruit rootstock appear to be the most suscep-

Soil Relations: Molybdenum deficiency is found on acid

Malnutrition Symptoms of Citrus

sands far more than on heavier and better types. Low nitro-
gen fertilizer on deep acid sands usually shows this deficiency
more than on the normal soils, and it is rarely if ever noted
on marl soils. Acid fertilizer aggravates the deficiency,
whereas neutral fertilizers and lime usually relieve it. The
availability of soil molybdenum seems to decrease with an
increase in soil acidity. It appears that extremely low
amounts of water soluble molybdenum are required, ranging
from 5/1000ths or less parts per million before the deficiency
symptoms develop. The deficiency is somewhat seasonal and
may disappear without any special treatment. Only in rare
cases does it influence production. Liberal amounts of dolo-
mite often correct the deficiency.
Treatment: The amount of molybdenum necessary for plant
growth, including citrus, is indeed very small, amounting to
grams rather than pounds per tree. The actual amount to
correct deficiency ranges from 1 to 2 ounces of sodium molyb-
date per 100 gallons of spray or equivalent amounts from
other soluble sources. It can be satisfactorily applied in lime
sulphur spray. Affected trees are rather responsive, and fav-
orable results show up 2 to 4 weeks following the application.
Wherever a deficiency is suspected, the application should be
made in the spring.
Historical Use: Floyd (13) first described this pattern as
yellow spot in 1908, reporting it as being present in many
groves in Florida at that time. Since then several attempts
have been made to determine its cause, all of which were un-

Figure 9. Molybdenum Deficiency in Orange leaves. This deficiency is charac-
terized by yellow circular chlorotic areas. (See text.) It was formerly known as

Department of Agriculture

successful until 1950, when Stewart and Leonard (41) of the
Florida Experiment Station showed experimentally that yel-
low spot was due to a deficiency of molybdenum.


Since deficiency symptoms of many nutrients involve a loss
of chlorophyll, it appears advisable to present the commonly
observed chlorosis and toxicity symptoms induced by certain
chemicals in order to avoid confusion and mistaken identity.
The following leaf abnormalities have been associated with
certain chemicals, namely: (1) Perchlorate Chlorosis induced
by impurities in Chilean Nitrate of Soda-Potash, (2) Biuret
Chlorosis induced by impurities in Urea, (3) Fluorine Chloro-
sis induced by fluorine arising from triple super phosphate
plants, (4) Arsenic toxicity chlorosiss) induced by excess
arsenic in sprays, (5) Boron toxicity resulting from excess
boron in either spray or fertilizer.

1. PERCHLORATE CHLOROSIS: The yellow tipping of
citrus leaves has been observed in Florida for many years and
was once thought to be associated with excess boron in cer-
tain fertilizers. The symptoms first develop at the leaf tip
and may be confused with boron toxicity, but careful exami-
nation reveals that the yellow tipping, that is, the chlorotic
areas, do not blend with adjoining green tissue. The transi-
tion from green to chlorotic areas is sharp and abrupt, pro-
ducing a patchy appearance; whereas the boron toxicity pat-
tern shows a gradual change from green to chlorotic areas,
producing a blend of colors. Furthermore, the under surface
of the yellow tipped leaves is free from resinous excretions
which are common with boron toxicity. The difference in the
patchy appearance and blends is illustrated in black and
white in Figure 10, and can be easily recognized by the cas-
ual observer without confusion. The yellow tipped pattern
has been experimentally proven to be due to perchlorate im-
purities in Chilean Nitrate of Soda-Potash (40). The chloro-
sis is less common now than in former years and has little or
no influence on production. Reports from producers indicate
that these impurities are being removed from the commercial

2. BIURET TOXICITY: A leaf chlorosis resulting from
sprays and soil applications of urea has caused considerable
attention during recent years. The chlorosis has been experi-
mentally shown by Oberbacker (26) to be due to Biuret im-

Malnutrition Symptoms of Citrus

Figure 10. Perchlorate Chlorosis in Grapefruit Leaves. The patchy-like chlorotic
areas, indicated by light color in above figure, are characteristic of Perchlorate

purities in commercial grades of urea. The symptoms first
develop at the leaf tips and margins, and the early stages may
be confused with the early stages of Perchlorate Chlorosis;
but with the Biuret, the green and chlorotic areas blend,
though some patchy appearance may be in evidence. The
color of Biuret chlorosis is yellow compared to an orange color
with the Perchlorate chlorosis. The advanced cases of Biuret
chlorosis may show a burning effect which is more severe on
immature than mature leaves. The chlorosis may spread over
the entire leaf and cause severe drops. The yellow color of
the Biuret chlorosis is similar to that of boron toxicity, but the
Biuret colors are somewhat patchy and free from gumming
on the under surface. Light and severe stages of the Biuret
toxicity are shown in black and white (contrasting the yellow
with green) in Figure 11, for comparative study.

3. FLUORINE TOXICITY: Certain chlorotic leaf patterns
have been observed near the triple super phosphate plants in
Polk and Hillsborough counties during recent years. But thus
far they have not produced serious leaf defoliation, and it ap-
pears that the phosphate plants have the fluorine fumes un-
der control. The early stages of the fluorine chlorosis are
somewhat similar to the early stages of boron toxicity, but the
under surface of the boron toxicity leaves usually carry the

Department of Agriculture

Figure 11. "Biuret" Chlorosis in citrus leaves following application of Uramon
containing Biuret impurity.
LEFT: Orange leaf showing slight Biuret pattern.
CENTER and RIGHT: Grapefruit leaves showing severe Biuret patterns. The
blends of chlorotic areas, light into green areas (black), differentiate the Biuret
Chlorosis from Perchlorate Chlorosis. The absence of gum on undersurface of
chlorotic areas differentiates the Biuret Chlorosis from Boron toxicity.

resinous excretion which is free from that of the fluorine
toxicity. Furthermore, the fluorine toxicity shows considera-
ble blends of different shades of green which sometimes are
confused with the shades of green in manganese deficiency.
There are no known treatments once the leaf patterns develop.

4. ARSENIC TOXICITY: The chlorotic leaf patterns fre-
quently observed following arsenic sprays is commonly known
as arsenic toxicity. The degree of chlorosis is usually in the
order of the amount of arsenic applied. Weak trees seem to
be affected more than healthy trees. The symptoms show a
loss of chlorophyll without any distinct patterns except that
of chlorosis. Arsenic toxicity may be confused with the man-
ganese deficiency patterns, but close examination indicates
that the chlorosis due to arsenic extends across the veins,
whereas, the chlorosis from the manganese deficiency is inter-
veined. Figure 12 (in black and white) contrasting the green
with chlorotic areas is a typical, arsenic toxicity pattern. Note
the differences in leaf veins in Figure 12 compared to Plate 4.

Malnutrition Symptoms of Citrus

Figure 12. Grapefruit leaves showing progressive stages of arsenic toxicity. This
pattern is sometimes confused with manganese deficiency. The chlorosis result-
ing from arsenic toxicity is identified by a bronze-like color which is irregular
and does not remain consistent with different shades of green so characteristic
with manganese deficiency.


Although the grower may be able to recognize and diag-
nose deficiency symptoms, it is much better for him to know
how to avoid deficiencies than to correct them because citrus
trees are considerably impaired in health before visible de-
ficiencies are in evidence.
The successful production of citrus or any crop is the result
of several factors operating simultaneously; namely, (a) Ade-
quate soil moisture, (b) Favorable temperature, (c) Favor-
able reaction (pH), (d) Favorable soil conditions to promote
penetration of fertilizer into the root zone, (e) Pest control,
(f) Soil Aeration, (g) Ample amounts of organic matter, and
(h) Adequate amounts of properly balanced plant nutrients.
If any one of these factors is not favorable, all of the others
are impaired.
In order to be a successful operator, it will be necessary for
growers to study and evaluate each factor affecting produc-
tion, including the kind and amounts of fertilizers applied on

46 Department of Agriculture

his individual soil. This involves a working knowledge of
what the crops actually remove from the soil, what nutrients
are lost through leaching processes, and what amounts are
needed to provide for tree and cover crop growth. This also
involves a knowledge of what nutrients combine with each
other and become insoluble and unavailable, and what bene-
fits are derived from cover crops, as well as a knowledge of
seasonal absorption as related to time of fertilizer application.
The major problem confronting most Florida growers is
that of applying the needed fertilizer nutrients in a balanced
form to avoid antagonistic effects resulting in deficiencies.
Other citrus areas do not use the poundage of commercial
plant food as do Florida growers.
Many growers are successfully practicing these manage-
ment factors through the use of soil amendments, irrigation,
cultural practices to include cover crops, pest control, and
fertilizer applications as needed.
Reliable records indicate that a large per cent of nutrient
deficiencies in Florida citrus is traceable to unbalanced and
often blind fertilizer practices. This is especially true for
growers on sands and sandy soils so common in Florida. Con-
tinued fertilizer application on such soils without regard to
accumulations and leaching losses, is a blind and expensive
operation. A cross section of data regarding these problems
is presented in the following tables which will serve as guides.
The first of these is presented in Table 1 which shows the
nutrient content of citrus as related to fertilizer materials.
The data in this table represents averages, and individual
cases could be expected to vary as much as 10 to 20%. From
these data, it may be seen that citrus fruits contain about 3
times as much nitrogen as phosphoric acid, and about 1.5
times as much potash as nitrogen. This is a basic starting point
regarding the nutrient ratios utilized by citrus. The content
of magnesium in the fruit is relatively high-almost that of
phosphorus-and several times that of the combined amounts
of copper, manganese and zinc. This explains the general
need of magnesium for citrus. The content of sulphur is also
high. But thus far this nutrient has been supplied as a carrier
of other nutrients and no need for extra additions have arisen.
Calcium is also a carrier of other nutrients and is rarely need-
ed as a nutrient, yet often needed as a soil correctant. Citrus
foliage contains remarkably high amounts of calcium, com-
pared to the other nutrients. It is of significant interest to

Table 1
(Data represents average analysis-Dry Weight)

Types of'

Nutrients in
Soil Amendments

Trace Elements

Usually Added
as Carriers of
Other Nutrients

ChemoicalI Foriic.
of ,,lant Nutri-
SIts (Gene-rally

Phos. Acid
Boric Acid

Percent of
in Fruit
Iry Basis

Lhs. iln
100 B5oxes

N 1.0 10 30
P2Os .38 3.8 15.2
K0O 1.50 15 30
MgO .30 3 9

MgO .30
CaO .80




Lbs. Needed
With Different
Efficiency Levels
lbs. Per Cent


Approximate Lbs. of
Following Materials
Required to Supply
Needed Nutrients
200# Nitrate Soda
75# Superphos. (20%)
50# Muriate Potash
50# Sulpomag

3 9 55# Dolomite
8 24 80# Dolomite
.07 .7 10% (a) 2.1# Borax
.007 .7 1% (b) 2.3# Cop. Sulphate
.025 2.5 1% (b) 7.5# Iron Sulphate
.009 .9 1% (b) 3.0# Mang. Sulphate
.016 1.6 1% (b) 3.5# Zinc Sulphate

Not usually
considered in making
up fertilizer

(a) Calculated on basis of 10 times crop removal, or 10% efficiency.
(b) Calculated on basis of 100 times crop removal, or 1% efficiency.
(e) Ample amounts of sulphur and chlorine are usually applied as carriers of other nutrients. If no sodium nitrate is included in ferti-
lizer, sodium may become a limiting factor.
(x) Since potash serves largely as a regulator and catalyst in the plant and does not leach as rapidly as nitrogen, and that phosphates
are not subject to leaching losses, a fertilizer analyzing 10-4-10-4-.4-.5-.8-.25 (Nitrogen, Phosphoric Acid, Potash, Magnesium, Manga-
nese, Copper, Zinc, Iron Boric Acid), applied at the rate of approximately 3 pounds per box of fruit annually, will supply the
needs for lemon rootstock on sandy lands. Sour root and sweet rootstock would require 15% to 25% more than the lemon root on
similar soils. Heavier soils such as clays and loams will need more phosphate and less nitrogen and potash; furthermore, organic
soils and soils carrying abundant leguminous cover crops will require still less nitrogen.
(y) Since molybdenum is required in such small amounts, less than 1 pound per acre, it is uuaslly applied in spray at the rate of 1 to
2 ounces per 100 gallons spray.

Table 2
(Primary plant Nutrients)
Lbs. Required to Give
FERTILIZER MATERIALS Nitrogen Phos. Acid Potash 20 Lbs. or 1 Unit
Percent Percent Percent Nitrogen Phos. Acid Potash
N P20, KO N PO, K20
Nitrate of Soda 16 ......... 125
Nitrate of Soda-Potash 14 .... 14 143 ...... 143
Nitrate of lime (Calcium nitrate) 15 .......... 134
Nitrate of Potassium 13 44 154 46
Cal-Nitro 20.5 ......... 98 ......
Sulphate of Ammonia 20.5 ........... 98 ............
"Ammophos" (Ammonium phos.) 11-16 20-48 ...... 125-182 42-100
Uramon & Urea 42-46 ... 44-48 ........
Calcium Cyanamide 22 ........... 91 ......
Nitrogen Solutions 37-44 ........... 46-54
Dried ground fish & Guano 6-10 4-6 ...... 200-334 334-500 ......
Animal tankage (1) 8.2 8 ...... 244 250 ......
Cottonseed meal & Castor meal 5-8 ......... 250-400 ....
Bonemeal 2-5 24 400-1000 83 ....
Ammoniated Superphosphate 4 16 500 125
Superphosphate (Acid Phosphate) ...... 16-20 ............ 100-125
Double & triple superphosphates ...... 32-40 50-63 ....
Basic slag ......8-16 .......... 125-250
Ground phosphate rock (2) ...... 4 ........... 500
Muriate of Potash ......50-60 ........... 34-40
Sulphate of Potash ............ 48-50 .... ...... 40-41
Sulphate of Potash-Magnesia.. 25 ........... 80
Manure salts ............ 20-30 ............ 67-100
Kainit ............ 14-20 ............ 100-143
Hardwood ashes ..... 2.-8 ............ 250-1000
(1) Many organic ammoniates are on the market, such as milorgranite, compost, humus, and so forth.
(2) Soft and "Colloidal Phosphates" are also considered as raw phosphates carrying from 15 to 32
ptr cent total P.O. and from 2% to 4% available P205.

Malnutrition Symptoms of Citrus

note that the citrus fruit contains more boric acid (a trace
element) than the combined amounts of copper, manganese
and zinc. It is of further interest to note that only grams and
not pounds of molybdenum are required.

Naturally the fruit does not absorb all of the nutrients re-
quired to produce the crop. The tree, cover crops, and soil
itself absorb considerable amounts. Moreover, leaching takes
its toll. Only under very favorable conditions does the fruit
absorb more plant food than is applied in the fertilizer, be-
cause of leaching losses, fixation and needs of cover crops.
Herein lies the secret of good soil management and efficient
production. The success of any science depends on the effi-
cient management of the factors involved, and the production
of citrus is no exception. The assumed efficiency levels given
in the table are reasonably good working units.


In order that a grower may better understand the utiliza-
tion of his fertilizer nutrients, the data in Table 1 are calcu-
lated to give the nutrient requirements for different efficiency
levels; namely, 33 1/3% for nitrogen, 25% phosphoric acid,
50% potash, 10% for boric acid, 1% each for copper, zinc,
manganese and iron. Records show that some groves have an
efficiency of less than 10% of the major nutrients and less
than 1% of the minor nutrients, while others have an effici-
ency of over 50 % of the major nutrients and 5 % of the minor
nutrients. As a rule the higher the efficiency, the higher the
net profit to the grower.

Groves of low fertilizer efficiency usually mean unprofita-
ble returns and are indicative of one or more vital factors
limiting utilization, e.g., moisture, acidity, alkalinity, deficien-
cy, diseases, etc. If copper is deficient in the soil, or its utiliza-
tion hindered by unbalanced nutrient conditions, the crop will
be seriously impaired, even though the actual pounds needed
are very small. The same may be true of zinc, magnesium,
and even iron. If the soil conditions are favorable and the
secondary elements applied in proper amounts the efficiency
of the major nutrients is increased, sometimes as much as
two to three hundred per cent.

The amounts of representative fertilizer materials needed
for 100 boxes of fruit are also listed in Table 1. From these

Department of Agriculture

Table 3


All plots received steamed bonemeal and sulphate of potash, and equivalent
amounts of nitrogen from sources indicated. The results are expressed in pounds
of fruit per tree*

Blood : Nitrate Nitrate
of Soda and of Soda
Nitrate of Sulphate of Dried Sulphate of Sulphate of
Soda Ammonia Blood Ammonia Ammonia
With With With With With
No *** No *** No *** No *** No ***
YEAR Copper Copper Copper Copper Copper Copper Copper Copper Copper Coppel
1927-28 63 198 138 97 157 88 176 185 33
1928-29 133 127 95 153 73 125 100 85 57 3'


1929-30 121 133 94 170 166 115
1930-31 158 317 250 375 167 288
1931-32 201 378 210 216 154 167
1932-33 110 323 77 161 18 124
1933-34 250 302 248 235 184 135

115 168 68 13
198 198 127 98
217 244 291 210
38 85 59 22
223 318 334 340

SUB TOTAL 1036 1778 1112 1407 919 1042 1067 1283 969 724

1934-35 96 318 85 153 70 82 28 44 63 12

1935-36 288 462 334 409 381 354 281 461 344 373

1936-37 12 350 16 158 28 165 6 86 5 204

1937-38 321 567 30 423 285 483 167 582 174 499

TOTALS 1753 3475 1577 2550 1683 2126 1549 2456 1555 1812

Data from Lake Alfred Experiment Station Mimeograph Report, 1938. Drops hot
included in records.
** Plot 10 received all nitrogen from compost until 1930.
*** Copper sulphate applied in two applications, Feb., 1934, and Nov., 1935.
Underlined figures are crops affected by application.
The superiority of inorganic sources of nitrogen over organic sources, has been fur-
ther confirmed by the Fla. Experiment Station in 1949 Proceedings Fla. State Hort.
Society. The above data show that dried blood as a source of nitrogen was not
as efficient as nitrate of soda and sulphate of ammonia without addition of copper
for a period of 7 years. The addition of copper in 1934 markedly Increased pro-
duction, with the inorganic sources of nitrogen in the lead. See discussion of this
table on page 51.

Malnutrition Symptoms of Citrus

data a grower may calculate the required nutrients for dif-
ferent size crops. For example, 100 boxes of fruit contain on
an average, 10 pounds of nitrogen, 3.5 pounds of phosphoric
acid, 15 pounds of potash and 2.5 pounds of magnesium. This
means that with 33 1/3 % efficiency for nitrogen, 25 % phos-
phoric acid, 50% potash and 33% magnesium, 100 boxes of
fruit will need 30 pounds of nitrogen, 15 pounds of phos-
phoric acid, 30 pounds of potash and 9 pounds of magnesium.
These are equivalent, respectively, to 200 pounds nitrate of
soda, 75 pounds 20% superphosphate, 60 pounds muriate of
potash and 75 pounds of dolomite, or 500 pounds of a 6-2-9-2
(nitrogen, phosphoric acid, potash and magnesium). Conser-
vative estimates indicate that bearing trees require about one-
half as much plant food as the fruit consumes, due allowance
should be made for cover crops and leaching losses. If the
fertilizer efficiency is less than 25% for the major nutrients
and less than 2 % for trace elements, the practice is wasteful
(see footnote Table 1). These data are cited for grower's
comparison with his own records.
Table 2 gives the composition of the commonly used com-
mercial fertilizer materials with the pounds needed to give 1
unit or 20 pounds plant food. A working knowledge of these
materials will be of great help to one trying to understand
his fertilizer problem. They are used in making fertilizer
mixtures, and unless a grower is familiar with their composi-
tion and properties, it will be difficult for him to intelligently
understand fertilizer problems.
The data in Table 3 give the relative efficiency of different
sources of nitrogen used in producing citrus under Florida
conditions. Although these data were secured on one soil
type (Lakeland sand), they are representative and compare
favorably with observations and data from other areas, and
are confirmed by grower experience. These records cover a
ten year period of continuous nitrogen comparison (nitrogen
being the only variable), and the data show that with the
addition of copper the inorganic sources were noticably su-
perior to the organic sources. This has been a debated ques-
tion for many years, but repeated trials by growers and re-
search workers (*) reaffirm the records that when the need-
ed secondaries and other nutrients are furnished, inorganic
nitrogen is more efficient than organic for citrus in Florida.
From an overall viewpoint it would appear that the organic

(*) Proc. Fla. State Hort. Soc. 1949.

Department of Agriculture

sources of nitrogen would be superior to the inorganic on
sandy soils in a humid climate, because the organic sources
are: (a) less leachable, (b) contain more trace elements, (c)
carry more calcium and magnesium, and (d) have more hu-
mus producing materials. However, repeated records by many
workers show that pound for pound the inorganic sources of
nitrogen when supplemented with needed secondaries and
trace elements are superior to the organic sources. This is of
particular interest to practical growers because the inorganic
sources are usually less expensive and more controllable. The
records indicate that the organic sources do not furnish
enough available nitrogen in the root zone during the critical
winter and spring months to take care of needs. Then during
summer, with more favorable temperature and moisture, the
organic sources become available and are apparently lost
through leaching processes or voltalization as gasses. Proper
recognition and use of these facts will be of great help to


Unless the leachability and relative losses of plant nutri-
ents are taken into consideration in formulating fertilizer
grades on sandy lands in humid regions, the grower cannot
escape confusion. The data in Table 4 show the total leach-
ings for a typical twelve month period (1924) from a repre-
sentative grove soil, receiving different sources of nitrogen.
These records show that insoluble organic nitrogen tends
to reduce the total leaching losses, and that calcium losses
were greater from superphosphate than from bone meal treat-
ments, and that nitrates, sulphates, magnesium, sodium and
potassium leach to a far greater degree than phosphates, iron
and ammoniacal nitrogen, regardless of whether the ferti-
lizer was acid or neutral.
The data in Table 5 show that almost 100 per cent of ni-
trate nitrogen is leached below the 24 inch soil level in typi-
cal soils, with 10 inches of water, whereas the same amount
of water leached about 2/3 of the potash. Only in excep-
tional cases will the leaching losses be as great from loams
and clay soils as from sands.
Growers can materially profit by carefully studying the
data in these tables when formulating fertilizer grades be-

Malnutrition Symptoms of Citrus 53

Table 4

Figures are in Pounds per Acre, Except Drainage as Noted (a)

TANK NO. No. 1 No. 2 No. 3 No. 4
Complete Fertilizer with
Different Sources of Sulphate
Nitrogen of Manure Blood Nitrate of
(P,O. from Superphosphate) Ammonia Soda
Total drainage
in acre inches 19.7 16.6 12.9 14.1
Total solids 16,317.00 6,365.00 8,735.00 1,243.20
Fixed solids 11,777.00 5,572.00 7,353.00 10,954.00
Ammonia 151.35 1.08 2.55 1.59
Nitrites 2.48 .13 .15 .40
Nitrates (b) 1,321.00 76.81 476.75 1,628.00
Phosphoric acid 7.30 3.36 3.68 3.25
Sulphates 6,815.00 2,775.00 3,868.00 4,724.00
Chlorine 115.77 145.24 111.12 269.50
Calcium oxide 3,130.00 1,076.70 1,948.00 2,134.00
Sodium oxide 375.75 338.55 382.95 1,820.50
Potassium oxide 960.15 782.55 643.80 836.00
Iron oxide 3.77 .99 1.08 1.04
Magnesium oxide 266.40 170.94 123.92

TANK NO. No. 5 No. 6 No. 7 No. 8
Complete Fertilizer with
Different Sources of Sulphate
Nitrogen Nitrate of of Blood Manure
(P.,0 from Bone Meal) Soda Ammonia
Total drainage
in acre inches 11.60 19.20 10.20 15.0
Total solids 4,570.50 7,524.00 4,801.50 3,987.50
Fixed solids 3,206.50 5,329.50 3,437.50 3,135.00
Ammonia 2.02 121.00 9.63 2.79
Nitrites .69 8.19 .68 .46
Nitrates (b) 1,265.00 1,155.00 675.00 555.00
Phosphoric acid 1.65 3.91 1.87 2.94
Sulphates 968.00 2,458.00 1,204.50 1,342.00
Chlorine 96.80 148.50 154.00 154.00
Calcium oxide 177.00 687.50 594.00 250.00
Sodium oxide 1,122.00 319.00 473.00 329.45
Potassium oxide 517.00 803.00 608.85 841.50
Iron oxide .54 1.38 .44 .63
Magnesium oxide 66.55 144.10 150.70 195.80

(a) From Florida Agricultural Experiment Station Report, 1925. (Calculated.)
(b) To convert nitrates into nitrogen divide by 4.4. For example, the 1,321.00 pounds
of nitrates in No. 1 would equal (1321+4.4),300 pounds nitrogen.
The leaching data in the above table represents the relative plant food losses
from Lakeland sand receiving different sources of nitrogen fertilizers with and
without bonemeal. Although the plant food losses from these heavily fertilized tanks
are much greater than field records, the losses from the ammonium sulphate exceed
those of the other treatments. This is largely due to the acidulating effect of the
sulphate radical. The conditioning effects of the manure and bonemeal had a pro-
nounced influence in retarding leaching losses.

Department of Agriculture

cause they show extensive leaching of some nutrients, and
relatively none with others. The losses must be restored,
otherwise crop production will be hindered. If one nutrient
leaches more rapidly than another, it would be reasonable to
assume that the one subject to the greatest leaching should
be used in proportionately larger amounts. To ignore this
principle means an unbalanced soil, and loss to the grower.
Furthermore, repeated applications of a nutrient which does
not leach will result in accumulation of such nutrient. This
has been confirmed by many workers. Accumulations and un-
balanced nutrients create more problems on sands than on
heavy soils. The records indicate that it is far better for a
grower to keep his soil nutrients balanced, void of extremes,
and supplement leaching losses, rather than to use blanket
applications year after year, and risk the danger of guessing.


Records by many workers show that repeated application
of high levels of available phosphates on sandy lands tends
to build a reserve of phosphates in the soil. The data in
Table 6 shows that in addition to phosphate accumulation,
copper and manganese tend to accumulate with repeated ap-
plications. To a certain extent calcium, magnesium and pot-
ash accumulate in soils, but nothing like phosphates and cop-
per. If properly managed, the principle of building soil re-
serves on sands is to be commended, but it is necessary to
guard against excesses which result in toxicities and antago-
nistic effects.

Too much emphasis can hardly be placed on the influence
of soil reaction on the leaching losses. However, pH records
are not enough. The amounts of calcium and magnesium in
the soil are more important than pH alone. Rain water has
an ideal pH, ranging from 5.5 to 6.5, yet it has no calcium.

Strongly acid soils mean dissolving and leaching loss of
bases, while alkaline soils mean a locking effect of certain
nutrients. The increased losses of calcium and other bases
with ammonium sulphate nitrogen in Table 4 are due to the
acidulating effects of this material. A reaction of pH 6.0 is
considered to be about optimum for citrus on sandy soils. A
soil reaction of pH 7.0 or above tends to lock such nutrients
as manganese, iron and zinc. These data will prove helpful
in studying the problem of leaching losses.

Malnutrition Symptoms of Citrus 55

Table 5
The soils were placed in aluminum tubes 2-i'" in diameter, 26" long, by
passing tube into soil without molesting soil column. The tubes were then
placed in racks with appropriate sieves to hold soils in place, and distilled
water added at rate of approximately 2 inches at a time. The nutrients were
determined in the leachate using standard procedures and technique.
A 6-6-6 fertilizer was applied at the rate of 2000 pounds per acre to both the
Lakeland and Gainesville soils and 1000 pounds per acre to the Leon soil, after
10 inches of water had been added. The first two soils had been fertilized prior
to drawing samples for study.

1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
(Grove Soil)
Nitrate Nitrogen 84 49 14 6 6 46 34 10 4 3
Phosphoric Acid 0.1 0.2 0.1 0.2 0.6 0.3 0.9 4 9 11
Potash 42 21 8 11 8 39 49 28 17 13
Calcium 52 32 19 10 7 47 41 17 6 2
Magnesium 34 20 10 2 2 26 23 4 3 1
(Virgin Soil)
Nitrate Nitrogen 6 4 3 3 2 19 18 4 1 0.5
Phosphoric Acid 3 0.5 0.2 0.8 0.5 10 36 14 6 3
Potash 1 2 3 2 1 12 37 8 3 2
Calcium 6 4 4 5 6 9 15 7 3 3
Magnesium 5 3 1 1 0.6 29 18 1 3 0
(Grove Soil)
Nitrate Nitrogen 34 16 5 5 4 20 46 13 8 5
Phosphoric Acid 0.2 0.1 0.2 0.7 0.4 0.6 0.6 0.6 0.4 0
Potash 14 7 3 8 6 15 38 31 19 10
Calcium 32 17 15 12 9 33 73 57 24 8
Magnesium 16 7 4 2 1 10 34 23 8 2

Comments: Numerous records indicate that these data represent what happens
to grove soils when fertilizers are applied. The records clearly show
the range of leaching losses with excess water, and that the losses
are directly related to the time of fertilizer application. From these
records it would be logical to assume that 8 to 10 inches of rainfall
within a period of a week would deplete the soluble nutrients from
these sands which are typical Florida sands. Furthermore, phos-
phates are leached in appreciable amounts from the Leon sand,
slight amounts from Lakeland sand, but only trace amounts from
the Gainesville sandy loam. It is of marked interest to note that
potash is retained by all the soils longer than the nitrogen and

(Data represents averages of samples taken at leaf drip November, 1955)
from Short Research Grove, Soil Science Foundation
Available Nutrients in Pounds Per Acre
Plot Soil Cal- Magne- Phos- Pot- Manga-
No. Treatment* Depth pH cium sium Acid ash nese Copper
1, 21, 31, 36 Standard 0-12 5.9 972 247 123 58 12.6 4.0
45, 59, 62, 76 (6-4-8-2-.5-.25) 12-24 5.2 83 19 35 21 4.3 T
24-36 4.8 T 8 13 16 3.6 T
8, 46 Standard with 46% greater 0-12 5.9 806 167 159 72 13.6 7.3
rate 6-4-8-2-.5-.25 12-24 4.7 24 22 40 22 3.0 T
24-36 4.6 T 16 15 19 3.0 T
17, 49 Standard with Phos. Acid 0-12 6.3 785 227 46 58 9.0 2.0 -
6-0-8-2-.5-.25 12-24 5.5 88 32 7 26 2.0 T
24-36 5.1 8 20 7 17 T T "
24, 68 Standard without Potash 0-12 6.1 732 155 106 19 9.0 4.0
6-4-0-2-.5-.25 12-24 5.3 60 16 27 7 4.0 2.0
24-36 5.2 12 11 8 5 T 1.5
14, 52 Standard with 1/2 regular 0-12 6.0 708 158 108 40 10.5 2.5
Potash, 6-4-4-2-.5-.25 12-24 5.0 12 12 23 10 3.0 T
24-36 4.9 T 4 5 12 2.5 T
6, 38 Standard without Mag- 0-12 5.3 600 4 100 58 11.0 4.0 2.
nesium, 6-4-8-0-.5-.25 12-24 4.6 T T 32 16 8.0 T
24-36 4.6 T T 17 19 3.0 T
35, 72 Standard without Copper 0-12 6.1 828 224 124 62 10.5 T
6-4-8-2-.5-0 12-24 5.2 36 23 44 24 1.5 T
24-36 4.9 T 13 16 16 T T
30, 35 Standard with 3 times 0-12 6.0 792 227 116 63 10.3 22.6
Copper, 6-4-8-2-.5-.75 12-24 5.2 40 21 28 20 3.0 .6
24-36 4.9 T 13 10 17 2.6 T
* The Standard fertilizer consisted of a 6-4-8-2-.5-.25-.2-.1 (N-P205-K-2U-MgO-MnO-CuO-ZnO-B203). respectively. This mixture was applied
in three applications per year. approximately 40% of the annual needs in November and 30% each in February and Tune. The ingredi-
ents were derived from standard materials. The mixture contained 17% insoluble organic nitrogen, and the balance one-half each from ni-
trate and ammonium nitrogen. Variations from the mixture are noted. The fertilizers were applied continuously to a Pineapple grove
(set on Lakeland sand in 19y3!., from 1942 to 1955, inclusive. The rates were according to accepted practice. increasing with age of the
Irees. The trees averaged I; boxes of fruit in 1956. The data taken from 1955 are typical and representative, showing the trends of the
different fertilizer nutrients. These records indicate that all nutrients are present in measurable amounts, even where none lias been
applied for a period of 13 years. This in itself is of significance because the practical grower wants to know how much is needed for
optilnium production, and only through analysis is it possible to lnow these nutrient needs. Without correlating the soil analysis data with
crop response, the analyses have relatively no value.

Malnutrition Symptoms of Citrus


In a measure, growing citrus on many Florida soils is simi-
lar to working with sand cultures in which the nutrients are
added in proportion to those required (absorbed) by the crop.
The sand culture method of growing plants has been suc-
cessfully used by many workers. Due allowance should be
made for leaching and fixation losses, even on sands. Where
this is done, records during the past two decades have shown
that the method is profitable. Here again it should be pointed
out that attempts to guess at the extent of nutrient reserves
and leaching losses, even on sands, are misleading, resulting
in unbalanced nutrients and wasteful practices. The exces-
sive accumulation of phosphates and copper in Florida groves
has been a result of blind guessing.
Since the availability of many nutrients depends almost di-
rectly on the amount of other nutrients present, the problem
of deficiencies and excesses are closely interrelated, especially
on sands. This means that an excess of one nutrient often
causes a need for another. For example, an excess of potash
increases magnesium losses. Furthermore, an excess of cal-
cium on sandy soils reduces the availability of zinc, manga-
nese and other bases. An excess of copper hinders the availa-
bility of iron.
It is generally known that clay and loam soils lower the
availability of phosphates by simple combination or chemical
precipitation. Heavy clay and loam soils will lock up millions
of tons of phosphate by chemical combination and render
them unavailable. The reverse of this condition exists in many
Florida groves where the content of iron and aluminum is
very low, and in some cases the phosphates have accumulated
to the extent of hindering the availability of secondary nu-
trients. It is interesting to point out that West (44) in Aus-
tralia first showed that excess phosphates rendered the zinc
unavailable. Later, Soil Science Foundation, Lakeland (Fig-
ure 2), and others confirmed West's reports. Moreover, rec-
ords show a greater need for copper to avoid dieback or
exanthema on highly phosphated soils than on low phosphat-
ed soils. It would be reasonable to assume that where the
water soluble phosphorus is high, as is the case in some
groves on sandy soils, the available iron, zinc, copper and
manganese would be unfavorably affected.
Growers can profitably use these records in formulating
their fertilizer grades from year to year. Some modifications
will be necessary because of seasonal and soil differences, but
when these are accounted for they are better than mere


Department of Agriculture

guesses. The practice of using one nutrient to excess and then
offsetting its effects by adding other nutrients is poor busi-
The effects of nutrient excesses may be classed under sev-
eral heads; namely, (1) over-stimulation of growth, as with
nitrogen; (2) excess of soluble salts producing a salt or burn-
ing effect on roots and foliage; (3) one nutrient reducing the
solubility of other nutrients, such as iron precipitating phos-
phates or vice versa; (4) toxic or poisonous effect, such as
copper and boron; (5) one nutrient being antagonistic to
another, reducing absorption and utilization, such as excess
copper reducing iron absorption and excesses of potash low-
ering magnesium absorption.
As a rule, the soil will go a long way toward offsetting the
ill effects of excesses, especially where carbonates of calcium
and magnesium are present, both of which have a balancing
effect on other nutrients.
In the case of burning as a result of excess amounts of
chlorides, nitrates and sulphates, flooding with water is a
practical remedy. Mulching with litter, muck and even soil
will be helpful. In most cases the burning effects are tem-
porary, being alleviated by rain.
If a nutrient has poisonous properties, as in the case of
boron, flooding is a good remedy. Hydrated lime at the rate
of 400 to 800 pounds per acre on sands will retard the ill
effect if watered or worked into the soil. In the case of ex-
cess copper, lime in sufficient amounts to raise the soil re-
action to pH 6.0 or above, should be used.
Unless the soil nutrients are reasonably well balanced, it
is not possible to have a highly efficient grove. The optimum
or proper balance for all nutrients is not known. But any
practice which tends to losses is not only wasteful, but may
cause injury resulting in years of expense to correct.


Numerous analyses over a period of years indicate that
available nitrogen is leached from Florida soils-because of
summer rains-to a greater degree than any other nutrient.
This is not true in areas of low rainfall. Furthermore, ex-
perimental records by Roy and Gardner (35), show that citrus

Malnutrition Symptoms of Citrus

trees absorb proportionately more nitrogen during the fall
and winter than any other nutrient. These findings have a
practical value.

Inasmuch as most of the vegetative growth, including bloom
and setting of citrus fruit, occurs from February to July, it
would appear advisable to apply the greater part, if not all
the needed plant food a few months prior to and during this
period. This may be done in two or more applications, but
records indicate that from one-half to two-thirds of the an-
nual needs should be applied by February 15th. Especially is
this true for groves which cannot be irrigated. Where mois-
ture is limited, during the fall and winter period, some time is
needed for the fertilizer to penetrate into the root zone. This
should be taken into consideration in applying fall and winter
fertilizer. Furthermore, insoluble fertilizers are less efficient
than soluble forms, because the roots can absorb only soluble
forms. And with limited moisture, heavy litter and grass will
retard the penetration of fertilizer into the rcot zone. Under
such conditions, irrigating and/or incorporation of the ferti-
lizer in the soil will prove profitable.

If the records show that a nutrient is needed, it should be
applied 30 or 40 days in advance of the growth period, pref-
erably longer in dry soils. If soil records show ample re-
serves of available nutrients, such as phosphates, magnesium,
potash, copper and manganese, there is nothing to be gained
by applying them. Maintenance amounts should be applied
sufficiently in advance of the needs to allow penetration and
Records show that fertilized trees hold fruit and withstand
drought and cold better than hungry trees. Furthermore,
summer applications of fertilizer are more subject to leach-
ing losses and are not as conducive for the high quality fruit
as winter and spring applications, which promote better
spring flush and foilage.
Young trees and trees with sparse and unhealthy foliage
will need fertilizer. Furthermore, heavily loaded trees and
cover crop may need summer fertilizer. But if 3/10 to 4/10
of a pound of nitrogen per box has been applied prior to
bloom and during spring period, together with other needed
nutrients, rarely will any summer fertilizer be needed. The
annual needs can be easily calculated from records of tree
capacity, using data in Tables 1 and 2.

Department of Agriculture


Unbalanced fertilizer is not only wasteful but leads to de-
ficiency problems and inefficient practices. Records by dif-
ferent workers indicate that a large part of the deficiency
problems confronting Florida growers is due to unbalanced
fertilizer practices. The conventional nutrient ratios of 1-2-2
and 1-2-3 (nitrogen, phosphoric acid and potash) can be
justified only on soils which have a high chemical fixing
power for phosphates and potash. Such is not generally true
for the sands commonly used for citrus growing in Florida.
The accumulated records during the past two decades
show that citrus fruit contain approximately three times as
much nitrogen as phosphoric acid, and approximately two-
thirds as much nitrogen as potash (Table 1). Moreover, re-
peated records in Florida (Tables 5 and 6) indicate that
nitrogen leaches rapidly and phosphates only sparingly, on
sandy lands. If the soil has little or no absorbing power for
phosphates, the needs for this element should not be greater
than one-third to one-half that of nitrogen; and if soils con-
tain ample phosphate reserves, additional amounts can hardly
be justified. This is true for all nutrients.
The data in Table 6 show that available potash is retained
by sands longer than magnesium and calcium. This is par-
tially confirmed by the fact that trees show no ill effects
when potash is omitted for twenty-tour months or more. The
overall interpretation of these leaching data, together with
the absorption data, indicates that for the sandy soils under
Florida conditions a grower would be entirely safe in apply-
ing potash at approximately the same rate as that of nitro-
gen. (See footnote Table 1.) This would furnish the needed
potash without causing the replacement of other elements
such as magnesium.
To secure a proper phosphate ratio in the fertilizer necessi-
tates a knowledge of the soil reserves of phosphates, especially
sands which have been fertilized for a number of years. As
a rule, the initial phosphate application for loam and clay
soils should be five or more times that of nitrogen, decreasing
the phosphate with time. To a lesser extent this is true for
the sands according to the records in the Short Research
Grove. But as the phosphates accumulate with the years of
treatment, some of this cumulative material is available. So,
it would be profitable for a grower to ascertain the extent of

Malnutrition Symptoms of Citrus

soil reserves. The progressive grower will want to have speci-
fic information applicable to his own soil. This can be had
only from the measurement of actual soil reserves from time
to time. Especially is this true for phosphates, calcium, mag-
nesium and the trace elements. Records over a period of
years show that the cost of such information is more than
offset by increased improvement. A general guessing pro-
gram cannot compete in efficiency with a scientific program.
Until more information is available, the suggested nutrient
ratio in Table 1 can be safely used in bearing groves on sandy
soils under Florida conditions.
The rate of fertilizer application will vary according to soil
type, variety and general management practices. As a rule,
the fertilizer rate is gauged by its nitrogen content. For many
years the rate of fertilizer has been based on the age of the
tree and extent of tree spread, but records indicate that the
age and tree spread are not the best guides to follow in de-
termining the needed fertilizer. The box capacity of the tree
offers a more direct method of determining fertilizer needs
than any known factor to date. When this is done with due
consideration to variety, rootstock and grove response, effi-
cient and profitable practices have been secured. This can
be boiled down to the principle of applying from .3 to .5
pound of nitrogen and other nutrients in proportion to needs,
annually, per box capacity of the trees for mineral soils; or-
ganic soils will need less nitrogen. Furthermore, soils receiv-
ing heavy leguminous cover crops would need less nitrogen.
For the bearing groves on typical sandy soils, approximately
.35 of a pound of nitrogen per box fruit can be used as a
guide for the annual application on rough lemon root. Sour
rootstock will need approximately .45 of a pound per box.
These rates are equivalent to 6 and 8 pounds of a fertilizer
containing 5% nitrogen, or 3 and 4 pounds of a fertilizer
containing 10% nitrogen. These rates can be gauged up or
down according to tree condition. But it is very important
that the tree have approximately one-half of the yearly sup-
ply prior to and during the bloom period. If the foliage is
sparse or off-color, the rate should be increased accordingly.
Where growers use greater amounts than these suggested
rates, no material gain will be had except in abnormal cases.
The problem may be moisture, poor mechanical condition of
the soil, disease, or some other factor. Records indicate, how-
ever, that some growers use as much as .9 pound of nitrogen,
and other nutrients in proportion, to produce a box of fruit.

Department of Agriculture

Characteristic citrus deficiency symptoms of the following
nutrients have been described and illustrated: nitrogen, phos-
phorus, potash, calcium, magnesium, iron, copper, manga-
nese, zinc, boron and molybdenum. These have been present-
ed in a non-technical manner understandable by the average
grower. In addition, the soil relation, treatment and symp-
toms of excess have been pointed out where known. Brief
statements regarding the historical use of the nutrients are
also given.
Some typical leaf chlorosis and toxicities of citrus are also
presented for study to avoid confusion with deficiency symp-
tom patterns. These are Perchlorate, Biuret and Fluorine
Chlorosis, and Arsenic Toxicity.
Research data dealing with fruit composition, soil relations
and practical phases of managing Florida soils have been dis-
cussed with the assumption that after a proper and accurate
diagnosis of deficiencies and the limiting factors, the most
practical method to approach for the grower would be a sim-
ple and logical procedure based on scientific data.
The available data indicate that if a grower will maintain
a soil reaction of approximately pH 6.0, and a nutrient ratio
on sandy soils, parallel to crop composition, using three to
five times the crop removal, avoiding deficiencies and ex-
cesses, he will be able to secure efficient utilization of his fer-
tilizer nutrients, other factors being favorable, and thereby
eliminate many of his wasteful practices and most of his mal-
nutrition problems.


The author wishes to take this opportunity to express his
sincere appreciation to Messrs. E. F. DeBusk, C. R. Hiatt and
A. S. Rhoads for assistance in selecting suitable illustrations
for this bulletin and critically reading the manuscript. And
to Dr. A. S. Rhoads for making most of the photographs and
critically reviewing the literature.
The author also wishes to express his indebtedness to the
Respess Engraving Company for helpful suggestions in mak-
ing the color plates; to the varied technical publications deal-
ing with the subject; to numerous Florida citrus growers for
suggestions regarding grower problems and needs, and to
the Board of Directors and members of Soil Science Foun-
dation for valuable counsel and assistance.

Malnutrition Symptoms of Citrus


1. BAHRT, G. M. Progress report of soil fertility and fertilizer experiments on
bronzing of citrus. Proc. Fla. State Hort. Soc. 47 (1934): 18-20.
2. BAHRT, G. M., and HUGHES, A. E. Soil Fertility and experiments on
bronzing of citrus. Proc. Fla. State Hort. Soc. 50 (1937): 23-38.
3. BRYAN, O. C. Potash deficiency in grapefruit. Florida Grower 43 (1):
14-16. January, 1935.
4. BRYAN, O. C., and DEBUSK, E. F. Citrus bronzing-a magnesium defi-
ciency. Florida Grower 45 (2): 6, 24. February, 1936.
5. BRYAN, O. C. Deficiency symptom patterns in citrus. Citrus Industry 19
(3): 11-15. March, 1938.
6. CAMP, A. F., and PEECH, MICHAEL. Manganese deficiency in citrus in
Florida. Proc. Amer. Soc. Hort. Sci. 36: 81-85. 1939.
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deficiency and excess of orange trees. Hilgardia 17 (19). 1947.
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its relation to the soils of Western India. Part 1. Bombay Dept. Agr. Bull.
155-45 pp. 1928.
11. FINCH, A. H., ALBERT, D. W., and KINNISON, A. F. A chlorotic con-
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Bull. 93-2 pp. 1908.
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15. FLOYD, B. F. Some cases of injury to citrus trees apparently induced by
ground limestone. Fla. Agr. Exp. Sta. Bull. 137: 161-179. 1917.
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leaves. California Citograph 35 (5). 1950.
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Citograph 22 (1): 6, 17 (2) 54, 62. 1936.
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167-181. 1938.

Department of Agriculture

25. McGEORGE, W. T. Some aspects of citrus tree decline as revealed by soil
and plant studies. Arizona Agr. Exp. Sta. Tech. Bull. 60: 329-370. 1936.
26. OBERBACKER, M. F. A chlorosis of citrus produced by Biuret as an im-
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