Tests with DDT for control of the pecan nut casebearer in the southeastern states

April 1948


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


TESTS WITH DDT FOR CONTROL OF THE PECAN NUT CASEBBARZR
IN THE SOUTHEASTERN STATES

By Arthur M. Phillips
Division of Fruit Insect Investigations
In Cooperation with the Florida Agricultural
Experiment Station


The pecan nut casebearer (Acrobasis caryae (Grote)) is sometimes a
limiting factor in the production of pecans in certain areas in the South-
eastern States. Most of the injury is caused by the first-generation larvae,
which attack the newly set nuts. A single larva may destroy an entire nut
cluster. The individual nuts that have been attacked can be recognized by
the characteristic borings, or frass, that are cast out by the larvae. The
damage is most evident when pecan trees set a light nut crop but may also
be severe in heavy crop years. In exceptionally heavy crop years the
damage may be more than offset by a beneficial thinning effect due to the
destruction of a portion of the nuts.

Field-plot tests conducted at the Pecan Investigations Laboratory,
Monticello, Florida, from 1944 to 1947 indicate that the pecan nut casebearer
may be controlled effectively and economically with one application of DDT
early in the season, when the tips of the young nuts are beginning to turn
brown. At this time most of the spring-brood moths have appeared and eggs
are being deposited, but few eggs have hatched to produce the young larvae
which enter the nuts. Although not considered entirely satisfactory in
some portions of the Pecan Belt, this method of timing nut casebearer
sprays has proved to be sufficiently accurate for practical purposes in
the Southeastern States.

In 1944 sprays containing technical DDT or DDT concentrate at the rates
of 1/2 and 1 pound of DDT per 100 gallons of water, with sodium laurel
sulfate as a wetting agent, were applied on May 3. Although these formula-
tions did not make satisfactory sprays, 1/2 pound of DDT per 100 gallons
gave a 62 percent reduction in the number of infested nut clusters, the
1-pound concentration a 69 percent reduction.

In 1945 tests were made with a commercial DDT-wettable powder and
a DDT-pyrophyllite formulation (50-50 micronized) that was prepared by
the Bureau of Entomology and Plant Quarantine. Both of these materials
made satisfactory sprays. In replicated single-tree plots that were
sprayed on April 25 with 4 pounds of the 25-percent-DDT wettable powder



1/ Consult U. S. Dept. Agr. Farmers' Bulletin 1929, Insects and
Diseases of the Pecan and Their Control, for information on the life history
of the pecan nut casebearer and a description of its stages.


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in 100 gallons of water, the reduction in number of cluster infestations
was 93 percent; in plots sprayed on April 26 with 2 pounds of the 50-
percent-DDT-pyrophyllite formulation in 100 gallons the reduction was 81
percent.

In 1946 and 1947 a commercial 50-percent-DDT wettable powder was test-
ed in replicated single-tree plots. In 1946 the material was used at the
rates of 2 and 4 pounds in 100 gallons of 4-1-100 bordeaux spray. The 2-
pound concentration was applied to different series of plots on three
dates to obtain information on the degree of accuracy required in timing
single applications of DDT for nut casebearer control. In 1947 the ma-
terial was used with and without a proprietary sticker, at the rate of 2
pounds in 100 gallons of 6-2-100 bordeaux spray. All plots in the 1947
tests also received the recommended scab-control spray program, consisting
of four applications of bordeaux mixture. The results of these tests
are given in table 1.

Table 1.--Field-plot tests with DDT for control of the pecan nut case-
bearer in 1946 and 1947

Pounds of 50-percent-DDT Date Reduction I Nut lIncrease in
wettable powder in 100 t of t in cluster I yield t nut yield t
gallons of bordeaux spray I appli- t infestation t per tree I per tree v
I cation t I I

Percent Pounds Pounds

1946 Tests

2 April 27 89 35-.7 5.7
30 95 58.2 8.2
May 2 97 45.9 15.9
4 2 97 50.6 20.6
None 30.0 -

1947 Tests

2 (with a sticker) May 13 89 13.5 10.4
15 85 11.9 8.8
2 (without a sticker) 15 94 9.5 6.4
None 3.1 -


Each of the treatments in 1946 gave good control of the pecan nut
casebearer, with corresponding increases in yield of nuts per tree. The
results indicated that 2 pounds of 50-percent-DDT wetteble powder per
100 gallons will be reasonably effective when applied at any time during
a 6-day period after the tips of the nuts begin to turn brown. They also
suggested that the period during which effective spraying with DDT is
possible may be even longer, since all the treatments gave good control.
Under comparable conditions, 2 pounds of the wettable powder gave approxi-






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mately the same control of cluster infestations as 4 pounds.

The 1947 tests confirmed the promising results obtained in previous
years and indicated that the addition of an adhesive or sticker adds
little, if anything, to the effectiveness of a DDT spray for nut case-
bearer control.

A large field test with a commercial 50-percent-DDT wettable powder,
in combination with 6-2-100 bordeaux mixture, was also conducted in 1947.
The test orchard contained 13.5 acres of the Moore variety of pecan end
9 acres of the Moneymaker variety. The entire orchard received the
recommended pecan scab control program. The 50-percent-DDT wettable
powder was applied at the rate of 2 pounds per 100 gallons of bordeaux
spray on May 12-13. The check plots containing 2 1/2 acres were sprayed
with bordeaux only.

The reduction of cluster infestation below that in the untreated
trees was 94.5 percent on the Moore variety and 93.2 percent on the Money-
maker. The treated Moore trees yielded 31.7 pounds of nuts per tree,
or an increase of 9.5 pounds over the check, and the Moneymaker trees
yielded 24.7 pounds, or 11.1 pounds per tree more than the check. Those
results were additional evidence of the effectiveness of DDT in controll-
ing the pecan nut casebearer and increasing nut yields.

Following the application of DDT in the orchard experiment, an in-
fest&tlon of mites (Tetranychus sp.) developed, possibly because of the
effect of DDT on the predators that normally hold mites in check. These
mites caused considerable defoliation on the Moore variety of pecan.
However, the increase in nut yields resulting from the control of the nut
casobearer more than offset the cost of the sprays that were required to
eliminate the mite infestation.

On the basis of 4 years of experimental work, 2 pounds of 50-percent-
DDT wettable powder in 100 gallons of water or bordeaux mixture is tenta-
tively recommended for pecan nut casebearer control in the Southeastern
States. A single application should be made when the tips of the small
nuts are beginning to turn brown. If a leaf scorch that is caused by mites
appears in ST-sprayed orchards, a 1-percent summer oil emulsion or some
other recommended materiel should be applied at once. Where mite infes-
tations are heavy, a second application 7 to 9 days after the first may be
required.





UNIVERSITY OF FLORIDA

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