United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
FIELD EUPLlifiEl.TS WITH DDT FOK THE CCATIOL
OF THE FEA V. LEVI L-PRCGRELS L1
By Ralph Schopp, Frank G. Hinman, and T. A. Brindley,
Division of Truck Crop Ad Garden insect Investigationsi/
Since 1937 rotenone-containing insecticides have been used and
considered satisfactory for the control of the pea weevil (Bruohus
pisorum L.). The wartime shortage of rotenone-containing materials
made it necessary to search for a substitute for this material. Ac-
cordingly an extensive program for testing insecticides was begun in
19%2 at Moscow, Idaho. Among various materials tested during 1942 was
a small sample of a dust mixture containing 2 percent of DDT. When
tested in the laboratory, it appeared to have little or no affect on
the weevils (1). In 1943 a second sample of a dust mixture containing
10 percent of DDT was obtained and tested in the laboratory without
further dilution. This material, applied at a heavier dosage, killed
some weevils, although it did not compare favorably with rotenone.
The lack of a promising insecticide other than rotenone for pea
weevil control and favorable reports on the use of DDT on other insects
led to its being included in field-plot tests during 19W4 Favorable
results in these preliminary field experiments led to more extensive
trials in 1945 and 1946 to compare this material with rotenone-dust ma-
terials then in use for pea weevil control and to compare the effect of
different concentrations of DDT and different rates of application.
Comparisons were made in small-plot and in field experiments.
Technique--Throughout this series of small-plot experiments the
randomized-block arrangement was used, except in a few instances as
described. The plots were 1/10 acre, and were made 25 feet wide to
permit them to be dusted with one swath of the power dusting machine.
They were arranged along the edges of pea fields where the weevils were
usually concentrated. All the plots of each block were grouped on the
same field and treated consecutively. Since time is an important factor
both in dusting and in population sampling, the blocks were treated as
/ In cooperation with the Agricultural Experiment Stations of
Idaho and Washington.
f7- -,-7 __-----I
The weevil population was sampled by use of a 15-inch insect-
collecting net. Two 25-sweep collections were made on each plot. Each
plot was swept before being dusted and on the first and second day
after being dusted when weather conditions permitted. When possible
during 1946 sweeping was continued over a longer period to gather data
on the residual effects of DDT as compared with rotenone.
A sample of 2000 dry peas was collected from each plot at harvest-
time and examined to determine weevil infestation.
194 4 Experiments-Five percent of DDT in pyrophyllite at 30 pounds
per acre was compared in 21 replicates with cube dust containing 0.75
percent of rotenone in talc at 20 pounds per acre. Rotenone-dust mix-
tures reduced weevil populations by 99 percent for the first 2 days after
dusting as determined by sweeping. The DDT dust reduced the weevil
populations by 98 percent 1 day after dusting and by 99 percent after
2 days. These results left little doubt as to the effectiveness of
DDT, but the control with both insecticides was so high that the rela-
tive value of the two could not be determined.
1945 Experiments--Further experiments were made with dusts con-
taining2.5, 5, and 10 percent of DDT in pyrophyllite. A dust
containing 0.75 percent of rotenone in talc was included for comparison.
All the materials were applied at the rate of 20 pounds per acre in each
of 27 replicates.
The weevil population was lowest the second day after application
when the reduction was 99 percent for each of the DDT treatments and
98 percent for the rotenone treatment, the difference not being of
mathematical significance. At harvesttime, however, the weevil infes-
tations in the dry peas from the DDT treatments were lower than in those
from the rotenone treatments. The percentages of peas infested were
9.2, 9.2, 10.1, and 13.5 for thelO-,5-, and 2.5-percent DDT, and the
0.75-percent rotenone treatments, respectively.
Field tests were also made on large areas in 1945. Four fields at
Moscow, Idaho, were each divided into two parts. One part of each field
was treated with the 5-percent DDT and the other with rotenone dust. In
20 locations on each treated area two sets of 25 sweeps were taken with
a collecting net before dusting and 1 or 2 days after dusting to deter-
mine the weevil populations. Samples of 2000 dry peas were collected
at harvesttime from each of the areas previously swept.
In these fields no weevils were found in any of the treated areas
2 days after application, but at harvesttime the weevil infestation in
the dry peas was consistently lower in the DDT-treated areas. After the
rotenone treatment 21 percent of the dry peas were infested, whereas
only 5.6 percent were infested after the DDT treatment, as shown in
- 5 -
At Toppenish, Wash., airplene dusting on two fields was compared
with ground-machine dusting on two other fields. The fields were divided
into two parts, one part being treated with the 5-percent DDT dust at
about 50 pounds per acre and the other with rotenone dust at 25 to 55
pounds per acre. Two 25-sweep collections were made at each of 10 loca-
tions in each division of each field before dusting and 1 day and 2 days
after dusting. There were no appreciable differences in the effective-
ness of the two kinds of treatments. In these collections a total of 689
weevils were netted before the application, 10 weevils 1 day after, and
4 weevils 2 days after the application.
1946 Experiments--Experiments were planned to determine the minimum
concentrations of DDT that would control the pest, the length of time
DDT would remain effective under field conditions, and the most effective
rate of application. Dusts containing 1 percent of rotenone were in-
cluded for comparison with DDT.
The first experiment was made on two fields early in the season
while the weevils were still flying into the fields. It consisted of
14 replicates of 4 treatments-5 percent of DDT in pyrophyllite at 10,
20, and 40 pounds per acre, and 1 percent of rotenone in talc at 20
pounds per acre. Sweeping was continued to the sixth day after dusting
to collect data on the residual effects of the treatment.
The results, as shown in figure 2, were practically the same for the
20- and 40-pound rates of application of DDT. Each of these treatments
was superior to the 20 pounds of 1-percent rotenone dust for the first
6 days after application. The 10-pound application of DDT was also more
effective than the rotenone after the first day. The light application
of DDT was slower in action, but eventually was almost as effective as
the heavier applications.
Weevils had been~flying into the field throughout the 6-day period;
therefore these results are a measure of the residual effect of the treat-
ments. It is evident that under the conditions of this experiment, the
residual effect of the DDT treatments exceeded that of rotenone, the
effect of which had decreased considerably by the fourth day and still
more by the sixth day. There were indications that the DDT treatments
were also losing their effectiveness on the sixth day, but increases in
weevil populations were still too small to be considered significant.
In the second experiment five more replicates of the three dosages
of 5-percent DDT and of rotenone dust were applied on a third field later
in the season. Rains prevented sweeping on this field, except on the
first day after dusting.
The results obtained In the entire series of 19 replicates are
presented in table 1. TIze weevil infestation in the dry peas was much
higher in field 3 than in the other two fields, and higher in the
rotenone plots than in the DDT plots. The 10-pound application was
almost as effective as the 4O-pound application, although it did not
reduce the adult-weevil population as rapidly.
Table l.--Control of the pea weevil with DDT applications at different
rates as compared with control with rotenone, in 1946
Rate Reduction of Weevily peas at harvest
Insecticide per adult weevils' Fields 1
S acre in 1 day and 2 Field 3
Pounds Percent Percent Percent
DDT, 5 percent i40 96 0.5 9
20 94 .7 -11
10 89 .5 13
Rotenone, I percent 20 90 1.5 17
Uniform rates of application of DDT dusts.--Dust mixtures con-
taining 5, 2.5, and 1.25 percent of DDT in pyrophyllite were tested,
together with a dust containing 1 percent of rotenone in talc. These
materials were applied on three fields in 22 randomized blocks at 20
pounds per acre.
Rain fell immediately after one field of seven replicates had been
dusted. That 16 to 28 percent of the weevils were surviving 4 days later
shows that neither DDT nor rotenone can be relied upon to control the
pea weevil if applied just before a rain. The fald was dusted with
1-percent rotenone 4 days after the experimental dusting, and weevily
peas at harvest ranged from 4.1 to 7.8 percent in the DDT plots and
averaged 5.4 percent in the rotenone plots, the differences being within
the limits of experimental error. The control obtained in this field
is attributed to the redusting with rotenone.
In the other two fields containing 15 replicates the weevil popu-
lations were reduced by 95 and 97 percent in 1 day, and the weevily
peas at harvesttime ranged from 12 to b16 percent, there being no appre-
ciable differences in the effectiveness of the 4 treatments.
Rains prevented sweeping on one of these fields after the first
day, and it was possible to study the weevil population in only five
replicates, all in one field, over an extended time. As shown in figure
2, throughout a period of 11 days there were fewer adult weevils in the
plots dusted with 5 and 2.5 percent DDT than in those dusted with
rotenone. There were as many weevils in the 1.25 percent DDT plots as
in the rotenone plots on the first and third days after dusting but not
during the remainder of the period. The 1.25 percent DDT dust was less
effective than the higher strengths.
Field Experiments in l9L16
In the experiments on larger field areas DDT, 5 percent in talc,
and rotenone, 1 percent in talc, were dusted on adjoining strips about
1,600 feet long and from 2b to 40 feet wide on five fields. The rest
of each field was dusted with either rotenone or DDT. At harvest 20
samples of 1000 peas each were examined from each strip.
As in 1945, in each field the percentage of infested peas was lower
after the DDT treatment than after the rotenone treatment (fig. 1).
The average infestation was 1.5 and 2.5 percent, respectively, for the
DDT and rotenone treatments, the difference being of mathematical
Cage Experiments in 19L6
A part of a pea field was selected on which no weevils could be
found by sweeping. A small part of this area was dusted with 1 percent
of rotenone in talc and a similar adjacent area was dusted with 5
percent of DDT in pyrophyllite to compare residual effects of DDT and
of rotenone. Both materials were applied with a 25-foot power duster
at approximately 20 pounds per acre. One day later two screen cages,
3 feet high and covering 12 square feet, were set out on each area,
and 25 weevils swept up from an undusted field were introduced into each
cage. Four more cages were set out in the same manner on the second,
third, fourth, and sixth days after dusting. No cages were set out on
the fifth day because 0.16 inch of rain fell. The weevils were put in
the cages as soon as possible after they were swept from the peas. The
cages were set out in a predetermined randomized plan.
Maximum temperatures while the cages were being set ranged between
68e and 80'F. Maximum temperatures for the following 5 days were between
85" and 86"F.
At harvesttime all peas under each cage were collected separately
and examined for weevil infestation. At the same time the peas were
also harvested from the dusted area around them. The results of this
experiment are presented in figure 53.
From 3 to 15 times as many infested peas were found under the
cages over the rotenone-dusted peas as were found under those dusted
with DDT. The large increase in infested peas on the plots caged on
the day after the rain may indicate that some of the dust had washed
off. The data indicate that DDT may have retained more of its toxicity
to the weevils than rotenone, even after 6 days and after a rainstorm.
Survey of Fields Dusted Commercially in 19%b
A survey was made of the Palouse area of Washington and Idaho in
19L6 to determine the success of commercial dusting with DDT for weevil
control as compared with rotenone. Information was obtained on 50
fields dusted with DDT. Each field was paired with the nearest field
dusted with rotenone on which data were available. In most of the
fields in the DDT group a dust mixture containing 5 percent of DDT
was applied. The fields of the rotenone group were about equally di-
vided, a 0.75 percent dust being applied on one half and a 1.0 percent
dust on the other. The rates of application ranged from approximately
7 to 20 pounds per acre, but usually from 10 to 15 pounds per acre.
All insecticides containing DDT were applied at about the same rate
per acre. Talc was the diluent for all commercial dusts used in the
Infestation records of -the peas from the fields were obtained
from the Federal pea-grading service of the Production and Marketing
The DDT-treated fields had the smaller weevil infestations in 41
of the 50 pairs. In the paired fields the 50 dusted with DDT had. an
average infestation of 2.3 percent while the 50 dusted with rotenone
had an infestation of 5.5 percent. This difference in control was of
high mathematical significance. Similar differences were obtained in
86 unpaired fields that were sampled. The data leave no doubt that
the growers obtained better control with DDT than with rotenone dusts.
Rec ommenda t ions
On the basis of these experiments the following reconmendations
are made: The use of 15 to 20 pounds of dust containing 5 percent of
DDT per acre Aopplied in the same manner and under the same conditions
as rotenone is recommended, except where pea ensilage or pea hay is to
be fed to dairy cattle. In such cases rotenone-containing dusts should
be aplifd as formerly recommended.
Results of field experiments from 1944 to 1946 have shown that
dusting with DDT is an effective control for the pea weevil (Bruchus
Five-percent DDT dust was nearly as effective when applied at 10
pounds per acre as at 20 and 40 pounds per acre but slightly slower
Applied at a uniform rate of 20 pounds per acre, a dust contain-
ing 2.5 percent of DDT was superior to a dust containing 1.25 percent
and as good as one containing 5 percent.
Both DDT and rotenone dusts had lost much of their insecticidal
effect after 4 days.
Weevil populations were always lower on the second day after dust-
ing with DDT than on the first day.
DDT, 5 percent, applied at the rate of 10 pounds per acre was more
effective than rotenone, 1 percent, applied at 20 pounds per acre.
DDT, 1.25 percent, applied at the rate of 20 pounds per acre, was
more effective than rotenone, 1 percent, applied at 20 pounds per acre,
except when applied just before a rain.
(1) Schopp, Ralph, and Brindley, T. A.
1944. Tests with DDT against the pea weevil. Jour. Econ. Ent.
- 8 -
DT 5% P
PERCENTITI I PEAS
PERCENT INFESTED PEAS
Figure 1.-Pea weevil infestations in dry peas
dusted with DDT and with rotenone.
,ooC p=...,= :=. IooC
**//** **r ^
I 7 '
....... j \p
95- 95 /'
,,i 851- 85-
3: ROTENONE 20 LBS/ACRE
Z-- DOT 40 LBS/ACRE-
- D---- DT 20 LBS/ACRE
Z .................. DOT 10 LBS/ACRE
Q 80- 80
-z 75- 75-
2 3 4 5 6 12 3 4
DAYS AFTER DUSTING
Figure 2.--Reduction in pea weevil populations
plications of DDT and rotenone dusts.
from paired fields and areas
DAYS AFTER DUSTING
on 1/10-acre plots after ap-
2 3 4
DAYS AFTER DUSTING
Figure 3.--Neevily peas found on caged plants on which weevils
were introduced on different days after dusting with 5-percent
DDT and 1-percent rotenone at 20 pounds per acre.
UNIVERSITY OF FLORIDA
II 11121 II1 Bill 1 Ill III 1 99 I1 Illll Bill I I I l1 I
3 1262 09239 1993