By S. F. Potts, Division of Forest
The demand for methods of insecticidal control which save labor and
materials has been accentuated by the war emergency. Conventional dusting
methods often result in wastage of materials and poor adherence of Lhe in-
secticide. Conventional spraying with dilute sprays is labor-consuming and
often requires heavy, expensive, high-pressure equipment. The application
of insecticides and fungicides in the form of concentrated sprays saves
labor, time, and materials. At present this method is restricted because
there is very little efficient equipment on the market designed specifically
for applying concentrates. Consequently the available equipment adaptable
for this purpose is not only limited, but it is not nearly so efficient as
are machines which may be developed and improved specifically for this pur-
pose at some later date. This paper is intended to indicate the equipment
which can be purchased or assembled at the present time, scme of its advan-
tages and disadvantages, and the insecticidal mixtures and concentrations
which are best suited for use in such equipment.
Concentrated sprays (excepting high-viscosity oils) are nearly as fluid
as water. Their insecticidal concentration is many times that of dilute
sprays. For example, a common lead arsenate concentrate contains 40 percent
oi lead arsenate as compared with 0.5 percent of lead arsenate in dilute
spray containing 4.2 pounds of insecticide per 100 gallons (838 pounds) of
mixture. Methods for preparing concentrated spray mixtures are discussed in
other papers.;j Concentrated sprays may be applied at any time to either
.. Potts, S. F. 1939. Concentrated Mixtures for Aerial Spraying. Jour.
Econ. Ent. 32 (4): 576-580. Potts, S. F. 1940. Concentrated Spray Mixtures
and Their Application by Ground and Aerial Equipment as Compared with
Standard Spraying and Dusting Methods. Bur. Ent. and P1. Quar. E-508, pro-
wet or dry foliage, as the spray does not drip or run off the leaves. They
adhere better than dilute sprays or dusts. This makes possible the applica-
tion of less insecticide and fewer treatments. Areas may be covered many
times more quickly with concentrated than with dilute spray. In general,
fine atomization makes possible the use of a small quantity of spray per
acre, and this necessitates the use of a high concentration of the insecti-
cide. It is, therefore, not practical to apply coarsely atomized concen-
trates. For given pressures, atomization increases as the rate of output
of spray mixture per aperture decreases. A difficulty with most equipment
is that it applies too much coarsely atomized concentrated spray per acre.
This makes necessary the use of lower concentrations, higher quantity rates,
greater insecticidal dilution, higher pressures, and higher pump capacities.
In order to obtain good coverage without using too much insecticide, concen-
trates should be applied as though they were dust materials rather than
As compared with water-borne sprays, undiluted oils are more finely
atomized, spread much better, evaporate less rapidly, and flow through
nozzle orifices at a slower rate, but are more expensive, and are less safe
on tender foliage.
Concentrated sprays may be applied with a type of hand-pump atomizer.
or with knapsack and power sprayers equipped with special nozzles.
The type of hand atomizer best suited for applying concentrates is shown
in figure 1. This type is far superior to the so-called continuous-pressure
atomizers because (1) the orifice of the tube which conducts the liquid from
the spray container to the outside ranges from 0.1 to 0.15 inch in diameter,
which is large enough to prevent clogging, and (2) it discharges the liquid
at a slower rate, which permits it to be more finely atomized. The use of
the hand atomizer is limited to yards, gardens, and small fields of plants
or trees that are not over 6 feet in height. When the plants are 2 feet
high or less, the operator is likely to become tired quickly unless an ex-
tension rod of 12 to 30 inches in length is used. It is often difficult to
cover the underside of leaves well with insecticide applied by existing types
of hand atomizers, since they are not provided with a means of directing
the spray at an angle.
Te degree of atomization provided by hand atomizers is not sufficient-
ly fine to give as good kill of certain small sucking insects when applying
concentrates as when applying dilute sprays. In order to obtain a kill as
good as or better than that obtained by dilute sprays, it would be necessary
for the concentrated spray droplets to be approximately one-fifth as large
as those provided by the present equipment when oil is used as the in-
secticidal carrier, or approximately one-tenth as large if water is the car-
rier. Atomization by existing hand equipment is sufficiently fine to control
effectively all sizes of chewing insects when the mixture does not contain
more than 2.5 pounds of powdered insecticide per gallon of water. At a
concei.tration of 2 pounds of' insecticide per gallon of mix ure, 5 ga !ns would
be required to give 10 pounds of insecticide per acre. Fungicides or combina-
tion insecticides can be added to the mixture. For example, a mtx
pound of copper oxide per gallon has been applied.
The usc of knapsack equipment 4s limited by the rate of ceL-very- and
degree of efficiency of the atomizing nozzles. Most nozzlcs delixer too
much mixture gallonss per hour) and do not atomize it sufficiently How-
ever, two types of roZzles 2/ atomized concentrates well enough at pres-
sures to be used for controlling many chewing insects, including hc gross
feeders that consume the whole or parts of leaves. The nozzle has On aper-
ture of 0.025 inch and delivers 5.04 gallons of water per hour at 75
pounds pressure, as compared with 33.6 gallons for ordinary one-sixteenth
inch aperture nozzles. When spraying truck crops the operator should move
fast enough to cover an acre with 8 to 10 gallons of mixture. Vell-stocked
ccnifercus plantations require 12 to 15 gallons per acre. These are average
figures which may be varied to meet specific conditions. Usually it is more
practical to use a single nozzle, except in cases where effective control
oa: be obtained by using a broom of two o three nozzles (fig. 2) spaced
15 to 18 inches apart.
The nozzle just described for the knapsack sprayer can be attached to
the broom, row bocm, or broadcast boom of power sprayers. The equipment
preferably should not be powerful or heavy. A 1-horsepower engine and a pump
capable of delivering 100 gallons of mixture per hour are adequate for a
6-row bocim, since only about 4 to 7 gallons will be applied per nozzle per
hour at a pressure of 100 pounds or less. There should be a suitable
straier in the spray line but none in the nozzle. A small increase or de-
crease in size of nozzle orifice makes a big difference in gallons cde."Liered,
but a small increase or decrease in pressure does not greatly increase or
decrease spray output. It is necessary to quadruple the pressure in order
to double the output. Increasing the pressure causes some increase in
atomization. Decreasing the size of the nozzle orifice also increases atomi-
2/ Nozzle, number IS is made by the Spray Engineering Ccifpany of
114 Central Street, Somerville, Mass. Its screen should be remo ed when
concentrates are to be applied. The IS nozzle is capable of applying all
insecticides dissolved in water or oil, such as nicotine solution, pyrethrum
extract, add derris extract, and suspensions of fine insecticide particles
such as copper oxide, lead arsenate, calcium arsenate, cryolito, etc., af-
ter these suspensions have been strained through a 40- or 50- iesh screen.
Another promising nozzle (number T68037) made by the same comrpany delivers
slightly less spray per hour, and has an orifice 2.2 times as large which
might reduce clogging. Only laboratory tests have been made with it.
nation. Nozzles with orifices as small as 0.018 inch in diameter can be
used when light oils and insecticides dissolved in water are being applied,
but they will clog when solid particles in suspension are being applied.
There is less abrasion at the nozzle orifices if this part of the nozzle is
made of hardened or stainless steel instead of brass.
A 4-row sprayer with two IS nozzles per row will deliver 40.3 gallons
Df spray per hour at 75 pounds' pressure and cover 5.82 acres at 6.93 gal-
lons per acre when traveling 4 miles per hour./ The quantity of insecti-
cide per gallon of mixture should vary with the number of gallons applied
in general, the power machines are limited to controlling the same
kinds of insects mentioned in connection with the knapsack sprayer, but
there are some exceptions. For example, Glasgow 4/ has used a power atom-
izer equipped with a special type of conventional nozzle to control thepea
aphid, using either rotenone extract or nicotine solutions in both water and
oil, This machine traveled 5 miles per hour and usually had a long canvas
trailer attached to it to increase the kill by fumigation when spraying with
with nicotine mixtures.
Sprayer units with a gasoline engine of 5 horsepower capacity or greater
and capable of delivering as much as 200 pounds pressure can be converted for
applying concentrates to trees up to 25 feet in height. This is done by
providing a high-velocity blower and blower tube, such as are used on
orchard dusters, and placing from one to five of the atomizing nozzles just
described at the end of the blower tube. The strong blast of air serves
to drive the spray into the trees. One gasoline engine drives both the
sprayer and the blower. This method can also be used for broadcast spraying
rial equipment now available consists almost entirely of airplanes
,,quipped with air-driven rotary or centrifugal devices for dispersing atom-
ized spray.5/ This type of device is satisfactory for many purposes. For
some purposes it is not entirely satisfactory since it tends to throw part
3/ To calculate the number of gallons that will be delivered per acre,
multiply the rate of travel (m. p. h.) of the sprayer by the width (in feet)
cDf strip or swath covered, and divide by 43,560 to obtain the acreage cov-
ered. Then multiply the number of nozzles by the number of gallons delivered
per P(nzzle per hour, and divide this product by the acreage covered.
4/ Glasgow, Hugh. 1942. The Use of Concentrated Sprays for Pea Aphid
Control. N. Y. (Geneva) Agr. Expt. Sia. Bull. No. 698, pp. 12 to 14.
5/ A centrifugal device is shown in the following paper: Whitten, R. R.,
. r. Potts, and E. H. Francis, 1941. Concentrated Spray Applied with an
Autogiro for Control of Cankerworms. Jour. Econ. Ent. 34 (5): 692-696.
of the mixture up on the aircraft, and it does not always cause sufficiently
fine atomization for best control of such insects as aphids. Ground and
preliminary aerial tests indicate that other types of apparatus which utilize
the principle of pressure or air atomization and which will be lighter,
simpler, and more efficient than centrifugal devices can be made to oper-
ate in the "slip stream".
As compared with airplanes, autogiros are able to fly at much lower
speeds turn in smaller areas, and land on and take off from much smaller
fields, and are safer to operate. Thus far helicopters have not been tried
for applying insecticides. It is believed that in the future the new types
of autogiros and helicopters now being developed will play an important role
in insect and disease control.
Companies Making One or More Types of Concentrated Spray Atomizers
John Bean Manufacturing Company, Lansing, Mich.
Root Manufacturing Company, 1311 West 50th Street, Cleveland, Ohio.
H. D. Hudson Manufacturing Company, 589 E. Illinois Street, Chicago,
Shell Oil Company, Inc., Technical Products Department, 50 W. 50th
Street, New York City, N. Y.
Electric Sprayit Company, Sheboygan, Wis.
Essick Machir.ery Company, 1928 Santa Fe Avenue, Los Angeles, Calif.
Breuer Electric Manufacturing Company, 5100 Ravenwood Avenue, Chicago,
Aerial atomizing apparatus:
Hawke Crop Dusting and Spraying Company, Modesto, Calif.
independent Crop Dusting Company, San Francisco, Calif.
Wilson Aerial Spraying Service, Seabrook Farms, Bridgeton, N. J.
Companies Making Autogiros and Helicopters
Pitcairn-Larson Autogiro Corporation, Willow Grove, Pa.
Kellett Autogiro Corporation, Willow Grove, Pa.
Vought-Sikorsky Aircraft, Stratford, Conn.
Platt-LePage Aircraft Company, Eddystone, Pa.
The United States Department of agriculture does not guarantee or en-
dorse the firms listed above or the reliability of their products. In fur-
.ishing this list no -claim is made that it is complete and no discrimination
is intended against any manufacturers not included.
Figure 1.-The type of hand atomizer found to be
useful for applying concentrated sprays.
Figure 2.--A hand-operated compressed-air type of
knapsack sprayer equipped with a 1/4-inch (diameter)
extension rod and a broom with three IS nozzles.'
UNITED STATES DEPARTMENT OF AGRICULTURE
OFFICE OF THE SECRETARY
WASHINGTON, D. C.
UNIVERSITY OF FLORIDA
3 1262 09230 3683
BUREAU ENT & PLANT OUAR
COLLABORATOR IN CHARGE
507 JOHN F SEAGLE BLDG
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