UNIVERSITY OF FLORIDA
Agricultural Experiment Station
SOME CASES OF
INJURY TO CITRUS TREES
BY GROUND LIMESTONE
B. F. FLOYD
FIG. 68.-View of a limestone-injured tree showing
Frenching of the foliage, and the defoliation and
bushy rosette-like growth of the terminal branches,
which characterizes the trouble.
The Station Bulletins will be.sent free upon application to the
Experiment Station, Gainesville
1. Use Finely Ground Limestone on Acid Citrus Soils.
2. Apply ground limestone in moderate amounts in keeping
with the. degree of acidity of the soil.
3. Apply ground limestone at long and regular intervals; an
application every three years should be sufficient.
4. Where possible, grow a crop of legumes in citrus groves
every year. Cut and turn the whole crop under every second or
5. Use the ground limestone cautiously on dry sandy soils
that are lacking in humus content.
6. Ground limestone used on such soils may cause injury
to the cover crop and trees.
7. The injury does not develop immediately after the ap-
plication of the limestone. Usually an interval of several
months elapses before it becomes evident.
8. The injury to citrus trees is characterized by a French-
ing of the foliage, a partial defoliation, the presence of multiple
buds on the defoliated terminal branches, a bushy somewhat
rosette-like growth of the terminal branches and a dying back
of the branches.
9. The cover crop seedlings show the injury by a French-
ing of their foliage, followed by yellowing and death before they
have made much growth.
10. The injury can be avoided by using the limestone in
moderation and conserving or increasing the humus content of
SOME CASES OF INJURY TO CITRUS TREES APPARENTLY
INDUCED BY GROUND LIMESTONE
BY B. F. FLOYD
Florida soils are for the most part lacking in chemical bases
and are acid in reaction. Blair and Macey, in Bulletin' 93 of
this Station, report the results of extensive investigations in
which they found that nearly 70 percent of the soils examined
were more or less acid; and that the cultivated soils were more
acid than the virgin soils. They concluded that the continued
cultivation and fertilization of the sandy soils tend to increase
The opinion is prevalent that a neutral to slightly alkaline
reaction of the soil is best for the growth and yield of citrus
trees, and that an acid reaction is detrimental. While it is
known that certain plants are very sensitive to an acid reaction
of the soil, it has not been proved that the citrus tree is in that
class. It is true that an excessive degree of acidity is unfavor-
able for growth, but a smaller degree is not necessarily detri-
mental. When other growth conditions are good, citrus trees
are known to make a thrifty growth and to give a good yield
on acid soils.
The correctives for soil acidity are any of the different
forms of lime, such as quick lime, hydrated lime, air-slacked
lime, finely ground limestone, marls and shells, hardwood ashes
and Thomas phosphate or basic slag. Of these different forms,
the finely ground limestone is used almost exclusively on citrus
soils on account of the ease with which is may be handled, its
slow action, and its supposed lack of ability to injure either the
tree or the soil even when used in excessive quantities.
On account of the belief that any reasonable quantity can
be used without injury, the ground limestone is usually applied
without any particular consideration of the degree of acidity,
the humus content or any other soil condition. Cost is the chief
consideration in determining the amount to use. The usual
application is from one to two tons per acre without further
application.. In some cases, larger applications are used or the
applications are repeated during successive years so that a con-
siderable amount of the limestone is mixed with the first six
inches of soil.
164 Bulletin 137, Limestone Injury to Citrus Trees
INJURY TO CITRUS TREES BY GROUND LIMESTONE
The attention of the Experiment Station has been called to a
number of groves in which the use of ground limestone has
apparently led to injury. This injury showed itself by a
marked frenched or chlorotic condition of the foliage. With late
development there was lack of growth, much defoliation, a de-
velopment of multiple buds, and a hard dry appearance of the
bark, giving the tree a general starved appearance. The roots
showed evidence of injury by the presence of very few live
feeding tips. Apparently the regions back of the fibrous roots
were in a healthy, normal condition.
That ground limestone should be suspected of inducing injury
under any condition has occasioned much surprise among the
growers. The general impression has been that it was a nat-
ural product which under all conditions was not only entirely
harmless but was highly beneficial to plant growth. From grove
observations and field experiments there is strong evidence in-
dicating that under certain limited conditions ground limestone
may induce injury to young citrus trees in Florida.
That injury may occur to plants from the presence of ex-
cessive calcium carbonate (lime) in the soil has long been
known. Certain plants are much more susceptible to such in-
jury than others. Frear, in a review of the literature on the
liming of soils (Sour Soils and Liming, Dept. Agr. Penn. Bul.
261, p. 45), calls attention to a number of plant diseases caused
by an excess of calcium carbonate in the soil.
Grapes growing upon certain limestone soils in France often suffer from
chlorosis, a white spotting of,the leaf, associated with great depression in
the vigor of the plant.
Other plants also than the grape became chlorotic under like influences.
G. Riviere and G. Bailhache observed that excess of calcium carbonate in
soil is attended by chlorosis of pears grown upon quince stocks, and that a
chlorotic appearance occurred when no more than 4 percent of the carbonate
was present; and that the attack was conspicuous with 17 percent of the
carbonate, and with 28 percent death ensued.
P. Maze, Ruot and De Moigne observed that the addition of 0.2 percent
of calcium carbonate to a water culture in which Vicia narbonnensis was
flourishing, causes chlorosis, also that the white lupine and the vetch became
chlorotic in the presence of an excess of calcium carbonate to which corn
was resistant; but Maze caused chlorosis of corn by keeping the excess of
lime carbonate, but diminishing the iron and sulphuric acid in the nutrient
Gile (Porto Rican Exp. Sta. Bul. 11) reported the failure of
pineapples with the appearance of chlorosis (frenching) on cer-
Florida Agricultural Experiment Station
tain areas of the Island where there was an excessive amount
of calcium carbonate in the soil. He made an extensive study
of the problem in the course of which numerous experiments
were carried out and many analyses made. He found that for
ordinary sandy soils, about 2 percent of calcium carbonate ren-
ders them unsuitable for pineapples. Smaller amounts than
this did not appear to be injurious. On the other hand, soils
containing as high as 40 percent of calcium carbonate but com-
posed principally of organic matter produced vigorous plants.
He was able to produce the trouble readily on sandy soil by the
addition of lime in quantity to the soil. He concluded that lime
reduced the availability of the iron in the soil, so that the
plant absorbed an excessive amount of calcium and an insuf-
ficient amount of iron. This reduced the ability of the plant to
form chlorophyll, which in turn led to further injury and finally
to the death of the plant.
An interesting point in the development of the trouble in the
field and in the greenhouse was that the plants, after being set
out, grew normally thru a period of several months before they
developed the diseased condition.
The root system of the chlorotic plants showed no evidence of disease.
The roots differed from those of normal plants in being somewhat larger and
not so thick; they were more like those of plants suffering from starvation.
The plants, however, that suffered from the chlorosis for some time had
many dead roots, but the functioning roots appeared to be perfectly healthy
and an examination by the pathologist failed to show any bacterial or fungus
The first case of apparent injury from ground limestone to
come to the attention of the Experiment Station was that in the
grove of W. L. Drew of Winter Haven. In September, 1913,
he addressed the Director of the Experiment Station as follows:
I have had an unexpected experience in causing frenching by the use of
ground limestone...... I have at Winter Haven, my own grove of 25% acres,
and joining it I have charge of my brother's grove of 16% acres. Twenty-
eight rows of trees in this latter grove are Duncan grapefruit. Each row
contains nineteen trees. Fourteen rows are on rough lemon roots and four-
teen on sour orange roots. These trees were set in December, 1910. The
trees of the two adjoining rows, the last row on rough lemon and the first
row on sour orange, were set in soil with which there had been mixed a
liberal quantity of ground limestone. No lime of any kind has, up to the
present time, been used in any other portion of the grove. The trees where
the limestone was used showed no difference in growth or appearance from
the other trees during the first summer-the summer of 1911.
On May 10, 1912, we scattered a liberal quantity of the ground limestone
around the trees of these two rows and all over the middle between the two
rows. In the summer of 1912 we failed to observe any effects of the ground
limestone in the trees that were on rough lemon roots. The trees of the
166 Bulletin 137, Limestone Injury to Citrus Trees
FIG. 69.-Citrus tree around which ground limestone was used.
row on sour orange seemed to be growing a little faster and looked a little
thriftier than the remainder of the trees on that root. I did not see the
trees from September, 1912, to July, 1913. At this time both of these treated
rows showed a large amount of frenching in great contrast with the trees
on either side that showed almost none at all. I took three men at different
times out to see the grove and telling them of this experience with ground
limestone asked them to point out the rows. This each one did, without
hesitation, long before he had reached them.
"The grove is situated on good average high pineland of the Winter-
haven section. All of the trees have had the same care and fertilizer from
the first. As there is no difference in the character of the land where these
two rows are, it is evident that the limestone has caused the frenching. It
may be that where limestone is used, a fertilizer of a different character
should be used. I can hardly believe that the lime itself has been injurious
and so I suspect it to be the lime and the fertilizer combined.
".....Beggarweed is the cover crop in this grove. I might add as a
result of this experiment, and another previously made, that it is clear that
on this land, where no fertilizer was applied, beggarweed is not benefited
by an application of ground limestone. I hesitate to state that it has been
injured but such seems to be the fact. There are spots all over both of
these groves where the beggarweed frenches and does not grow well, at
least in the absence of fertilizer, and this condition seems to be more pro-
nounced where ground limestone has been applied."
Florida Agricultural Experiment Station
SUBSEQUENT HISTORY OF GROVE.-Since September, 1913,
when this letter was written, the trees in the two rows have
made slow growth. Their appearance has varied with the sea-
son. At all seasons the marked frenched condition has prevailed
more or less. In the winter of 1915, they had a general starved
appearance. The type of growth which had developed was quite
different from that of the trees in the adjoining rows. Instead
of general growth all over the tree, it was somewhat confin4l
to rather strong shoots toward the center of the tree. These
had made more or less of a straight lengthy growth, giving the
tree a rather upright type of growth instead of a compact
spreading type that characterized the trees in the other rows.
A general lack of foliage gave the trees a very open appear-
ance. The frenching and defoliation occurred more toward the
tips of the branches. The tip leaves were often completely yel-
FIG. 70.-Citrus tree around which ground limestone was not
used. Tree is of same age, same variety, on same stock
and in adjoining row to one shown in fig. 69.
168 Bulletin 137, Limestone Injury to Citrus Trees
FIG. 71.-View in citrus grove of middle over which ground limestone has
been spread. Trees to left on sour stock. Trees to right on rough lemon
stock. Note absence of cover crop.
low. The leaves toward the base of the branches were more
plentiful and had a somewhat normal size and color. Multiple
buds were more or less plentiful on many of the short terminal
branches. These branches were frequently completely defoli-
ated. The bark of the large branches and of the small ones
a year or more old had a rather hard dry look. The fibrous
roots were brown and dead. Very few live ones could be found.
The main roots appear to be alive and normal.
The difference between the cover crop between the two rows
and in the remainder of the grove was very noticeable. Be-
tween the two rows, it had evidently been very sparse, whereas,
in the remainder of the grove it was more or less plentiful. In
the former the plants had come up, made a little growth, turned
yellow and died; in the latter they had made complete develop-
ment. Cowpeas had been planted between the two rows but had
made very little growth.
In April, 1916, the trees had put out some new growth that
gave them an improved appearance. The old foliage and some
of the new showed frenching. The abnormal condition still ex-
isted in the soil. At the end of a period of ten days during
which no cultivation had been done on account of a rain, the
volunteer cover crop seedlings were coming through the soil
very plentifully in the grove; very few were evident in the area
between the affected trees, except at one end where some stable
manure had been applied during the spring of 1915.
Florida Agricultural Experiment Station
FIG. 72.-View in citrus grove of middle adjoining one shown in fig. 71. No
ground limestone has been applied. The trees of both rows are on sour
stock. The row on the right is the same as row on the left in fig. 71.
FERTILIZER TREATMENT.-The fertilizer given the two rows
was the same as that given the remainder of the grove up to
August, 1913. It was as follows:
. .................4-6-6 from sulphate of ammonia, sulphate of
potash, dissolved bone black, blood and
bone tankage, about 1 lb. per tree.
...............4-6-6 from same sources, about 1 lb. per tree.
-................4-6-12 from sulphate of ammonia, sulphate of
potash, and acid phosphate, a little over
1 lb. per tree.
.................5-6-6 from sulphate of ammonia, sulphate of
potash, and dissolved bone black, a little
over 2 lbs. per tree.
..................5-6-5 from nitrate of soda, sulphate of ammo-
nia, tobacco stems, steamed bone flour,
dissolved bone black, and sulphate of
potash, about 2%8 lbs. per tree.
August, 1913 (except trees
1 to 9 in both rows)...........5-6-5 from the same sources, 2 lbs. plus per
From August, 1913, to January, 1915, the fertilizers applied
were as follows:
October 16, 1913...............Trees 1 to 9, both rows (not fertilized August,
1913), 3% lbs. each of Painter's Dieback
Fertilizer of formula 8 percent phos-
phoric acid and 13 percent potash.
December 13, 1913....... ...All trees, 2 lbs. per tree of formula 3-6-13
from sulphate ammonia, acid phosphate,
and double manure salts.
March 26, 1914.......................All trees, 2% lbs. per tree of formula 4-6-6
from nitrate of soda, sulphate ammonia,
acid phosphate, ground steamed bone,
and sulphate of potash.
170 Bulletin 137, Limestone Injury to Citrus Trees
June 18, 1914......................... All trees, 4 Ibs. per tree of formula 4.25-6-12
from nitrate soda, sulphate ammonia,
ground steamed bone, low grade sulph-
ate of potash and floats.
In January, 1915, the two rows were divided into plots and
fertilized according to a plan outlined by a fertilizer representa-
tive. The treatment was as follows:
January 2, 1915 ..................... Trees 1 to 4, both rows, 6 lbs. per tree of for-
mula 3-6-10 from nitrate soda, sulphate
ammonia, dried blood, acid phosphate
and sulphate of potash.
Trees 5 to 7, both rows, 6 lbs. per tree of a
fruit and vine brand.
Trees 8 to 10, both rows, 9 lbs. per tree of the
mixture: 4-12-6 from sulphate ammo-
nia, dissolved bone black and sulphate
potash .............................................. 27 Ibs.
Copperas ............................................ 3 lbs.
Goat manure................................30 lbs.
Trees 11 to 13, both rows, 9 lbs. per tree of
the mixture: 3-10-6 from sulphate am-
monia, nitrate soda, dried blood, acid
phosphate and sulphate potash......37 lbs.
Copperas .................................. 3 lbs.
Trees 14 to 16, both rows, 13% lbs. per tree of
the mixture: Hardwood ashes......25 lbs.
Copperas .......................................... 4 lbs.
Steamed bone...............................2...5 lbs.
Goat manure...................................... lbs.
Nitrate soda.................................... 3 lbs.
Trees 17 to 19, both rows, 11 lbs. per tree
of the mixture: Steamed bone....30 lbs.
Copperas ........................................ 3 lbs.
Goat manure......................................30 lbs.
Nitrate soda .................................... 3 lbs.
In March, 1915, only a part of the trees were fertilized. The
plan as outlined in January was discontinued on account of the
unfortunate death of the fertilizer company's representative.
The fertilizer applied in March was:
March 11, 1915......................Trees 1 to 4, both rows, 6 lbs. per tree of for-
mula 3-6-3 from sulphate ammonia, ni-
trate soda, acid phosphate, goat manure,
tobacco stems and potash.
Trees 5 to 7, both rows, 6 lbs. per tree, a fruit
and vine brand.
Trees 8 to 19, both rows, not fertilized at this
time. Expected to continue experiments
but stopped on account of death of rep-
About this time a light application of stable manure was
spread over the area between the first two trees of both rows.
A cover crop developed quickly over the area but the applica-
tion was apparently without benefit to the trees.
From June, 1915, to April, 1916, all of the trees were fer-
tilized alike, as follows:
Florida Agricultural Experiment Station
June 23, 1915............................All trees, 6 lbs. per tree of Painter's ammoni-
ated Dieback fertilizer.
December 31, 1915...................All trees, 7 lbs. per tree of formula 3-8-2 from
sulphate ammonia, acid phosphate,
ground tobacco stems and goat manure.
February 10, 1916...................All trees, 4 lbs. per tree of formula 4-8-0 from
nitrate soda, sulphate ammonia, and
April 15, 1916..........................All trees. 4 lbs. per tree of formula 4-8-0 from
sulphate ammonia and acid phosphate.
DIscussIoN.-Since, up to the time that the injury was first
noticed, the only difference in treatment between the two rows
and the remainder of the grove was the ground limestone ap-
plied, and since soil conditions are practically the same where
they were planted as in the remainder of the grove, it seems
quite evident that the ground limestone has been the direct or
indirect cause of the injury to the trees. How the limestone has
induced the injury is a matter of conjecture. The wide use of
ground limestone in the citrus groves of Florida without any
apparent injury and with apparent benefit indicates that the
injury can occur only under very special conditions. The con-
ditions prevalent in this grove must be an indication of the
conditions necessary for the development of the trouble. A
cursory review of these showed that the tendency of the soil to
dryness and the lack of humus were probably the chief abnor-
mal conditions present. The grove practices are such that the
humus supply would not be conserved or increased. The inti-
mate mixture of the ground limestone with the soil in the holes
where the trees were planted is probably another factor in the
development of the injury.
The greatly increased growth of the trees on the sour stock
receiving the ground limestone over those on the same stock
not receiving it indicates that the first effect of the limestone
was to bring about a soil condition that was stimulating to
growth. This was followed by a condition that was conducive
to injury not only to the trees but also to the cover crop.
The application of the manure in 1915, enabling the cover
crop to grow readily, is indicative that the injury of the trees
may be due to a lack of bacteria in the soil.
The application of the organic sources, dried blood and goat
manure, in connection with the plot treatments in January,
1915, did not bring about any marked increase of the cover
crop. Therefore it is probable that the stable manure was valu-
able more on account of the bacteria that it added to the soil
than on account of the organic matter added.
172 Bulletin 137, Limestone Injury to Citrus Trees
This same appearance of the trees and lack of growth of the
cover crop has been observed in other groves where limestone
was not used but where the soil had apparently been injured by
excessive cultivation. Such injury has not been observed ex-
cepting in groves planted on dry sandy lands lacking in humus.
Where such injury has occurred the limiting of cultivation to
the spring season, the adoption of grove practices that build
up the soil, and severe pruning have brought about a recovery
of the trees.
In a number of other groves where ground limestone has been
used the same type of injury to the trees and to the cover crops
has developed. All of these groves were planted on dry, sandy
lands lacking in humus. None of the trees was more than seven
to ten years old. Injury to the trees followed a period of nor-
mal growth. The first indication of injury was frenching. This
was followed by the development of a general starved appear-
ance in spite of the fact that the trees were well fed. However,
in these groves it was very difficult to trace the injury to the
ground limestone because it had been applied uniformly over
the groves. No part was left without it. If ground limestone
can cause injury to citrus trees it probably has done so in nu-
merous cases in the past, but the connection has been over-
looked thru attributing the injury to other causes or thru a
lack of checks for comparison.
EXPERIMENTAL GROVE, TAVARES
The Experiment Station has a fertilizer experiment at Ta-
vares, Florida, in cooperation with Mr. G. M. Wakelin (Fla.
Agr. Exp. Sta. Rep., 1909, p. xxvii). There are 47 plots re-
ceiving fertilizer treatment and one plot without fertilizer. Of
these there are three that have received ground limestone in
addition to the fertilizer. The limestone was applied first soon
after the trees were set out in January, 1909, and at irregular
intervals since. Each application consisted of 10 pounds per
tree. During the first few years after the experiment was
started frenching was general thru the grove on account of the
presence of Dieback in the trees. During the year 1915 the
trees had mostly recovered from the Dieback conditions and the
plots showing frenching stood out in more or less marked con-
trast to the remainder of the plots.
Five plots showed a severe attack of frenching (Fla. Agr.
Florida Agricultural Experiment Station.
Exp. Sta. Rep., 1915, p. c).. The fertilizer treatments given and
the order of severity of the attack is as follows:
Plot 21...............5-6-6 formula from cottonseed meal, acid phosphate,
sulphate of potash with ground limestone.
Plot 11...............5-6-6 formula from sulphate of ammonia, acid phos-
phate, and sulphate of potash with ground lime-
Plot 30................5-6-6 formula from nitrate soda, acid phosphate, and
Plot 28..............5-12-6 formula from nitrate soda, Thomas' slag, sulphate
Plot 39...............5-6-6 formula from sulphate of ammonia, acid phos-
phate, and sulphate of potash with ground lime-
Plot 21, where the ammonia of the fertilizer applied was de-
rived from cottonseed meal and ground limestone was used as
a soil addition, shows by far the greatest amount of frenching.
During the winter of 1915 the foliage on these trees became
quite yellow and there was much defoliation.
None of the trees in the frenched plots was as markedly in-
jured as the trees in the Drew grove. However, here no ground
limestone was mixed in the holes where the trees were planted.
In the summer of 1916 the trees through the whole grove had
put on a good growth and all except the trees in the frenched
plots showed a more or less normal color. Frenching was still
persistent in plots 21, 11, 28, and 39. Plot 30 had recovered
and showed very little yellowing. But plot 20, which received
the same fertilizer treatment (5-6-6 from cottonseed meal, acid
phosphate and sulphate of potash) as plot 21, but without the
ground limestone, now showed a marked case of frenching.
It is thus seen that all of the ground limestone plots in this
grove, in addition to some others, showed injury.
POT EXPERIMENTS WITH GROUND LIMESTONE
As a part of other experiments in the greenhouse, the fol-
lowing pot experiment was carried out, using ground limestone
in pure sandy soil and without fertilizer. The purpose was to
determine the effect of the limestone upon the plant in the ab-
sence of other materials (such as fertilizer) which might inter-
fere with its action. Under the conditions of the experiment
it was to be expected that the plants would show the effect of
starvation as the soil used was a pure sand almost without
organic matter and therefore lacking in the food elements.
Grapefruit seed were planted in the pots on February 8, 1915,
and allowed to grow until about June 22. At this time the
174 Bulletin 137, Limestone Injury to Citrus Trees
(Ir' ; r" t.XE r *
FIG. 73.-Pot experiments with ground limestone. No. I, grown in sand to
which 48 grams of ground limestone had been added. No. IX, grown in
sand without the limestone.
plants were free from the seed and entirely dependent, upon the
sand for food. Five pots were included in a series and five seed
were planted in a pot. The sand used was a coarse sand from
the shores of Lake Weir in Marion county. The pots were six-
inch pots, the walls of which had been soaked in paraffin. The
experiment was carried out on the east bench of the greenhouse
.. .. ..
::''''' .' :'r
Florida Agricultural Experiment Station
under uniform light conditions and under as nearly uniform
moisture conditions as the average greenhouse watering will
The series and their treatment are as follows:
Series I ...........Ground limestone....................48 grams
Series II ................Ground limestone............... .....32 grams
Series III ..............Ground limestone....................24 grams
Series IV ................Ground limestone....................16 grams
Series V ................Ground limestone....................12 grams
Series VI ................Ground limestone.................... 8 grams
Series VII ................Ground limestone................ 4 grams
Series VIII................ Ground limestone............... 2 grams
Series IX ................Ground limestone.................... 0 grams
The ground limestone was well mixed with the sand before
placing it in the pot.
RESULTS.-Table 10 shows the results of measurements made
upon the plants when the experiment was closed late in June,
1915. From these, it is evident that the plants of all series
excepting I and II made a growth that was no better than that
of series IX which received no limestone. The plants of series I
and II made on the average 7 and 11 percent greater growth
respectively than the plants of series IX without limestone.
This increase is comparatively small.
Pot Experiments with Citrus Seedlings
Series Stem Stem Leaf Leaf Fresh Dry
No. Length Diam. Length Breadth Weight Weight Av.
A B A B A B A B A B A B
I ....:............ 58.3 124 2.3 105 30.9 101 15.1 94 1.27 122 .41 121 111
II ........... 54.1 114 2.3 105 30.5 100 15.8 99 1.17 113 .38 112 107
III ................ 54.5 115 2.3 105 29.3 96 15.1 94 .98 94 .32 94 100
IV .................. 49.8 106 2.2 100 29.4 96 15.4 96 .93 89 .30 88 96
V .................. 50.4 107 2.2 100 29.3 96 15.0 94 1.00 96 .32 94 98
VI ................. 52.9 112 2.2 100 31.0 102 15.1 94 1.10 106 .34 100 102
VII .............. 47.5 101 2.2 100 29.9 98 15.3 96 1.02 98 .33 97 98
VIII .............. 49.7 105 2.2 100 28.8 94 14.7 92 1.04 100 .32 94 97
IX ...- 47.2 100 2.2 100 30.5 100 16.0 100 1.04 100 .34 100 100
A.-Average measurements in millimeters.
B.-Relative measurements (check series, 100).
The most marked difference between the plants receiving
ground limestone and those not receiving it was in the leaf color
and in the root development. The plants of Series I to VI in-
clusive showed marked frenching with a yellowish-green back-
ground. There was very little variation among the different
series. The plants of series VII and VIII showed only traces of
176 Bulletin 137, Limestone Injury to Citrus Trees
frenching. The plants of series IX were entirely free from
frenching but had the yellowish-green color indicating at least
There was an appreciable difference in root development be-
tween the plants receiving ground limestone and those not re-
ceiving it. This difference was noticeable even where only two
grams of limestone were used per pot, but was more pronounced
where the larger amounts were used. The roots in all cases
were slender but were longer and more profusely branched in
the limestone series. All roots, with the limestone as well as
without the limestone, appeared normal. No dying of the tops
MANNER OF GROUND LIMESTONE INJURY
From these experiments and grove observations, it seems
evident that ground limestone can, under certain limited condi-
tions, induce injury to citrus trees. Three conditions charac-
terize the sandy soils upon which the injured trees have been
observed. They are, a tendency of the soil to dryness, a lack
of humus or organic matter, and the use of grove practices that
do not conserve or build up the organic content of the soil.
The manner in which this injury can be induced is still un-
known. The stimulating effect upon growth following the ap-
plication of the limestone, the long time interval preceding the
development of the injury to the soil and to the tree, the ready
response of the plant growth to the application of stable
manure, its slow response to the application of the organic fer-
tilizers, all indicate that the injury may be caused indirectly
by the action of the limestone upon the micro-organisms of the
soil. It is possible that iron starvation may also be a factor.
The soil and tree injury have not been observed in groves
where the trees are more than ten years old. It is possible
that the shading effect of the larger trees upon the soil affords
conditions that are unfavorable for the development of the in-
jury. The deeper rooting of the older trees may also be a
The limestone injury of citrus trees has some points of simi-
larity to the trouble known as Mottled Leaf which occurs in
California. Both are characterized by a lack of green color
between the veins of the leaves. This form of chlorosis is
known in Florida as Frenching, and as Mottled Leaf in Cali-
fornia. During later stages of the trouble, the trees are char-
Florida Agricultural Experiment Station
acterized by partial defoliation and dying back of the branches.
Many of the defoliated twigs show multiple buds. The general
vigor of the trees is impaired and their yield is reduced to
almost nothing. Whereas much Frenching occurs in the groves
throughout Florida, the extreme cases, with the exception of
individual trees in groves, have been observed only in connec-
tion with the ground limestone injury of citrus trees.
METHODS OF PREVENTION
It is not the purpose of this bulletin to recommend to the
citrus grower that he avoid the use of ground limestone and
other forms of lime in his grove. But it does recommend that
they be used with care especially on dry sandy soils that are
lacking in humus. It should not be used in any great excess
of the needs of the soil. Blair and Macey* found that the lime-
stone required to neutralize the acidity in the first nine inches
of cultivated high pineland citrus soil varied from 180 to 2,520
pounds per acre. The average was about 1,000 pounds per acre.
From these figures, it is evident that a ton of ground limestone
per acre is greater than the actual needs of these soils, but it
is probably not excessive. But if this, or a greater application,
is repeated annually, the unused amount may accumulate in
the soil to such an extent that it may prove injurious if the
humus content of the soil is low. It is safer to make regular
applications of the limestone at wide intervals. An average
application every three years is probably sufficient. It is not
necessary to add limestone to the soil until it no longer turns
litmus paper red.
Ground limestone hastens the decay of organic matter and
its loss from the soil. Therefore, it is necessary to take extra
precautions to maintain the humus content of the soil. The
lack of humus is probably a very important factor in the de-
velopment of the ground limestone injury. Where possible, a
good legume crop should be grown in the grove every year
during the summer. A good system is to cut and turn the
whole crop under every year, or every third year; and to cut
and remove it for hay in the alternate years. Continually cut-
ting and removing the cover crop as hay without turning under
any organic material excepting the stubble, may lead to soil
178 Bulletin 137, Limestone Injury to Citrus Trees
It is not safe to try to increase the humus content of the
soil too rapidly. Excessive quantities of decaying organic
material in the soil may give rise to sappy growth, coarse fruit
and in some cases may induce the gum disease, Dieback. How-
ever, there is not much danger of this if the crop is cut and
allowed to dry and partly decay before being turned under.
CARE REQUIRED IN APPLYING MANURE
Ordinarily, stable manure should be used with a great deal of
care on grove soils because of its likelihood to induce the disease
Dieback. Once in a while, a grower has used it in rather large
quantities in the grove without serious results and to good
advantage. But it is more often the experience that when used
at all liberally, it makes coarse fruit and induces Dieback. If
the cover crop does not grow well in the grove, a light applica-
tion of stable manure well scattered from tree to tree and not
repeated until after a long interval, will be found safe and bene-
ficial. It should not be used on account of its fertilizing value,
but on account of the organisms that it adds to the soil. It
may be applied either in the early spring or just before the
grove is laid by for the summer. If applied in the early spring,
it may be plowed under, but in the summer, it should be ap-
plied sufficiently early to be worked into the soil with the har-
row before cultivation is stopped. The grove should not be
plowed at that time of the year.
The grove should be fed as regularly as if it were in a
normal condition. The best results will probably be obtained
by using a complete fertilizer, applying it in three regular appli-
cations during the year.
The ground limestone can be used more liberally on soils with
a good average moisture and humus content. Muck soils re-
quire the largest applications of the limestone.
It is not safe to mix the limestone with the soil in the hole
where a young tree is to be planted. Neither should the amount
to be applied to an acre be spread in narrow circles about the
trees. It is better to broadcast it from tree to tree, scattering
it evenly over the soil.
METHODS OF TREATMENT
Experiments in the treatment of ground limestone injury
have not been concluded. While the growers have not been
very successful in their control of the trouble, there is evidence
Florida Agricultural Experiment Station
from their experience to indicate that the following practices
may prove helpful for bringing the trees and soil back into
1. Discontinue the applications of ground limestone;
2. Use limited quantities of fertilizer from organic sources;
3. Use a light application of stable manure spread evenly
for the purpose of soil inoculation;
4. Plant and turn under a crop of cowpeas, velvet beans or
5. Mulch the trees heavily where it appears feasible to do so.
It will be well to give the trees a severe pruning when the
character of the cover crop and tree growths indicate that
the condition of the soil has become normal again. By removing
the weakened and stunted growth from the top, the tree will
be given opportunity to form a new head of stronger growth.
The cover crop will be the first to show that the soil conditions
have been improved. In cases of severe injury, the trees will
be slow in recovering. It may require a year or more for them
The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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