Phytotoxicity of DDT dusts and sprays to truck crops in Wisconsin

Marcn lv47 E-715



United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine



PHYTOTOXICITY OF DDT RISTS AND SPRAYS TO TRUCK CROPS IN WISCONSIN

Preliminary Observations


By J. E. Dudley, Jr.
Division of Tracx Crop and Garden Insect Investigations I 2/


During the summers of 1944, 1945, and 1946 experiments were
conducted at two truck farms on the outskirts of Madison, Wis., to
determine whether DDT dust mixtures, and in one year sprays, had
any deleterious effect on the foliage or fruit of the common truck
crops grown in that area. The effect of DDT residues in the soiJ
was not studied in these experiments, and no attempt was made to
determine the effect of DDT on the yield of plants. The crops were
grown under commercial conditions in fertile, well-drained Miami
silt loam soil.

In reporting on the toxicity of DDT many authors have noted
briefly its effect on the host plants, and a few experiments have
been conducted in different parts of the country primarily to
determine the tolerance of plants to DDT. Young (6) tested a 50-
percent DDT dust mixture on 17 species of plants under field con-
ditions, including cowpea and tomato, and no foliage injury was
observed. Bottger and Levin (1) reported no injury from DDT sprays
(8 lb. per 100 gal.) to the foliage of pumpkin, squash, bean, collard,
potato, and tomato.

The New Jersey Agricultural Experiment Station (4) reported
injury by DDT to squash, cantaloup, cucumber, snap bean, and tomato.
White (5), in summarizing the results of field experiments with DDT
in several States, reported injury under some conditions to squash,
cucumber, and pumpkin, and listed 26 truck crops, including snap
bean, tomato, and cantaloup on which no injury had been observed.
A dust containing at least 5 percent of DDT was applied to each of
these crops. Bruce and Tauber (2) reported experiments in which
3-percent DDT dust injured Acorn squash and muskmelon, but did not


l/In cooperation with the Wisconsin Agricultural Experiment
Station.

2/The writer acknowledges the assistance of Dorothy H. Custer,
R. J. Zamzow, A. Witt, G. Co Schuetze, Jr., and P. V. Stone, who
applied the insecticides and obtained data during the experiments.





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cause foliage injury to potato, cabbage, Hubbard squash, or Butter-
cup squash. Hervey and Schroeder (3) reported a decided difference
in the susceptibility of the foliage among cucumber varieties to
injury from DDT. In general these reports indicated a high tolerance
to DDT of most truck crops, except cuourbits.

A classification of all the truck crops included in these
experiments is presented in table 1.







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A total of 9 families, embracing 26 species, with additional
varieties within a species and 56 or more horticultural or named
varieties, were included in the 3-year study.

Throughout the studies all dusts were applied with plmunger-type
hand dusters. Pyrophyllite, talc, or a mixture of both materials,
was employed as a diluent for dust mixtures.

DDT Dusts in 1944

Since very little was known about the toxicity of DDT to the
foliage of truck crops, only a few plants of each crop were included
in the first tests. After these first trials the plots averaged
about 1.3 percent of an acre but the size varied considerably. All
crops were treated with both heavy and light applications of dust
mixtures containing 10, 5, a&d 2.5 percent of DDT in pyrophyllite
and talc. One half of each plot was given two applications one week
apart whereas the other half was given only the first application.

To make the heavy application enough dust was expelled from a
duster to thoroughly cover the different types of foliage with a
uniform deposit. For the light application a very light, if not
always uniform, deposit was made. Considerable variation in the
size of the different crop plants, their distance apart in the row
and between the rows, the adherence of dust to the different types
of foliage, and varying (although low) wind velocities resulted in
a wide range in the rate of application, when figured on an acre
basis. The rate of the heavy application averaged about 55 pounds
per acre and the light application, 10 pounds per acre.

In 1944 the two applications at the two farms were made a week
apart between June 28 and July 10. No maximum temperature of 90 F.
or above occurred before August 2. One rain amounting to 0.79 inch
fell 3 days after the second application at one farm, while another
rain totaling 1.03 inches fell the day following the second appli-
cation at the other farm. Three additional rains from July 25 to
27 totaled 1.60 inches.

Of 18 horticultural varieties of crops treated, the only injury
observed was on the foliage of 4 kinds of cucurbits--cucumber (mixed
varieties), and Crookneck Sumer, Straightneck Summer, and Table
Queen (Acorn) squash. This injury was evident following the heavy
application of all three strengths of DDT and following light appli-
cation of the 10-and 5-percent strengths. Occasional slight injury
could be found where a light application of the 2.5-percent DDT bad
been made.






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On cucumber a chlorosis and mosaic effect appeared on most of
the treated plants and persisted for weeks. These symptoms were
confined to the dusted foliage and new growth was not affected.
Because of the effective control of the striped cucumber beetle
(Diabrotica vittata (F.)) with DDT and the consequent reduction in
the amount of bacterial wilt occurring on treated plants, it was
difficult to determine whether the foliage injury caused by DDT
resulted in stunting the plants.

The Crookneck and Straightneck squash revealed a chlorosis and
dwarfing of the leaves following both applications. New growth was
not affected, but slight stunting of the plants probably resulted,
especially from the heavy rate of application, because after a month,
even though all the plants were intergrown, the dusted ones did not
appear quite so luxuriant as those not dusted.

Table Queen squash was treated at both farms, and was more
severely injured than the other cucurbits. A general chlorosis and
mosaic effect became conspicuous following both applications. Al-
though new growth did not show these symptoms, the plants (particularly
at one farm) were stunted, as evidenced by the reduced size of leaves
and length of runners.

DDT Dusts in 1945

The 1945 experiment was planned to test only a dust mixture
containing 5 percent of DDT, 45 of pyrophyllite and 50 of talc applied
to larger areas than had been treated the previous year, and to reg-
ulate the rate of application so that a uniform, medium coverage
would be obtained. Two applications, 8 or 9 days apart, were made,
using an average rate of 13 pounds of this dust mixture per acre.
Crops were not nearly so far advanced in 1945 as they had been in la44,
and therefore required less dust in 1945 to obtain a uniform coverage.
The area of each crop dustedc at each application averaged 1,000 square
feet, or 2.3 percent of an acre.

The two applications were made between July 9 and 19. Two rains
totaling 0.62 inch fell during this period, and another of 0.54 inch
2 days after the applications were completed. There were three ad-
ditional showers totaling 0.98 inch during the last 4 days of the
month, and nine rains totaling 3.94 inches during August, over half
of it falling in the first 2 weeks. Maximum temperatures of 90 to
96 F. occurred on 5 days between July 19 and 31.

Of 30 horticultural varieties of crops dusted, the only injury
that occurred was on the foliage of 5 kinds of cucurbits--cucumber
(A 500 and mixed varieties), and Table Queen, Warted Hubbard, Butter-
cup, and Straightneck Simmer squash. Pumpkin was uninjured.






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On cucumber, treated at both farms, a slight chlorosis and
mosaic effect was evident on most of the dusted leaves 8 days after
the second application, and treated plants were not quite so ad-
vanced as the untreated ones. A month later, however, both treated
and untreated plants appeared to be equally large and healthy.
At one farm a few of the untreated plants exhibited, in slight
degree, the chlorosis and mosaic effect observed on treated plants,
but the amount on the untreated plants was less than on the treated
ones.

Table Queen squash, also treated at both farms, revealed no
injury due to DDT at one farm. At the other farm, however, a
slight chlorosis was evident on a few treated leaves a week after
the second application, and although persisting for weeks it was
not sufficient to be considered damaging to the crop.

A week after the second application slight chlorosis was ob-
served occasionally on Warted Hubbard, Buttercup, and Straightneck
squash. This condition lasted for 2 weeks, but was not considered
severe enough to be of any concern. Injury to squash was not so
pronounced in 1945 as it had been in 1944.

DDT Dusts in 1946

In 1946 dusting with DDT was continued. Two mixtures contain-
ing 5 percent of DDT were employed. In the first, DDT was ground
in a diluent, as was done in the two previous years, and in the
second, the DDT was dissolved in a volatile solvent before being
added to the diluent. To make the latter mixture 3 pounds of
technical DDT was dissolved in 2J quarts of acetone, and the
solution was then sprayed, one quarter at a time, into 57 pounds
of talc in a revolving mixing machine containing stones. Ten
minutes was allowed for mixing each aliquot so that most of the
acetone would evaporate. After all the solution had been intro-
duced, the batch was mixed for one-half hour, at the end of which
time practically all the acetone had evaporated.

Again, as in 1945, two applications were made, each designed
to give a uniform coverage at a medium rate. The rate of appli-
cation averaged 31 pounds per acre, although because of the dif-
ference in the stage of crop growth, it averaged nearly twice as
much at one farm as at the other. The area of each crop treated
averaged 436 square feet, or 1 percent of an acre.

The two applications with each dust mixture were made on
July 15 and 26. Maximum temperatures of 90 to 96 F. occurred
on 8 days between July 18 and August 16. Rain in the amount of






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0.07 inch fell 2 days after the first application, while three
showers totaling only 0.30 inch fell in the week following the
second application. Except for one storm with 1.04 inches of rain
on August 9, there was little rain during the month.

Twenty-seven horticultural varieties of crops were treated, in-
cluding eight kinds of cucurbits. Cucumber, Table Queen and Butter-
cup squash were treated at both farms, and Straightneck Summer and
Warted Hubbard squash, pumpkin, watermelon, and muskmelon were treated
at one farm or the other.

The only foliage injury which could be attributed to DDT oc-
curred on Table Queen squash at one farm, where a bronzing with
some chlorosis on dusted leaves was evident following both appli-
cations with each dust mixture. New foliage produced subsequent to
application was not affected, and the plants were not stunted.

There was a possibility of slight DDT injury to the foliage of
cucumber and watermelon at one farm, but inasmuch as both crops
suffered from drought and exhibited some yellowing and chlorosis on
both treated and untreated portions of the planting, no injury could
be laid to DDT. In fact, most of the cucurbits at both farms suffered
from drought and wilted from time to time. Some were attacked by
foliage disease with consequent spotting and yellowing of the leaves.
In 1946, then, no injury attributable to the use of either formulation
of DDT occurred, except on Table Queen squash at one farm.

During the three sumner seasons no injury from DDT appeared on
the fruit of any crop.

DIDT Spray in 1945

Toward the latter part of the season a single application of
two spray mixtures was made. An emulsion spray was prepared by mix-
ing technical DIDT 0.2 percent, xylene 0.35 percent, and a phthalic
glyceryl alkyd resin (Triton B-1956) 0.025 percent in water. 5/ A
suspension spray, made from a proprietary preparation containing
DDT, spreading, wetting, and suspension agents, plus a diluent, was
diluted with water to contain 0.2 percent of DDT. The sprays were
applied by means of a knapsack sprayer operated at a pressure of 75
pounds per square inch at an average rate of 35 gallons per acre.


_/The water used in all sprays was from the city of Madison
water supply. It contained 8.8 p. p. m. of chloride,and its hardness
rating was 19.7 grains per gallon.






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Cucumber, Table Queen squash, cabbage, broccoli, bush lima
bean, eggplant, tomato, bush snap bean, cauliflower, sweet pepper,
and onion were treated. All 11 crops were sprayed with the sus-
pension, but only the first 4 were treated with both sprays.

On several varieties of cucumber marked injury from the :emulsion
was evident, 3 weeks after application, as a yellowing of the treated
foliage and a stunting of the plants. Slight injury to cucumber from
the suspension was revealed as a chlorosis at the tips and margins
of the leaves.

No injury was observed on the other crops from either spray.

Sumnary

During the summers of 1944, 1945, and 1946, DDT dust mixtures
and, in one experiment, DDT sprays were applied to 56 or more horti-
cultural varieties of truck crops in small field plots by means of
hand dusters and sprayers.

Definite foliage injury occurred on several varieties of cucumber
and the following varieties of squash: Crookneck summer, Straight-
neck summer, Table 4ueen (Acorn), Buttercup, and Warted Hubbard. No
injury traceable to the application of DDT could be discerned on any
other crop.

Results of the experiment did not indicate that high temperatures
contributed to DDT foliage injury. Rain, on the other hand, appeared
to be associated with injury from DDT. The greatest amount of injury
was recorded in the year having the highest rainfall during or close-
ly following the applications, while only slight injury, to one crop,
occurred in the year having a very light rainfall during or closely
following applications.

LITERATURE CITED

(1) Bottger, G. T., and Levin, Clemence.
1946. Comparative toxicity to insects of benzene hexachloride
and DDT. Jour. Econ. Ent. 39: 539-41.

(2) Bruce, Willis h., and Tauber, Oscar E.
1945. Trials with DDT on potatoes, cabbage, and squash.
Jour. Econ. Ent. 38: 439-41.




UNIVERSITy OF F _o Fg,
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(3) Hervey, G. E. R., and Schroeder, W. T.
1946. The varietal response of cucumbers to DDT control.
Jour. Econ. Ent. 39: 403-4.

(4) New Jersey Agricultural Experiment Station, New Brunswick, N. J.
1945. Experiments with DDT conducted by State agricultural
experiment stations, agricultural colleges, and other
non-federal research organizations. U. S. Bur. Ent.
and'Plant Quar. E-644s, 9 pp. (Processed.)

(5) White, W. H.
1946. Summary of results with DDT against truck crop, tobacco,
and sugar beet insects during 1945. U. S. Bur. Ent.
and Plant Quar. E-692, 17 pp. (Processed.)

(6) Young, Hiram C.
1944. DDT against the white-fringed beetle and the velvetbean
caterpillar. Jour. Econ. Ent. 37: 145-7,