STATE F'LA,, L BOARD
July 1950 E-780, revised
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
DDT SPRATS EOR CONWTOL OF THE COBI EARVORM
AID THE BUDWORM IN SWEET CORN
Ry R. A. Blanchard and V. A. Douglas, Division of Cereal and
Forage Insect Investigations, G. P. Wene, Texas Agricultural
Experiment Station, and 0. B. Vooten, Bureau of Plant Industry,
Soils, and Agricultural Ingineering and also of Mississippi
Agricultural Experiment Station /
The use of sprays for commercial-scale control of the corn earvorn
(Heliothis armigera (Hbn.))is still in the experimental stage, but has
been successful in a number of places. The methods here described are
based on experiments conducted in Illinois, Indiana, Kiesissippi,
Missouri, and Texas during the years 1945 to 19149, -clusive.
Many insecticides have been tested in sprays and dusts, and DDT
has given the beet control. TDE has also given fairly satisfactory
control, but is rated as somewhat inferior to DDT on the basis of tests
that have been run. TDO and other newer insecticides may be found
after further tests to be as satisfactory as DDT. lone of the insecti-
cides tested have given satisfactory control of heavy earvorm infestations
when applied as dusts. However, very good control has been obtained with
DDT in mineral oil solution and emulsions.
Jour types of equipment for applying the sprays were used suc-
cessfully a knapsack sprayer, a paint-spray machine, and tvo power
sprayers, one with nozsles for hand application and the other with
A!pack Sprayer.- A small knapsack sprayer was used to apply
both oil solutions and emulsions to individual ears in small-scale
tests. Such a sprayer asay be used to treat corn in small fields, but
considerable labor and time are required to keep the spray pressure at
the 40 to 45 pounds which seems to be necessary. It is possible to
provide the desired pressure by means of a small portable pressure
V/ D. J.. McAlexander, Farm Manager for 7. H. Vahlsing, Inc., Elsa,
Tex., assisted in these studies.
tank such as was used during the war for inflating life rafts. If
such a tank is used, the knapsack sprayer should have an air-intake
valve welded on it. An air-pressure gage is also necessary to keep
from adding more air than the tank will stand and to be sure that the
proper pressure is naintainea. Where this type of sprayer is used to
apply an emulsion containing oil, the liquid must be kept agitated by
occasional shaking as it is being sprayed; otherwise the oil and water
in the emulsion will separate.
Paint-Spray Machine.-- Another type of equipment used for applying
sprays to individual ears was a small paint-spray machine with a
compressor run by a gasoline motor. This outfit, operated at a pressure of
30 pounds per square inch, breaks up the spray well and drives it into the
silk mass. The equipment used in our tests had a 1-quart liquid container,
but it might be feasible to use a machine having a large liquid container
from which several gans are operated at the same time. Some means of
agitating the spray, such as a pipe to conduct compressed air from the
compressor to the bottom of the spray tank, is necessary where an
emulsion containing mineral oil is used.
Power -.rayer with Nozzles for Hand A lication.- Both oil
erlutions *sad emulsions have been successfully applied to the individual
ears wvth nousles attached to hoses on a power sprayer. Zach nozzle was
equipped with a shut-off valve operated by hand. The spray outfit was
mounted on two automobile wheels and was pulled by a mule between two
rows of corn, A boom mounted above the corn had outlets for eight
20-foot hotce p&ced the same distance apart as the corn rows, so that
e4.t me. ccrdA spr&y the ears in eight rows as the machine was pulled
throng the field The men walked ahead of the machine, which was
operated at a treed slow enough to allow them to spray each ear. The
sprayer was operated at a pressure of 100 pounds per square inch.
About 30 acres per day were treated in this manner.
Power Sprayers with 7itad Nozzles.- Two types of power sprayers
!.-th the nozzles mounted in fixed positions have been used piston-type
pujap on one and on the other a gear-pump to supply pressure. The spray
rig employing the piston pump was suspended between two corn rows below
a high clearance oarriee and was drawn by one mule. Several spray rigs
using gear pumps were used in different areas. They were all self-
propelled with the spray outfit mounted on a high-clearance corn-
detasseling machine. On one rig using a gear pump, an air-cooled gaso-
line engine drove the machine and also operated the pump for spraying.
A second rig of this type had an automobile engine mounted on a
detasseling machine. In a third self-propelled rig the power unit was
a small tractor with the chassis raised above the wheels to obtain the
necessary clearance. The rear wheels were driven from the rear axles
by roller chains. This type used a gear pup to supply pressure.
Zither a piston-type pump or a gear-type pump such as is widely used
on weed sprayers could be used with the two last-named power units.
Means of agitation are necessary when emulsions containing mineral
oil are to be sprayed. A mechanical agitator in the spray tank is beet,
and power sprayers with pie ton-type pumps are usually so equipped.
Where an automobile engine or small tractor is used to supply power,
an agitator can easily be arranged to work with the gear pump. This
may be somewhat more difficult where the spray rig is propelled by an
air-cooled engine driving the front wheel. Some agitation say be
provided by a hose from a bypass valve connected between the bottom of
the tank and the pump, but such an arrangement may not be very satis-
factory if the spray tank is large.
One spray rig used in 1949 had a large air-cooled engine to drive
the front wheel and a smaller engine mounted on the tank to drive the
pump and agitator.
To obtain satisfactory results the pump used must be large enough
to provide adequate pressure for the number of rows it is desired to
spray at one time. The manufacturers of the low-gallonage nozzles rate
the output in gallons per minute or gallons per hour. The pump should
have sufficient capacity to carry the combined output of all the largest
nozzles to be used on the rig at 150 pounds per square inch.
To prevent clogging, it is important that a strainer of 80- to
100-mesh brass or copper wire be fastened over the opening from the spray
tank into the supply line and that a similar strainer be coupled into
the line between the pump and the nozzles. The strainers, especially
the one between the pump and nozzles, should be large enough to allow
unrestricted flow of the maximum amount of spray required for the
number of nozzles in use. Otherwise the required nozzle pressure cannot
be maintained. Use of a line strainer of insufficient capacity was one
of the principal difficulties with the first large sprayers tested.
The drops carrying the spray nozzles can be attached to the bojs
in at least two different ways (fig. 1), as follows: (1) The supply hose
to the individual drops can be either screwed into the boom or can be
supplied from a smaller manifold attached to the boom. The drop may be
rigid (fig. 1, A), with vertical adjustment of the nozzles being made
by raising and lowering the droppwhich is held in place by a set screw.
(2) A drop-pipe (fig. 1, B), which is semirigid. A short piece of hoe
is used to reduce vibration. The pipe is held in a straight line with
the row by clamping it to a piece of strap iron as shown. Vertical
adjustment of this type of drop is accomplished by raising and lowering
the boom. The drops in both types are suspended midway between the rows
and the attaching parts are welded to the boom if fixed row widths are
used. If the row widths are to be varied, as in cases where othpr crops
are to be sprayed, a clamp may be devised for attaching the drops to the
boom. This will allow changing of row widths. The nozzle cluster for
both types of drops is shown in figure 2.
Two pairs of nozzles, one pair 5 inches above the other, can be
attached to each drop, making four nozzles per row. One nozzle of each
pair is directed at a row on either side of the drop. The nozzles should
be set above the ears, about l4 inches from the cornstalks, and inclined
downward to cover the silks and upper parts of the ears with spray.
Equally good results have been obtained with nozzles putting out a flat-
fan-shaped spray and ones with a hollow-cone-type spray, provided the
output of each type is the same. In case of the flat-fan type, the upper
rozzle on each side of the row can be directed forward and in toward the
row at about a 45-degree angle and the lower one on each side backward
and in at about 45 degrees. The nozzles should be adjusted so that the fan
of spray is spread vertically, not horizontally. Apparently the best
results with the hollow-cone-type nozzles are obtained when the two
nozzles on each side of the row are aimed directly at each other or the
--oper ones slightly forward and the lover ones slightly backward. The
m-actine should be operated at a minimum pressure of 100 pounds per
-1au-re inch, and in experiments in 1949 increasing the pressure to
l10 pounds increased the effectiveness of the spray.
Kinds of Sprays Suggested
Formulations for Sinjle Hand Application to Individual Ears.- A
sol'.iion =or; -.irng 1 pounds of technical DDT in 25 gallons of white
miners oil o:- 65 to 95 seconds Saybolt viscosity can be applied to
individual ears with knapsack sprayers or by men operating nozzles
atte-ched -to a po'-er spryer, or with a paint-tpray gun. This solution
soul1 i ot D gained until l6fter the ears have been fertilized, ie.,
t 7il t7, s' i hPave wilted and begg to turn brown at the outer ends.
kAn 8lsoa made ;rom- 3 quarts of factory-prepared 25-percent DDT
-mulFifi&ble c^icnLrate plus 6 gallons of the above-described white
mineral oil c-iluted to 2; gallons with water can also be applied in
this maniner.1/ Mhe oil and T)DT concentrate are aixed together and
then stIred into the water until a uniform milky-white liquid is
fo',d. If sufficient agitation is provided by the spray machine,
the oil and the DDT can be poured directly into the required amount
of water in the spray tank. This emulsion should be applied as soon
as 90 to 100 percent of the ears are in silk. A single application
made at that time will not injure the ears.
Not more than teaspoonful of the oil solution or J teaspoonful
of the emulsion should be applied per ear. Only one application should
be made to each ear. The oil solution penetrates the ears better than
the emulsion and may give slightly better control of the worms, but will
prevent the filling out of kernels at the ear tips. Although the emulsion
gives a somewhat lower kill of the worms, the ears will fill out better
./Iuilsifiable concentrates containing 30 to 34 percent of DDT are
also on the market, Five pints of the 30-percent concentrate or 4 pints
of the 34-percent concentrate should be used in 25 gallons of the spray.
The amount of oil remains the same.
at the tips. Zither formulation will give good control if applied as
A nozzle giving a very fine hollow cone of spray should be used for
the hand applications. The angle formed by the cone of spray should not
be wider than 50 degrees at 100 pounds' pressure. Otherwise, it will be
difficult to get pro per coverage of the silks and ear tips. The nozzle
should be held 3 or & inches above the ear tips and care taken to spray
the entire silk and not just one side of the ear. Nozzles suitable for
use with a power sprayer are manufactured by several spray-equipment
companies, but extreme care should be used to select one that does not
put out too large a volume of spray or too large droplets. Nozzles with
capacities at 100 pounds' pressure of 1.5 gallons per hour where the oil
solution was used and 2.5 gallons where the emulsion was used were found
satisfactory. The nozzle assembly should be equipped with a lever-type
shut-off valve that is easy to operate with one hand and has a positive
cut-off. The same specifications also apply to the type of paint-spray
gun selected, if that method of application is used. These sprays a&-e
not recommended for application by machines with fixed aozzles because
of cost of the spray and the difficulty of getting good control with only
Formulations for Two or Three Hand Applications.-- Hand applications
by the methods just discussed of an emulsion containing 10 percent white
mineral oil of 65 to 90 seconds Saybolt viscosity will give excellent
control if two properly timed applications are made. The first application
should be made 1 day after 7 to 10 percent of the ears are in silk and
the second 2 or 3 days later. Experience has shown that to determine
accurately the percentage of ears in silk, actual counts must be made in
the field beginning when the first silk appears. The general formula
for the spray is 3 quarts of 25-percent DDT emulsifiable concentrate
plus 2j gallons of white mineral oil diluted to 25 gallons with water.
Because of the presence of the oil, this emulsion must be stirred up
well and must likewise be shaken periodically or otherwise kept agitated
as it is beng applied. Ears that have silks, as well as shoots on which
the silks have not yet developed, should be sprayed. The knapsack sprayer,
paint-spray gun, and power sprayer have all been used successfully for
applying the emulsion containing 10 percent mineral oil. Vith the
knapsack sprayer, however, it is important not to let the pressure drop
below 40 pounds.
Power Application from Nozzles in Fixed Positions.-- Tests in a
number of areas have indicated that an emulsion containing 5 or 10 percent
of white mineral oil of 65 to 90 seconds Saybolt viscosity is best for
applications from nozzles in fixed positions. Two or three properly
timed applications should be made. Two applications have given good
control, but the percent of worm-free ears was somewhat greater where
three applications were made. The third application gives added assurance
of a high percentage of perfect ears. If three applications are made the
oil in the emulsion aay be reduced to 5 percent. Here three applications
are planned, the first should be made t-., i-
1 day after the first silks appear and the second and third applications
at intervals of 2 days. Where two applications are planned, the first
should be made 1 day after 7 to 10 percent of the ears are in silk and
the second after an interval of 2 or 3 days.
The general formula for the sprays where two machine applications
are to be made is the same as for the two hand applications already
mentioned -- 3 quarts of 25 percent emulsifiable DDT 2/ concentrate
plus 2J gallons of white mineral oil diluted to 25 gallons with water.
If three applications are to be made the formula is the same, except
that the oil in the emulsion may be reduced to 1i gallons. If care is
exercised to see that not over 10 percent of mineral oil is put into the
spray, no damage to the corn should result. This is true whether two
or three applications of the material are made from fixed nozzles on a
power sprayer or two applications from a knapsack prayer, paint-spray
gun, or hand nozzles attached to a power sprayer. r7
A minimum of 25 gallons per acre per application should be used.
Spray nozzles with an output of 8 to 9 gallons per hour each at 100
pounds' pressure have given excellent results where the machine was
operated at a speed between 3 and 3A miles per hour. ?or operation at
higher speeds correspondingly larger nozzles should be used. Nozzles
of the same output capacity giving either a flat-fan or hollow-cone-
shaped spray pattern have given equally good results. The angle formed.
by the spray as it comes from the nozzle should not be over 600 at
100 pounds' pressure. If the spray comes out at too wide an angle, it
will cover too much of the plant, thereby lessening the amount reaching
Fixed Nozzle Spraying for Budworm Control.- The earvorm and the
fall armywor T (phya frugiper T (A. and S.)) often attack sweet corn
before and during tassel formation. When they infest corn in this way,
they are commonly called budworms. They may injure the plants severely,
and the large larvae may later travel from the tassels to attack the
It was found that a single application of emulsion containing DDT
and 5 percent of mineral oil would effectively control such worms. The
material can be applied with a machine on which the nozzles are held in
a fixed position somewhat as already described. However, two nozzles
should be set directly above the plants to shoot downward, and two should
be directed at the ear-bearing sections of the plants. A single nozzle
fixed directly above the plant and one fixed on each side might be suf-
ficient to give control. The formula recommended is 3 quarts of
25-percent DDT emulsifiable concentrate 2/ and 1* gallons of white
mineral oil of 65 to 95 seconds Saybolt viscosity, diluted to 25 gallons
J/Country Gentleman hybrids appear to be more susceptible to injury
from DDT emulsions applied by hand than are other hybrids.
with water. A single application made just as the damage begins to te
general over the field should protect the plants and young ears from
damage. In most instances this spray application will not protect the
ears after they begin to silk but, if damage does not become too severe
in the field before silks begin to emergetwo or three regular earworm
sprays designed for protection of the ears will also kill larvae migruting
from the tassels to attack the ears.
Factors Influencing the Effectiveness of Control Measures
Even with the most severe infestations observed to date, 85 to
100 percent of marketable ears can be expected from any of the treatments
outlined, if properly applied and timed. This high percentage of control
has been obtained in fields where 35 percent or more of the ears in
untreated checks have been unmarketable. Up to 90 percent of worm-free
ears have been obtained in very severely infested commercial fields under
certain conditions. Some of the conditions known to affect the percentage
of worm-free ears are given below.
Tp of Hybrid.- Hybrids with open growth and few tillers fP.ciitate
spraying of the ears properly, either by hand or machine. Conversely,
hybrids that have a bushy type of growth with many tillers make it
difficult to obtain a high percentage of worm-free ears. Hybrids that
are less injured by earworms because of relatively long, tight husks,
or for other reasons, are easier to protect from earworm damage than
are those more subject to severe injury.
Rate of Planting.-- EBarworm control by any method will be diffi-
cult if plants are too close together in the row in drilled corn or
if there are too many plants per hill where corn is planted in checkrows.
Actual data on the effect of spacing on control are not available, but
it is known that the percentage of control is reduced if plants are less
than 10 inches apart in drilled fields, or where there are more than 3 or
4 plants per hill in checkrowed corn. Under most conditions the number
and size of ears are seriously reduced by close planting. Excessively
thick planting is thus a source of loss rather than profit.
Spacing of Corn Rows.- If it is planned to spray corn by a machine
with fixed nozzles, particular care should be taken to space the rows
uniformly when it is planted. If the spaces between rows vary greatly,
the nozzles on each side of some rows will not be at the right distance
from them for best results.
Discussion and Precautions
The effects on the plants and on the ears of the materials tested
and the methods of applying them have been carefully studied. No bad
odor or taste has been detected in repeated trials of sweet corn that
had been treated with the sprays and by the methods described in this
paper. Furthermore, no evidence has been found that any of the materials
or methods of application recommended were detrimental to the corn,except
for some failure of tip kernels to fill out when an oil solution of DDT
was used. However, the materials and methods recommended should be used
with caution. The strengths of the formulations and the dosages recommended
should not be exceeded, for otherwise the corn may be damaged. Emulsifiable
DDT concentrates with strong odors should be avoided. Under no conditions
should kerosene or an oil with a kerosene odor be used.
A considerable number of samples of the corn that had been treated
with the insecticides suggested in this paper have been analyzed for the
-:F-sence of DDT residues. These analyses have shown that the husked ears
are entirely safe for use as food, but that appreciable residues of DDT
may be present on the husks, silks, leaves, and stalks. Although these
residues are not likely to cause acute poisoning of livestock to which
tte plants are fed, very small quantities of DDT may be secreted in the
&ill.r and absorbed into the fatty tissues of such animals. Therefore,
the treated plants should not be fed to dairy animals or to meat
entimals that are being finished for slaughter.
I I SUPPLY HOSE
I -(-- 0. I';fOP PIPE
I I CROSS
4.0" row 12" to 14"
36" row 8" to 10"
30" row 2" to 4"
Figure 2.-- Nozzle Cluster.
UNIVERSITY OF FLORIDA
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