LII RARY United States Department of Agricltire
STATE PLANT BOARD Agricultural Research Administration
# Bureau of Entomology and Plant Quarantine
STUDIES WITH DDT AS A CONTROL
FOR WIREWORF.i IN IRRIGATED LA.1DS--PROGREbbSS REPORT-'
By M. C. Lane, M. W. Stone, H. P. Lanchester,
E. W. Jones, and K. E. Gibson, Division of Truck
Crop and Garden Insect Investigations
During the course of investigations by the Walla Walla, Wash., and
Ventura, Calif., laboratories on the control of the Pacific Coast wire-
worm (Limonius canus Lec.) and the sugar-beet wireworm (L. californicus
Mann.) in irrigated lands, DDT was found to be toxic to these wireworms
and to offer a promising means of control to supplement soil fumigation
and cropping practices. These two species have high moisture require-
ments; therefore their r-eaction to DDT may be different from that of
other species under other evriroriental conditions. The studies with
DDT for wireworm control were begun in 1943 and are being continued.
The purpose of this paper is to suT-arize the progress made during the
last 5 years. For convenience the results obtained by the two laboratories
are given in separate sections.
Some of the results of these experiments have been summarized briefly
by White (5). Experiments on the use of DDT for the control of wirerorms
in the Eastern States have been reported by Greenwood (2), Kulash (2), and
Pepper et al. (4). Wilson and Choudhri (6) have found that soil organisms
and the accumulations of nitrate in the soil are not seriously modified by
applications of 0.5 gram of DDT to 125 grams of soil containing 25 grams
Young and Gill (7) tested the tolerance of rye, tomato, strawberry,
sweet pepper, collards, eggplant, and onion to DDT that had been applied
to the top 3 inches of field plots in Tifton fine sandy loam soil. Rye,
tomato, and strawberry were the most susceptible to the DDT, and were in-
jured by 10, 25, and 100 pounds of DDT per acre, respectively. Fleming (1)
reported that 25 pounds of DDT per acre worked into the top 3 or 4 inches
of soil did not injure a large number of plant species, including rye. He
also observed that the growth of a limited number of plants of strawberry,
tomato, onion, soybean, lima bean, bush bean, and spinach was retarded by
this dosage. The soil type in which each crop was grown was not specified.
1/ The experiments by the Walla Walla laboratory are presented by M. C.
Lane, H. P. Lanchester, E. W. Jones, and K. E. Gibson. Some of these ex-
periments were conducted at Prosser, Wash., in cooperation with the Washing-
ton Agricultural Experiment Station. The experiments at Ventura are pre-
sented by 1. W. Stone.
Effect of DLT on i.'ireworms in the Eastern Washington Area
In preliminary laboratory tests at '+alla 'Jalla late in 1943, rela-
tively large dosages of technical DDT were mixed with soil. The action
of the DDT on wireworms was slow but very effective. Apparently the
DDT changed the moisture content of the wireworms, because those that
were affected began to shrivel and then dried up. With smaller
dosages of DDT it took longer to kill the wireworms, but these dosages
were promising for practical control because of the long time a wireworm
Laboratory tests with dusts shmvowed that DDT, either alone or when
mixed with soil, vwas not sufficiently repellent to wireworms to keep
them from crawling through the dusts. The DDT was cumulative in its
action on wvireworms, and later work showed that intermittent exposures
to DDT in the soil, 1 to 16 weeks apart, gave the same percentage of kill
as an equal amount of continuous exposure.
Early in the season of 1944 several outdoor soil cages (4 by 5 by
-l feet with cement bottoms) were prepared with dosages of 16, 32, 48,
and 320 pounds per acre of technical DDT mixed with ..alla Wialla silt
loan soil in a cement mixer. The DI. was applied as a 10-percent DET-
pyrophyllite dust. Six inches of untreated soil was placed in the bottom
of each cage and 9 inches of treated soil on top. ',,ireworms in untreated
soil were caged in small screen containers, and the containers were then
placed in the treated soil of the large cages. None of the wireworms were
affected in any way, which shows that there was no fumigating effect from
the DZT. At intervals composite samples of soil taken from these treated
cages were put with wirewormas in salve tins. Four years after treatment
the 320-pound dosage of DDT killed all wireworms in 5 weeks, the 48-pound
dosage killed 98 percent, the 32-pound dosage 61 percent, and the 16-
pound dosage 37 percent. Lhiese results show that the outdoor weathering
and the action of the soil for 4 years did not completely decompose the
T)DT. It should be emphasized, however, that some of these dosages were
excessive, that the mortality tests were made at a constant temperature
near the optimum for wireworm activity, and that the DDT was more thor-
oughly mixed with the soil than would be possible under field conditions.
Seeds of barley, heatea, beets, peas, beans, onions, carrots, spinach,
cucumbers, and sweet corn, and potato seed-pieces and tomato plants were
planted in the outdoor cages. Seedling counts in the soil treated with
the 320-pound dosage showed a retardation of germination, and most of the
crops were more or less affected by the DIT. Peas, beans, and barley were
badly dwarfed. The growth of corn and wheat was definitely affected.
Potatoes were the only crop apparently not damaged by this excessive dosage.
Termination and growth of all crops seemed to be normal in soil treated
vrith the la.er dosages. A year later, in 1945, barley, peas, corn and
squash were planted in the cages containing soil treated at the 320-pound
dosage, with about the same results. The peas and the squash were badly
dwarfed and the barley and the corn were affected. Peas were planted in
1946 and 1947 and were again dwarfed by the 320-pound dosage, although
less than in previous years.
In the spring of 1945 a series of field plots in 7alla Jalla silt
loam soil were prepared with replicated dosages of 10, 20, and 40
pounds per acre of technical DDT. The DDT was applied in the form of a
10-percent dust in pyrophyllite. One-half the dcsa&e was broadcast on
the surface of the soil, mixed by disking, and then plowed 9 inches deep.
The other half was broadcast and disk-harrowed to a depth of 6 inches,
The ten vegetable crops--lettuce, peas, beans, carrots, beets, spinach,
tomatoes, cabbage, onions, and potatoes--were grovm in each plot, the
tomatoes, cabbage, and onions being grown from transplants. The growth
and yield of these crops were not affected by the DDT. The reduction
in wireworms at the end of the season was 80, 96, and 17 percent in the
plots treated with 10, 20, and 40 pounds of DDT, respectively. The total
potato damage at harvest was 35 percent in utrea1-r- plo' ss ...--'
with 10, 4, and 3 percent in the plots treated I-th 10, 30, a-: 40
of DDT. These figures are statistically significant and show a much re-
duced population of wireworms and less damage to tubers 6 months after
treatment. There was still further reduction in population and -h.-je
during 1946 in these same plots. Chemical tests to determine whether IT
was absorbed into the plant tissues gave negative results in all cases
In 1946 an experiment similar to the above and located adjacent to
it was begun with dosages of 5, 10, and 20 pounds of "_.' per acre. An
identical experiment was begun in the same fie-. in 1947. 2- *
dosage was the only one that gave more than 50 percent reduction of vire-
worms (exclusive of new brood) in 6 months. After 18 months, however, in
the 1946 experiment, 42 wireworms were found in 40 quarter-square foot
samples from the untreated plots as compared with 18, 16, and 0 in the plots
treated with the 5- 10-, and 20-pound dosages of DDT, respectively. The
yields of potatoes in 1947, as given in table 1, show that although 20
pounds of DDT per acre was required to appreciably reduce wireworm .-'..
(sufficient to throw tubers out of gr&.-_-) the first season t-tert
the 10-pound dosage was effective for the second and third season after
treatment. These results are in agreement with experiments in commercial
fields and, as indicated by the toxicity data obtained in the laboratory,
are due to the slow kill of the larger wireworms and the outstanding ef-
fectiveness of the treatments in killing new brood.
During 1945 considerable work was done with testing the effects of
DDT on the adult and egg stages of wireworms. DDT was found to have no
effect on the eggs and pupae in soil. The adult beetles reacted rather
slowly to DDT in the soil. DDT applied after formation of pupal cells
by the full-grown larvae did not significantly affect the production of
adults. Tests with DDT dusts on the soil surface in the spring did not
stop the female adults from laying eggs in the treated plots. Egg pro-
duction might be somewhat reduced in adults that contact sufficient
amounts of DDT on the surface, but it appears that rather large quanti-
ties would be required. It seemed more practical to mix the DDT with the
soil and let it kill the much more sensitive newly hatched wireworms.
Laboratory tests with DDT against the newly hatched wireworms showed
that more than 80 percent were killed in a week's exposure to soil treated
with 5 pounds of DDT per acre, and that 100 percent were killed at dosa -es
of 10 pounds or more per acre. Soil samples taken in July from each of
the field plots,and washed through screens to obtain a count of the newly
hatched wireworms of that season's brood, showed no survival of new-brood
wireworms in any of the plots treated with 10 pounds of DDT or more per
During the season of 1946 more than 100 field tests were made with
DDT dust formulations to find the most practical dosage to use against
wireworms in the soil. In most cases a 50-percent DDT dust was considered
the cheapest. The dust was applied to the surface by hand or with a ferti-
lizer spreader and then plowed and harrowed to give as thorough a mix as
possible within the plo depth of soil (6 to 9 inches). ;i7ireworm popula-
tions were determined by baiting and by sifting samples of soil from
treated and untreated portions of the same field. Reductions of 50 to 75
percent in the wireworm infestation were obtained with the 10-, 15-, and
20-pound dosages of DDT, with no significant differences between the dosages.
The 5-pound dosage was inferior. Except for the 5-pound dosage, almost no
new-brood wireworms survived. There were no appreciable differences either
in yields or in the growth of the potato plants. The 10- to 20-pound dos-
ages, however, reduced wireworm damage to the tubers 50 to 60 percent.
During the 1947 season 58 field tests with DDT in sandy loam and silt
loam soils gave results consistent with those obtained in 1946. New-brood
mortality was 100 percent in the soils treated with 10 and 20 pounds of
DDT per acre and 66 percent with the 5-pound treatment,
Some differences were noted in the action of DDT in soils of different
types. A slightly better and more consistent reduction in wireworms was
noticed in the sandier types of soil than in loam types containing more
clay. Laboratory tests on the relative susceptibility of sugar-beet and
Pacific Coast wireworms to DDT failed to show differences,
The Effect of DDT on Yiireworms in the Ventura, Calif., Area
Tests to determine the effect of DDT on wirewormns have been in pro-
gress at the Ventura laboratory since 1944. In preliminary laboratory
tests wireworms were introduced into 2.7 cubic feet of Yolo fine sandy
loam soil in 25-gallon containers. The soil had been treated with DDT
at the rate of 15, 30, or 60 pounds per acre. Uhen the scil was sifted
2 months later, 60, 93, and 98 percent of the wireworms found were dead,
as compared with 4 percent in untreated soil. After 3 months very few
wireworms remained alive in the treated soils.
In field tests in 7arch 1945 a 10-percent DDT dust in pyrophyllite
vwas applied on the soil surface of 1/8-acre plots in Yolo fine sandy loam
at the rates of 25, 50, and 100 pounds of technical DDT per acre, in two
2/ The field tests reported were made possible through the kindness
a.d cooperation of Messrs. Frank, Ralph, and Robert Borchard, who also
threshed the beans from the individual plots in 1946 to 1947, H. Bruns,
I1. Vujovich, R. Bard, and 0. Kitchen assisted in the tests, G. Claypool,
J. Pinkerton, S, Stuart, R. Hudson, and E. ilerritt were especially help-
ful in obtaining data on wireworm populations in the field plots.
randomized blocks. The DDT was incorporated with the soil by disking and
cross-disking to a depth of 8 inches and then ararji.g to pack the soil.
The dragging reduced the loss of moisture from the soil and provided an
optimum soil condition near the surface for the wireworms to move around
in. Lima beans were planted in these plots on lay 15, or 6 weeks after
the treatments had been applied. The soil from each plot was sampled
from time to time for wireworms by sifting 20 quarter-square-foot samples
of soil to a depth of 16 inches. The plots treated with 25 pounds of DDT
had, since 1940, been used for cover-crop experiments, and there had been
an average of 3 :ireworms per square foot during the spring of the 4 years.
Prior to treatment in 1945 there were 2.3 wireworns per square foot. ,-ith-
in 5- months the infestation dropped to 0.3 wireworm per square foot, and
after 1 year no wireworms could be found. In untreated plots the infesta-
tion from 1940 to 1945 had averaged 1.5 wireworms per square foot, the
lower population being due to the lack of winter cover crops, and in the
spring of 1946 there were 1.3 wireworms per square foot. The check plots
had yielded more lima beans than the other plots, but in 1945 the yields
of dry lima beans were 14.0 and 16.7 sacks per acre for the check and
treated plots, respectively. The results with the 50- and 100-pound treat-
ments were similar to those w;ith the 25-pound treatment.
In the laboratory wireworms were confined in samples of the upper 6
inches of soil from the 25-pound plots taken at random7- 5 months after
treatment. All the wireworms were dead in 1 month. irewormrs placed in
similar samples taken 1 year after the treatment died in 3 months. 2ine-
teen months after treatment a 3-month exposure caused 96 percent mortality.
mortalities in untreated soil in 3 months ranged from 6 to 14 percent. The
pHi of the soil averaged 7.9.
In 194.6 two experiments were conducted in one field of Yolo sandy to
fine sandy- loam. The dosages used were 5, 10, and 20 pounds of technical
DDT per acre, the 5-pound dosage being omitted in the second experiment.
-'he plots were 0.4 acre in size, and were replicated four times in each
experiment in randomized blocks, -Le p1l of the soil averaged 7.8. The
DDT ;as dusted on the soil surface and then incorporated with the soil
by disking and cross-disking to a depth of 8 inches. The soil surface
was then rolled with a clod masher to reduce the loss of moisture in the
soil. In one experiment DDT was applied 4 weeks before irrigation and 8
weeks before planting; in the other 2 weeks after irrigation and 2 weeks
The wireworm infestations and yields are given in table 2. The 5-
ound dosage, although it did not give a high initial kill, greatly re-
duced the wirewormn population by the second year and continued to be
effective into the third year. 7oth the 10- and 20-pound applications
controlled the wireworms and gave outstanding increases in yield the first
year after application. The wireworm infestation remained low the second
year after treatment and the yields were rood; but the infestation in the
check plots also decreased the second year and these plots also produced
good yields. -This decrease in infestation is not unusual, as studies of
wireworm populations in experimental field plots over a period of years
show that there is usually a decline in the number of wireworms the year
following heavy infestations. The third year no wireworns were recovered
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in the soil samples taken in plots treated with the 20-pound dosage. Only
9 wireworms were recovered in 64 4-inch by 4-inch by 3-foot soil samples
taken in the bean rows of the plots treated with the 10-pound dosage. There
was no appreciable difference in the effectiveness of the 10- and 20-pound
dosages of DDT or of the two times of application. There was a tendency,
however, for the early 20-pound dosage to be the most effective.
Samples of soil from the above experiments were taken from time to
time and tested in the laboratory for toxicity to wireworms. These tests,
which are summarized in table 3, show that the soil remained toxic to
wireworms a year after treatment with DDT, but that it was not so toxic
as it was after 6 months.
In 1947 DDT was included in a randomized block experiment on Yolo
very fine sandy loam. There were four replicate plots 0.5 acre in size
for each treatment. The DDT was applied at the rate of 10 pounds per
acre on .Arch 20 by dusting it onto a cover crop of sweetclover before it
was plowed under preparatory to planting lima beans. The sweetclover was
about 8 inches hirgh. Lima beans were planted on May 10. The stand of
lima bean plants in the treated plots was about twice that in the untreated
plots. The number of ;vireworms per foot of lima bean row was 0.3 in the
treated plots as compared ;.ith 3.8 in the check plots, and the yield in the
treated plots was 20.4 sacks per acre as compared with 11.6 sacks from the
On Tay 20, 1947, a tolerance experiment was initiated to determine
whether DLT at 20 and 40 pounds per acre in Yolo fine sandy loam soil
not infested with wireworms would affect the growth and yield of certain
crops. The entire experimental area had been fumigated for wireworm and
nematode control in February with 30 gallons per acre of a crude mixture
of l,2-dichloropropane and 1,3-dichloropropylene, and on Tay 9 with 20
gallons per acre of 10-percent ehylene dibromide. The DDT was applied as
a suspension spray to the soil surface and thoroughly worked into the
soil to a depth of 6 to 8 inches on .lay 20. Each plot was 12-1 feet wide
and 172 feet long and was planted with 10 crops between Iay 23 to 30.
There were four replicate plots for each treatment. The yields of lima
beans, potatoes, cabbage, and lettuce were significantly higher in the
untreated plots than in the plots treated with 40 pounds per acre of DDT.
Tomato growth appeared to be affected by this treatment, but the yields
were within the limits of experimental error. A 20-pound dosage of DDT
did not appear to affect the growth or yield of sweet potatoes, carrots,
peppers, peas, and sugar beets. Winter cover crops of vetch, sweetolover,
fenugreek, and peas planted in October 1947 were not injured by the DDT
treatments. The results of this experiment illustrate the danger of using
excessive dosages of DiT, and indicate the possibility of crop injury from
accumulations of DDT in the soil when repeated applications of the insecti-
cides are made to the soil and to crop foliage.
Laboratory tests on the toxicity of DDT to the Pacific Coast wire-
worm (Limonius canus Lec.) and the sugar-beet wireworm (L. californicus
Hann.) have been -u-erway at -Jalla '.ialla, Wash., since 1943. Field
experiments on the control of these wireworms have been conducted by the
,.alla 'alla, aash., and the Ventura, Calif., laboratories since 1944. L.
canus and L. clif' nicus are the most common species of wireworms that
TL. crop -i---- s _n irrigated lands and have high moisture require-
men"- ,fie action ; DDT on them is slow. After contact with the chemical
the affected A i os live for weeks and appear to be desiccated slowly.
Wireworm sr no. repelled by the chemical. Low concentrations of DLT in
the soil ve toxic, and because of the apparent cumulative effect of
the DDT, wireworms that repeatedly come in contact with the material in the
Dos"-es -f' 10 to 20 pounds of DDT per acre remain toxic to wireworms
the second season after application. DDT has no effect on eggs or pupae.
Its action on dults is slow, as after exposure mating and egg laying take
Lc *fore the adults die. The most sensitive stage of these insects is
the first few weeks of their existence as young wireworms,
i.any field tests under a variety of soil conditions in the Columbia
F--:ver aea eastern -7"shington and Oregon have shown that a dosage of
10 pounds technical DDT per acre, either dusted or sprayed on the sur-
face in the spring and thoroughly mixed with the soil to a depth of 6 to
9 inch uat reduces wirewormn numbers. Even though this treatment
has not otected crops planted immediately after treatment, it has re-
duced the damage to late tuber and root crops for three seasons. No
appreciable number of the new brood of wireworms survived for three sea-
sons. Over a 4-year period the 10-pound dosage has not been detrimental
to plants and soils when the DDT was thoroughly mixed with fine sandy
loam, sandy loam, silt loam, or loam soils.
In sandy loam to very fine sandy loam in Ventura County, Calif., the
yield of lima beans was substantially increased when 10 to 20 pounds
of L-L" was applied per acre 3 to 6 weeks before planting. The insecticide
was applied as a 10-percent dust and was disked well into the soil to a
depth of 6 to 8 inches. As in Washington, reductions in wireworm popula-
tions were slow but persisted for the third season.
Excessive dosages of DDT in the soil have injured plants. In view of
the stability of DDT in the soil, crop injury may result from accumulations
of DDT when repeated applications of the insecticide are made over a
period of years to the soil and to crop foliage.
- 8 -
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Table 3.-4lortality of wire,:oms 4 months after they :ad boen placed in
sandy loam soil treated 5 to 12 months previously rith r .
Founds of : Date of : Time be Ten:
DiT applied : treatment : treatment and : ortality of wvirerorras
per acre : : exposure of : In untreated soil : In treated soil
Swireworms : ____ ___
1946 IJ.'onths Percent Per cen
10 _arch 6 15 91
12 12 38
April 5 24 7
11 12 12
20 .]arch 6 15 99
12 12 70
April 5 24 98
11 12 84
(1) Fleming, .*. .
1947. Effect on plants of D72 applied to soil for the destruction
of Japanese beetle larvae. U3. 9. ur. Ent. and Plan .tr.
E-737, 20 pp. (Processed.)
(2) Greemnwood, D. E.
1947. Benzene hexachloride and wirevorm control. Jour. Lcon. Lnt.
(3) Kulash, JT. I .
1947. Soil treatment for .wirewvorrs and cutw.or:;s. Jour. '.con. nt.
(4) Pepper, D. B., 'Jilson, C. A., and Carmpbell, J. C.
1947. Benzene hexachloride and otier compounds for control of '-ire-
worms infesting potatoes. Jour. -'con. nfrt. 40:727-730.
(5) ..nite, J. H.
1946. Stui.mary of results vrith LDT against truck crops, tobacoc, .
sugar beet insects during 1945. u. ur, nt. o, l!ant
Quar. E-692, 17 pp. (Irocessed.)
(6) T.ilson, J. *K1., and Choudhri, P. S.
1946. Effects of DuT on certain microbiological processes in the
soil. Jour. Econ. Ert. 59: 537-538.
(7) Young, I. C.,and Gill, J. D.
1948. Soil treatments with LL2 to control the wrhite-frined beet)l.
U. 3. Bur. Ent. and Plant ,ua'*-. E-750 8 pp. (Processed.)
UNIVERSITY OF FLORIDA
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