The comparative effectiveness of poisoned bait and sprays for grasshopper control in Lyman County, S.Dak., 1947

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Material Information

Title:
The comparative effectiveness of poisoned bait and sprays for grasshopper control in Lyman County, S.Dak., 1947
Physical Description:
22 p. : ill. ; 27 cm.
Language:
English
Creator:
Shotwell, R. L ( Robert Leslie )
United States -- Bureau of Entomology and Plant Quarantine
Publisher:
U.S. Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C
Publication Date:

Subjects

Subjects / Keywords:
Grasshoppers -- Control -- South Dakota -- Lyman County   ( lcsh )
Insect baits and repellents -- Testing -- South Dakota -- Lyman County   ( lcsh )
Genre:
federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

Statement of Responsibility:
by R.L. Shotwell.
General Note:
Caption title.
General Note:
"E-771."
General Note:
"March 1949."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030293616
oclc - 780156186
System ID:
AA00025164:00001

Full Text
LIBRARY
STATE PLANT BOARD
March 1949 E-771


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



THE COMPARATIVE EFFECTIVENESS OF
POISONED BAIT AND SPRAYS FOR GRASSHOPPER
CONTROL IN LYMAN COUNTY, S. DAK., 1947

By R. L. Shotwell, Division of Cereal and
Forage Insect Investigations 1!


South-central South Dakota has been plagued annually by widespread
or local outbreaks of the differential grasshopper (Melanoplus dif-
ferentialis (Thos.)) since 1929. Other species have added to the damage
wrought by M. differentialis, but it has been by far the worst offender.
The climate and the type of agriculture, consisting of small grains,
corn, and sorghum fields interspersed with native short-grass hay and
pasture lands, are most favorable in this area for the maintenance of
this species in numbers of annual economic importance.
The life history and habits of Melanoplus differentialis and the type
of infestation it produces in southern South Dakota have made it difficult
to control this species with poisoned bait. The main hatching period
usually lasts throughout the entire month of June, a rainy period. Its
eggs are deposited in sod land adjacent to dense, succulent crops and
weedy places into which the hatching nymphs quickly move for the
purpose of feeding. In such places it is often impossible to effect a
good kill with poisoned bait spread among the young nymphs. Further-
more, the dense foliage in these places, under localized outbreak and
late hatching conditions, usually affords enough food for the young hoppers
without their seriously damaging the small-grain crop. Generally
speaking, it is only when this crop is cut that the migrations of M.
differentialis, then in the fifth, sixth, and adult stages of development,
from the small-grain fields become an immediate threat to cultivated
crops, mainly corn and the sorghums. Crop protection by a satisfactory
reduction in numbers of this pest under such conditions of continued
movement requires three or more applications of poisoned bait at a
time when the farmers are harvesting their greatest cash and feed crop,
the small grains.

I/ This work was conducted in cooperation with the Division of Grass-
hopper Control. Valuable assistance was rendered by the agricultural
agent and other officials of Lyman County, and county facilities and equip-
ment were made available for mixing, storing, and applying spray and
bait materials.






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The development of chlordane and toxaphene sprays, with their high
efficiency and residual effectiveness as grasshopper insecticides, seemed
to offer a way of overcoming some of the difficulties encountered in the
use of poisoned bait. When vegetation is treated with these materials,
grasshoppers have no choice of unpoisoned food such as they have when
poisoned bait is used, and are poisoned whenever they feed. This is true
not only of the grasshoppers present when the insecticides are applied
but also, in varying degree, of those which hatch later in the treated area
and of those which migrate into it. The time during which chlordane and
toxaphene continue to kill depends upon weather conditions and dosages
used, but the period generally extends from I to 3 weeks. This extended
period seems particularly favorable to their effective use for controlling
Melanoplus differentialis infestations in south-central South Dakota.
When poisoned bait is used, grasshoppers have a choice of food and
may prefer succulent vegetation. In that event bait will be ineffective
even though it is properly mixed and distributed. Another weakness of
the baiting method under these conditions is that success depends upon
the grasshoppers feeding heavily on the bait while it is still moist, since
it loses much of its attractiveness to them after it has dried out.
Any grasshopper insecticide, to be useful to the farmer, must be not
only effective under the prevailing conditions but also applicable and
reliable enough to meet with his approval. To establish the worth of the
three insecticides--chlordane sprays, toxaphene sprays, and poisoned
bait--they were tested in actual control programs against local farm
infestations in Lyman County, S. Dak., during the 1947 season.

Objectives

In these tests the ultimate measure of control resulting from the
different treatments was the number of egg pods per square foot present
in the egg beds at the end of the season. Good control was considered
to be not only crop protection but reduction of infestations to the point
where they ceased to be a threat for the following year or, with proper
attention, for years to come.
Control efforts were divided roughly into two phases. All three
insecticides were first used against infestations during the hatching
period and early nymphal stages, when the young hoppers were still
concentrated on the egg beds and along field margins. Later these
insecticides were used against migrations of the late instars and adult
hoppers moving into corn and sorghum fields from the harvested small-
grain fields. In each test all the infested portions of a unit area were
treated with the same insecticide. A unit test area consisted of a whole
farm or section. Such large areas were necessary to do away with
interference from outside infestations.






-3-


Materials and Methods

The poisoned-bait formula was that recommended by the Bureau of
Entomology and Plant Quarantine. It consisted of 3 parts of sawdust and
1 part of bran (by volume) with 6 pounds of sodium fluosilicate per 100
pounds (dry weight) of the mixed bait. Enough water was added to this
mixture so that a few drops could be squeezed out of a handful of the
bait. A standard power mixing machine and power spreader were used
to mix and spread the bait at the rate of 30 pounds of wet bait per acre.
All baiting operations followed the general pattern of such operations in
an organized county grasshopper-control program.
The chlordane spray consisted of 1 pound of chlordane dissolved in
1 quart of No. 1 distillate with 25 ml. of Igepal CA Extra High Concen-
trate (condensation product of ethylene oxide and an alkylated cresol),
and water to make 4 gallons.
The toxaphene spray consisted of 2 pounds of toxaphene dissolved in
1 gallon of No. 1 distillate with 100 ml. of Igepal CA Extra High Concen-
trate, and water to make 4 gallons.
Usually 4 gallons of spray was applied per acre, although the actual
dosage varied at times. All the sprays were applied with a sprayer of
the high air-velocity blower type mounted on the back end of a 1-ton
truck. This sprayer had a side delivery, which facilitated the spraying
of borrow pits along roadways, fehcerows, and field margins by keeping
the truck on roadways or comparatively firm ground during wet weather.
The stock spray solutions were made up in large quantities so that they
could be carried out to the farms as such and then diluted from local
tanks and wells as needed. All spray ingredients going into the spray
tank were strained through a fine-mesh milk sieve to keep the nozzles
from stopping up. The sprayer was calibrated to deliver 8 gallons of
liquid with the truck traveling one-half mile at 10 miles per hour and
covering a strip 2 rods wide. Since the prescribed speed could not
always be maintained, the quantities used out of the spray tank were
determined by means of a calibrated measuring stick, and speedometer
mileages were recorded. The rates per acre were calculated from these
figures. Although rather cumbersome at times, the blower type of
sprayer applied the spray quickly and effectively under most of the field
and margin conditions occurring in the test areas. Incidentally, the
mixing and application of the sprays was much easier, simpler, and less
disagreeable than the mixing and spreading of poisoned bait.
Whether dilute or stronger solutions of the spray or different quan-
tities of bait per acre were used to meet certain conditions and urgent
situations, all records were kept and summarized in pounds of wet bait
or of chlordane or toxaphene per acre-application. The treated acreages
given in this report as baited or sprayed are the actual acreages covered,
irrespective of the number of times they may have been treated.






-4-


Costs were not considered in these tests. Only as much of an insecti-
cide was used as was necessary to secure absolute control of the infesta-
tion. From the number of pounds used per acre given herein, costs may
be calculated on the basis of current prices, whatever they may be.

Results

Table 1 affords ready comparisons of the results obtained with the
three insecticides. The numbers of hoppers per square yard at the
beginning and end of operations are estimates made at definite stages in
an ever-changing population, the first during the hatching period and the
second during the period of continuous migration after the small grain
was cut. Because of the residual effect of the sprays in killing off the
grasshoppers as fast as they hatched or moved into the sprayed area,
the beginning population is not the total population concerned in the spray
tests. For example, in test 9 the population is given as 1,000 per square
yard for the margins and 1- for the field. Since this was the population
when the spray was first applied on the margin and when only 50 percent
had hatched, the total population in the margin could have theoretically
reached 2,000 per square yard if no spray had been applied. In other
tests, such as test 2, after early spraying had wiped out the infestations
of immediate threat to a field, reinfestations came from adjacent har-
vested small-grain fields- which had been lightly infested from untreated
egg beds. Therefore, since both hatching and migration swelled the
numbers of hoppers involved in any test, the percent reduction figures
are conservative.
Most of the figures under "Percent of hopper damage" refer only to
the damage to the ears of corn or the corn-grain yield. In tests 1, 5, 9,
10, and 11 the small grains were threatened with total destruction by the
grasshoppers when the first applications of the chlordane and toxaphene
sprays were made. For all other tests the small grains matured and
were harvested without damage, regardless of any attempt to control
the grasshoppers. The percentages of grasshopper damage might not
have been so large if yields had not been limited by lack of moisture.
In this section of the State, where a normal yield of corn is 40 bushels
per acre, the severe drought in July and August reduced yields as much
as 10 to 20 bushels per acre in the best fields. Whether yields are good
or poor, the ears of corn damaged per acre by a given number of grass-
hoppers per unit area presumably would be about the same. The per-
centage of ears damaged is therefore a relative matter, and the same
degree of control of the same intensity of infestation might result in a
10-percent loss in a year of poor yield and a 5-percent loss in a good
year.
The last column in table 1 is a record of the average number of egg
pods per square foot found in all the possible egg beds in the October
egg survey of each test area. The sampling was restricted to grassy
















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-6-


roadways, prairie margins, or fence rows adjacent to or a short distance
from the fields. The sampling procedure followed was the same as that
used by the Division of Grasshopper Control in its general survey of egg
abundance, except that a greater area was included and more square-
foot samples were taken in surveying the areas marginal to each field
than would have been taken in the general survey.

Examples of Actual Tests

Since a comprehensive account of the problems and conditions that
influenced the work performed in conducting each test could not be given
in table 1, diagrams of six test areas are shown (figs. 1, 2, and 3.)
The dotted portions of the diagrams give some idea of the proportion of
the areas that were actually sprayed or baited during the season to
produce the results shown in table 1. They also show where the spray
or poisoned bait was applied. Each row of marginal dots represents a
sprayed strip 2 rods wide. Some of these areas were sprayed twice, and
two of them three times. In the bait test, parts of the dotted areas were
treated three or four times. The numbers in circles correspond to the
test numbers shown in table 1. All possible egg beds affected by each
infestation were surveyed for eggs in October, and the numbers of egg
pods per square foot found at each place at the end of the 1947 egg-
laying season are recorded in the diagrams at each place surveyed.

Chlordane Emulsion Sprays

In test 1, 54 pounds of chlordane was applied to 31.6 acres to protect
a 100-acre contoured field composed of 40 acres of corn, 10 acres of
cane sorghum, and 50 acres of wheat, all in strips as shown on the dia-
gram (fig. 1,A). Egg infestations before hatching had averaged 17 pods per
square foot along the west edge, 2 to 6 along the east and north edges of
the field, and 2 to 6 around the 200-acre wheat field to the east. Corn in
the countoured field had been destroyed by grasshoppers in 1946.
During the first week of June 1947, the highway borrow pit was
sprayed once. On June 16 and June 26, a total of 6 pounds of chlordane
was applied on 6 acres of the egg bed on the western margin in which
hatching was in progress. When 40 percent of the eggs had hatched,
the population of nymphs was 150 per square yard. On July 2, 4 pounds
was applied on 3.6 acres of the roadway and margin to the east, where
hatching was complete and the infestation was 60 per square yard. The
single applications killed all the hatched hoppers and remained 100 per-
cent effective for 10 days. On August 6 the margins of the corn and
sorghum strips, as indicated by the dots in the diagram, were sprayed
with 12 pounds on 10 acres. Populations at this time ran 4 to 8 hoppers
per square yard in the corn.






-7-


About August 10 the 200-acre wheat field to the east was cut, and a
general migration from this field into the southeast corner of the con-
toured field took place. By August 12 a population of 30 hoppers per
square yard, fifth- and sixth-instar and adult Melanoplus differentialis,
was riddling the eastern third of the standing crop. On this date 32
pounds of chlordane was sprayed on 12 acres of the roadway, fence row,
and eastern third of the corn and sorghum strips, as shown in the diaIgr'Lm.
Twenty-four hours later more than 95 percent of the grasshoppers were
dead or dying, and the residual effect on incoming hoppers lasted 26 days.
The dead numbered at least 2.00 per square yard in the sprayed area on
September 8, with a population of less than 1 live grasshopper per square
yard left. Most of these were dying. Grasshopper damage to the corn
was held to 20 percent and the number of egg pods from 1 to 1.4 per
square foot, as shown in the diagram.
This test illustrates that light, or noneconomic, egg infestations of 4
or less egg pods per square foot in the marginal areas, producing 10 or
less hoppers per square yard in the small grain, become a definite threat
to adjacent corn when the small grain is cut. It also demonstrates that
these corn or sorghum strips can be used as trap crops for reducing
infestations to a minimum by treatment with an effective spray. The
cane sorghum strip in this test toe.I. the brunt of the migration. It made
a better trap crop or barrier than did the corn, because of the lower
growing and denser foliage in which to trap the hoppers and check the
migration. It was also easier to spray the shorter cane plants and to
obtain a good distribution of the spray on the foliage than it was to spray
the corn plants.
Test No. 5 was an attempt to save a 100-acre contoured field of
barley and corn (fig. 1,B) from total destruction from a grasshopper
population of 150 per square yard in the barley. In the field margins,
mostly weedy, they numbered 300 per square yard in an area 4 rods wide.
In the weedy draw shown in the southeastern quarter of the field there
were 500 per square yard. Altogether there were about 15 acres of
weedy margins. This infestation came from all four margins, where the
egg pods had averaged 10 to 30 per square foot. Hatching was practically
complete, and the nymphs were in the first to third instars. All the
hoppers were in the margins and in the barley, which was headed out.
The corn was a foot high and, although it was free of hoppers, the situation
looked hopeless.
On July 1 and 2, 42 pounds of chlordane was applied to 50 acres of
barley and weedy margins, including the weedy draw. Except for a
small wet spot in the barley, this one application completely destroyed
the initial infestation, and the results were quite spectacular to all those
who saw them. A second application of 6 pounds on July 29 was sprayed
on 4 acres in strips 2 rods wide along the edges of the corn. A rein-
festation of these margins had come from outlying weedy places and the
small untreated area in the barley which had been too wet to spray .1iuring






-8-


the first application. Again on August 4 a third application of 6 pounds
on 6 acres of corn margins was necessary as a mopping-up measure.
Populations in the first 5 rows of the corn amounted to 10 to 15 hoppers
per square yard in places, but less than 1 in the middle portions of the
corn strips. This last reinfestation came from neighboring small-grain
fields which had been cut the last week of July. In both of these latter
sprayings of the corn margins, the spray was blown directly into the
corn and covered the first 10 rows. All the grasshoppers died within
this sprayed area and no live hoppers got beyond it. The population in
the corn strips themselves never reached 1 hopper per square yard.
There was no damage to the barley and not more than 5 percent to
the corn. Fifteen hundred bushels of barley were harvested from the
50 acres and the owner expected the corn to yield between 10 and 20
bushels per acre. Without spray, these fields would have yielded nothing.
Furthermore, as shown in the diagram the 1947 fall survey of egg pods
in the beds surrounding the field averaged only 0.2 to 0.8 per square foot.
The egg infestation in the previous spring and fall averaged about 20
pods per square foot in these places. Thus there was a 98-percent re-
duction in egg infestation due largely to spraying 54 pounds of chlordane
on 60 acres.
In test 6, on the quarter section to the west of the area included in
test 5, there was a 40-acre cornfield almost surrounded by adjacent
small-grain fields. Along the south edge of this cornfield there was a
strip of prickly wild lettuce, 10 feet wide and head high, which was
utilized as a barrier in the spray operations against migrations from
the oat field to the south. This oat field was weedy and at harvesttime
contained a population of 8 grasshoppers per square yard. There was a
weedy shallow draw 2 to 4 rods wide running diagonally through the oat
field, which had a population of 60 per square yard. Along the north
edge of the corn, there was a sparser weedy barrier 6 feet wide, and on
the west edge there was a somewhat weedy field road (fig. 1, B).
The eastern margin of this cornfield had already been protected by
the early spraying operations in test 5. When the small grain was cut
in the half of the section where this cornfield was located, a concentra-
tion of 60 grasshoppers per square yard developed in a strip 10 rods
wide along the south edge of the corn. The grasshoppers were kept out
of the corn by the 10-foot barrier of prickly lettuce. Another concen-
tration of 40 hoppers per square yard, which had penetrated into the corn
for 1 rod, developed in a strip 3 rods wide along the north and west edges.
I On July 28, 12 pounds of chlordane was sprayed on 10 acres, con-
sisting of the weedy draw, a strip 2 rods wide adjacent to the western
edge of the corn and including 5 rows of the corn, and the 10-foot weed
barrier just south of the corn, together with a 5-rod strip of the adjoin-
ing oats. The initial kill was 70 percent. A second application was made
on July 30 of 12 pounds on 10 acres, including the south 5 rows of the
corn, the 10-foot weed barrier, and an adjacent 10-rod strip of the oats.






-9-


In this area the hoppers numbered 60 per square yard. Another strip 4
rods wide along the north edge of the corn.was included in this applica-
tion. Here the population was 40 hoppers per square yard and the in-
festation had come from the wheat crop to the north, which was just
being cut. For the south margin this was the second and last application.
The infestation here, which had come from the oats, was practically
wiped out with the two sprayings of the barrier.
On August 4, 6 pounds of chlordane was applied on 6.4 acres, con-
sisting of the draw and a strip 4 rods wide along the northern edge of
the corn. 'On August 8 another 5 pounds was applied on a 2.4-acre strip
along the northern margin. The 6-foot sparse weedy barrier and the
first 5 rows of corn were treated with the three applications made along
this northern margin, together with an adjacent 2- to 4-rod strip of the
wheat stubble. These sprayings were on places where the movement
from the harvested small grain to the corn was continuous. The object
of these repeated applications was not to let these migrations get beyond
the first 5 rows of corn.
On August 11 the populations were 1 to 2 hoppers per square yard
along the weedy barrier on the southern margin, less than 1 in the corn,
small-grain stubble including the oats, and the weedy draw, and 3 to 8
per square yard in a strip 1 rod wide along the north edge of the corn.
The damage to the corn was held to less than 1 percent and the hopper
population reduced almost 100 percent. The damage would not have been
noticeable except that the first 2 rows along the north edge of the corn
were completely destroyed. Since there were few weeds along that edge
which could be used as a barrier to protect the corn, the first 5 rows
had been used as a barrier. Along the south edge the 10-foot barrier of
sprayed weeds saved even the first row of corn from damage, although
the populations here had been three times as great as those along the
northern edge.
The yield of corn was estimated to be 10 to 20 bushels per acre, a
low yield due to dry weather, but without spraying all the crop would
have been completely destroyed. In the egg survey made after control
operations, the number of pods averaged 0 to 0.8 per square foot in all
the possible egg beds, as shown in the diagram. In the combined opera-
tions on tests Nos. 5 and 6, in which 89 pounds of chlordane was sprayed
on 88.8 acres, 90 acres of corn (1800 bushels) and 50 acres of barley
(1500 bushels) were saved from total destruction, and the potential egg
infestation was reduced more than 95 percent.
This farm is one of several that have suffered partial or total crop
losses from grasshoppers every year since about 1930. In this area and
on this farm poisoned bait had been used as recommended but, according
to the farmer, with poor results. In 1947 this farmer and his neighbors
saw for the first time a grasshopper infestation almost completely de-
stroyed and more than 95 percent of the crop saved by control opera-
tions.






-10-


Toxaphene Emulsion Sprays

Tests 9 and 10 can be considered as one operation in the spraying
of egg beds during the hatching period. Test 9 was conducted on a
prairie margin where the egg pods averaged 13 per square foot and test
10 was conducted on a grassy roadway averaging 7 pods per square foot.
On June 18 the hatch was 50 percent complete. The population in the
area included in test 9 ran 1,000 hoppers per square yard in a winter
wheat strip 3 rods wide, and 500 on an egg bed 2 rods wide adjacent to
the south. In the area included in test 10 the population was 600 per
square yard along the roadway. On that date 10 pounds of toxaphene
was applied to 5 acres in test 9 on the winter wheat strip and egg bed.
On the same day 10 pounds was applied on 6 acres in test 10 along the
roadway and along the east and north margins of the wheat. The dotted
areas on the diagram (fig. 2,A) show where these applications were
made.
At this time the owner of the farm planted a strip of corn 16 rods
wide by 80 rods long along the south edge of the wheat in the southwest
quarter of the section. This corn strip was planted as a trap crop for
later spraying to control grasshoppers migrating from harvested small-
grain fields.
Continuous hatching of the eggs took place in both tests from June 18
to July 1, when all hatching was completed. Heavy hatching was noted
on June 20, 23, and 26. The first application of the spray wiped out the
initial infestations, mostly first instars, in both tests. After the first
application in test 9 another heavy infestation built up on the egg bed in
the southeast section as the hoppers hatched out. After each period of
heavy hatching the reinfestation was destroyed by the residual effect of
the poison from the one application. The newly hatched nymphs were
not able to move more than 2 rods from where they hatched before
they succumbed to this residual action of the toxaphene. These
nymphs were often found in a dying condition immediately after
hatching while they were still whitish in color. The toxaphene spray
applied on June 18 continued to kill newly hatched nymphs on the area
sprayed until July 1, when the hatch was completed.
A total rainfall of 0.58 inch in several showers on June 21 to 22 and
on June 29 had no adverse effect on the residual activity of the poison
in test 9 or in test 11, which was conducted in the next section to the
west.
Supplementary areas were sprayed in both tests 9 and 10. In test 9
6.7 pounds of toxaphene was applied on July 1 to 3 acres of weedy
patches at the ends of the original area, and on August 8, 3.6 pounds was
applied on 3 acres of fence row and other weedy places. In test 10,
3.5 pounds was applied on June 26 to 4.5 acres of the roadway because
of poor coverage in the first application, and 12 pounds was applied on
August 8 to 5.5 acres consisting of the 1-acre corn strip and the






11 -


roadway on the east. Part of the corn strip and wheat stubble on the east
side had developed an infestation of 40 hoppers per square yard over 1
acre. There .'. also some concentration along the road'.,.L,y, ,i.:K all .
the infestation came from the egg bed on the northern ed.,u,- of the small-
grain fields in the east half of the section.
Populations at the end of the operations in both test 9 and test 10
were reduced to less than 1 hopper per square yard in the field and 3 in
the weedy margins. The number of egg pods found in the October o
survey averaged from 0 to 2.7 per square foot in the seven places
examined and 0.8 pod per square foot for all egg beds on the section,
which was at least a 92-percent reduction from the number of e(,g pods
found in the spring egg survey. The corn strip in test 10 showed a total
of 15-percent damage to the ears, mostly in the east end for 0.1 mile.
As indicated by its location in the diagram, this strip of corn would have
been subject to severe damage by grasshoppers coming out of adjact: rit
small-grain fields if nothing had been done to suppress the severe in-
festations therein. Yet a corn crop estimated at from 15 to 20 bushels
per acre was made. The oat field in the east half of the section just north
of the area included in test 9 would also have been severely damaged or
possibly destroyed by the severe infestations along the south and west
edges if no spraying had been done. The owner estimated that a 60-
bushel crop was harvested from this field. For a total of 45.8 pounds
of toxaphene applied on 26.5 acres, at least 130 acres of small grain,
which included part of the wheat in the west half, were saved and the
infestation was almost wiped out.
In test 11 a 47-acre wheat field was threatened with total destruction
by an invasion of grasshoppers hatching on the prairie-margin egg beds
to the north and west of the field (fig. 2,B). On June 18 this invasion had
reached 10 rods into the field from the north and west, with an averngc
population of 600 per square yard over 15 acres. The egg bed to the
north, on the basis of the empty egg pods found, averaged about 30 pods
per square foot before the eggs hatched. The wheat was 12 to 15 inches
high and was being destroyed. Furthermore, 20 rods to the north was a
25-acre corn strip and still farther north in the same half-section another
cornfield 50 acres in size, both of which were threatened by this infesta-
tion.
On June 18, 30 pounds of toxaphene was sprayed on 15 acres of the
wheat field and '.xeedy margins, as shown by the dotted area in the
diagram. Because of a half-acre patch missed in the northwestern
corner of the field during the spraying operation, it took 8 days for the
infestation in the field to disappear. On June 26 a few newly hatched
nymphs were observed making their way into the weedy margin of the
field from the egg bed on the north, but these nymphs were dying within
the first 2 rods across the sprayed area and none penetrated farther
into the field. On June 29 hatching was completed and a few first-instar






-12-


nymphs were found in a dying condition in the first 2 rods of the weedy
margin to the north. There were no grasshoppers in the wheat field
itself on that date.
A survey of adults made on August 11 showed an average of 3 hoppers
per square yard in the 2-rod-wide weedy margin and other margins of
this field after the wleat was cut, but none in the wheat stubble. The
owner reported a crop of 15 bushels per acre on the 47 acres, a poor
yield due to poor soil and a poor stand. Nevertheless, the two cornfields
to the north owed their survival in part to this one application of the
spray.
Test 12 was a late spraying to save two cornfields in the quarter-
section north of the area included in test 11 from migrations from
adjacent small-grain fields during harvest. Three applications were
made in the dotted area shown in the diagram (fig. 2, B). On July 28,
20 pounds of toxaphene was applied on 10 acres of the north
and west margins of the 25-acre corn strip and north and east edges of
the adjacent wheat strip. Again on July 30, 12 pounds was applied on
12 acres of the same margins. A third application of 18 pounds on 10
acres was made on August 4. This third application included the road-
way alh ,g thV northern edge of the quarter section. Infestations in the
sprayed areas ran 50 to 100 hoppers per square yard, mostly fifth- and
sixth-instar and adult Melanoplus differentialis. In spite of excellent kills
with each application, these numbers were maintained by continuous
migrations until the third application destroyed most of the remaining
grasshoppers coming from the oats to the west and the wheat strip
between the cornfields.
There was no natural barrier along the north edge of the 25-acre
corn strip, so the first 10 rows of corn was used as such. Three
applications on this barrier piled up the dead hoppers in the sprayed
area and held damage to the first 5 rows. Here damage was graduated
from stalks eaten to the ground in the first row to damaged stalks of
normal height in the fifth row. In the same area on August 11, 7 days
after the last spraying, there were still freshly dead and dying hoppers,
and the population in the corn was 2 per square yard and 7 in a strip
1 rod wide along this north edge. The infestation in the 50-acre corn-
field to the north was less than 1 hopper in the field and averaged 3
along all margins.
Estimated reduction in corn yield amounted to 6 percent in the 25-
acre field and less than 1 percent in the 50-acre field. The estimated
yield in both fields was 20 bushels per acre.
For the areas included in tests 11 and 12, therefore, 80 pounds of
toxaphene on 47 acres saved 47 acres of wheat and 75 acres of corn.
The number of egg pods in the possible egg beds of any consequence was
also held down to 0 to 3 per square foot. The 7 pods per square foot
shown at the west edge of the alfalfa patch in the northeast quarter and
the 10 pods per square foot adjacent to the northwestern corner of the






-13-


milo field in the southeast quarter represent only very small egg beds.
The true average egg infestation for all the field margins on the half
section by the end of the 1947 season was about 1 pod per square foot.
In some of the late spraying on this section, at an air temperature
of 107 F., the residual effect lasted only 5 to 7 days, as compared with
10 to 14 days from the early spraying at the same dosages.

Poisoned Bait

Test 17 was an unsuccessful attempt to control hatching nymphs
along the margin of a wheat field and prevent their spreading into the
crop (fig. 3,A). The spring egg survey showed an average of 10 pods
per square foot in the prairie margin across the road to the west and
4 in the adjacent prairie margin to the north of the wheat field.
On June 19, 500 pounds of wet bait was spread on 12 acres of field
margin to the north and west. On June 25 the infestation had spread into
the field from these directions to a depth of 10 rods, as shown by the
dotted lines and area in the diagram. The population in this area aver-
aged over 100 hoppers per square yard, and less than 5-percent kill was
obtained with the first baiting. The infestation extended over 25 acres
on that date, and it was baited with 700 pounds of wet bait. Not more
than a 10-percent kill was obtained with this second baiting. By June 27
the infestation had moved another 10 rods into the field and 1,000 pounds
more of the bait was spread on 35 acres, which included most of the
field infestation. This application did little or no good, and baiting
operations were discontinued here, as the hoppers were not being checked
in their spread through the wheat field. A similar attempt in test 18
(see table 1) to obtain control by the early baiting of nymphs on the egg
beds and along the margins of the fields was also ineffective.
Test 20 was an attempt to save corn in strip plantings of an 80-acre
contoured field of wheat and corn (fig. 3,A) from an infestation which
developed from 5 to 10 egg pods per square foot in the grassy margins
around the field. An abortive attempt to stop the newly hatched hoppers
from moving into the wheat strips was made on June 25, when 50 pounds
of wet bait was spread on 2 acres of the roadway on the east. By July
28 the population in the corn strips was 20 hoppers per square yard and
in the margins 40 to 50, mostly fifth- and sixth-instar and adult
Melanoplus differentialis, and there was 20 percent damage to the ears.
Four applications of bait were made as follows: On July 28, 1,500
pounds of wet bait on 50 acres of the corn itself and weedy margins;
on July 30, 1,600 pounds on the same area; on August 1, 1,800 pounds
on the same area and on margins of the wheat-stubble strips, 55 acres
in all; and on August 6, 1,000 pounds on 30 acres of the still heavily
infested places.
With the first three applications, beginning July 28, the population in
the corn rows was reduced from 20 to 10, from 10 to 6, and from 6 to 3






- 14-


per square yard, respectively. Although more bait was spread on the
weedy fence row and roadside on the north and other weedy places than
elsewhere, the populations remained 20 to 40 hoppers per square yard
in these weed patches. A final survey of adults on August 10, after the
fourth application, showed 1 to 4 per square yard in the field and 18 in
the weedy fence row and margin on the north.
A survey on September 9 showed a 90-percent loss of ears from
hopper damage and a reinfestation of 4 to 8 hoppers per square yard in
the corn. From July 28 through August 6, 5,900 pounds of wet bait was
spread over 185 acres in four applications. The population was reduced
85 percent, but the damage to the ears had been done. Furthermore,
the survey in October of the egg beds surrounding this field, as shown
in figure 3, averaged 1.7 to 15 pods per square foot, or an average of
8.2 pods for all the egg beds. The average in the spring survey had been
6.2 pods; so it is apparent that the baiting program as actually conducted
not only resulted in unsatisfactory control during the current season but
also did not reduce the prospect of severe infestation the following year.
This test may appear to be an untimely one, because baiting was not
started until after the wheat strips were being cut and the hoppers were
moving into the corn. However, this situation is typical of the locality.
The wheat was not being damaged, and the owner did not want anyone
driving through this field in what might prove to be a vain attempt to
control the infestation in the wheat. Intest 17, an attempt had been
made, without success, to check the early movement of the hoppers into
the small grain, and there was considerable evidence that control could
not have been obtained in the wheat in the area for test 20. Since all the
conditions of the area for test 20 were common to the locality, they were
accepted as typical and the test was made. For a direct comparison
with the situation found in the area for test 20, however, chlordane spray
(test 7) was used on a 40-acre cornfield containing a heavier infestation
of 25 grasshoppers per square yard in the field and 50 along the margins,
and where damage to the ears had already amounted to 20 percent. The
results of the two tests are compared under the heading "Other Tests in
Table 1."
Test 19 was an attempt to protect by use of poisoned bait 100 acres
of corn from grasshoppers migrating out of small-grain fields that had
been harvested (fig. 3, B). Three applications of the bait were made as
follows: On July 29, 900 pounds of wet bait on 23 acres, once around the
field and into the field from the south; on July 31 and August 1, 1,650
pounds on 50 acres of the corn and a 3-acre strip 8 rods wide into the
oat stubble to the south; on August 8, 2,500 pounds on the entire 80 acres
in the cornfield. On these dates the populations in the baited areas were
10, 7, and 5 per square yard, respectively. These numbers were less
than a third of those encountered in any of the other bait or spray tests.
Not much was accomplished with the first two applications, but by
August 10, after the third application, the population had been reduced



I






-15-


70 percent. On that date the average was less than 1 hopper per square
yard in the field and 4 to 7 along the margins. On September 9 a re-
infestation of 5 hoppers per square yard was observed in the corn. This
reinfestation had come from adjacent small-grain fields that had been
cut. On the 100-acre area protected by test 19, 5,050 pounds of bait was
used on 156 acres.
During the 10-day period from July 29 to August 8, grasshoppers con-
tinued to damage the ears until only a 50-percent yield was possible.
There was only one-fourth to one-half a crop because of the dry weather.
If weather conditions had permitted a good yield, the percentages loss
would have been proportionately lower or around 20 percent. In view of
the short crop, however, the only saving here would have been to forego
control so that the materials and effort used in the baiting operations
would not have been wasted. This argument overlooks the beneficial
results of a 70-percent reduction of the original population but does
follow the reasoning of the farm operator. The fall egg survey showed
that the number of egg pods around this field averaged 0.8 to 2.4 per
square foot. This is a noneconomic infestation. However, when these
figures are compared with those from the spray tests, it must be re-
membered that the grasshopper populations in all the spray tests were
many times greater.

Other Tests in Table 1

Control practices similar t, those described in the previous para-
graphs were used in all the other tests listed in table 1, and some
mention should be made of them.
For chlordane, tests 2, 3, and 4 were mainly the early spraying of
egg beds in uncultivated margins adjacent to fields containing crops
followed by mopping-up applications. Test 7 deserves special discussion
because it was on a 40-acre cornfield when the corn was 6 to 8 feet
high and infested with late-instar nymphs and adult Melanoplus
differentialis numbering 25 per square yard in the field and 50 along
the margins. This migration had come from harvested small-grain
fields adjacent to the north, east, and west edges of the field. The corn
was being stripped of leaves, tassels, and silks. On August 5, 20 per-
cent of the ears were damaged, and there was a heavier infestation in
taller and denser corn than in poisoned-bait test 20 (fig. 3,A) with
which it may properly be compared.
On August 5, 60 pounds of chlordane was sprayed over the entire
40-acre cornfield of 200 rows of corn, one-half mile long. Thirteen
trips lengthwise of the field were made in which 2 rows each trip or
26 rows altogether were knocked down by the truck on which the sprayer
was mounted. The end result, given in table 1, test 7 for chlordane,
shows a reduction of 88 percent in population and holding of further loss
due to hopper damage to 5 percent, not including the total loss of the






-16-


26 rows or 13 percent of the corn knocked down in applying the spray.
There was an estimated total loss of only 25 percent due to the grass-
hoppers, as compared with bait test 20 in which there was a 90-percent
loss, and the yield was about 10 bushels per acre. The residual effect
of the spray lasted 10 days and was reflected in a much reduced egg in-
festation averaging 1 pod per square foot for all the possible egg beds
affected by this infestation.
Test 8 with chlordane was the one failure in all the spray tests. This
spray was applied to a 50-acre flax field in which all the leaves and two-
thirds of the bolls had been chewed off. On August 7, 60 pounds of
chlordane was sprayed on 50 acres of flax in a wind of 15 miles or more
per hour. There was no foliage to catch and hold the foglike spray, and
a large portion of it was carried away by the wind. In tall, dense foliage
such as corn, winds up to 15 miles per hour helped spread the spray
without carrying it away.
In tests 13 and 14 with toxaphene, the emulsion spray was applied
on newly cut alfalfa where there was much bare ground and little foliage.
This work was done near Buffalo Gap, S. Dak. The spray was applied
when the air was still, and the foglike spray settled over the ground in a
cloud for several minutes. Excellent kills were obtained under these
circumstances.
In tests 15 and 16 toxaphene was used with No. 1 distillate as a
concentrated oil solution. The results were the same as for the emulsion
sprays in initial kills and residual effect, but the oil spray burned the
foliage severely. Because of its burning effect and its higher cost, this
spray was unsuitable for practical use.
The last item in table 1 is the record of an egg survey made of an
untreated 80-acre cornfield destroyed by a migration of grasshoppers
from harvested small-grain fields on all sides. Most of these grass-
hoppers came from a field across the road to the south. No control was
attempted for this field. The adult population averaged 25 per square
yard in the field and 100 along the margins. These numbers were
comparable to most of the other infestations where spray and poisoned-
bait tests were conducted. The numbers of egg pods in all the possible
egg beds affected by this infestation ran from 4.3 to 13.3 pods per square
foot and averaged 9.9. The greatest differences in egg deposition occurred
between this untreated infestation and infestations sprayed with either
chlordane or toxaphene.

Discussion

In the farm-scale tests against Melanoplus differentialis reported in
this paper, the chlordane and toxaphene sprays proved much more effec-
tive than the poisoned bait. The initial and residual effects of the sprays
proved to be an immediate check to further crop damage by the spread-
ing grasshopper infestations. The infestation was almost wiped out and
there was only a small amount of egg deposition.






-17-


The results with poisoned bait were not so satisfactory. Neither the
spread of the infestation nor the crop damage done by the grasshoppers
was successfully checked with poisoned bait, because of its poor initial
kills and lack of residual action. Although sizable reductions of adult
hopper populations were obtained by three or four repeated applications
of bait late in the season, these treatments were ineffective in reducing
egg deposition.
The main argument against the use of sprays and for the use of
poisoned bait has been that the initial cost of the spray ingredients makes
them much more expensive to use than the relatively cheap bait materials.
As has been said before in this report, results, not costs, guided the use
of both the sprays and bait in these tests. The data given in table 1 and
the acreage of corn protected by the use of different insecticides were
used to calculate the comparative efficiency of the insecticides. The
results are shown in table 2.

Table 2.--Comparative effectiveness of chlordane and toxaphene sprays
and poisoned bait applied to corn for the control of grass-
hoppers. Results based on one treated acre.

,Pounds Corn Percent Percent Average number
Insecticide per acreage reduction of of corn of egg pods per
acre I protected infestation damaged square foot

Chlordane 1.23 2.37 93.0 12.8 0.8
Toxaphene 1.56 2.34 95.0 3.0 1.4
Poisoned
bait 32.11 0.44 77.5 70.0 4.6


An average of 32.11 pounds of wet bait per acre served to protect
less than one-fifth of the corn acreage protected by spraying 1 acre with
1.23 pounds of chlordane or 1.56 pounds of toxaphene. Furthermore, with
the quantity of bait used in these tests there was less reduction in in-
festation, damage, and egg deposition than was obtained from the use of
the other two insecticides. These factors, and the ease and certainty of
obtaining control, must be considered in comparing costs. Although the
bait is cheaper, the use of either chlordane or toxaphene spray might
be more economical, in view of their greater efficiency in killing grass-
hoppers, saving crops, and preventing fall egg deposition that may result
in recurrence of infestation the next year.
Judging from these experiments, an initial kill of 95 to 100 percent,
with a 2-week residual effect, may be expected from the early applica-
tion of 1 pound of chlordane or 1.5 pounds of toxaphene per acre against
first- to third-instar nymphs. Ten to 90 percent of the infestation of any
of the major economic species of grasshoppers will hatch in 15 to 20 days.






-18-


Thus with the spray remaining effective for 2 weeks, one application
when 25 to 50 percent of the hatch has been completed will destroy most
of the infestation. A second application may often be necessary, however,
as a mopping-up operation in this early spraying of egg beds.
For late-summer spraying when the hoppers were migrating from
cut small grain fields and were mostly in the fifth and sixth instars, and
adult stages of development, an increase in dosage to 1.5 pounds of
chlordane or 2 pounds of toxaphene per acre was apparently necessary
to obtain good initial kills and effective residual action for 5 to 10 days.
The need of heavier dosages for late-summer spraying is probably due
to the increased size of the grasshoppers and growth of vegetation. At
any period in the season a heavier dosage will lengthen the residual
effect. For example, in the tests of chlordane on corn during August,
1.5 pounds per acre remained effective for 10 days whereas 2.7 pounds
per acre remained effective for more than 26 days. In late-summer
spraying two applications or heavier dosages on barriers apparently
will be needed when there is a continuous immigration into the barrier.
Heavy or repeated applications may also be necessary in other situations,
as during a prolonged hatching period early in the season. Whatever the
situation, the single spray application must be effective enough to stop
the infestation from any further spread or damage for a few days at least
and until a decision can be made as to the need for further treatment.
An attempt should always be made to kill Melanoplus differentialis
infestations while the grasshoppers are still concentrated on or near the
egg beds. A fully effective program of control by spraying, however,
will require applications of spray to natural or crop barrier strips,
when light infestations in the small-grain fields start moving into corn
or other late-maturing crops as the small grains are harvested.
The heaviest rain affecting either the early- or late-season spray
tests, 0.45 inch in 24 hours, had no noticeable effect on the efficiency
of the spray residues from either toxaphene or chlordane. Winds up to
15 miles per hour had little effect on the results, when the foliage was a
foot or more high, and dense enough to catch the foglike spray. On
shorter and sparser vegetation the best results were obtained when the
air was quiet. With the blower-sprayer it was possible to force the
spray down on and into the short grassy vegetation on the egg beds. By
elevating the nozzle of the blower and with some wind, good coverage
of a strip of tall, dense corn 2 rods or 10 rows wide could be obtained
with a single application.
Strips of sorghum, especially cane sorghum, and strips of corn
almost invariably catch and hold any infestations moving out of adjacent
small-grain fields after cutting. It is therefore feasible and economical
to plant trap strips of these crops in strategic locations, and spray them
to destroy infestations that may move into them from as far as a mile
away. These crop strips, as well as weedy strips and the first 5 or 10
rows of cornfields were no other barriers are available, make excellent






19-


barriers against migrating hoppers when thoroughly spray ;d once or
twice at the proper time. Where the outside rows of a r-gular corn
planting are sprayed to form a barrier, the hoppers may '.. stroy as
many as five of the rows.
The results of these acutal farm tests indicate that chlordane and
toxaphene sprays can be used effectively against infestations of
Melanoplus differentialis and may become important control me -. 1, s
for this species. This report is merely a summary of the results 't el
in preliminary field tests, however, and is not intended to be a general
recommendation of sprays for grasshopper control. Vegetation that ,
been treated with either of these insecticides should not be fed to dairy
cows or to animals that are being fattened for slaughter.







-20-


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