L I ,` A Y
STATE PLA.N t .'
E-530 DERTMENT March 1941
ENTOMOLOGY AND /
CONTACT INSECTICIDES FOR CHINCH BUG CONTROL ON CORN
By E. V. Walter and Curtis Benton,
Division of Cereal and Forage Insect Investigations
The protection of growing corn from the iava.es of chinch bugs by
the use of insecticides has generally been considered impractical because
of the high cost of the treatment as ccrpared with the relatively low per-
acre value of the crop. When a portion of a field becomes seriously in-
fested by chinch bugs migrating into it before a barrier has been con-
structed, the usual custom has been to locate the barrier ahead of the worst
of the invasion and to abandon the more heavily infested portion of the crop.
A well-constructed barrier built in advance of the arrival of the bugs is
still the cheapest and most effective means of protection. Occasionally,
however, a crop of more than usual value, such as inbred or hybrid seed corn
or market sweet corn, becomes infested and an attempt to save as much of it
as possible becomes desirable.
Nicotine, soap, or kerosene emulsion sprays, and nicotine or calcium
cyanide dusts have been recommended but have not been found entirely satis-
factory on account of their high cost, low efficiency, or caustic effect on
the plants. An effort has therefore been made during the period of 1938-
1940, inclusive, to find a safe, effective, and readily prepared insecticide
that would be cheap enough to use at least on particularly valuable corn.
To date an emulsion of a highly refined white mineral oil to which has been
added either nicotine sulfate or derris extract has given the best results.
This spray is a modification of the lubricating oil emulsion and nicotine
sulfate spray recommended by Horton and Satterthwait in U. S. Department of
Agriculture Farmers' Bulletin 1223. The investigations are not complete,
but the results thus far indicate that so much protection can be obtained
at a moderate cost that immediate publication of the information seems
Habits of the Chinch Bugs
Chinch bug infestations usually oriair.ate from eggs laid in the
spring or early in the summer by the overwintered adults that have migrated
to the fields of small grain. As these grains mature or are prematurely
killed, the partly grown nymphs leave them in search of food and so invade
nearby fields of young corn. Thus the bugs are usually first observed late
in June and early in July on a few rows of corn nearest the grain fields.
At this time the corn usually is from -L to 3 feet in height. The bugs
normally remain to feed on these first rows until they have killed the
plants, or are ready to molt.
Infested corn should be treated as soon as possible after the bugs
are found. However, if the bugs are still migrating, it is advisable that
a barrier be constructed first to prevent more bugs from coming into the
field. The sprays mentioned have some repellent action, consequently, unless
a barrier is constructed, many of the bugs coming in after spraying is dcne
will go farther into the field to the unspraycdi plants, thus spreading the
infestation. In some of the tests, plants unprotected by a barrier were
sprayed. In spite of the fact that they afterward became densely covered
with bugs, many lived and produced ears, thus indicating that the bugs did
not feed readily on the sprayed plants.
When ready to molt, especially in very hot weather, the bugs often
crawl under clods or trash, where it is cooler and more humid than on the
plants, and remain there for several hours. Also, many hide in such places
during very windy weather. Thus many bugs ray be missed by insecticidal
treatment during such times, making a second application necessary in
Type of Oil
The oils thus far tested as insecticides for the control of chinch
bugs on corn were white mineral oils having an unsulfonatable residue of
at least 96 perci;;it. There did not seem to be any significant difference
in the effectiveics: of oils of the different viscosities used, which were
within the range from 85 to 210 seconds Saybolt at 100 F. Since the lighter
oils are usually clicaper than the heavier oils, they are recommended for the
Commercial miscible ind summe,"- S2ry oils rire effective but should
he lj.ed with caution ,s c.ses of severe iJ.Iq.y from their application to
corn have been obsrYrvrd.
Mineral oils of the t.pe mentioieid1 ane easily emulsified according
to the following formula:
1 p.)juLd jota.h yelloww) lLl.,'y .1.cp
[,.jllon hot soft water
1 g.1llon oil
Dissolve the soap in the water and, while still hot, add the oil slowly and
beat until emulsification is complete. If a spray pump of the bucket or
wheelbarrow or power type is available, the mixture canr be easily emulsified
by pumping it through the nozzle and back into the container. Small quan-
tities may be readily emulsified by use of a rotary egg beater.
Well-prepared emulsions made by this formula contain approximately 62
percent of oil. They are quite stable and have shown no breakdown or
separation when allowed to stand for a year or more.
Several brands of ready-prepared emulsions of mineral oils of the
types used in these experiments are on the market. They may be as effective
as the home-made emulsion but are usually much higher in price. One such
brand containing 83 percent of oil and intended for greenhouse and garden
spraying has been used with good results.
Many different dilutions of the oil emulsions, and combinations of
them with varying amounts of nicotine sulfate, rotenone, pyrethrum, and
other insecticides, were tried experimentally. The cheapest mixture that
gave satisfactory results was one in which 1 part by volume of the home-
made oil emulsion containing 62 percent of oil was mixed with 30 parts of
water and fortified by the addition of one-eighth ounce, or approximately
1 teaspoonful, of nicotine sulfate (40 percent nicotine) per gallon. A
number of tests indicated that a similar quantity of a derris extract
containing 5 percent of rotenone can be substituted for the nicotine sulfate
with equally good results. Oil emulsion to which different amounts of
pyrethrum extract were added gave but little better results than the oil
The strength of the spray material mentioned above is the minimum
that gave satisfactory results when used against migrating chinch bugs when
many of them were in the fourth and fifth instars or adult stage. Slightly
better kills were secured by increasing either the oil or nicotine content
of the spray, but the results did not appear to be enough better to com-
pensate for the increased cost.
Water dilutions of the oil emulsion alone and also of the nicotine
sulfate, rotenone, pyrethrum, and many commercial insecticides have been
tried, but none has given as good results as the combination of oil emulsion
with either nicotine or rotenone.
When very hard water is used for spraying, enough of a good water
softener should be used to break it before the emulsion is added. This
prevents separation of the oil and the formation of a scum of insoluble
soaps that might interfere with the spraying. The kind and amount of the
water softener used will depend on the degree of hardness of the water and
the minerals involved. Do not use too much, as an excess of some types
may injure the plants.
Cost of Treatment
Several of the mixtures which showed the best results in the experi-
mental tests were mixed and applied under field conditions to determine the
cost of materials and the time required to treat an acre of corn. It was
thus found that approximately 70 to 75 gallons of spray mixture would be
required to treat 1 acre of corn from 2 to 4 feet in height. It was also
found that a man using a knapsack type of compressed-air sprayer could
treat approximately 3,200 hills, or slightly less than 1 acre, per 8-hour
day. (There are 3,556 hills per acre when planted in hills 3 feet each
The cost of materials for mixing 70 gallons of spray, when purchased
at common retail prices, may be distributed approximately as follows:
Oil, 1 .4 gal. at $0 .50..................................... ..................... $0 .70
Soap, 1.4 lb. (about 2 bars) .................................................. .08
Nicotine sulfate, 12 oz. at $2.25 per 1-lb. bottle...... 1.69
The comparative cost and insecticidal value of a number of the
sprays used in these tests are shown in table 1. The cost is based on
retail purchase of the quantity of each article necessary for 70 gallons of
spray. It is almost impossible to arrive at a definite percentage of the
chinch bugs killed, so ratings based on observations in from 6 to 16 rep-
lications of each combination and strength were used. These are as follows:
P, poor, under 30 percent dead; F, fair, 30 to 60 percent dead; G, good,
60 to 90 percent dead; and VG, very good, 90 to 100 percent dead.
Table l.--Comparative cost and insecticical value of insecticides
tested for the control of chinch bugs on corn, based on the retail price of
enough of each material to mix 70 gallons of spray.
oz. per gal.
Home-made oil emulsion
Liquid soap (40% dry
G ... 4.66
Injury to Plants
No burning or other injury was observed when emulsions of the highly
refined white mineral oils described above were applied, in the dilutions
recommended, to the leaves or lower parts of the stalks of corn that v.was
12 inches and over in height. Some occasional injury was observed on very
small corn, especially when the spray material was allowed to collect in
the top of the plant. Occasional slight injury was also observed on heavily
sprayed suckers of 12 inches or less in height. Plants 3 feet or more in
height were apparently uninjured when experimentally sprayed to hc1 their
height with the pure oil. %'T
Summary P T AND
An emulsion of a highly refined mineral oil combined with either
nicotine sulfate or rotenone was found effective for killing chinch bugs on
growing corn. Such a spray is rather expensive for use on corn grown for
feed but is cheap enough for use on crops of inbred or hybrid seed or market
sweet corn. It is not recommended as a substitute for the creosote barrier
UNIVERSITY OF FLORIDA
3 1262 09224 7518
but only to kill the bugs that reach the corn in spite of the barrier or
before it is constructed.
Emulsions of all the highly refined mineral oils so far used have
been found safe for application on corn 12 inches or more in height. Com-
mercial emulsions of similar oils gave good results but the cost was greater.
Commercial miscible or summer spray oils should be used with caution.
Properly prepared oil emulsions are stable and will keep for a year
or more without separation. An easily followed formula is given.
A combination of the oil emulsion with either nicotine sulfate or
rotenone gave much better results than either alone, even at very much
greater strengths. The addition of pyrethrum extract did not materially
increase the effectiveness of the oil emulsion.
The minimum strength of spray that gave satisfactory results con-
tained 2 percent of oil and had one-eighth ounce of nicotine sulfate (40
percent nicotine) or of derris extract (5 percent rotenone) per gallon.
Approximately 70 gallons of such spray, costing $2.47 when materials
are purchased in small lots at retail prices, were required to spray 1 acre
of corn that was from 2 to 4 feet in height.
A man using a knapsack-type sprayer can spray slightly less than an
acre in an 8-hour day.