FLORIDA STATE HORTICULTURAL SOCIETY
145
SYMPTOMATOLOGY OF DEFICIENCIES AND TOXICITIES
OF CITRUS
DR. A. F. CAMP
Citrus Experiment Station
Lake Alfred
The ability to recognize the symptoms of de
ficiencies and toxicities as they present themselves
in citrus trees has become of prime importance in
the fertilization and handling of groves. Our
soils work has not yet reached the point where we
can definitely correlate soils analyses with tree
condition even when such soil analyses are made
in the laboratory under closely supervised con
ditions. Even after such correlations are estab
lished it will be necessary to develop accurate
quick methods adapted to our soils before such
tests can be put into actual commercial use.
On
the other hand, the citrus tree itself has been
found a very accurate indicator of nutritional con
ditions and the symptoms indicative of certain de
ficiencies have been found very specific as well as
extremely sensitive.
The symptoms of four de
ficiencies in citrus have now been worked out in
a fairly complete way and will be presented in
detail in this paper together with the symptoms of
one toxicity which has frequently been mistaken
for a deficiency of some sort. The four de
ficiencies discussed will be those of zinc, copper,
manganese and magnesium and the toxicity will
be that of boron.
It should be pointed out perhaps that no attempt
will be made to go into the realm of conjecture
concerning other deficiencies that may exist but
for which the exact symptoms have not been de
termined. Various types of plants have widely
different mineral requirements. Crotalaria, for
instance, will grow luxuriantly on a soil so de
ficient in zinc that tung trees will hardly grow at
all; thus, a soil that might be deficient in some
element in terms of a certain crop may contain
adequate for another. Moreover, symptoms of
certain specific deficiencies vary widely in dif
ferent crops; thus, typical "frenching" is due to
zinc deficiency in citrus, but equally typical french
ing in tung trees is caused by manganese de
ficiency; so that it may not be concluded that be
10—Horti
cause citrus shows a certain symptom which re
sembles the symptom of a deficiency in cotton,
that this same deficiency actually exists. The sub
sequent descriptions will, therefore, be limited to
those symptoms which have been carefully worked
out on citrus. Any discussion as to the reasons
for their occurrence will have to be omitted for
the present owing to lack of time.
In this paper the term deficiency will be used
in connection with such things as Frenching and
Dieback, i. e., sine deficiency and copper deficiency.
While it may be argued that this may not prove
to be technically correct, such terminology has
the distinct advantage of tying up the name with
the element used as a corrective. Moreover, the
fact that there is a particular derangement that
responds only to the application of a certain ele
ment and that this application can be made to the
tree instead of the soil, would tend to substantiate
the idea that it is a deficiency. The fact that the
process involved is complicated and indirect would
not vitiate the correctness of the term.
ZINC DEFICIENCY OR FRENCHING
As far as possible this description will be limited
to the symptoms per se and the manifestations
present when other deficiencies modify the symp
toms will be omitted.
Foliage Symptoms: Frenching as observed in
Florida has characteristic leaf symptoms which
can be easily recognized. It is characterized by
green areas along the midrib and the main lateral
veins, the remaining areas being light yellow to
almost white. The relative amounts of green and
yellow tissue vary from a condition of mild
frenching in which there are only small yellow
splotches between the green veins to a condition in
which only a portion of the midrib toward the
base of the leaf is green and the remainder of the
leaf light yellow to almost white. In immature
leaves some of the smaller veins may be green
146
FLORIDA STATE HORTICULTURAL SOCIETY
and present a lacework of green on a light yellow
background. As the leaves mature the small veins
crop strain.
may lose their green color, but small green spots
affected as budded trees, but on occasion may
2 or 3 mm. in diameter may persist.
suffer seriously.
In the milder
other early oranges, and thus may be related to
Seedling trees are seldom as severely
Generally speaking, frenching is
cases the leaves are almost normal in size, while
commonest in Pineapple oranges, but can be found
in severe cases the leaves are small and abnor
in any varitey of citrus.
mally narrow, having not over a tenth of the area
of normal leaves.
The tendency to produce un
usually narrow pointed leaves is one of the very
distinct symptoms of frenching.
Growth Symptoms:
Modifications of Frenching:
The above descrip
tion applies primarily to frenching uncomplicated
by other deficiencies.
In such cases a zinc spray
applied during the spring will cause the frenched
In mild cases,
frenching
may appear on occasional weak twigs, the rest of
leaves to green up rapidly and this will be fol
lowed by a flush of growth with normal leaves
the tree remaining green, or it may be general
and
over the tree with little reduction in leaf size.
In
do not grow appreciably after they have become
the latter case the growth is likely to tend to an
unusual erectness in contrast to the usual spread
ing growth. When more severe, frenching occurs
green, but continue on the tree, giving a peculiar
mixture of foliage. In contrast to the above there
are many cases complicated by other factors such
over the entire periphery of the tree.
as magnesium or copper deficiency.
The growth
is shortened and this combined with the short
narrow leaves gives the tree a peculiar brushy ap
pearance and this is accentuated by the develop
ment of numerous adventitious shoots. All the
twigs are weak and die off quickly so that there
is always an excess of dead wood in the tree.
In contrast to the persistent dying back over the
periphery of the tree there is a vigorous develop
ment of watersprouts on the large limbs and
These watersprouts are commonly free
of frenching and give the tree a dense center of
characteristics.
The
small
frenched leaves
Unfortunately
such combinations of deficiencies are more common
than a straight zinc deficiency and such cases do
not respond satisfactorily unless all the needed
elements are supplied. Frenching was long con
sidered a symptom of dieback, copper deficiency,
because it is almost always associated with dieback. This sort of situation is not strange since
factors that tend to produce a deficiency of zinc
are likely to also eliminate or tie up such ele
trunk.
ments as manganese, copper and magnesium.
growth in contrast to the weak, dying appearance
COPPER DEFICIENCY OR DIEBACK AND AMMONIATION
of the outer portions of the tree.
Such trees may
decrease in size very rapidly due to the dying
back of the twigs.
Fruit Symptoms: The fruit borne on weak
twigs carrying small frenched leaves is unusually
small, the rind very smooth and the color, when
ripe, is unusually light. The pulp of such fruits
is woody with a very low juice content. In con
trast to the fruit borne on the frenched twigs is
the large coarse fruit on the watersprouts. In
severe cases the production is mostly culls which
are either very large or very small, and very little
good fruic is produced.
(Exanthema of Fawcett)
Dieback and its associated ammoniation is con
fused with frenching only through persistent as
sociation of the two troubles. When separated
from frenching the symptoms are distinct as will
be noted from the following description. B. F.
Floyd has described dieback in detail so only the
main points will be mentioned here.
Foliage: The foliage in the earlier stages is
unusually dark green, the leaves are large and
thick and unusually vigorous, which is the first
symptom looked for. On the severely affected
I wigs which will be mentioned later, a few small
on
weak leaves may develop and shed, but these are
oranges than on grapefruit and least common on
only on twigs in the process of dying.
Growth: One of the first growth symptoms
Distribution:
Frenching is
more
tangerines, though alt may be affected.
common
The seedy
varieties of oranges, such as Pineapples, are usu
ally more severely affected than Valencias, while
it is still less common on Parson Browns and
looked for is the appearance of "S"-shaped, soft,
over-vigorous twigs. These combined with the
dark green foliage mentioned above are taken as
147
FLORIDA STATE HORTICULTURAL SOCIETY
definite first indication of dieback.
As the trouble
MAGNESIUM
DEFICIENCY
OR BRONZING
progresses gum pockets appear between the bark
The term bronzing or copper leaf is rather more
and the wood, and an unusual excretion of gum
loosely applied than the terms frenching and die-
will take place at any break or cut.
Severely af
fected twigs will show excrescences of gum near
the terminal end and such twigs usually lose their
leaves and die back for some distance.
As the
case progresses the tree will show a body of dark
green, heavy growth with a great many dead ter
minal twigs.
Multiple buds are numerous so that
a great many twigs develop and many of these die.
The bushy growth of small twigs frequently con
sidered symptomatic of dieback are primarily as
sociated with zinc deficiency rather than copper
deficiency.
Fruit:
The manifestations of copper deficiency
on the fruit have long been termed "ammoniation."
back and is used to designate a type of chlorosis
which is very common throughout the citrus belt.
It has been particularly severe during the last sev
eral years on the lighter sands and has caused a
very
pacity
considerable
of
trees.
reduction
The
in the
symptoms
beanng
ca
described here
are limited to those apparently caused by a de
ficiency of magnesium, although it is common to
find the symptoms of severe manganese deficiency
included.
The
narrower
limitation seems
more
desirable since the broader use of the term is
likely to cause misunderstanding.
Foliage:
Bronzed leaves do not show the pat
tern of green veination which is characteristic of
The young fruit is light green in color disfigured
frenching, but do show in the later stages an over
by light brown markings, or excrescences which
all cadmium yellow
darken as time progresses and may become black
start as two elongated patches, one on each side
by the time the fruit is half grown.
of the midrib,
Severely af
fected fruits are likely to drop while less than
\JA to 2 inches in diameter, splitting is common
and a considerable percentage of the splitting will
be across the axis.
Gum pockets are common in
the rind and around the seeds of ammoniated fruit.
Less severely affected fruits will be large and
coarse, with large dark markings and frequently
gum around the seeds.
In severe cases, no fruit
of first or second grades will be produced, but a
scattering of ammoniated fruits is commonly the
forerunner of severe dieback and a truer indi
cator of copper deficiency than twig or leaf symp
toms
for zinc and magnesium
may be
so
severe as
to
deficiencies,
and
restrain the vigorous
growth of twigs and leaves so that the commonly
recognized
foliage and
growth
symptoms
never
appear.
Distribution:
to bronze cast.
This may
and spread outward to the pe
riphery of the leaf until only a green midrib is
left and the green along the midrib may gradually
fade until it is only a wedge-shaped area at the
base of the leaf which remains green.
In some
cases the entire leaf takes on an over-all yellow
to bronze cast and no green at all is apparent.
Leaves when affected with this trouble never show
the narrowing that is characteristic of frenched
leaves and normally are all full size, having de
veloped first as normally-appearing green leaves
and later becoming bronzed in contrast to leaves
on zinc deficient trees which are
the beginning. In severe cases the
slightly reduced in size and this
characteristic of the type in which
frenched from
leaves may be
is particularly
the leaf is en
tirely yellow.
Bronzing usually appears in the late summer or
early fall on heavily fruited trees and particularly
The use of copper sulfate for the
on limbs carrying a cluster of fruit, whereas light
correction of this trouble has been known for
fruited trees or limbs that are not carrying fruit
many years and this combined with the general
will remain green..
use of bordeaux has kept copper deficiency at a
and a large proportion of the leaves is affected,
When the trouble is severe
minimum, but there is evidence to indicate that
there will be a heavy leaf fall and a consequent
it would be general throughout the citrus growing,
heavy reduction in the effective leaf surface of
area if it were not for the use of copper.
the trees.
It is
Such trees do not respond to fertilizer
generally worse on oranges than on grapefruit or
treatment satisfactorily and while the leaf char
tangerines.
acteristic may be and probably is associated with
FLORIDA STATE HORTICULTURAL SOCIETY
148
crop strain, it cannot be restrained through ap
Growth:
Trees affected primarily with bronz
ing do not take on the bushy appearance of trees
affected either with dieback or frenching.
back may also appear, but not in its character
istic form due to the restrained growth.
They
retain their naturally spreading shape, but con
siderable dead wood appears and frequently large
limbs will die out and have to be removed so that
the trees in severe
and where copper sprays have not been used for
disease control or for corrective purposes, die-
plication of nitrogeous fertilizer.
cases become progressively
MANGANESE
DEFICIENCY
Manganese has been used extensively on citrus
on calcareous soils for what is known as marl
chlorosis or marl frenching. Its use on. acid
thinner both as to foliage and growth so as to
soils as well as marl soils has been recommended
become almost skeletonized. The profuse devel
opment of watersprouts characteristic of both die-
by Bahrt and his associates along these lines with
back and frenching does not take place and the
tree has a hard, weak appearance.
Fruit:
In the early stages of bronzing, trees
usually bear heavily, but as the trouble progresses
the production is reduced due to the reduction
in bearing surface and also due to the production
of large quantities of small sizes. Other than
that the fruit seems to have a normal quality and
fair texture until the advanced stages are reached
and the tree is almost dead, at which time the
production may drop to almost nothing. In mild
cases of bronzing production may be maintained
at a high level for several years and the fruit
have a reasonably good quality.
In such groves
the trees seem to recover during the spring and
by Bahrt and considerable work has been done
excellent results.
The symptoms have not been
thoroughly described, however, probably due to
the fact that they commonly occur associated with
frenching and it is only since the work on zinc
has reached an extended scale that manganese de
ficiency symptoms have been accurately separated
from frenching. The symptoms as given below
will be incomplete because of the fact that the
work on this phase of symptomatology has not
been completed at the present time.
Foliage:
Leaves showing manganese deficiency
take on much the same pattern as is present in
frenching with a green midrib and green lateral
veins.
The
tissue
between the veins,
however,
does not take on a yellow color, but remains a
early summer and bronzing appears in the fall and
light green so that there is a dark green pattern
the trees become progressively weaker until the
crop is removed, at which time the trees start
to green up again. This may be considered a
of midrib and veins with a background of lighter
marginal case which may suddenly develop into
of the leaf between the lateral veins. On the
immature leaf this pattern will be fairly bright
a very severe form with a heavy loss of wood.
green.
In mild cases it may resolve itself into a
scries of light green patches along the periphery
Bronzing is generally much worse
and quite easily observed, but as the leaves mature
on grapefruit than on oranges or tangerines, and
they take on a peculiar dull slate cast and unless
the investigator is looking closely, the pattern
Distribution:
is particularly associated with seediness in grape
fruit.
Marsh Seedless very seldom shows a great
may be overlooked.
This dull slate cast seems to
amount of bronzing and the same is true of the
be rather definitely associated with manganese de
Thompson Pink, which is a seedless pink sport of
ficiency not only in citrus but in other plants and
Marsh. It appears to a considerable extent on
oranges, however, and seems to be worse on Pine
apple and probably next on Valencias, thus being
associated with both seediness and late maturity
and the consequent crop strain that results.
Early varieties such as Parson Brown and Ham-
makes the
leaves
extremely
difficult to
photo
graph. On the marl soils the pattern is usually
more pronounced and the leaves as they mature
take on a grayish to slate cast. This peculiar
symptom is probably due to a combination of zinc
and manganese deficiency with the latter being
It is not very pronounced
predominant, but with the more pronounced zinc
deficiency covering it up to a certain extent. • The
on tangerines, but occasional cases occur. It is
very common to find it associated with frenching
use of manganese for more characteristic types of
frenching was common a number of years ago,
lin do not show as much of this, but on occasion
may show severe cases.
FLORIDA STATE HORTICULTURAL SOCIETY
but experiments in the last few years by the author
have indicated that the characteristics of frenching
occurring on these soils do not respond to man
ganese treatment but to zinc.
Both on the marl
soils and on the acid sands, frenching if present
in abundance will almost completely mask man
ganese
deficiency and it will
after zinc has been applied.
only be observed
The leaves do not
manganese
deficiency. Where frenching is se
vere, characteristic manganese deficiency can sel
dom be found, but commonly appears as soon as
zinc is applied. Particular attention is called at
this time to manganese deficiency because of the
fact that many growers have noticed it and have
merely considered it partially corrected frenching
instead of a distinct deficiency.
take on the characteristic shape that is associated
with frenching and will only have a pronounced
pattern when they are quite young.
The trouble
seems to be associated primarily with growth con
ditions and appears to the greatest extent on trees
that are in vigorous growing condition.
Growth:
No characteristic growth
symptoms
have been observed to date, but Bahrt and the
author have observed an improvement in tree con
dition and a general improvement in growth fol
lowing manganese treatments
Fruit:
on deficient soils.
No definite fruit symptoms have been
associated by the author with manganese deficiency,
but Bahrt reports increased intensity of color fol
lowing
applications
of
manganese and
has
re
ported this to be particularly noticeable in tan
gerines.
and
He has also reported the fruit is firmer
better
able
to
withstand
shipping.
Some
chemical relationships have also been established
and the readers are referred to Bahrt's paper on
this subject.
Distribution:
The symptoms of manganese de
ficiency have been found general throughout the
citrus belt during the last year both on acid sands
and on the alkaline soils along the coast.
They
have been much more pronounced on grapefruit,
tangerines and Temple oranges than they have
on round oranges.
They have been found almost
universally on tangerines except in those groves
where manganese has been used either alone or
in the fertilizer. Where frenching or dieback or
149
BORON
TOXICITY
Coincidental with the increased use of borax
and other boron compounds in packing houses,
there has been occurring in groves a peculiar
chlorotic condition which has been found to be
due to excessive applications of borax or other
boron compounds to the soil. This has been
brought about mainly through two practices: first,
the dumping of culls in the grove and the careless
inclusion of fruit that has been dipped in borax
and not thoroughly washed afterward, and seconally, the leaving of boxes which have been
treated with borax in the field for extended
periods so that the rain may wash the borax off
the boxes onto the ground around the trees. It
has also occurred to a considerable extent around
packing houses where borax has been extensively
used and the borax tanks are allowed to drain
near adjacent citrus trees. In some cases where
the entire box of fruit including the box is dipped
in borax solution and the boxes after removal of
the fruit have been stacked on a platform, the
rain has often washed enough borax from the
boxes to kill all the citrus trees and other vege
tables near the box platform. The grower who
finds this trouble in his grove and who is unfa
miliar with it commonly associates it with french
ing because there is a certain amount of reremblance between the two troubles. For this
reason the symptoms of boron toxicity will be
both are present in profusion, or where bronzing
is severe, only an occasional typical leaf may be
given below.
found, but when such groves are treated so as
to eliminate the other deficiencies, manganese de
ficiency will show up in abundance. The observa
amount of a boron compound to a tree, the leaves
will begin to show a yellowing near the tip fol
lowed by a splotchy yellow coloration along the
tions in connection with this work have indicated
that frenching probably occurs under practically
the same soil conditions as manganese deficiency,
but due to its more pronounced pattern and also
to its effect on growth, masks the symptoms of
Foliage:
Following application of an excessive
peripheral portions of the leaf.
The yellow color
will increase in intensity to become a dark bronze
color. Semicircular areas of dead tissue will oc
cur around the edges of the leaf or the entire tip
of the leaf may be killed. These leaves shed at
FLORIDA STATE HORTICULTURAL SOCIETY
150
the junction between the petiole and the leaf, and
starts on a process of recovery with the loss of
in severe cases the trees may become quickly de
wood never being very pronounced.
foliated.
Almost immediately such trees will put
out a succeeding flush of growth in which the
leaves will be almost white with a narrow green
midrib.
This stage and the succeeding stages are
quite commonly mistaken for frenching, but the
characteristic narrowing of the leaf is not present
and in fact as the flushes progress in severe cases,
tlie leaves become smaller and rounder than nor
mal.
The
severely
affected
leaves
mentioned
above will shed quite early and successive flushes
will follow and where the rains are plentiful or
where irrigation water has been used to wash the
borax out of the soil, they will gradually begin
to recover with the leaves showing less of the
yellow
condition
and
more
green.
The yellow
color occurs nearer the tip of the leaf and does
not have the characteristic light yellow to white
of frenching, but soon takes on a deep yellow which
is very distinct. In the early stages the leaves
may show a large number of small yellow dots
scattered over the surface of the leaf and these
are particularly noticeable on the under side of
the leaf and near the tip.
The leaves also have
a peculiar characteristic leathery texture which is
distinct from the ordinary smooth, hard texture
of citrus leaves and this symptom combined with
the coloration makes it very easy to identify the
trouble and to separate it from frenching.
Trees that have
received
an unusually large
amount of borax will continue to put out flushes
of growth for some time with the leaves becom
ing gradually smaller and rounder and showing a
great many dead spots around the edges and the
trees may become almost defoliated.
In milder
cases a gradual recovery is made as the borax is
leached from the soil and the leaves become very
large and thick and the pattern disappears.
Growth:
In severe cases of boron damage there
will be a considerable loss of wood throughout
Fruit:
Severely affected trees usually lose their
fruit quickly and do not put on succeeding crops
of any size until recovery is practically complete.
Distribution:
Grapefruit trees have been found
to be unusually susceptible to boron damage and
most of the cases observed have been oh grape
fruit, although a few severe cases have been found
on other varieties as well.
In experiments it has
been found that it takes considerably smaller quan
tities of borax to produce severe symptoms on
grapefruit than is the case with other varieties.
The trouble is usually limited to small areas in
the groves where boraxed culls1 have been dumped
or where loads of boxes carrying borax on them
have been left through a rainy period.
It is sel
dom found evenly distributed over a grove and
may only affect two or three trees here and there
where either truckloads of culls or piles of boxes
have.been left.
The only treatment that has been
found of value is an application of irrigation water
if available or to wait for the rains to leach it
out of the soil.
this
will
usually
If the trouble is not too severe
occur
within
twelve
months.
The commonest place to find this trouble is around
packing houses where borax is used extensively
for
fruit
treatment.
Treatment
with
lime
is
sometimes helpful, but the damage has usually
been done before the trouble is noted so that ap
plications are too late to be of great value.
Other deficiencies and toxicities will undoubt
edly be worked out from time to time, but specu
lation concerning these is idle except as a guide
to research.
It is almost certainly true that as
the deficiencies above are supplied, the chances of
identifying others become greater as is evidenced
by the fact that the use of zinc has made the
identification of manganese deficiency easier.
It
is possible, too, that as the work develops, soil
the tree and in extremely severe cases the tree
tests may become increasingly useful, but at the
may be entirely killed.
present time the tree itself is the best indicator
Usually, however, a cer
tain amount of dead wood develops and the tree
of its needs.