Experiments with DDT, sabadilla and pyrethrum dusts for control of Lygus spp. on seed alfalfa

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Material Information

Title:
Experiments with DDT, sabadilla and pyrethrum dusts for control of Lygus spp. on seed alfalfa
Physical Description:
7 p. : ; 27 cm.
Language:
English
Creator:
Lieberman, F. V ( Frank V )
United States -- Bureau of Entomology and Plant Quarantine
Publisher:
U.S. Dept. of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C.
Publication Date:

Subjects

Subjects / Keywords:
Lygus -- Control   ( lcsh )
Spraying and dusting in agriculture   ( lcsh )
DDT (Insecticide)   ( lcsh )
Botanical insecticides   ( lcsh )
Genre:
federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

General Note:
Caption title.
General Note:
"E-658."
General Note:
"May 1945."
Statement of Responsibility:
by F.V. Lieberman.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030289677
oclc - 779847890
System ID:
AA00025116:00001

Full Text



May 1945 E-658




United States Department of At-ricult'irp
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine

ZXERIMENTS WITH DDT, SABADILLA, ANID PYRP.F-.HFU' ZTSTS
FOR COITTROL OF LYGUS SPP. ON SEED ALFALFA

By F. V. Lieberman
Division of Cereal and Forage Insect Investigations

In past years insecticidal control of Lygus spp. on alfr-lfa
grown for seed has been unsuccessful, largely because immediate rein-
festation resulting from continual hatching of nymphs and immigration
of adults has required several aronlications of the contact poisons
tested and has rendered effective control impractical and prohibitive
in cost. In a field-plot test of three insecticidal dusts on seed
alfalfa during the summer of 1944 at Gandy, Millard County, Utah,
DDT (l-trichloro-2,2-bis(p-chlorophenyl)ethane), one of the two new
materials being given preliminary trial, was found to be highly toxic
to Lygus spp., effective for weeks after application, and definitely
promising as a satisfactory control for these bugs.

Since cross-pollination of alfalfa flowers is now considered
essential to profitable seed production, this experiment was made at
an isolated ranch settlement where alfalfa-visiting wild bees, espe-
cially-Nomia melanderi Ckll., sometLaes called the alkali bee, occur
in numbers adequate fo? effective pollination of the crop. In this
locality both Lygas hesperus Knight and Lygus elisus Van D. occur, the
latter heavily predominating.

Twenty-five plots, 60 feet wide by 145.2 feet long, were laid
out side by side in a single row without use of buffer strips. One
plot in each consecutive 5 was selected at random for dusting with 10
Percent of DDT in pyrophyllite, 10 percent of ground sabadilla seed in
a 1:S mixture of hydrated lime and Georgia talc, 20 percent of ground
sabadilla seed in a 1:3 mixture of hydrated lime and Georgia talc, or
S10 percent of pyrethrum extract in pyrophyllite (0.2 percent pyrethrins);
the fifth plot was employed as a check. Applications were made with a
duster mounted on the rear of a farm tractor and operated off its pull-:.
Its 22-foot boom was carried at plant-top level and trailed by a 15-foct
canvas apron. The tractor was driven lengthwise of the plot 3 tira,
each dusted strip being lanned somewhat to assure complete cover-,p.
The speed of the tractor was approximately 3.7 miles per hour. f'stinv
and all subsequent operations in handling, harvesting, and threshing-
the crop closely apn-oroached actual farm practice. Population, count
taken in the plots were based on 25 strokes of a 15-inch inrect net.







-2-


To avoid repelling or killing alfalfa-visiting bees, the
insecticides were applied before many of the plants had produced
flowers, or while they were essentially in the prebloom stage. Used
at this time none of the insecticides showed repellent effects on
the wild bees; they visited the plots in proportion to intensity of
the bloom. No kill of wild bees is believed& to have occurred, but
mortality would be extremely difficult to observe or determine in the
field. No domestic honeybees are present in the Gandy area.

Effectiveness of the different treatments in destroying Lygus
is shown in table 1. Results of dusting with DDT are based on all
five plots treated. Inadvertent irrigation prevented redusting of
two plots treated with each of the other insecticides used; data
from these plots are therefore excluded in the presentation. Popula-
tion data for three check plots are also omitted, because they were
affected materially in varying degree by drift from DDT plots adjacent
to their south borders. The best-yielding sabadilla and pyrethrum
plots were those located next to plots dusted with DDT, which indi-
cates that these plots also were affected by DDT drift. It was impos-
sible, however, to distinguish the effect of the DDT from that of the
sabadilla or pyrethrum. The data from these plots have therefore been
included without correction for this effect.

Of the two check plots for which data are given in table 1, the
first is highly representative of the unaffected portions of all three
check plots omitted. In check plot 2, which had a much lower initial
Lygus population than any other plot, treated or untreated, the slower
increase in population allowed bloom to occur and seed to set before
infestation became severe.

DDT was outstandingly successful in accomplishing Lygus control
because of its ability to remain toxic throughout the period required
for flowering and podding of the seed crop. One dusting of the
alfalfa growth reduced and held the nymphs to negligible numbers. The
sabadilla and pyrethrum dusts gave substantial population reductions,
considering concentration and dosage of each, but with rprid hatchinrg
of eggs the population of nymphs was speedily rebuilt to menacing
strength, and economic destruction of reproductive parts of the plants
was resumed. The fact that DDT was much more effective than the other
insecticides in killing Lygus adults is difficult to appreciate from
the data in table 1. Reinfestation by flight occurred daily in all
plots, irrespective of treatment; it was greatest in the more succulent
plots. Higher mortality of adults in the DDT lots is indicated by the
fact that early morning sweepings yielded fewer adults on these plots
than on the others, whereas durin- the flight period lNter in the dpny
adult abundance on DDT-trrted growth became nrogressively closer to
that on other treated alfalfa. Furthermore, since some adults swept
from DDT plots were unable to coordinate leg movements, it was evident
that mortality rather than pmrrnr.tion was responsible for their corn- ra-
tive scarcity in these plots in the morning.





-3-


Table l.--Iffectiveness of DDT, sabadilla, and pyrethrum dusts in sup-
pressing gus populations on alfalfa grown for seed, July-August
1944. Treatments applied July 19 and 26

Average number of Lygs bugs
Dosage -per net stroke
Dust (pounds er acre) Stage Days after first dusting
Pirst Second 0 3 7 9 22 33
treat- treat- Days after second dusting
ment ment 0 2 15 26

DDT 10% 27.5 None Nymphs 6.6 0 0 0 0.1 0.1
Adults 1.6 .2 .9 .6 1.0 .3
Sabadilla:
20% 29 32.5 Nymphs 5.1 1.2 5.0 1.0 5. 5.1
Adults 2.1 .5 2.3 .1 2.4 .g

10o 25 32.5 Iymph 6.1 1.5 2.9 1.7 5.5 3.9
Adults 2.1 .7 1.2 .2 1.7 1.1
Pyrethrum 10%Y 14 16 mphs .3 2.6 4.0 3.P .2 3.6
Adults 1.7 1.0 .8 .7 2.0 .5

Checks (untreated):
No. 1 None None Nymphs 6.1 9.3 9.7 6.6 1.7
Adults 1.3 1.7 1.0 .1 .0
No. 2 None None Nymphs 2.7 4.1 5.6 12.3 5.7
Adults 2.4 2.8 2.3 0 3.2 .5


l/ Duster failed to deliver this dust at
per acre.


desired dosage of 25 pounds






- 4.


Weather may have influenced the effectiveness of all dusts used.
No precipitation occurred duriatg the `9-day interval from dusting to
cutting of the crop. However, the period was characterized by exces-
sive wind, frequently strong enough to be suspected of removing
insecticidal dust.

All treatments were definitely beneficial as measured by the
extent of flowering and setting of pods. After the pods had been
formed in plots receiving two treatments of 20 percent sabadilla dust
7 days apart, the appearance of these plot indicated a prospective
yield approximately equivalent to that of the plots dusted once with
DDT. Lygus feeding on seed in immature pods and the sharply curtail-
ing effect of an early severe frost substantially reduced the promising
yields of these plots as well as those of most others. The entire plots
were harvested for seed. Results of threshing, recleaning, and examina-
tion of seeds from pod samples taken just before frost are given in
table 2.

Yields from plot to plot under the same treatment varied widely.
This variation is attributable mainly to a corresponding difference in
plant succulency due to variations in soil moisture within the field
and intensified by precipitation deficiency. Late in August intensely
drying winds reduced yield prospects in all plots, particularly in
those already dried to excess. Variation in succulency and also in
yield was greatest among the DDT plots. Tardy spot irrigation at vari-
ous times during the flowering and podding period only added to the
variation in plot condition without giving the benefit that timely water-
ing could have provided. Nevertheless, the better yields under each
treatment represent those that may be expected under normal seasonal end
field conditions.

Without extensive tripping of flowers it would have been impossible
to obtain the very high yields realized from the two DDT plots that were
only slightly affected by drought and frost. Observations showed that,
in proportion to the bloom on the plants, pollinating bees were no more
abundacnt in treated plots than they were on a large adjacent acreage of
blooming alfalfa that was untreated, These high yields were produced
under bee activity normal to the locality. They are not theoretical
yields achieved by extreme concentration of pollinating Insects onto
small patches of blooming plants.






-5-


Table 2.--Yield and quality of seed
sabadilla, or pyrethrum, 1944


from alfalfa field plots dusted with DDT,


Yield
(pounds oer acre) Number Percent of seed in pod samples-
Treatment Tesher- Re- Percent of Viable Not viable
run cleaned shrink- seeds Normal Off- Imma- Destroyed by--
seed. seed age / exam- color color ture L s Chalcids
________ined ....-.... .....


DDT 10%


Sabadil
204


10%


345
650
725
285
135
Av. 428


lla:
83
343
285
Av. 237

85
200
1i3
Av. 156


Pyrethrum 70
148
115
Av. 111


Checks
No. I

No. 2


Checks af-
fected by
DDT drift
Av.


30
260
188
310
175
224


322
593
629
264
118
385


57
282
21
185

69
187
146
134

50
128
89
89


6.6
8.82/
13.3-
7.4
12.9=2
9.8


31.1,-/
17.5o/
21T,5
24.5

19.4
6.42/

15.r
28.62

13 .6
22. 2-
21.5


23 21.8


179
169
285
147
200


31.1-/
10.0
8.22/
16.2-5
11.5


501
505
50Z
502
505


453
500
501


249
499
500


1499
o106
501


0.3
.6
.6
1.2
1.4
0.8


0.2
1.8
1.0
1.0

0
3.0
1.0
1.3

0.2
0
1.0
0.4


8 25 13


500
436
513
500


28 7 60


5 0.4


0.5
0
3.4
1.3


i/ Determined from 100- to 300-gram portions of total plot yields.
recleaned seed calculated by use of these percentages.


Yield of


2/ Thresher operated with inadequate power; shrinkage was larger than it
would have been otherwise.






-6-


The cleanliness of thresher-run seed due to the excellent
protection of developing pods by DDT is shown by the low shrinkre
in recleaning and the small proportion of insect-damaged seed found
in pod samples (table 2). Field observations indicated th-t the
crops in all DDT-treated plots were maturing slightly faster than
in the other plots. These observations were confirmed by the smaller
percentages of immature seeds found in pod samples as indicated in
table 2. A slight tendency to dry out the alfalfa plants as they
neared maturity appeared to be creditable to DDT, but further obser-
vations under conditions less influenced by drought and drying winds
are needed to decide this point. The remarkable -orotection -iven
the check plots that received drift of DDT dust indicates that direct
application of dosages of this insecticide lower than those used in
this experiment will give adequate kill.

The pods from DDT-treated plots contained an average of 4.77
seeds per pod; pods from plots treated twice with 20 percent sabadilla,
10 percent sabadilla, or pyrethrun dust contained an average of 2.56,
2.92, and 2.91 seeds, respectively. The lower averages in the
sabadilla and pyrethrum treatments were due to the more frequent occur-
rence of pods with only 1 or 2 seeds. Samples from checic plots 1 and 2
averaged 1.33 and 3-55 seeds per pod, respectively, the former being
representative of the condition that would have prevailed in the
treated plots if they had remained untreated. Many pods in these areas
contained no seeds at all. In fact, the 8 seeds present in the sample from
check plot 1 (table 2) represent the total production on 25 stems.
Check plots affected by drift of DDT averaged 3.06 seeds per pod. Seeds
in pods from DDT plots were slightly smaller than those from the check
or other treated plots, although no definite relationship to probable
causal factors could be established.

A composite sample of recleaned seed from the DDT plots had a
commercial purity of 99.25 percent (premium grade); an official commepr-
cial germination test indicated viability to be within normal ranife for
alfalfa seed of this area during the fall season. Quick-germinating
seeds averaged 40.75 percent and hard seeds 53.75 percent to rIve a
total estimated germination of 94.50 percent.

Samples of the alfalfa for analysis of DDT residues were taken
from treated plots Just before and after threshing, 95 to 96 days after
the treatment was applied. No rain but much drying wind occurred 6ur-
ing the 59-day period between treatment and cutting. Three rains total-
ing about 3/4 inch fell during the 36-day period between cutting ani
threshing. During this period the alfalfa was in cocks ani was turned
three times. The analyses indicated that the DDT residues were not
over 17 parts per million (p.p.m.) in the alfalfa before trsh'nf and
less than 10 p.p.m. in the chaff after threshing. Alth.-.?,h these rpsi-
dues exceed the current tentative DDT tolerance cf 7 p.p.m., in view of
the high degree of -s control ;ecir-d in the 1944 tests it seems
likely that dosa-ges cnn be r,'uced sufficientlv to brin-- the 17T reqidues
within the tolerance an still -.ciintnin satisfact'r. Lyv-a controll and
economically -rofitable seed production.






-7


In this experiment collection of actual data on reduction of
insect population was restricted to Lygus. However, large aphid and
thripa populations that existed in all plots at the time of dusting
were practically eliminated in the DDT-treated plots and slightly
reduced in the other treated plots. DDT was also observed to reduce
populations (nymphs and adults) of Nabis ferus (L.), ladybirds, end
grasshoppers. lost of the specimens of these common alfalfa-field
insects observed in the DDT plots after they were dusted probably
were immigrants.

Further information is needed on the best dosages and mixtures
of DDT for use against Lygus spp. infesting alfalfa, on timing of
applications to avoid the killing of honeybees and other alfalfa-
pollinating bees, and on the livestock-poisoning hazard resulting from
DDT residues on alfalfa, especially that which may be pastured or cut
for hay instead of seed.




UNIVERSITY OF FLORIDA

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