STATE Pj.ANi k
April 1951 E-7g0, revised
United States Department of Agriculture
Agricu ltural Research Administration
Bureau of Tntomolorr and Plant quarantinee
DDT SPRAYS FOR CONTROL OF TH, COP.N TANORM
AND THE BITD'JCF,!1 IN SWVT' CORN
By R. A, Blanchard and W. A. Douglas, Division of Cereal and
Forge Insect Inv-st;aitions, G. P. Wene, Texas Agricultural
Experiment Sta'tion, and 0, B. Wooten, Bureau of Plant Industry,
Soils, and Agricultural En-,ineer17g and also of Mississippi
Agricultural Experiment Station --
The use of sprays for commercial-scale-control of the corn earwormn
(Heliothis armigera (Hbn.)) has been successful in a number of places.
The methods here described are based on experiments conducted in Illinois,
Indiana, Mississippi, Missouri, and Texas during the years 1945 to 1950,
Many insecticides have been tested in sprays and dusts, and DDT has
given the best control. TDI has also given fairly satisfactory control,
but is rated as somewhat inferior to DDT on the basis of tests that have
been run. TDE and other newer insecticides may be found after further
tests to be as satisfactory as DDT. None of the insecticides tested have
given satisfactory control of heavy earworm infestations when applied as
dusts. However, very good control has been obtained with DDT in mineral
oil solution and emulsions.
Four types of equipment for applying the sprays were used suc-
cessfully a knapsack sprayer, a paint-spray machine, and two power
sprayers, one with nozzles for hand application and the other with fixed
Knsack Sprayer. -- A small knapsack sprayer was used to apply
both oil solutions and emulsions to individual ears in small-scale
tests. Such a sprayer may 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.
JL_ D. J. McAlexander, Farm Manager for F. H. Vahlsing, Inc., Elpa,
Tex., assisted in these studies.
tank such as was used .during the war for Infl.ating life rafts. If
. .ch a ': .L is uased, the knapsack sprayer ak(.\'id have an air-Intake
I ve wLdw on it. An air-pressure gage is also necessary to keep
f-3. ,c.!'i&iL 7 ,-e, r1d\ thin the tank wf.li stand a..d to be sure that the
-prr ,, :sure is iantainea, V.iere this type of sprayer is used to
L^plr3 aa OulC:w containing oil, bthe liquid. wt be kept agitated by
a' >...a-.i- p. it is baing sprayed; otherwise the oil and water
_. the omulsi.on Aill separate.
t^l-ir-l i ^ e,~k Anotcrr tyrje of ecu%Ayent -ased fr.r applying
s:ryv to ind1i<'4:k.a" ears was a small -alat-spray achine with a
,.pTT-- :or run by a gasAliLn motL.-. This outfit, operated at a pressure of
3 pou.-sB per square inch, breaks up the spray well and drives it into the
eilkL maa,, The equipment used in our tests had a 1-quart liquid container,
but it might be feasible to use a .achine having a large liquid container
from which '?veral guns 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 Sprayer with NoEsles for Hand plication.-- Both oil
solutlans Rnd emulsions have been successfully applied to the individual
ears with notiles attached to hoses on a power sprayer. Each nozzle was
equipped with a shut-off valve operated by hand. The spray outfit was
marted oc tw'o au ,mobile wheels and was pulled by a mule between two
..t t"s spray the e&rs in eight rows as the ma -bine was pulled
I.-roul Uh field. The men walked ahead cf the machine, which was
oppratW, at -.peed l: enough to allow them to spray each ear. The
sprayer sw- oprated at a preasurs of 100 pounds per square inch.
About 33 acres per &Vy. were treated in this manner.
Fow.?r rnyerr vith iryed Nozzles.-- Two types of power sprayers
vwth the nosles &-.'nted in fixed positions ha'e been used-piston-type
-p on one and on the other a gear-pump to supply pressure. The spray
r16 employing the piston pump was suspended between two corn rows below
a hig cle6s.ance carriage and was drawn by one mile. Several spray rigs
usin.; gear pamp were used in different areas, They were all self-
pr7pellied Wth '.he Apray outfit mounted on a high-clearance corn-
d;.taaeling .chiAne, On one rig using a gear pump, an air-cooled gaso-
lin.e e-ngine ds ve 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 pump 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 best,
and power sprayers with pipton-type puxps are usuvI.11 so equipped.
Where an automobile engine or small tractor is used to supply powrr,
an agitator can easily be arranged to work with pump. This
msy be somewhat more difficult where the spray r11 i .elld by an
air-cooled engine driving the front wheel. Some : tat. may be
provided by a hose from a bypass valve conre'cted f.tween *V bottom of
the tank and the pump, but such an a:-rangr., it --* not 'e v-r;- -" i'."-
factory if the spray tank is large.
One spray rig used in 1949 had a large air-cooled et-inei 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 u.st ;. large enough
to provide adequate pressure for the number of rowsve it is de pred to
sprey at one time. The manufacturers of the lo-. l" g nozles rte
the output in gallons per minute or gallons per hvtxr. The puamp should
have sufficient capacity to carry the combined outtt of all the largest
nozzles to be used on the rig at 150 pounds psr square "-:.
To prevent clogging, it is portant that a etr.: ... of .-
l00-wrh bras' or ,.oppeT wire be fastened over the f-' -
tank into the supply line and that a similar stralne' K' i ned t
the line between the pum-p and the nozzleso T1:m strtr. .ers. oeco 'lr
the one between the pump and nozzles, should be large enc %,C_- to '.ow
unrestricted flow of the maximum amount of 3iray requIr-6 for te
number of nozzles in use. Otherwise the required n-,TC!- oresl r8 co
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 ato ed to the boom
in at least two different ways (fig. 1), as follows; (1) The supply hoe
to the individual drops can be either screwed into the boom or can be
supplied from a smaller manifold attached to the boom. The drcp may be
rigid (fig. I, A), with vertical adjustment cf the nozzles be!nr/ made
by raising and lowering the dropwhich is hfld in place by a set screw.
(2) A drop-pipe (fig. 1, B), which is semiri-ild. A short piece of hnse
is used to reduce vibration. T'he pipe is hel: 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 other 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, orZe pl 5 inches above the other, can be
attached to each ,'o, ncklng four na-zaes per row. One nozzle of each
pair is directed r-: a row on either side of tho drop. The norzles 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 noq?!es putting out a flat-
fan-thaped spray and oaee with a hollrw-e-one-ty-e sprFy, provided the
output of each type is the same. In case of the flat-fan type, the upper
nozzle 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 t-o
nozzles on each side of the row are aimed directly at each other or the
upper ones slightly forvard and the lower ones slightly backward. The
machine should be ,perated at a minimum pressure of 100 pounds per
square inch, and in experiments in 1949 increasing the pressure to
150 pounds increr..s-d tie effectiveness of the spray.
i.-ids of Sprays Suggeste,
Torisilations for Single Hand Application to Individual Ers-- A
solution containing 1* pounds of tP'chpical DDT in 2-5 gallons of wh.'.te
mineral oil of 65 co 15 seconds Saybolt viscosity can be applied to
individual ears with knapsack sprayers or by men operating nozzles
attached to a powey sprayer, or with a paint-Ppray gn. This solution
should not b.e E-Li-d until after .the ears have been fertilized, ie.,
not until the silks have wilted and begn to turn brown at the outer ends.
An emulsion made from 3 quarts of factory-prepared 25-percent MDT
emulsifiable concentrate plus 6 gallons of the above-described white
mineral oil diluted to 25 gallons with water can also be applied in
this manner.g/ The oil and DDT concentrate are aixed together and
then stirred into the water until a uniform milky-white liquid is
formed. 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 a c7ition or J teasl.oonlTul
of the emulsion should be applied per eax Cal r one application should
be made to each ear. The oil solution pnet-.at e the ears better than
the emulsion and may give slightly better co. tol of the worms, but will
prevent the filling out of kernels at the ear t'ps. Although the 4rulsion
gives a somewhat lower kill of the worms, the ears will fill out better
2g/!Emulsifiable concentrates containir,'- 30 to 34 percent of DIT are
also on the market, Five pints of the 30-pereent 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. Either 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 poundst pressure. Otherwise, it will be
difficult to get proper coverage of the silks and ear tips. The nozzle
should be held 3 or 4 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 poundst pressure of 11 gallons per hour where the oil
solution was used and 2P- 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 are
not recommended for application by machines with fixed nozzles because
of cost of the spray and the difficulty of getting good control with only
Formulations for Two or Three Hand Apolications. Two hand applications
by the methods just discussed of an emulsion containing 10 percent of white
mineral oil of 65 to 95 seconds Saybolt viscosity will give excellent control
under most conditions. The first application should be made 1 day after
7 to 10 percent of the ears are in silk and the second 3 days later. To
determine 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 21
gallons of white mineral oil diluted to ?5 gallons with water. Because
of the presence of the oil, this emulsion must be kept agitated as it is
beinrX applied, Ears that have silks, as well as shoots on which the silks
have not yet developed, should be sprayed. Knapsack sprayers, paint-spray
guns, and power sprayers have all been used successfully for applying the
emulsion containing 10 percent mineral oil. With the knapsack sprayers,
however, it is important not to let the pressure drop below 40 pounds per
Where the infestation is severe, applications of an emulsion containing
7,5 percent of white mineral oil may be required to give a high percentage
of worm-free ears. The first application should be made 1 day after the
first silks appear and the second and third after intervals of 2 days.
The formula for three applications is the same as for two, except that
the oil should be reduced to 1 3/h gallons for 25 gallons of emulsion.
Power Application from Nozzles in Fixed Positions. Tests in a
number of areas have indicated that an emulsion containing 7.5 or 10 percent
of white mineral oil of 65 to 95 seconds Saybolt viscosity is best for
applications from nozzles in fixed positions. Two applications have given
good control, but a third application gives added assurance of a high
percentag-e of perfect ears. If three applications are made)only 7.5 percent
of oil should be used. The first application should be made 1 day after
the first silks appear and the second and third after 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 3 days later.
The general formula for the sprays where two machine applications
are to be made is the same as gr the two hand applications 3 quarts
of 25-percent emulsifiable DDT-' concentrate plus 2J gallons of white
mineral oil diluted to 25 gallons with water, For three applications the
formula is the same, except that the oil in the emulsion should be reduced
to 1 3/4 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 are made from fixed nozzles
on a power sprayer or two applications from a knapsack sprayer, paint-spray
gun, or hand nozzles attached to a power sprayer.,1
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 31 miles per hour. For operation at higher speeds
corr-spondingly larger nozzles should be uqed. Nozzles of the same output
capacity giving either a flat-fan or hollow-cone snrry pattern have
given equally good results. The angle formed by the spray as it comes
from the nozzle should not be over 60 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 the ears.
Fixed-Nozzle Sraing for Budworm Control. The earworm and the
fall armyworm (CphZma fruigperda (A. a-nd 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?/ and 1L 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 be
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 emerge,two or three regular earworm
sprays designed for protection of the ears will also kill larvae migrating
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.
T!p of Hybrid.- Hybrids with open growth and few tillers facilitate
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,
er for other reasons, are easier to protect from earworm damage than
are those more subject to severe injury.
Rate of Planting.-- Zarworm 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.
Sacin of Corn Bows.- 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
presence 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
the plants are fed, very small quantities of DDT may be secreted in the
milk and absorbed into the fatty tissues of such animals. Therefore,
the treated plants should not be fed to dairy animals or to meat
animals that are being finished for slaughter.
^ -X z
UNIVERSITY OF FLORIDA
3 1262 09239 2074
I SUPPLY HOSE
0- -- DiOP PIPE
40" row 12" to 14"
36" row 8" to 10"
30" row 2" to 4"
Figure 2.-- Nozzle Cluster.