Title Page
 Table of Contents

Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 273
Title: A preliminary report on zinc sulphate as a corrective for bronzing of tung trees
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00027079/00001
 Material Information
Title: A preliminary report on zinc sulphate as a corrective for bronzing of tung trees
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 34 p. : ill. ; 23 cm.
Language: English
Creator: Mowry, Harold
Camp, A. F ( Arthur Forrest ), 1896-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1934
Subject: Zinc sulphate   ( lcsh )
Tung tree -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Bibliography: p. 33-34.
Statement of Responsibility: Harold Mowry and A.F. Camp.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00027079
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924337
oclc - 18207204
notis - AEN4955

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Full Text

December, 1934





Fig. 1.-Malformation of terminal leaves, an early symptom of "bronz-
ing" in the tung-oil tree.

Bulletins will be sent free to Florida residents upon application to

Bulletin 273


John J. Tigert, M.A., LL.D., President of the
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
Harol I Mowry, M.S.A., Asst. Dir., Adm.
J. Francis Cooper, M.S.A., Editor
R. M. Fulghum, B.S.A., Assistant Editor
Jefferson Thomas, Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant


W. E. Stokes, M.S., Agronomist"
W. A. Leukel, Ph.D., Agronomist
G. E. Ritchey, M.S.A.. Associate*
Fred H. Hull, M.S., Associate
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant

A. L. Shealy, D.V.M., Animal Husbandman"*
R. B. Becker, Ph.D., Dairy Husbandman
W. M. Neal, Ph.D., Associate in Animal
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Asst. Veterinarian
W. W. Henley, B.S.A., Asst. Animal Hus-
P. T. Dix Arnold, B.S.A., Assistant Dairy

R. W. Ruprecht, Ph.D., Chemist"*
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Associate
H. W. Winsor, B.S.A., Assistant
H. W. Jones, M.S., Assistant

C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage. M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant

Ouida Davis Abbott, Ph.D., Specialist*
L. W. Gaddum, Ph.D., Biochemist
C. F. Ahmann, Ph.D., Physiologist
J. T. Hall, Jr., B.S.Ch.E., Asst. Physiologist
J. R. Watson, A.M., Entomologist"*
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
J. W. Kea, B.S.A., Assistant
A. F. Camp., Ph.D., Horticulturist"
G. H. Blackmon, M.S.A., Horticulturist
A. L. Slahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot, M.S.A., Specialist, Fumigation
R. D. Dickey, B.S.A., Assistant Horticulturist
W. B. Tisrlale, Ph.D., Plant Pathologist"
George I. Weber, Ph.D., Plant Pathologist
R K. Voorhees, M.S., Assistant
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Assistant Botanist

In cooperation with U.S.D.A.
** Head of Department.


Geo. H. Baldwin, Chairman, Jacksonville
A. H. Blanding, Bartow
A. H. Wagg, West Palm Beach
Oliver J. Semmes, Pensacola
Harry C. Duncan, Tavares
J. T. Diamond, Secretary, Tallahassee


L. O. Gratz, Ph.D., Plant Pathologist in
R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
R. M. Crown, B.S.A., Asst. Agronomist
Jesse Reeves, Farm Superintendent

John H. Jefferies, Superintendent
Geo. D. Ruehle, Ph.D., Associate Plant
W. A. Kuntz, A.M., Assoc. Plant Pathologist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Asst. Entomologist

A. Daane, Ph.D., Agronomist in Charge
R. N. Lobdell, M.S., Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
G. R. Townsend, Ph.D., Asst. Plant Patholo-
B. A. Bourne, Ph.D., Sugarcane Physiologist
J. R. Neller, Ph.D., Biochemist
R. W. Kidder, B.S., Asst. Animal Husband-
Ross E. Robertson, B.S., Assistant Chemist

H. S. Wolfe, Ph.D., Horticulturist in Charge
W. M. Fifield, M.S., Asst. Horticulturist
Stacy 0. Hawkins, M.A., Assistant Plant

E. W. Sheets, D.Agri., Animal Husbandman
in Charge*
W. F. Ward, M.S.A., Asst. An. Husbandman*


M. N. Walker, Ph.D., Plant Pathologist in
W. B. Shippy, Ph.D., Asso. Plant Pathologist
K. W. Loucks, M.S., Asst. Plant Pathologist
J. W. Wilson, Ph.D., Associate Entomologist
C. C. Goff, M.S., Assistant Entomologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
R. E. Nolen, M.S.A., Asst. Plant Pathologist
A. S. Rhoads, Ph.D., Plant Pathologist
A. H. Eddins, Ph.D., Plant Pathologist
G. B. Fairchild, M.S., Assistant Entomologist
David G. Kelbert, Asst. Plant Pathologist
E. R. Purvis, Ph.D., Assistant Chemist,
Celery Investigations



Introduction .......... ... Page 8
H history .................... .... .. ........... ...... .... Page 4
Bronzing of Tung Trees... ..... .... .. ..... ........... Page 6
Experim ents .............. .......... ... ... .... .... ........ Page 10
Effects of Other Salts in Combination with Zinc Sulphate Page 18
Effect of Zinc in Sprays .. ................. Page 19
Experiments in Columbia County............... ...........- Page 19
Zinc Treatments in Connection with Fertilizer Tests .. ... ........ Page 20
Miscellaneous Experiment ....... Page 24
General Observations ............ ..... Page 28
D discussion ................. ... .......... ...... Page 30
Literature Cited....... Page 33


During the course of the development of the tung-oil industry
in Florida, an unthrifty tree condition locally known as "bronz-
ing" has been the cause of loss in many groves and considerable
apprehension on the part of growers. Within the past few years
this trouble has occurred with increased severity, affecting many
newly planted groves and also occurring more extensively in
some of the older groves that apparently had been fairly free
of it during the early life of the trees. In the earlier plantings
it appeared to be confined rather definitely to certain soil types
and considerable investigational work was done in an effort
to discover soil treatments that would correct it, but without
success. Bronzing has not made its appearance in all groves,
although in some it has been a matter of grave concern.
Experiments started in 1931 have shown that the trouble in
most cases apparently can be corrected by applications of zinc
sulphate, either to the soil or to the tree. The recovery of many
severely affected trees following treatment with this material
has been truly remarkable and as a result of these experiments
hundreds of acres of tung trees in Florida were treated by the
owners in 1933 and the spring of 1934, with excellent results.

The authors acknowledge the assistance of Messrs. R. D. Dickey and
Waiter Reuther of the Department of Horticulture in the collection and
tabulation of data.

Florida Agricultural Experiment Station

While many questions relative to rates and times of application
still remain to be answered, it was felt desirable to publish
a preliminary report at this time for the information of growers.
The areas of commercial tung tree production in Florida
are to a large extent coincident with areas in which Satsuma
oranges are grown, although the tung tree is much the hardier.
On some soils the Satsuma orange tree is commonly affected
with "frenching," a physiological trouble manifested by chloro-
tic foliage and poor tree growth. Trees so affected do not
grow satisfactorily and are extremely susceptible to cold in-
jury, even by the low temperatures of the average winter. This
condition in Satsuma trees has been found to be quickly remedied
by applications of small amounts of zinc sulphate to the soil
about the tree or by direct application of a zinc sulphate-lime
spray to the foliage.

In 1930 Newell, Mowry and Barnette (16)' reported on the
occurrence of "bronzing" in tung trees and showed that in
many cases bronzing occurred on soils underlaid with phos-
phatic limestone and that such soils contained large amounts
of phosphatic salts (determined as P2Os). The soils were all
slightly acid in reaction. Experiments with sulphuric acid,
ferrous sulphate, manganese sulphate and various forms of
lime and phosphates failed to remedy the condition.
The later experiments here reported, initiated in 1931, were
based on the theory that since the trouble was not of parasitic
origin nor caused by a lack of plant food derived from common
fertilizer materials it might be due to a deficiency of some
essential element or elements. This theory was based on growth
reaction and appearance of the trees themselves and the light
and porous character of the soil which indicated the probability
that compounds present in only small amounts might be leached
easily from it. No information was available on the fundamen-
tal nutrition of tung trees, so several elements that had been
found necessary for the growth of plants, and that had not been
tried in previous experiments, were utilized. Since, of the
many chemicals tried, only zinc sulphate gave favorable results,
only literature pertaining to the use of zinc sulphate will be
1 Figures in parentheses (Italic) refer to "Literature Cited" in the back
of this bulletin.

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 5

As early as 1869 Raulin (17, 18) showed that growth of a
fungus (Aspergillus niger) was greatly stimulated when zinc
salts were added to the nutrient solution. The role of zinc in
the growth of fungi has been variously discussed subsequent
to that work, but it was not until Maze (12, 13, 14 and 15)
studied the role of so-called rare elements that the importance
of zinc to the growth of higher plants was discovered. The
work of Sommer and Lipman (23) and Sommer (21, 22) es-
tablished more definitely the importance of zinc in plant nutri-
tion but no field experiments were carried out. Roberts and
Pierce (19) used a zinc-lime spray as a fungicide on peaches
and in their reports called attention to the fact that the spray
frequently seemed to produce greener and more vigorous leaves.
Allison, Bryan and Hunter (3) reported positive responses
in field trials from zinc sulphate treatment on several crops
(peas, corn, cane, soybeans, etc.) on the peat soils of the Ever-
glades. Besides the work reported above, lengthy investiga-
tions had been carried out in the department of horticulture
at the Florida Experiment Station on the use of zinc salts and
other chemicals in propagation experiments with favorable re-
sults. It was believed, therefore, that the basic information was
sufficient to render it worth giving zinc sulphate a trial.
Subsequent to the starting of the work reported here, a series
of reports on the field use of zinc salts have been published and
these reports, while not including any work on tung trees, are
of considerable interest as bearing on the probable relation-
ship of this trouble (bronzing) to a definite soil condition af-
fecting many kinds of plants. Chandler, et. al. (4, 5 and 6),
reported positive results from the use of zinc sulphate on "Iittle
leaf" of deciduous trees. Alben, et. al. (1 and 2) reported posi-
tive results from the use of zinc sulphate on "rosette" of pecans.
Apparently in both instances the use of zinc had its inception
in, and was the result of, experiments with impure iron sulphate
which had been previously reported as correcting these trou-
bles. Subsequent investigational work has shown the correc-
tive value of zinc sulphate on "little leaf" or "mottle leaf" of
citrus (Johnson (11) and Thomason (24)) and further work has
been published on pecan "rosette" by Finch (9), Finch and Kinn-
son (10), Cole et. al. (7), and Demaree (8). These results are
of particular interest since, immediately adjacent to the badly
bronzed tung-oil grove at the Florida Experiment Station, blocks

Florida Agricultural Experiment Station

of citrus (Satsuma) trees showed frenching to a severe degree
and pecans very striking cases of rosette.
"Bronzing" of tung-oil trees is a non-parasitic disease that
'has made its appearance in plantings over a wide area and
which for some years has been quite baffling in that it could
not be overcome by the use of the common fertilizer elements, by
cultivation methods, or by cover-cropping. The severity of attack
has been variable, in some instances the tree appears to be
brought to a virtual standstill insofar as growth is concerned,
and in others the tree died outright within two or three seasons.
Extended observations have shown that a "bronzed" tree is
.---materially weakened and is subject to injury by the ordinary
low temperatures of winter that have no injurious effect on
vigorous trees. (It is to be clearly understood in any reference
herein to cold injury of the woody parts of the tung tree that
trees so injured have been bronzed to some degree; healthy
trees, from one to 12 years old, have withstood 150F. with no
damage that could be detected.)
The first noticeable symptom of "bronzing" is a b onzed
coloration of few to many leaves, coupled with a deforJnation
of the terminal leaves which may be very slight or extremely
severe (Fig. 1). The first leaves on the shoot may be normal
but successive ones are usually slightly smaller and finally
severely deformed leaves may appear. The foliage later takes
on a typical dark bronze color, becomes more or less spotted, and
ultimately parts of the leaves die, giving them a ragged ap-
pearance. In maAy instances, twigs become partially or en-
tirely defoliated. -fOn newly-affected trees the trouble usually
starts in the very late spring or early summer but seldom ap-
pears with the first growth of the season and evidences of it
may not appear until very late summer or early fall. Following
the appearance of the initial symptoms the severity of the
trouble usually increases rapidly. Successive new leaves are
more severely affected, being smaller and badly malformed,
and the intern/des are shortened, giving a bunched appearance
to the foliage and the usual long heavy growth does not de-
velop. The affected twigs are smaller in diameter and de-
finitely weaker, and adventitious buds start growth on the
older wood giving the tree a "feather-legged" effect in severe

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 7

cases. Some dying of twigs and terminal buds may take place
during the first season in which the trouble occurs, but this
is unusual. During the first season the trouble may appear
on one limb only and that limb or branch may become badly
affected before any of the rest of the tree is visibly affected,
but eventually the remainder of the tree becomes involved.

Fig. 2.-Three-year-old tung tree severely affected with bronzing, after
having made a good initial growth.

Trees that have been affected by bronzing during the sum-
mer season are apparently much weakened and predisposed to
cold damage during the succeeding winter even though the<
temperatures are not markedly low. The first cold weather
usually kills many of the terminal buds and many of the "thin"
twigs that have developed. Further killing of wood occurs

Florida Agricultural Experiment Station

during the winter and such trees flush quickly in the early
spring, making themselves susceptible to marked injury by
late frosts. The tree comes into leaf in the spring with a great
loss of wood and buds and, commonly, an actual reduction in
size due to the death of many of the larger branches.
With the advent of spring trees affected the previous sum-
mer leaf out freely but the twigs, while they may be numerous,
are very slender, the internodes short and the leaves small.
Definite bronzing of the leaves occurs as soon as the initial
growth has hardened up in early summer and usually increases
in severity as the season progresses. In severely affected trees,
adventitious buds may develop freely on the trunk and main
limbs. The shoots produced during the second season are us-
ually abnormally slender and by early summer typical leaf
malformation and twig dying has appeared. While consider-
able twig growth may appear, this frequently dies back and the
tree, if badly affected, actually shrinks in size during the
growing season. This, combined with increased winter killing,
may bring the tree into the third season after the trouble has
appeared, almost dead, having been reduced from a good sized
tree to little more than a stub (Fig. 2).
The severity of the trouble may vary considerably, rang-
ing from very severe cases resulting in the death of the trees
to much milder forms. The age of the tree when the first
symptoms appear may vary considerably also. In many cases
the tree may reach several years of age before showing damage
and may thrive splendidly during that period, as far as can be
detected by observation. On the other hand, there have been
groves under observation in which trees developed the trouble
during the first year after transplanting, and nursery stock
in its first season has been noted as severely affected.
The relationship of bronzing to soil type is rather indefinite
and there sometimes appears to be at least as much of a relation-
ship between the condition of the soil as regards previous cul-
tural treatment, as there is to the soil type as such. In October
of 1932 a survey of tung tree groves throughout the state was
made by the senior author and R. M. Barnette of the Chemistry
and Soils Department. The soil types in the various groves
were determined, and the occurrence or absence of bronzing
noted. The following is a list of the soil types on which tung-
oil trees were found, the asterisks indicating the soil types on
which bronzing occurred:

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 9

Naturally Well-Drained Soils
*coarse sand
*medium fine sand
*fine sand
*sandy loam
*fine sandy loam
*fine sandy loam
*medium fine sand
*medium fine sand
*medium fine sand
*fine sand

Medium Natural Drainage
Norfolk-Flat Phase
medium fine sand
loamy fine sand
medium fine sand
*fine sand
Naturally Poorly-Drained Soils
fine sand
fine sand
medium fine sand
fine sand
medium fine sand

It will be noted that bronzing was found on the majority
of the soils examined, though the starring does not indicate that
the bronzing was necessarily severe-merely that it occurred
in some degree-and it also does not indicate that bronzing was
found in every case examined on that soil type but that it was
found to occur on that soil type in one or more groves. Since
plantings had not been made on all soil types occurring in
Florida, and on some but few trees were found, the indications
of lack of bronzing on a soil type may be misleading in that
further plantings may show bronzing on those types on which
affected trees were not found and here noted as free of the
In earlier studies it was indicated that bronzing is probably
related to the presence of natural phosphatic materials in the
soils in what may be excessive amounts for the tung tree. Such
phosphatic materials occur in many soils in north-central Flor-
ida and where tung trees are found on such soils "bronzing"
commonly occurs. In the last three or four years as the plant-
ings have become older, bronzing has been more widespread
and has not been limited to soils high in phosphatic material.
It is becoming increasingly apparent that the condition of the
soil as regards previous cultivation is a large factor in the occur-
rence of bronzing. In a number of very severe cases, the lands
on which the trees were planted have been under cultivation
for many years. Plantings have been made on rolling lands
formerly used for growing cotton and other farm crops and,
in the case of some of the most severe occurrences of the trou-
ble, the land has been under cultivation for periods of 50 years
or more. These lands could be classed as depleted soils, since

Florida Agricultural Experiment Station

the growing of general farm crops constituted a very consider-
able drain upon soil fertility, and, until recently, cover-crops
were not used to relieve this drain nor were crop rotations us-
ually followed. Bronzing is not limited, however, to old soils,
since it has occurred on newly-cleared lands and on lands which
have been cultivated for only a short time.
The first applications of zinc sulphate to tung trees were
made in the fall of 1931 and spring of 1932, the 1931 treatment
having been made by R. Buckley, at the suggestion of the senior
author, on a few trees in a commercial planting, and the 1932
applications on plantings of the Experiment Station. In both
instances the zinc salt was broadcasted on the soil under the
spread of the trees. The 1931 application was made subsequent
to the last seasonal flush of growth and no response was noted
that year. However, an examination of those trees in the sum-
mer of 1932, following the demonstration of recovery so marked-
ly apparent on the treated trees at the Experiment Station,
showed them to have made a definite growth response during
the spring months as the result of the zinc applied the previous
At the Experiment Station, the work was carried out on
a block of tung trees containing 19 rows of 30 trees each that
had been planted in 1930 for the purpose of comparing the
yield and growth reaction of budded and seedling trees. The
plan of the planting made possible the later laying out of com-
parable zinc treatments on both budded and seedling trees.
At the time of the initiation of this work in 1932 many of the
trees had made an unsatisfactory growth because of bronzing
and had been replaced with younger ones from the nursery.
The trees of the plot were thus somewhat irregular in size and
thrift due to replacement, soil variation and varying degree
of bronzing.
Both Hernando and Norfolk soil types, as well as a mixture
of the two, are represented in the plot. This grove had been
given excellent care insofar as fertilization, cover-cropping
and cultivation were concerned, but growth response was un-
satisfactory except in irregular areas where the thrift of the
trees was reasonably good. Trees in the south five rows were
most seriously affected with bronzing and many had died back
to stubs at the time of the first treatments. On the north side

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 11

of the plot the trees were in better condition but quite variable
in thrift. This situation made the laying out and checking
of experiments quite difficult and it was necessary to utilize
adjoining trees as checks in all cases, rather than full check
rows across the block.
Like rosette of pecans, bronzing of tung-oil trees is very
difficult to experiment with, owing to the great irregularity in
occurrence. Small groups of trees may bronze severely but
be surrounded by trees apparently unaffected. This condition,
in all probability, is the result of soil variation and was par-
ticularly marked in this planting.
Inauguration of this work on the Experiment Station trees
was delayed until bronzed foliage began to appear in June,

Fig. 3.-Tree treated June 11, 1932, with one-half pound ZnSO,.7THO.
Photograph made Aug. 29. On June 11 the appearance of the tree was
similar to that shown in Fig. 2.

Florida Agricultural Experiment Station

1932. The first experiments were laid out in the south portion
of the above block of trees, using for the most part only trees
which had died back heavily during the previous year. As part
of a series of treatments, which included salts of boron, nickel,
copper, manganese, magnesium, potash and calcium, as well as
zinc sulphate, three badly affected trees were treated with one-
half pound each of chemically pure zinc sulphate (ZnS04.7H20).
All materials were broadcasted on the soil around the base of
the tree. Two of these three trees were in their third year in
the field and had been greatly reduced in size by bronzing and
the resultant winter killing, being smaller than they were the
previous year; the third tree was a two-year-old replant.
Within 30 days the trees treated with zinc sulphate had
put on new and apparently healthy growth and the response
was sufficiently marked to justify applications to other trees.
(It was at this time that an examination disclosed a marked
recovery of the trees treated in the preceding fall by Buckley.)
By August 1, approximately seven weeks after treatment, the
vigor of the three trees apparently had been fully restored
as was shown by new growth from three to five feet in length
with large and normally developed foliage (Fig. 3). The favor-
able condition continued through the fall months and the trees
went into the winter with the heavy buds and robust twigs
which are characteristic of the tung tree in normal growth.
All withstood the cold of the following winter without loss
of wood, while neighboring untreated trees were killed back
in varying degree as is common in cases of severe bronzing.
Most of the untreated trees bloomed early and were injured
by a late March frost, whereas the treated trees remained
dormant and were uninjured. Their growth during the fol-
lowing season (1933) was vigorous and no bronzing appeared
(Fig. 4), though one of the three showed indications of a need
of additional zinc in the late fall. Untreated neighboring check
trees declined steadily during the same season.
Two additional trees were treated July 28, 1932, with one-
half pound each of zinc sulphate. These trees were in bad
condition but showed a decided improvement within six weeks
and survived the winter without injury. In the regular check-
ing of grove condition on June 25, 1933, they were given a
rating of "Excellent" with no bronzing apparent, whereas sur-
rounding untreated trees were badly bronzed and were rated
as "Poor" to "Very Poor."

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 13


Fig. 4.-Same tree as shown in Fig. 3, but picture taken June 1933.
Received one-half pound ZnSO4.7H2O in June of 1932.

Ten trees, all in fair to poor condition, were treated August
5, 1932, five receiving one-half pound each of ZnSO4.7H20, and
the five others one-fourth pound each. Due to lateness in the
season, no new growth appeared immediately following the
applications and the trees showed no recovery during the fall.
By June of the next season all of the trees had recovered to a
marked degree but the primary spring growth evidenced some
indications of bronzing. The later growth, however, was in

Florida Agricultural Experiment Station

excellent condition and free of the trouble. All of these trees
had made a marked recovery by fall as compared to checks,
with the exception of one which had received a treatment of
calcium carbonate at approximately the same time as the treat-
ment of zinc sulphate. This tree was badly bronzed and in
very poor condition. Recovery of these trees was not as marked,
however, as was that of those treated with zinc sulphate earlier
in the season of 1932. Also, on August 5, 1932, five trees were
treated with one-half pound of ZnSO,. 7H1O and two pounds
of muriate of potash each. Three of these trees showed marked
recovery by the fall of 1933 as compared with checks, and the
other two, which were in extremely bad condition when treated,
failed to recover.
On September 19, 1932, a more extensive system of experi-
ments was laid out to determine the rate and time of application.
Instead of the salt with the seven waters of crystallization that
had been applied previously, that with only one water of crys-
tallization (ZnSO4. 1H2O) was used, and in all subsequent
experiments, unless mentioned otherwise, this latter salt was
the one employed. Two rows of 30 trees each across the field
were treated with one-half pound of zinc sulphate each and
one row was treated with one-fourth pound per tree of the
same salt. It was too late to note any results from these applica-
tions during 1932 and treatments were continued in 1933. One
of the rows receiving one-half pound per tree in 1932 received
a like amount in March of 1933, and one-half of this row (15
trees) was treated with an additional one-half pound per tree
in June of that year. The row receiving one-fourth pound of
this salt in 1932 was similarly treated with one-fourth pound per
tree in March and in June of 1933, as above outlined. These
two rows were separated by another row, and 10 trees in the
center of this row were used as a check. The row receiving
only the single application of one-half pound in September of
1932 was some distance removed from the above three rows
and the trees were of a larger size and in markedly better con-
dition, so that it was necessary to use an untreated row adjoining
it as a check.
For convenience in presenting results the notes were con-
verted into numerical values for each tree and averaged to
give a comparative value for the plot. This was done in the
following manner: The trees were examined from time to time
and bronzing noted by numbers as follows: 1 indicated very
slight bronzing and 4 represented extremely severe bronzing

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 15

with all of the growth affected, while 2 and 3 represented inter-
mediate conditions. These values were converted to a basis
of 100 with 4 equal to 100, 3 to 75, 2 to 50 and 1 to 25 (zero
indicating no bronzing). The values for the individual trees
were added and then divided by the total number of trees in the
plot to arrive at an average figure. The condition of the trees
as to health and growth had been noted as excellent, good,
fair, poor and very poor, and these values were translated into
100, 80, 60, 40 and 20, respectively, and the average value for
the plot calculated. While this was purely an arbitrary method
of calculation, it was considered fair to all plots since they were
all subjected to the same errors.
In interpreting these figures it will be noted that a tree in
excellent condition will rate high numerically in the condition
column, whereas a badly bronzed tree will show a high value
in the bronzing column. It is necessary to compare each plot
with its corresponding check and the figures given cannot be
compared from group to group owing to the great variability
in the grove. The treated trees on the south side of the property
were almost invariably in very poor condition and badly bronzed,
whereas the plots on the north side were variable and even with-
out treatment would give better condition values in many in-
stances than would the treated trees on the south side.
The final examination made in October of 1933 has been
taken as a basis for the interpretation of results for most of
the experiments and for the experiments started in the latter
part of 1932, the values for the various plots are as follows:
Amount per Tree
Dates of Applications per Application Bronzing Condition
9-19-32, 3-11-33 .................. Y2 20 75
9-19-32, 3-11-33, 6-23-33 ........ 17 67
Check ...................................... 85 10

9-19-32, 3-11-33 ...................... 42 57
9-19-32, 3-11-33, 6-23-33 ......... 47 53
Check .... ........... ........... 57 40

9-19-32 ...................................... 29 67
Check ...................................... 43 43

Florida Agricultural Experiment Station

It will be noted from these results that there was a very pro-
nounced improvement in the plots given two and three applica-
tions of one-half pound each. The smaller applications, while
showing a distinct improvement as compared with the checks,
were, nevertheless, not always entirely satisfactory.
Additional experiments along the same line were laid out
in 1933 and included plots receiving one-half and one-fourth
pound applications in March of 1933, half of these plots re-
ceiving additional applications at the same rate in June of 1933.
These plots were laid out on the extreme north side of the field
where the trees were still in good condition and had made a
vigorous growth but showed some bronzing and indications
that increased trouble would soon ensue. The plots contained
20 trees each and 30 comparable trees were maintained as checks.
At the October inspection the comparisons were as follows:

Amount Zinc Sulphate
Dates of Treatment per Tree Bronzing Condition

3-11-33 ..-............. .... ....... 2 22 74
3-11-33, 6-26-33 ...................... Y 10 82
3-11-33 ..................................... 1/4 26 76
3-11-33, 6-26-33 ...................... 14 81
Check .. ................. ............... 28 53

It will be noted that while the response had been very marked
bronzing had not been entirely eliminated, though it had been
reduced materially in amount as compared to checks and the
condition of the trees had been greatly improved. The superi-
ority of the treatments which included June applications of
either one-half or one-fourth pound amounts is suspected to
be due as much to the time of making the application as to the
amount, and other evidence would seem to bear out this. The
March applications were made just before the leaves appeared
and it would seem that the full value of the application was not
obtained as compared with later applications made after the
trees were in leaf.
Further experiments were carried out to determine the op-
timum time and amount of application. In March 1933, 15
trees were treated with one pound each of zinc sulphate broad-
casted. All of these trees were in very poor condition and most
of them were little more than stubs with a few sprouts. The
response was remarkable and by June these treated trees had
eclipsed all others in response to treatment and had new growth

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 17

three to five feet long and no trace of bronzing apparent. In
June, five of these trees were treated with an additional ap-
plication of one pound each. It was noted that by August these
latter trees were superior in color and growth to the remain-
ing 10, though all were in excellent condition and growing nor-
mally. By October very slight symptoms of bronzing had shown
up on four of those receiving the single application and no
evidence of bronzing had appeared on those receiving two ap-
plications. Considering that these trees were in very poor con-
dition in March, this recovery was remarkable. The marked
superiority of the trees receiving the second application in June
is of considerable interest when compared with other results
which indicate the inferiority of too early applications. This
is further borne out by the reaction of 15 additional trees that
were treated with one pound each of the salt broadcasted in
June. These were in an adjoining row and in very bad condi-
tion generally. Two of these trees previously had been treated
with one-half pound ZnSO4.7HO and two with one-fourth
pound on September 19, 1932. All but one of the latter had
shown definite recovery but the remaining 11 were in very bad
condition when the treatment was applied. By October, all
but two of the 15 trees had shown marked recovery and showed
only the slightest trace of bronzing.
For the purpose of comparing broadcast applications with
ring applications, 30 trees in a single row which had been
mulched with tung-oil hulls were utilized; 10 trees were treated
in June 1933 with one pound each of zinc sulphate broadcasted,
10 with two pounds each broadcasted and 10 with one pound
each in a trench around the trunk of the tree, the soil having
been removed so that the salt could be applied in a ring on the
crown roots, and after the application the soil was replaced.
By October these trees had all shown a marked response as
compared with the adjoining row, the trees of which also had
been mulched with the same material. The results given on a
numerical basis, as above outlined, are as follows:
Amount of Application Method ]|
per Tree of Bronzing* | Condition*
(lbs.) Application 1I 7/17 10/10 1 7/17 1 10/10
1...................................... Broadcast 25 10 84 82
2........... ................... Broadcast 27.5 5 88 88
1-... ............................... 'Ring 22.5 10 84 80
Check ................ ..... ... ... 22.5 22 91 75

Values computed as explained on page 14.

Florida Agricultural Experiment Station

I Other applications of two and five pounds each were made
on very badly, affected trees, some of which appeared almost
dead. Both the broadcast and ring methods of application were
utilized. All made definite recovery with strong growth but no
difference could be noted between the two methods of application,
although there may have been a slight margin in favor of the
broadcast applications. In connection with these experiments
it should be noted that where the trees were in extremely bad
condition when treated the new shoots which developed following
the applications, while very vigorous and strong, continued
growth very late into the fall and were in some cases injured
by frost in November. To attempt to restore trees that have
been so severely affected as to be reduced to stubs is of doubtful
value, since the planting of a new tree, with zinc applications
from the beginning, will probably give the better final results.
A number of experiments were carried out to determine the
effect of large applications. Amounts as high as 20 pounds per
tree on three-year-old trees were used with no damage apparent
after a lapse of one year. The effects of these large applications
have shown no difference thus far from the effects of applica-
tions ranging from one-half to five pounds per tree. After sev-
eral years, however, some damage may appear and such large
applications may not yet be considered as definitely safe.
In the early spring of 1933 a considerable number of mixed
applications were made in which zinc sulphate was combined
with other salts and of these there was some indication that the
mixture containing magnesium sulphate might have partially
nullified the effectiveness of the zinc sulphate. Further appli-
cations were made in June, using one pound of zinc sulphate
in combination with varying amounts of magnesium sulphate,
from one-half to four pounds. These treatments were applied
to selected trees, all of which were badly bronzed. By October
all had recovered almost completely as compared with other trees
receiving a June application of one pound of zinc sulphate and
there was no indication of either beneficial or detrimental effect
due to the use of the magnesium sulphate. No improvement in
effectiveness was obtained with any of the combinations which
included salts of copper, manganese, nickel and potassium.

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 19

The possibility had been suggested that if zinc sulphate were
mixed with superphosphate in fertilizers there might be a re-
action that would prevent the effective action of the zinc sulphate.
Mixtures, therefore, were made using for each mixture one
pound of zinc sulphate and from one-half to four pounds of
superphosphate. These mixtures were allowed to stand in the
fertilizer barn for two days and then were applied to badly
bronzed trees. These applications were made on June 28, 1933,
and by October all of the trees had shown marked recovery and
no bronzing was apparent in any of them, whereas adjoining
checks had shown a steady decline.
Starting in July 1932, experiments were carried out on the
effect of applications of zinc sulphate applied as a spray to the
trees. Since sprays of zinc sulphate and water alone burned
the foliage, a spray was used which contained six pounds of hy-
drated lime and three pounds of 89 percent zinc sulphate in 50
gallons of water, with a calcium caseinate spreader added. These
sprays gave definite responses comparable with the results ob-
tained from soil applications except for the fact that the spray
effect did not extend beyond the season of application. These
sprays were not continued on an extended scale owing to the
fact that spraying is not a commercial necessity in tung-oil
groves for pest control and the small amount of zinc sulphate
necessary in soil applications would make the purchase of special
spraying equipment uneconomical for small acreages. In ex-
periments with citrus, however, the spray has been of outstand-
ing importance and excellent results have been obtained with it
and there are indications that the spray may prove superior to
soil treatments in certain instances. The experiments have
shown that spraying would have to be done every year to be
effective and while it would seem that yearly soil applications
are desirable, yet there is definitely more holdover effect than is
the case with sprays.
In a cooperative planting in Columbia County, an experiment
had been started in February of 1930 to test the relative value
of budded and seedling trees. This block of trees was made up
of 21 rows of 17 trees each; 10 of the rows were budded and 11

Florida Agricultural Experiment Station

were seedlings. The planting was on rolling Norfolk land which
previously had been cropped to cotton and other farm crops and
bronzing began to show up severely in 1932. In February, 1933,
four rows across the planting were treated with one-half pound
of zinc sulphate per tree. The treated rows were alternated
with untreated ones so that the plot might be said to consist of
four treated rows and five check rows. Growth increments are
shown for the 1933 season in Table 1. There was a marked
response in growth as the trees were observed in the field and
it will be noted that this response is borne out in the growth
increments for height, spread and area of cross-section of the
trunk, the treated trees having a marked advantage over the
untreated ones. It is interesting to note also that these trees
that year bore their first small crop and that there was a marked
increase in yield in the treated trees.

I Increase Increase Increase in Trunk
Row Treatment j No. Trees in in I Cross-Section
Height (ft.)l Spread (ft.)I (sq. inches)

Check....................... 22 1.0 1.2 3.13
*ZnSO.H.O ............ 22 1.5 2.8 3.26
Check......... ............ 22 0.7 1.3 2.75
ZnSO4.HO ............ 22 1.9 3.0 3.70
Check............ ..... 22 1.4 1.6 2.93
ZnSO..HO ............ 22 1.5 2.3 3.63
Check....................... 21 1.1 1.5 2.62
ZnSO..H2O .....-........ 22 2.1 3.1 3.84
Check..... ......... 21 1.3 1.9 2.96

Check (avg.)....... .......... ....... 1.1 1.5 2.88
Treated (avg.) ................ ...... 1.8 2.8 3.61

A fertilizer test on tung-oil trees was started in 1931 in co-
operation with a commercial grower in Alachua County. In
some of the plots bronzing developed, its occurrence apparently

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 21

being associated with certain soil variations rather than with
the kind of fertilizer used, though some fertilizers evidently had
an effect in correcting bronzing in those areas conducive to its
development. Each fertilizer plot consisted of four rows of nine
trees each, or a total of 36 trees. On March 15, 1933, four trees
at each end of each plot were treated with one-half pound each
of zinc sulphate broadcast, and eight adjacent trees, similarly
arranged, with one-fourth pound each of the same chemical.
During the summer the usual notes on each tree were made
covering the occurrence of bronzing and condition of growth and
following the 1933 growing season the usual measurements of
height, spread and area of cross-section of trunk were taken
and the increments for the season determined. Growth incre-
ments and tree condition for the zinc-treated and untreated trees
in each plot are shown in Table 2.
Of the measurements made, those of cross-section area of the
trunk are the most significant since they are taken at the same
point each year and can be measured with a reasonable degree
of accuracy. It will be noted that in only five cases out of 27
did the increase in cross-section area of the trunk on the un-
treated trees equal or exceed that of treated trees. Of those
five cases, there were two in which the values were practically
the same, so that in only three cases out of 27 did the untreated
trees show a definitely larger figure than did the treated trees.
Owing to the irregularity in the shape of the tree, measure-
ments of maximum height and spread are not as satisfactory
and are less significant. However, the measurements of increase
in spread check very closely with the results found for increase
in cross-section area but the height measurements are less con-
sistent. Taking the data as a whole, a definite superiority is
indicated for the treated trees. This is particularly significant
since many of these plots had not shown severe symptoms of
bronzing and yet showed a superiority in size and vigor for
treated over untreated trees.
The continuation of this experiment will probably prove of
very definite value in establishing the role of zinc sulphate in
fertilizer practices. As a result of these and similar experiments
the definite value of chicken manure as a corrective for bronzing
has been established and analyses have shown that this is prob-
ably due at least in part to the amount of zinc contained in these

II Trunk
Plot Fertilizer Treatment for Plot Height Spread Cross Sec. Bronzingt Conditiont
(ft.) (ft.) (sq. in.)
1 general fertilizer* 3.5** 4.2** 10.4** 0** 95**
Ck 3.0 4.1 7.6 14 81
2 ammophoska plus superphosphate 1.9 3.6 5.0 0 84
Ck J 2A 2.1 3.1 [ 5.6 0 84
3 chicken manure 3.2 4.2 10.3 0 99
Ck I 2.6 4.4 8.6 0 94
4 i 5-8-4$ nitrogen from calcium nitrate 3.1 4.1 i 8.3 0 95 '
Ck -I -3.3 2.8 6.9 0 81
5 nitrophoska No. 7 2.6 4.2 1 6.6 0 96
Ck 1.9 3.5 6.3 0 90
6 nitrophoska No. 8 2.2 3.2 6.0 0 84
Ck I 1.6 2.6 3.9 0 82
7 general fertilizer* 2.7 4.3 9.0 0 99
Ck 3.0 3.8 8.4 0 99 4
8 no fertilizer 1.2 2.7 3.1 0 81
Ck I ______ 1.1 2.7 1.9 0 76
10 stable manure 3.5 4.8 8.2 0 94
Ck 1 4.8 5.9 1 8.2 1 91
11 5-8-4, mixed nitrogen source 2.3 5.3 6.9 2 95
Ck I _2.5 4.2 6.5 3 93
12 general fertilizer* 3.3 4.1 9.6 0 96 '
Ck I1.9 3.5 6.2 1 84
13 5-8-4, nitrogen from tankage 3.1 4.6 8.6 0 94
Ck _2.5 3.7 5.3 0 89
14 5-8-4, nitrogen from nitrate of soda and castor pomace 2.7 3.8 7.3 8 88
Ck I 3.0 4.0 8.6 0 97
15 5-8-4, nitrogen from nitrate of soda and cyanamid 2.6 I 4.7 6.1 0 90
Ck i 12.4 | 4.0 6.1 15 82


Plot Fertilizer Treatment for Plot

16 5-8-4, nitrogen from nitrate of soda and sulphate of ammonia
17 general fertilizer*
19 general fertilizer*
20 same as Plot 11 + nitrate of soda
21 same as Plot 11 X 2
Ck I
22 same as Plot 11 X 3
Ck I
23 5-8-4, mixed nitrogen source
Ck _
24 general fertilizer*
25 same as Plot 11 + mulch
26 5-8-4, nitrogen from calurea
Ck nitrogen fr
27 6-8-4, nitrogen from fish scrap




remainder of the plot.

* Fertilized by the grower in accordance with his usual procedure.
** The top figure for each pair is for the trees treated with zinc su'phate, the lower figure for the
t Condition and bronzing values computed in same manner as explained on page 14.
$ N-P-K.

t _
Cross Sec. Bronzingft Conditiont
(sq. in.)
5.6 0 86
5.0 10 81
7.2 5 88
4.5 21 75
4.4 0 76
1.9 45 43
5.9 2 89
6.2 1 91
9.0 0 96
7.6 3 87
9.8 0 97
8.1 14 _81
6.6 2 80
5.4 35 63
4.6 3 73
2.7 55 47
9.2 5 93
7.8 9 89
3.9 0 83
3.1 25 69
5.0 5 81
4.3 24 69

Florida Agricultural Experiment Station

In addition to those previously mentioned there has been a
number of other experiments and observations which have added
to the information available.

Fig. 5.-Small untreated A. montana trees in foreground of center row.
Seedlings in vacant row area succumbed earlier in season. Trees in back-
ground treated with zinc sulphate in June. All trees from seeds planted
February 1933. Photograph made September 1933.

Mu-Oil Tree-While there are two 10-year-old Aleurites mon-
tana trees in the old test grounds of the Experiment Station that
have made excellent growth, great difficulty has been experienced
in attempts to grow nursery stock in other locations. The seed-
lings became chlorotic early in their first summer, made little
growth and by late fall were in such a weakened condition that
they easily succumbed to cold.

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 25

Fig. 6.-Malformed and severely frenched foliage of A. montana. Foliage
of bronzed trees is very subject to attack by fungi and plants are common-
ly defoliated in late summer as a result. (Compare with Fig. 7.)

In February of 1933 a row of Aleurites montana seed was
planted in the nursery along with several rows of Aleurites fordi.
By June of the same year the seedlings of the former were in
very bad condition with marked chlorosis and were small for
their age. Half of the row was treated at the end of June with
zinc sulphate at the rate of about one pound per hundred feet
of row. Within three weeks a marked recovery' had started and
by the first of September the difference between untreated and
treated seedlings was signally marked and the most outstanding
of any results obtained. Fig. 5 shows a view with the untreated

Florida Agricultural Experiment Station

trees in the foreground and the treated in the background. The
condition of the foliage on the untreated trees is shown in Fig. 6
in contrast with the foliage of treated trees as shown in Fig. 7.
The untreated trees were dead by the end of the winter, whereas
the treated trees, while injured by cold as is common with small
plants of this tender species, were alive and suitable for trans-
planting. In the same nursery Aleurites fordi trees showed some
response to zinc sulphate treatment but since only a little bronz-

Fig. 7.-Healthy foliage of A. montana as a result of treatment with
zinc sulphate. (Trees of Figs. 6 and 7 were growing some 10 ft. apart.)

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 27

ing showed in the untreated trees the results were not very
marked. This would indicate a wide variation in zinc require-
ment even in different species of the same genus.
Satsuma Oranges-Adjoining the block of tung-oil trees where
bronzing was very severe there is a block of Satsuma orange
trees which were originally planted as a rootstock test. These
trees were planted at different times, the first in 1927, and con-
sistently failed to grow satisfactorily in spite of the best known
methods of fertilization and cultivation. The chlorotic condition
known in Florida as "frenching" was in evidence on all trees
and with it the characteristic bunchy growth common to trees
so affected. The soil was of the same types as that on which
the tung-oil grove was planted. In March 1933 two rows of 21
trees each were treated with one-fourth pound of zinc sulphate
per tree and two rows with one-half pound per tree. One row
of each pair received an additional treatment in June.
By late summer all of the treated trees showed normal growth
for the first time since they were set in the grove, whereas the
untreated trees were still badly frenched. During the winter
the check trees were severely damaged by cold and in late frosts
lost a considerable portion of their foliage, whereas the treated
trees showed dark green foliage typical of Satsuma trees in good
condition and lost no leaves and showed no other cold damage.
The trees having only a one-fourth pound treatment were slight-
ly frenched by spring, indicating that this amount had not been
large enough, whereas there was little difference in the rest of
the treatments, and all treated trees showed promise of complete
Pecans and Field Crops-In plantings of the Experiment Sta-
tion, closely adjacent to the tung-oil and Satsuma blocks where
zinc sulphate treatments were initiated, both "rosette" of pecan
and "white bud" of corn were common and resulted in the prac-
tical failure of the pecan trees and lowered corn yields. Black-
mon* obtained a favorable response in the pecans with zinc
sulphate applications, and Barnette and Warner* have found
that "white bud" of corn could be overcome by the use of small
amounts of the same chemical. These results with widely dif-
ferent plants indicate the widespread nature of what tentatively
may be termed a zinc deficiency on certain soils.
Blackmon, G. H., Horticulturist; Barnette, R. M., Chemist; and Warner,
J. D., Asso. Agronomist, of the Florida Experiment Station.

Florida Agricultural Experiment Station

One large tung-oil property was planted in 1928 on newly
cleared lands with phosphatic subsoils. Trees on this property
had shown bronzing persistently with resultant unsatisfactory
growth, though the bronzing occurred without the land having
been exhausted by previous cultivation. In March 1933 the
grove was treated with about four ounces per tree of ZnS04.7H20.
The trees made a marked recovery and put on normal growth
during the season of 1933 and there was comparatively little
dying back during the winter of 1933-34.
One of the oldest large plantings, made in 1924 on rolling lands
which in some parts are high in phosphatic material, has con-
sistently shown large amounts of bronzing. It was on this prop-
erty that the first results were obtained from zinc treatments,
as previously noted. However, more extensive treatments start-
ed here in 1933 did not show consistent results and in no case
were marked results visible until late in the growing season. It
was at first thought that this variable response was due pri-
marily to the age and hardness of the trees which reduced their
ability to respond to treatment. There is some indication at
present, however, that it may be due to the soil condition and
that some other method of application may be desirable.
In portions of another large planting some bronzing had been
showing up consistently in some areas with the result that much
replanting had been done. The bulk of the planting was two and
three years old in 1933 and was treated with two ounces per tree
of zinc sulphate applied to the soil in solution. The results were
very marked and additional treatments were given to individual
trees developing signs of bronzing with the result that the grove
went into the winter in very excellent shape and suffered prac-
tically no winter killing. Experimental plots in this grove showed
the same satisfactory results, so they will not be reported in
One large grove was of outstanding interest since it repre-
sented probably the worst case of bronzing observed. The trees
were planted in the winter of 1931-32 on old lands mostly of the
Hernando series that had been in cultivation for many years.
The grove made a splendid initial growth that continued until
late summer when bronzing of the foliage appeared to a pro-
nounced degree. An early cold resulted in very severe damage
and the trees died back badly and followed this with more dying

Zinc Sulphate as a Correctire for Bronzing of Tong Trees 29

back of growth during the entire winter so that it was found
advisable to cut back severely most of the trees the following
spring. In March 1933 plots were laid out in the worst affected
areas in this field, according to the following standard procedure:
Row 1-one-fourth pound ZnSOi.HO in March
Row 2-check
Row 3-one-half pound in March
Row 4-check
Row 5-one-fourth pound in March, one-fourth pound in June
Row 6-check
Row 7-one-half pound in March, one-half pound in June.
Each row contained 10 trees. Two such plots were laid out in
the worst two areas in the grove, a number of trees being already
dead in each plot and an additional plot was laid out in a block
of young trees that was planted during the winter of 1932-33.
The treated trees generally responded markedly to the treatment
while the checks remained in very poor condition and put on a
very unsatisfactory growth. When the fall check was taken
there was a marked difference in favor of the treated trees,
though of course the growth was far from that which would
be considered desirable for two-year trees. During the winter
of 1933-34, however, there was again very bad cold damage in
all of these plots, the treatment failing to entirely prevent this.
In view of the very unfavorable conditions in these plots, how-
ever, this is probably more significant of the very bad conditions
than it is of the value or lack of value of the treatment.
The entire planting with the exception of nine rows was treat-
ed with about four ounces to the tree of zinc sulphate in April,
1933, and responded splendidly within three weeks while the
nine rows were in such bad condition by comparison that they
were also treated. While, as above mentioned, there has been
severe dying back in certain areas, a very considerable portion
of the planting seems to be recovering satisfactorily and the
winter killing in 1933-34 was not excessive. Considering the
fact that the trees lost their entire top following the first season
it is remarkable that they have recovered as well as they have.
It is particularly significant that where small patches of woods
had been cleared to square out the property and where old hedge
rows were cleared the tung trees have not been affected by bronz-
ing and have grown splendidly. This would seem to establish
the fact that newly cleared land of this type is not zinc deficient
though the old cultivated land is markedly so.

Florida Agricultural Experiment Station

The experimental work here reported has not been continued
long enough to answer definitely the question of optimum times
and amounts of applications of zinc, or even the form of appli-
cation, since either new salts or new methods of application may
prove eventually to serve the purpose better than the application
of zinc sulphate to the soil. The experiments, however, have
been reported somewhat in detail so that the breadth of the work
and the variability of the conditions worked with may be under-
It would appear from the work to date that bronzing of tung-
oil is associated with certain soils and soil conditions which are
rather common in north central Florida and that zinc sulphate
is a specific treatment for the trouble when applied either to the
soil or to the tree in the form of a spray. Whether the trouble
is due to a zinc deficiency in the strict sense or whether it is a
condition that can be corrected by the physiological action of
zinc has not been determined. The fact that the spray, when
applied to the top of the tree, corrects the trouble would indicate
that it was not a case of zinc replacing and rendering soluble in
the soil some other ion in which the plant was deficient. At least,
as a working hypothesis it would seem that bronzing of tung
trees should be considered as a zinc deficiency until proved
The work to date would indicate quite clearly that bronzing of
tung trees is not an isolated trouble peculiar to the species. The
fact that Satsuma oranges in a block adjoining a badly bronzed
lot of tung trees showed a consistent and severe chlorosis
(frenching) which responded to zinc treatment and that adjoin-
ing pecan trees were badly affected by rosette which responds
to zinc treatment and that "white bud" of corn also occurs in
the same field and has been shown to respond to treatment with
zinc sulphate shows quite clearly the widespread nature of the
disease, though the symptoms in different species are somewhat
different, as might be expected.
The work with the two species, Aleurites fordi and Aleurites
montana, shows quite clearly that 'even two species of the same
genus may be differently affected as to degree of injury and the
fact that many plants grown in the same areas do not show
visible signs of the same sort of trouble would indicate that
plants may vary widely in ability to tolerate such a deficiency.
Until experiments can be run for a sufficient period of time

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 31

it is difficult to make recommendations of more than temporary
nature. For trees under four years of age in groves where only
a small amount of bronzing has occurred a treatment of about
one-fourth pound of the 89 percent salt, or its equivalent, per
tree should be beneficial. This application should be made in
April or May and if scattering trees show bronzing later an
additional treatment of one-fourth to one-half pound per tree
may be made. If the bronzing is not general but severe on
occasional trees a treatment of one-fourth to one-half pound
may be given to each tree that is so affected. For older trees
showing severe cases of bronzing treatments of one pound per
tree and possibly higher will be necessary.
The question as to whether a treatment should be generally
applied to all trees or only to affected trees is a difficult one to
answer at this time, but the indications are that in any planting
that has bronzing generally distributed through it a general v
treatment with zinc sulphate will improve the condition of the
grove. If this application is relatively small it can be followed
up later as above indicated with additional treatments for trees
that still remain bronzed.
In the case of groves that are bronzed but which fail to react
satisfactorily to soil treatments as outlined above the use of a
spray consisting of five pounds of zinc sulphate and five pounds w
of lime to 50 gallons of water is recommended for trial in an
experimental way. There are some indications on other crops
that this may be a more satisfactory way of overcoming zinc
deficiency under some conditions than is the application of zinc
sulphate to the soil. In carrying on spraying experiments all
of the tree should be covered, since it has been found that un-
sprayed portions of the tree are not improved by the spraying
of the rest of the tree.
For the present it is believed advisable to keep down the size
of the applications of zinc sulphate to the soil, using no more v
than is absolutely necessary to eliminate bronzing. Up to the
present there is uncertainty as to what happens to the zinc sul-
phate after it is put on the soil and large applications may ac-
cumulate in the soil and possibly may later have very injurious
results. For the above reason it is advisable to make small but
fairly frequent applications, gauging them by the condition of
the trees. A small application may be made over an entire plant-
ing in April and followed by a further application in June on
those trees which develop bronzing; these applications could be

Florida Agricultural Experiment Station

in the range of one-fourth to one-half pound per tree for trees
under eight years of age.
Some difficulty has been faced by growers purchasing zinc
sulphate owing to the different products that are placed on the
market. Three different types of zinc sulphate are likely to be
encountered on a basis of water content. This water is technical-
ly known as water of crystallization and is bound up closely with
the zinc sulphate but it is nevertheless water as far as the pur-
chaser is concerned. These three forms contain 89%, 63% and
56% zinc sulphate (approximately) and prices should be ad-
justed accordingly. One hundred percent zinc sulphate will
probably not be encountered. Some manufacturers identify
these three forms on the basis of zinc sulphate content as above
and others designate the actual zinc content and for the sake of
comparison the following table is given:
] Relative Relative
Formula % Zinc %I Zinc % Water I Amount Value
Sulphate I Necessary* per Pound**
ZnSO4.1H2O 89 36 11 1 5.0c
ZnSO,.5H O 63 25 37 1.4 3.5c
ZnS04.7H.O 56 22 44 1.6 3.1c

Value based on weight of compound equal in zinc content to 1 pound
or other unit of 89% zinc sulphate.
** Five cents per pound for 89% zinc sulphate was arbitrarily used as
a standard of comparison.

Purchases should, of course, be made on a basis of zinc or
zinc sulphate content as the water is of no value to the tree. All
prices should be figured on delivered basis, since freight would
have to be paid on the water content; thus in 100 pounds of 56%
zinc sulphate, freight will be paid on 44 pounds of water.
All grades of zinc sulphate can be used satisfactorily for cor-
,recting bronzing. Fo-,soil applications the cheapest form (based
on zinc or zinc sulphate content) should be used. In making up
sprays for experimental purposes care must be used in dissolving
the 89% material. The zinc sulphate should be added slowly
to water with constant stirring. If large amounts are added
suddenly, or water is added to the dry salt it will cake badly
and be very slow in dissolving. The 56% material dissolves
very readily in water and is preferred by some for making up
sprays for that reason. In using the lower percentage materials
it is necessary to increase the amounts as indicated.

Zinc Sulphate as a Corrective for Bronzing of Tung Trees 33


1. ALBEN, A. O., COLE, J. R., and LEWIS, R. D. Chemical treatment of
pecan rosette. Phytopath. 22: 595-601. 1932.

2. New developments in treating pecan rosette with chemicals.
Phytopath. 22: 979-981. 1932.

3. ALLISON, R. V., BRYAN, O. C., and HUNTER, J. H. The stimulation of
plant response on the raw peat soils of the Florida Everglades
through the use of copper sulphate and other chemicals. Univ. of
Fla. Agr. Exp. Sta. Bul. 190. 1927.

4. CHANDLER, W. H., HOAGLAND, D. R., and HIBBARD, P. L. Little-leaf or
rosette of fruit trees. Proc. Am. Soc. Hort. Sci. 28: 556-560. 1931.

5. Little-leaf or rosette of fruit trees, II: Effect of zinc and
other treatments. Proc. Am. Soc. for Hort. Sci. 29: 255-263. 1932.

6. Little leaf or rosette of fruit trees, III. Proc. Am. Soc. for
Hort. Sci. 30: 70-86. 1933.

7. COLE, J. R., ALBEN, A. O., SMITH, C. L., and SITTON, B. G. Nutritional
diseases; rosette. Proc. Tex. Pecan Growers' Assoc., 13th Annual
Meeting. 1933.

8. DEMAREE, J. B., FOWLER, EARL D., and CRANE, H. L. Report on progress
on experiments to control pecan rosette. U. S. Dept. Agr., Albany,
Ga., mimeographed release. 1933.

9. FINCH, ALTON H. Pecan rosette, a physiological disease apparently
susceptible to treatment with zinc. Proc. Am. Soc. for Hort. Sci. 29:
264-266. 1932.

10. FINCH, ALTON H., and KINNISON, A. F. Pecan rosette: Soil, chemical
and physiological studies. Tech. Bull. 47, Ariz. Agr. Exp. Sta. 1933.

11. JOHNSTON, J. C. Zinc sulphate promising new treatment for mottle
leaf. Cal. Citrograph. Feb. 1933.

12. MAZE', P. Influences respective des Blements de la solution minerales
sur le dvveloppement du mais. Ann. Inst. Pasteur, 68, 21-68. 1914.

13. Note sur les chloroses vegetaux. C. R. Soc. Biol. Paris, 77,
539-541. 1914.

14. -- Determination des elements min6raux rares necessaires au
d6veloppement du mais. Compt. Rendu. Acad. Sci., 160, 211-214. 1915.

15. Recherche d'une solution purement mindrale capable d'as-
surer le evolution complete du mais cultiv6 a l'abri microbes. Ann.
Inst. Pasteur, 33, 139-173. 1919.

16. NEWELL, WILMON, MOWRY, HAROLD, and BARNETTE, R. M1. The tung-oil
tree. Univ. of Fla. Agr. Exp. Sta. Bul. 221. 1930.

17. RAULIN. Ann. Sci. Nat. 2: 224. 1869.

34 Florida Agricultural Experiment Station

18. -- Ann. Sci. Comp. rend. 56: 229. 1870.

19. ROBERTS, JOHN W., and PIERCE, LESLIE. A promising spray for the
control of peach bacterial spot. (Abst.) Phytopath. 19: 106-107. 1929.
20. Zinc-lime: a fungicide for the peach. Phytopath. 22: 416-
427. 1932.
21. SOMMER, A. L. The search for elements essential in only small amounts
for plant growth. Sci. 66, 482-484. 1927.
22. Further evidence of the essential nature of zinc for the
growth of higher green plants. Plant Phys., 3, 217-221. 1928.
23. SOMMER, A. L., and LIPMAN, C. B. Evidence on the indispensable na-
ture of zinc and boron for higher green plants. Plant Phys., 1, 231-
249. 1926.
24. THOMASON, H. L. Observations on the use of zinc sulphate in citrus
groves. Citrus Leaves 13: 12; 6-7. 1933.

If information of a related character, additional to that
contained in the foregoing bulletin, would be of service,
you are cordially invited to write for it. List of bulletins
on the sundry phases of Florida agriculture also will be
furnished on request. Criticisms of the contents, and
suggestions for making these bulletins more helpful to
farmers and growers, will be received with appreciation.
Wilmon Newell, Director


Results of the investigations and research carried on at the Florida
Agricultural Experiment Stations are recited in the bulletins pub-
lished by this farm service agency. During the period of approaching
50 years that have elapsed since the work was begun, in 1887, more
than 270 of these bulletins have been issued. In print at the present
and available for distribution are some 95 of them, covering nearly
as many subjects vitally important to farmers, fruit growers, live-
stock raisers and truck crop producers. Any of these bulletins will
be furnished free on application, as will a list giving the titles, from
which selections may be made.
Application in practical agriculture of research findings, according
to methods of demonstrated merit, is described in bulletins which the
Florida Agricultural Extension Service publishes. Dealing primarily
with the "how" of doing the things that research endeavor has shown
to be feasible, these bulletins bring together science and practice.
Titles of the 25 issues now in stock will be supplied free on receipt
of request. Bulletins desired then may be obtained through the offices
of county farm and home demonstration agents or from the office of
Communications for either the Agricultural
Experiment Stations or the Agricultural Ex-
tension Service-both cooperative agencies of
state and federal governments-should be ad-
dressed to Gainesville, Florida, where they are
operated under the College of Agriculture in
the University of Florida, which also has a
division of resident teaching.


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