LIBRARY
ATE PL.ANT POAWO
E-508 July 1940
\\ DER\RTMENT
AGRICULTURE
BUREAU OF
ENTOMOLOGY AND
PLANT QUARANTINE
CONCENTRATED SPRAY MIXTURES AND THEIR APPLICATION BY GROUND AND AERIAL
EQUIPMENT AS COMPARED WITH STANDARD SPRAYING AND DUSTING METHODS
By S. F. Potts, Division of Forest Insect Investigations
Contents
Page
Introduction 2
Aerial and ground equipment for applying concentrates 2
Aerial equipment 2
Ground equipment 3
Physical properties of mixtures in relation to equipment 4
Degree of atomization desired 6
Laboratory and field studies of concentrated spray mixtures 6
General procedure followed in preparing mixtures 7
Description of the mixtures 8
Lead arsenate 8
Calcium arsenate 8
Synthetic cryolite 8
Barium fluosilicate 8
Sulfur 8
Nicotine compounds 8
Derris 9
Solidified derris extract 9
Phenothiazine : 9
Copper compounds 9
Oil concentrates 10
Storage tests 10
Wetting and spreading agents 10
Oils in relation to concentrated spray mixtures and plant injury 12
Discussion of field investigations of insecticidal residues 13
Foliage-injury tests 13
Deposit and adherence resulting from the use of dust, ordinary
spray, and concentrated spray 15
Advantages and disadvantages of concentrated spray applications
as compared with dusting and standard spraying methods 19
Summary 20
- 2 -
INTRODUCTION
Standard methods for ground and aerial dusting have not been generally
effective against forest and shade-tree pests; and standard methods for
spraying, while often effective, are limited to relatively small areas,
they require large accessible water supplies and expensive high-pressure
equipment, and they involve high labor costs.
The search for better methods of control resulted in the development
of methods of applying insecticides in the form of highly concentrated spray.
The use of concentrated spray mixtures represents an important step in the
development of methods for treating areas more quickly, cheaply, and ef-
fectively.
These investigations were conducted during the seasons of 1927 to
1938, inclusive, at various points in Massachusetts, New Hampshire, Con-
necticut, and New Jersey. Standard and special ground equipment, and air-
planes and autogiros equipped with devices for disseminating dust and highly
concentrated spray, were used.
Although the information reported herein is mostly concerned with con-
centrated spray, data on dusts and standard spray mixtures are included,
primarily for comparative purposes. The advantages and disadvantages of ap-
plying insecticides in the form of dust, ordinary spray, and concentrated
spray are discussed.
AERIAL AND GROUND EQUIPMENT FOR APPLYING CONCENTRATES
The application of insecticides in concentrated liquid form is a dras-
tic departure from standard spray methods. Distribution is best accomplished
with equipment designed to produce a fine mist by applying air pressure to the
liquid as it is released from the spraying device. Application requires very
little pressure, time, or labor. The ingredients may be mixed in the spray-
ing apparatus or carried to the field already mixed.
Aerial Equipment
Aerial equipment for atomizing spray has consisted mostly of air-
driven rotary or centrifugal devices. These devices have not been entirely
satisfactory since they tend to throw part of the mixtures up on the air-
craft, and they do not always cause fine atomization. Ground 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.i
^Detailed descriptions of aerial apparatus used in the tests are contained in
two unpublished manuscripts that have been offered for publication, and in
the following published paper: Potts, S. F. Spraying woodlands with an
autogiro for control of the gypsy moth. Jour, v-^on. Ent. 32: 381-387,
illus. 1939.
- 3 -
Ground Equipment
Certain types of ready-made equipment now available on the market can
be assembled or modified for use in applying concentrates, although it is
believed that equipment designed especially for this purpose would be much
more efficient. The following types of equipment were tested: A hand atom-
izer, a knapsack sprayer, a wheelbarrow sprayer, a power orchard sprayer, and
a portable, power, paint spray assembly. Two new types of nozzles were used:
One (fig. 1) for applying concentrates with ordinary ground spraying equip-
ment, and the other, an ordinary paint spray gun (fig. 5), for use with
paint spray outfits (fig. 4).
The ordinary hand atomizer, of | to 2 pints' capacity and costing not
over 25 cents, offers inexpensive equipment to any home owner for applying
concentrates quickly to small areas of low-growing plants, trees, and shrubs
(table 1). Although it exerts less than 10 pounds of air pressure, this
simple apparatus deposited 1,000 droplets of lead arsenate spray per squart?
inch of leaf surface, averaging 0.2 microgram of lead arsenate per droplet,
when lead arsenate was used at the rate of 15 pounds per acre. To compare
the rate of coverage of a concentrate applied by a quart-sized hand atomizer
with that of a standard spray mixture applied by a 2-2— gallon knapsack spray-
er, two 0.07-acre plots of low deciduous growth were treated with the two
forms of spray, 1 pound of lead arsenate being used for each plot. One quart
of concentrate and 3/4 hour were required to cover one of the plots by means
of the atomizer, while 3v3 gallons of standard spray mixture and 5 hours were
required when application was made to the other plot of the same size by a
knapsack sprayer. When the aperture (1/32 inch, or 0.8 millimeter) of the
knapsack sprayer nozzle was fully open, the standard spray mixture was de-
livered at the rate of only 12 gallons per hour, and it was necessary to re-
fill the tank with spray 16 times, and to pump air into the tank 48 times,
while delivering the 33 gallons of mixture. On the other hand, it was neces-
sary to fill the atomizer only once.
Knapsack sprayers cover areas rapidly with concentrates, but the atcmi-
zation is not sufficiently fine (fig. 2) for effective control of sucking
insects, although effective control of most leaf-eating insects can be ob-
tained. The disc type of nozzle v/hich accompanies most knapsack sprayers
produces a hollow cone type of spray. A type of nozzle (fig. 1) which pro-
duced a solid cone type of spray was made, and its use resulted in a more
satisfactory application of the spray to specific parts of the plants being
treated. It reduced the spray output by half and considerably improved the
atomization and distribution.
With a wheelbarrow sprayer from 2/3 to 1^ acres of low growth were
treated per day with ordinary spray mixtures, whereas 4 acres were treated
per day with concentrated spray.
High-powered orchard equipment was next tested by applying concentrates
and conventional sprays through standard vermorel and disc nozzles at
300 pounds' nozzle pressure to dense stands of 2,000 to 3,000 Japanese black
pine and red pine trees per acre. The trees were in large nurseries and
- 4
were 5 to 9 feet tall
reduced water hauifng' and lade 't '""'I °'- '"*" "''^ " *'" """"^''^t-
-prayer^ whereas 6 labore-s Lie P""'"^^ '°^ ^ l^""-"^^- t° operate the
applying the conventional sprav' Cove" *° °P"^t« t^i^ °«flt when
rate of 6 acres oer dav »=, ^' /"^^^^^^^ "^t" concentrates was at the
vontional sprl^.'^Elg h't gairoTof *' \ '°. ' ''''' ''' '^^ ^" '''' ^«"-
spray were appUed pef acre , talle 1 ?sf ^ ' °'' f ° ^^'"""^ °^ "^i""^
the concentrate were satlsfirto; } ' ^tomization and distribution of
leaf-eating insects whe„ the It " =.™t™l""g medium-sized to large
=pray wasL coasetToonUollTn u"'"' ■''"'''"^ "''' ^''^- ^"* *'-
lets were aeposited ^'^s^re" nch^rftlifge^^^^lL^o '^TT °"'^ '° ^™^
the nozzle »an to „ove rapidly in order to avoid ove^sprayirg ;'"'''"' '°'
oo^^tr.^/Ts^T-^7^rr^ T' tT ^^"=lr*-V ^- ^PPlyin. con-
gasollne engine an air rn„„ ^ assembly consists of a small
tions and hold the insecticide r/tur^ -all tanK to remove pressure pulsa-
of Which carries air while tl°t'^^^^ -' "' '''*"'"* *■"""' '"■■' ""■■"
=.1 "":, ■ -; ■ £—":"•"—=•"*"-:•:
nozzle apertures for air w?th a c^Ud surface arel Toll rTV'' '"'
great as that of the apertures for the llouid tI f *° ^ '""^^ ^=
ranged from 1 to 2 millimeters (1/25 to 1/^9 ■' • > T'*"^ '^°"' ^i''""
ciduous growth (figs. 3 and 6 wa Yovered If ^he r'at of sT'"' '/" '^-
rie^f ::s/^ ^'"^ - ^'^^ ---- orco;!::n:LiT; - -''i:-
trees u^ triHo 2^1 eTln Te^igW ^^T ^ilVb" ^^^'^^"^ concentrates to
types Of machinery and accessories'for t "es over 20 feeT"^. *\':''''°'= "^*
to apply from 3 to 10 gallons of cr^nZJ t ^° height, in order
ery which now applies SCO to 1 000 »![f P^^^ ^"«. instead of the machin-
New equipment should be designed to f "' °f ^'^"''^''' ""*"« P^"^ ^^''s-
lops, or to drive it into the ees f o™ fceT Z'u'^ "''''' *°^^ ^'''^ t^^«
Such an outfit should be lilht '^ndV.Z '"^^^ " ""^•■' ^^ '°' "^^^ts.
pressure for alomrzatron 'w ho'e a«rn:: T f T." ^'^""'^ ^^^^ "*"«
The outfit should require very ntUe latr fo '- '"'" '"' ''^"■
areas rapidly with a minimum of cost °P«''='tion and should cover
Physical Properties of Mixtures in Relation to Equipment
equipmelrne''etitr'ri'';arplL':t":'"7? ''T' ^"""^""^ ''^ '"^' ^
they contain corase grarmlar ma?p.,»; Z ■"^>=tures are very viscous or if
ordinary mist nozzles.' rTereforfrnorder't " ' "? \'°' '''''' ^''^""^'^
.esirable either to strain the mixture r^o It/reTt ^ttK^-tfe ^^rryl^"
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device by means of a power-driven blower, or by air pressure as shown in
figure 6. Most of the mixtures applied flowed nearly as freely through small
spray hose, attachments, nozzles, and viscosimeters (fig. 7) as ordinary spray
concentrations. Such a mixture is called a fluid mixture.
In some aircraft the available space for an insecticide container is
very limited. This problem has been partially solved by applying the in-
secticide in the form of a liquid instead of as a dust, since a given weight
of material occupies less space as a liquid than as a dust. Dusts usually
weigh from 15 to 30 pounds per cubic foot, while liquids weigh from 56 pounds
per cubic foot, in the case of light oils, to 113 pounds per cubic foot, in
the case of the heaviest mixtures. A 5-cubic-foot {37-gallon) tank holds 450
pounds of lead arsenate concentrate, of which 210 pounds is lead arsenate,
whereas a dust hopper of the same volume holds only 100 pounds of the same
brand of uncoated dust.
Degree of Atomization Desired
Finely atomized droplets cause less foliage injury and are more ef-
fective as a stomach poison against small insects or as a contact poison
against sucking insects than coarsely atomized spray. Finely atomized spray
drifts more than coarse spray, but not nearly so much as dusts. A small
droplet is equal in volume and weight to a number of dust particles. For a
given bulk the liquids were from 2 to 7 times as heavy as dusts. A deposit
of 1,200 oil droplets per square inch was sufficient to give complete cover-
age, since the droplets coalesced and the oil spread over the entire surface.
When applied as a stomach poison for most leaf-eating insects, 300 droplets
per square inch was found to be sufficient. For some of the snout beetles
and extremely small chewing insects a deposit of as many as 1,000 droplets
per square inch was required, whereas for small sucking insects a deposit of
at least 1,200 droplets per square inch was essential. Microscopic counts of
droplets of finely atomized sprays on leaves showed that an average deposit
of 5,000 to 7,500 droplets per square inch is attainable. Thinning and
v/etting agents considerably increased the atomization of all oils, the in-
crease in number of droplets deposited per given area being from 5- to
10-fold in the case of heavy oils,
LABORATORY AND FIELD STUDIES OF CONCENTRATED SPRAY MIXTURES
In the laboratory special attention was given to methods of combining
ingredients necessary to make the most fluid, concentrated, stable, eco-
nomical, and effective mixture . 2 The ingredients were mixed in lots of
i to 1 gallon by means of an electric mixer.
20ther methods of preparing concentrated spray mixtures are discussed
in two unpublished manuscripts that have been offered for publication, and in
the following published paper: Potts, S. F. Concentrated mixtures for
aerial spraying. Jour. Econ. Ent. 32: (4): 576-580, 1939.
General Procedure Followed in Preparing Mixtures
Except in the case of undiluted oils, the mixtures contained an in-
secticide added, in the form of powder, extract, or oil, to an oil or water
carrier, plus one or more of the following: (1) A wetting or spreading
agent, (2) an adhesive such as casein or an adhesive oil, or (3) certain ma-
terials such as glycerine or diethylene glycol to absorb atmospheric moisture
and resist too rapid drying of the mixtures. Mixtures containing water as a
carrier were quick-breaking emulsions of the oil-in-water type, 3 to which
water can be added to make a,ny dilution desired.
When an insecticide and water were mixed with oil and such wetting
agents as sodium lauryl sulfate or aresket, the wetting agent was dissolved
in a volume of water equal to the volume of oil to be used. This solution
was poured slowly into the oil while it v/as stirred or agitated until a good
emulsion resulted. The insecticide vms then added and the mixture agi-
tated.
When the insecticide and water were to be added to oil and oleic acid
plus triethanolamine N (C2H40H)3; the last three ingredients were mixed to-
gether first. Then an equal volume or weight of water v;as added slowly, and
stirred until a creamy emulsion resulted. Then the remainder of the water was
stirred in and the insecticide added.
When either casein or casein glue (casco) v/as used as a sticker, tri-
ethanolamine was dissolved in the total amount of water, the casein product
was added, and the mixture was stirred until a good emulsion resulted. The
insecticide was then added. In water, casein glue dissolved slowly, but ca-
sein (slightly acid) was insoluble. Therefore triethanolamine (pH 10 to ]1
in water) was used to dissolve casein in v/ater, at the rate of 0.05 to 0.15
part of triethanolamine per 1 part (by weight) of casein.
When casein glue and triethanolamine were used as a spreader, the
casein glue and organic amine v/ere dissolved in 3 parts of v/ater. Oil was
added, and the mixture stirred until a good emulsion resulted. The remaining
water was then added and the insecticide stirred in.
When sulfonated castor (turkey red) oil was used as a wetting agent or
emulsifier, the turkey red oil and other oil to be added were mixed and
stirred in an equal volume of water. Stirring was continued until a good
emulsion resulted. The remaining water was added and the insecticide stirred
in. More turkey red oil was required than alkylphenylbenzenesulfonic acid,
but it was cheaper and less likely to decompose certain insecticides.
=A different mixing method sometimes used in the field for powdered
insecticides consisted of adding a wetting agent to the water, and then add-
ing the insecticide and oil, in the order given, while the mixture was being
agitated.
- 8 -
The general procedure outlined above was followed in preparing the
mixtures described below. These preparations represented the most concen-
trated fluid mixtures obtained with the materials and methods used.
Description of the Mixtures
L ead arsenate . — All lead arsenate mixtures contained some water, and
usually an adhesive oil and a v.'etting agent (fig. 7) were added. All lead
arsenate used was the ordinary acid form. Without a wetting agent, 2 to 4
pounds of water were required per pound of lead arsenate. With all 14 brands
tested, the use of suitable wetting agents made possible the preparation of
fluid mixtures containing 1.25 pounds of water per pound of lead arsenate.
A common mixture contained 1.25 pounds of water, 0.02 to 0.04 pound of wet-
ting agent (as sodium lauryl sulfate), and 0.2 pound of corn oil or soybean
oil per pound of lead arsenate. A gallon of this mixture weighed 11.33
pounds and contained 4.25 pounds of lead arsenate. Three and one-half gal-
lons of this mixture were required for applying 15 pounds of lead arsenate
per acre. In using colloidal lead arsenate paste, 3 pounds of water were
required per pound of insecticide to produce a fluid mixture.
A laboratory-prepared lead arsenate, which v/as not so fine as com-
mercial brands, required only 0.88 pound of water per pound of arsenical in
making a fluid mixture. The final mixture, including wetting agent and ad-
hesive, contained 51 percent of lead arsenate by weight. Particle size and
shape had an important bearing on the quantity of water necessary to make a
fluid mixture.
Calcium arsenate. — The most concentrated fluid mixtures prepared con-
tained 0.03 pound of triethanolamine and 1.5 pounds of water per pound of
calcium arsenate. All calcium arsenate used was the ordinary comm-ercial form.
Syntheti c cryolite . — The most concentrated fluid mixtures prepared
contained 1.2 pounds of water, 0.2 pound of an adhesive oil, and 0.02 pound
of triethanolamine per pound of pure cryolite. Some brands of cryolite con-
taining a dye and 17 to 25 percent inert ingredients, required 2.5 pounds of
water per pound of powder to make a fluid mixture.
Barium fluosilica te . — The most concentrated fluid suspension contain-
ing an adhesive consisted of 0.8 pound of water, 0.2 pound of oil, and 0.02
pound of alkylphenylbenzenesulfonic acid (aresket) per pound of barium fluo-
silicate.
Sulfur. — One pound of sulfur or of sulfur-bentonite clay was used in
mixtures containing 1.25 pounds of water, and 0.2 pound of soluble casein
glue, high-fat-content soybean flour, or paraffin oil. The addition of tri-
ethanolamine or aresket increased the fluidity of the mixtures.
N icot ine comp oun ds. — Highly concentrated mixtures were prepared con-
taining nicotine sulfate or free nicotine, either in oil or in oil and water.
A mixture frequently used contained 6 pints of water and 2 pints of oil per
- 9 -
pint of nicotine solution; it was applied at the rate of 2 to 4 gallons per
acre.-* In nicotine sulfate mixtures a dissolved ncnalkaline emulsifying
agent should be added to the water in quantities sufficient to iiake a good
suspension. No emulsifier or spreader is needed for free nicotine mixtures.
When nicotine was used as a stomach poison, semidrying oils were superior to
drying and nondrying oils as carriers. When only contact action was desired,
a nondrying plant or mineral oil was superior.
The most concentrated fluid mixture of dual-fixed nicotine (containing
7.5 percent of nicotine, of which part is soluble and part is insoluble) con-
sisted of 1 pound of dual-fixed nicotine, 2 pounds of water, 0.4 pound of
oil, and 0.02 pound of aresket, making a nicotine content of 2.2 percent in
the final mixture.
The most concentrated fluid quebracho-fixed nicotine mixture applied
contained 1 pound of quebracho-fixed nicotine, 0.67 pound of water, and 0.3
pound of oil. It is interesting to note that oil slightly increases the
fluidity of this mixture, since the opposite result was expected. It is
better to add the fixed nicotine to the water than to reverse the procedure.
The oil is added last.
Derris. — Derris and cube are easily wetted with aresket. The most
concentrated mixture prepared contained 5 pounds of water, 0.04 pound of
this wetting agent, and 0.3 pound of semidrying oil per pound of derris or
cube.
So lidified de rris extract . — The most concentrated mixture prepared
contained 1 pound of derris extract (containing 25 percent of rotencne),
2 pounds of acetone (or preferably some noninflammable solvent when applied
by aircraft), and 1 pound of oil. This mixture is 577 times as concentrated
in rotenone content as a mixture of 3 pounds of derris (containing 4 percent
of rotenone) per 100 gallons (834 pounds) water. The contact effect of der-
ris and derris extract was improved by extracting in certain plant oils,
such as cottonseed oil, cashew nut oil, or peanut oil, and then diluting with
white mineral oil of 50 seconds Saybolt viscosity.
Phenothiaz ine . — Before being added to the mixture, the phenothiazine
should be passed through a 12- to 20-raesh screen to break up the lumps. The
most concentrated mixture prepared contained 1.2 pounds of water and 0.04
pound of aresket per pound of phenothiazine. This mixture possessed prac-
tically no adhesiveness, but the addition of casein glue and soybean flour
greatly increased adhesion without causing plant injury. The addition of oil
caused foliage injury.
C opp e r comp o und s. — Bordeaux mixture concentrate contained from 6 to 8
pounds of water per pound of copper sulfate in the mixture, when water was
-♦The question is often asked as to whether talc or dye material should
be added to certain concentrates to render the deposit more perceptible on
the foliage. Tests made thus far indicate that this is not necessary.
-lo-
used as the carrier. When oil was used as the carrier for dehydrated copper
sulfate-hydrated lime concentrates, from 5 to 8 pounds of volatile (45
seconds Saybolt viscosity) mineral oil containing 0.05 to 0.2 pound of suit-
able oil-soluble wetting agent (such as Vatsol O.T. or Grasselli IN2503)
plus 0.3 pound of drying oil was used per pound of copper sulfate.
When lime was omitted, 3 pounds of water was used per pound of copper
compound in concentrates containing copper in the form of basic copper sul-
fate, copper ammonium silicate, copper oxide, or copper hydroxide. Since all
mixtures prepared at this concentration were very fluid, it is likely that
the proportion of water in the mixtures can be considerably reduced. As these
unlirced copper compounds v/ere applied late in the season it was not deter-
mined whether they are safe on tender foliage.
Q.i.1 cgncentrateg. — Unemulsified oils as well as oil emulsions and
miscible oils can be applied as contact insecticides. Thick oils do not
atomize or spread so well as thin oils. Therefore, when the viscosity was
greater +han 100 seconds Saybolt, from 10 to 50 percent (by volume) of a
volatile "thinner" or solvent, such as acetone, refined kerosene, or petro-
leum ether, was often added to the oil. The "thinner" evaporated quickly and
therefore caused no plant injury, In some cases from 20 to 40 percent (by
volume) of v/ater was added to miscible oils and oil emulsions to increase
the rate of flow and atomization.
Storage Tests
Field tests of numerous concentrated spray mixtures that had been
held in storage for 3 years show that m.nxtures containing arsenicals and many
other insecticides can be stored safely and sold on the market ready for use
vvithout further mixing or dilution. Some organic insecticides, as derris,
could not be stored for long periods of time owing to the adverse effect of
bacteria and fungi. To prevent the development of bacteria and fungi, small
quantities of coal-tar dyes, sodium benzoate, or copper sulfate were added to
these mixtures. Most of these preservatives stopped the action of the organ-
isms, but the best kind and quantity of preservative to use is still not def-
initely known. Light, air, and high temperature tend to decompose certain
organic materials, as derris. Containers should therefore exclude light, and
should be airtight and filled to the top. They should then be stored in a
cool place.
Wetting and Spreading Agents s
Wetting or spreading agents and oils were among the most common and
important materials used in concentrated spray mixtures and were given care-
ful consideration with respect to their effects on the plant, insecticide,
and cost of treatment.
sSome brands of insecticides were colored with an organic pigment
(beta naphthol and tobias acid, derived from coal tar) which reduced the
sfficiency of sodium lauryl sulfate but did not affect the use of such wet-
ting agents as turkey red oil and triethanolamine oleate.
- 11 -
In order to learn the phytotoxicity of v/etting or spreading agents
alone, 5-percent concentrations of areskap, ultrawet, aresket, aresklene,
triethanolamine, sodium lauryl sulfate, or triethanolamine oleate were ap-
plied to wild black cherry. Although rain on the third day after treatment
removed all the spreader, serious injury was caused by them in the descending
order as listed above. At this concentration, casein, casein glue, soybean
flour, and sulfonated castor oil caused no injury. At concentrations com-
monly used in applying standard sprays, oil emulsions, or miscible oils, a
number of the 27 wetting and emulsifying agents investigated contained suf-
ficient alkali or acids to cause at least slight injury to tender plants.
Insecticidal decomposition, solubility, and foliage injury were re-
duced to a minimum by using concentrated spray mixtures, since only 4 to 14
percent as much wetting agent and 0.4 to 2 percent as much water was applied
per acre as is used in applying ordinary spray concentrations. Often the
wetting agent can be omitted entirely, as in the application of undiluted
oils and free nicotine.
Leaf analyses showed that when most spreaders were used in standard
spray mixtures the initial deposit was only about half as great as when
they were omitted. Furthermore, they increased the loss of deposit by
rain from 25 to 40 percent. In concentrated spray applications there was
no reduction of initial deposit by run-off and drippage, and wetting agents
caused no great loss of deposit by rain.
Wet foliage increased the spreading of concentrated spray deposits and
made possible the use of less spreader than when the foliage was dry. Also,
when added to concentrated spray mixtures, compounds which absorb moisture
from the air increased the spreading of the deposit.
The cost of wetting agents is reduced to a minimum when applied in con-
centrated spray. For example, the application of 18 pounds of insecticide in
a conventional spray, consisting of 3 pounds of insecticide per 100 gallons
of water, required 6 pounds or $1.50 worth of wetting agent, but when ap-
plied as a concentrate only 18 cents worth of wetting agent was required.
Suitable wetting agents should reduce the amount of water or carrier
required to make a fluid concentrate, improve the physical properties and
spreading of the mixture, and facilitate quicker mixing. They should not be
expensive, cause excess foaming, reduce adherence of deposits, or cause
foliage injury.
- 12 -
Oils In Relation to Concentrated Spray Mixtures and Plant Injury
Oils serve one or more purposes in concentrated spray mixtures, de-
pending on the kind of oil and the end sought. They may serve as a carrier,
adhesive, spreading and penetrating agent, or solvent for oil-soluble in-
secticides, or to protect tender foliage by coating the insecticidal par-
ticles. They may prevent too rapid drying of the insecticidal mixture, re-
duce volatilization of certain insecticides, and retard decomposition of the
insecticide by weathering. Oil can be used as a carrier in place of water
for free nicotine, pyrethrum extract, rotenone, and derris extract. How-
ever, when most powdered insecticides, oils, oil emulsions, and miscible oils
are being applied, an oil should not be used as the carrier, owing to the
large volume of oil carrier required per given weight of insecticide, its
cost, and the danger to tender plants in the case of a nonvolatile, non-
drying oil.
Unemulsified drying and semidrying oils, as linseed, fish, corn, soy-
bean, and cottonseed oil, were good adhesives and safe on tender foliage.
They arrested the decomposition or volatilization of such organic insecti-
cides as free nicotine, derris, and derris extract. Drying oils form a pro-
tective dry film or coating around the insecticide particles. This film
apparently prevents dew and rain water from attacking or dissolving the in-
secticide and at the same time protects the plant against direct contact with
the insecticide. The drying oil remains with the insecticide and spreads
less than a nondrying oil. Nondrying oils and volatile oils are poor adhe-
sives, and their use often makes frequent retreatments necessary.
When finely atomized concentrates containing water and drying oil were
applied at temperatures of 73° F. or higher, accom.panied by relative humidi-
ties of 50 percent or less, too rapid drying of the oil often occurred, caus-
ing the formation of hard, dry pellets which rolled off or blew off the
foliage. This condition was corrected either by substituting a semidrying
oil (such as corn oil. soybean oil, or cottonseed oil) for the drying oil,
or by mixing 1 part of nondrying oil with 2 to 5 parts of drying oil. Peanut
oil, motor oil, or a paraffin oil costing 15 cents per gallon have been added
to the drying oil for this purpose. Large proportions of either non-
drying oils or emulsifying agents tend to reduce the adhesive value of the
drying oil
- 13 -
In cases where it ir.ay be undesirable for the insecticide to adhere
firmly to the plant for long periods of time, there are several alternatives,
such as (1) omitting or greatly reducing the quantity of adhesive oil in the
mixture, and (2) substituting for the adhesive oil a volatile or nondrying
oil, or glycerine, diethylene glycol, or Yumidol (a nonvolatile, hexahydric
alcohol), which absorb atmospheric moisture and cause the insecticide
to be picked up on the feet and bodies of insects crawling over sprayed
surfaces.
DISCUSSION OF FIELD INVESTIGATIONS OF INSECTICIDAL RESIDUES
Although numerous compounds appear to be very toxic to insects in the
laboratory, only a small percentage of these are at present of practical
value in the field. This may be due to a number of reasons, such as failure
to obtain a sufficient insecticidal deposit on plant parts or insects; poor
adherence; decomposition after exposure on the leaves in moisture which
usually contains dissolved carbon dioxide and plant acid from the leaves;
weathering; and injury to foliage.
In the field special attention was given to the deposit, atomization,
spreading, drift, distribution, adherence, and phytotoxicity . Concentrates
(table 3), prepared in the manner just described, were applied to approxi-
mately 3006 plots ranging in size from 0.02 to 0.07 acre (900 to 3,000
square feet), of uniformly stocked deciduous sprout growth 4 to 8 feet tall.
For comparative purposes the same quantity of insecticidal agent was applied
per plot when concentrates were used as when conventional sprays v/ere used.
Ordinary spray concentrations (table 2) were applied with a 'knapsack sprayer.
Dust mixtures were applied with a bellows-type knapsack duster to plots of
0.1 to 0.4 acre.
The text which follows is a discussion of the degree of foliage in-
jury, the degree of adherence, and the quantitative measurement of deposits
resulting from the use of various insecticides and insecticidal combinations,
applied from the ground or from the air in the form of dust, ordinary spray
concentration, or concentrated spray.
Foliage Injury Tests
Tables 2 and 3 show the injury caused by certain insecticidal prep-
arations to foliage of the most susceptible woodland tree (wild black
cherry). Table 2 is concerned with ordinary spray concentrations, while
table 3 is concerned with concentrated spray mixtures. Both tables give the
spray ingredients used, the degree of concentration, adherence, solubility,
and the degree of plant injury which followed.
eLack of space does not permit data on hundreds of the concentrated
spray, ordinary spray, and dust mixtures tested to be included in the tables
and the discussion which follows.
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- 15
When bordeaux mixture wac added to arsenicals, the injury was reduced.
The copperas-lJme mixture (mixture 9, table 2, and mixture 21, table 3)
greatly reduced the injury caused by lead arsenate. The addition of spread-
ers in most cases tended to reduce the deposit and adherence and increase the
injury, particularly in the case of ordinary spray concentrations.
When lead arsenate (mixture 3, table 2) was prepared in a standard
spray concentration. 650 milligram.s of AsaOs were soluble per pound of lead
arsenate in the mixture, while only 55 milligrams were so:luble in the concen-
trate (mixture 1, table 3). When calcium arsenate (mixture 1, table 2) was
applied in a standard spray concentration, 1,385 milligrams of As 2O s were
soluble per pound of calcium arsenate, while only 4 milligrams were soluble
in the concentrate (mixture 2, table 3). When calcium arsenate was applied
in a hydrated lime-soybean flour-casein glue mixture (mixture 19. table 3)
there was practically no solubility or injury. The concentrated spray
mixtures applied caused much less injury to wild black cherry than the
ordinary spray concentrations, as found by comparing the items -in the last
column of table 2 with those of table 3.
By using concentrated sprays (table 3) it was possible (1) to apply,
mixtures which contained less water-soluble insecticide (column 5, table 3)
because of the small amount of water and wetting agent present, and (2) to
coat effectively the particles or residue with casein or drying and semi-
drying oils, thus protecting both insecticide and plant. Therefore, the use
of concentrated sprays makes it possible to avoid or greatly reduce foliage
injury caused by many of the more common insecticides, such as the arsenic-
als, cryolite (mixture 22), or barium fluosilicate (mixture 23). Mixtures
1 and 2 contained no adhesives, spreaders, or "safeners." They caused more
injury and had poorer adherence than mixtures 11, 14, 19, 21, 22, and 23,
which contained adhesives, spreaders, or "safeners."
Nondrying mineral oils were slightly m.ore toxic to plants than non-
drying plant oils Drying oils, as fish oil, linseed oil, and tung oil, and
semidrying plant oils, as cottonseed oil, soybean oil, and corn oil, were
relatively non-toxic to plants, even when heavy applications of the undiluted
oil were made.
Dust deposits caused less injury than ordinary spray deposits, since
fl) the quantity of initial dust deposit per given leaf area was less than
the initial spray deposit following the application of a given quantity of
insecticide and (2) the loss of dust deposit caused by wind and rain was far
greater than the loss of spray deposit. Therefore the plant was exposed to
les:s of the phytotoxic agent over any given period of time when the insecti-
cide was applied as a dust.
Deposit and Adherence Resulting from the Use of Dust,
Ordinary Spray, and Concentrated Spray
Twenty-five concentrated spray mixtures, most of v/hich gave uniformly
,iigh adherence, are shown in table 3. Figure 8 shows additional data on the
deposit and adherence resulting when certain insecticides were applied as
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- 18 -
dust, as ordinary spray, and as concentrated spray to relatively large areas.
About 1,350 acres of v/oodland were treated in the experiments represented by
figure 8. In this figure the plots represented by columns 3 and 4 were sprayed
from the ground, while those represented by columns 1, 2, and 5 were
treated from the air. The growth ranged from 35 to 90 feet in height. The
first 4 columns represent plots exposed to between 0.86 and 1.14 inches of
rain, or an average of 1 inch. The concentrated spray (last column) was ex-
posed to an average of 5.7 inches of rain.
When ordinary spray concentrations of lead arsenate were applied there
was considerable variation in the deposit on different types of foliage,
whereas the quantity and distribution of concentrated spray deposit were
equal on all surfaces. The ordinary spray deposit on foliage of trembling
aspen and gray birch, and on the growing leaves and needles and waxy buds of
pine was only 36 to 73 percent of that on mature oak and maple foliage.
Forty-two percent of the standard spray mixture fell to the ground
(columns 3 and 4, figure 8) when sprayed on oak trees 40 feet in height, ^
and when sprayed on trees 70 to 90 feet in height the loss was 65 percent.
Part of the ground deposit of ordinary spray was due to drippage and "run-
off." The first inch of rain removed 68 percent of the initial leaf deposit
when no adhesive was added and 35 percent when fish oil was added.
When lead arsenate was applied in a concentrated spray mixture only 10
to 18 percent of the insecticide fell to the ground at the time of applica-
tion and only 12 percent of the leaf deposit was removed by 5.7 inches of
rain. In the region covered by the investigations there is an average of
3.4 inches of rain per month during the summer, with 10 to 12 days per month
on which rain falls, averaging 0.3 to 0.34 inch every third day. The amount
and frequency of rainfall are important factors in influencing adherence of
dusts and standard spray mixtures.
When applied in standard spray concentrations, lead arsenate adhered
better than all other common insecticides except lime-sulfur and bordeaux
mixture. Lead arsenate dust adhered much better than all other uncoated in-
secticidal dusts.
Figure 8 shows great differences in the final deposits of dusts, or-
dinary sprays, and concentrated sprays. The unshaded portion of column 1
represents the percentage of total dust applied which d id not s e ttle on th e
foliage plus the percentage which was remo ved by _ w ind averaging 5 miles per
hour. The unshaded portion of column 2 represents only that portion of the
dust applied which, in the absence of air movement, did not settle on the
'The method used in determining the quantity and percentage of total
insecticide applied which fell to the ground, or was deposited on the foli-
age, is fully described in the following paper: Potts, S. F. A method for
determining the quantity of foliage per acre of woodland. Jour. Forestry
37 (12): 922-923. 1939.
- 19 -
foliage. The two kinds of insecticidal loss included in the unshaded portion
of column 1 are much greater than the loss caused by rain. A very striking
contrast is seen by comparing dust (columns 1 and 2) with concentrated spray
(column 5) . The initial concentrated spray deposit was 2.27 and 6.8 tines as
great as the dust deposits. After 10 days' v/eathering the concentrated spray
deposit averaged 7 to 17.5 times as great as the dust deposits. When a given
quantity of lead arsenate was applied under favorable dusting conditions from
the ground as a concentrated spray and as a dust, the deposit per unit of
area after an average of 10 days' exposure was 5 times as great on areas
treated with concentrated spray as on those treated with dust. After an
average of 10 days' exposure, an average of 15 percent of the dust applied
was on the foliage as compared with 75 percent in the case of concentrated
spray. Loss of the dust deposit was greatest at the tree tops.
Close examination of the action of dust particles in motion around the
leaves showed that most particles passed over the leaves like smoke without
adhering. This was partly due to the difference between air temperature and
leaf temperature, v/hich causes air currents at the leaf surface. This con-
dition was less pronounced on conifers than on broad-leaved trees. These
facts dem.onstrate the marked superiority of concentrated sprays over dusts,
whether applied from the ground or from the air.
Advantages and Disadvantages of Concentrated Spray Applications
as Compared with Dusting and Standard Spraying Iilethods
In some cases aerial dusting has an advantage over spraying vn.th con-
centrates in that more insecticide can be carried, owing to the absence of
water. This is not always true, hov/ever. For example, several times as much
of the toxic principle can be carried in a given weight or volume of liquid
concentrates, in the form of derris extract, pyrethrura extract, nicotine
solution, etc., as can be carried in a dust. For ground dusting from 4 to 9
parts of carrier are usually used per part of insecticide. Therefore, in
order to apply 20 pounds of insecticide per acre it is necessary to use
from 100 to 200 pounds of dust. In general, during the period of actual
operation, areas may be covered more rapidly by dusting than by spraying with
concentrates, but owing to unfavorable wind conditions the number of hours
available for dusting is only about one-fourth as great as for spraying with
concentrates.
As compared with dusting, spraying with concentrates gives a heavier
initial deposit (without loss of initial deposit by wind), better adherence,
and less drift, requires less tank or hopper space, can be accomplished over
more rugged terrain, and is more effective.
Many powdered insecticides which cannot be applied as contact dusts
can be r-pplied as contact sprays in the form of concentrated spray mixtures.
Furthermore, liquid insecticides, such as bordeaux mixture, lime-sulfur, un-
diluted oils, oil emulsions and miscible oils, derris extract, nicotine solu-
tion, and nicotine tannate, may be applied as concentrates, whereas they can-
not be applied effectively or at all as dusts. Sulfur and such organic dusts
as derris and pyrethrum cause serious fire hazards in aerial dusting work,
but this hazard is removed when these materials are applied as concentrated
sprays.
- 20 -
The standard spraying method has one advantage over both dusting and
spraying with concentrates in that often the tendency of excess spray to run
off the foliage serves as an automatic check against excessive deposits. On
the other hand, experience gained thus far indicates that, as compared with
the standard spray method, the concentrated spray method covers areas more
quickly and requires less insecticide, labor, equipment, and expense. It
gives a heavier deposit, better adherence, and less foliage injury. Instan-
ces will doubtless occur, however, where standard spraying and dusting methods
will be preferable to the concentrated spray method, and a final appraisal
of the different methods is withheld until the entomological, chemical, and
mechanical phases of the latter are fully developed.
SUMMARY
Although a new kind of equipment is needed for applying concentrated
sprays, certain types of ready-made devices, such as hand atomizers, paint
spray outfits, and conventional sprayers equipped with special nozzles, can
be used at present or m.odified and assembled for use. Experiments which
suggest the kind of apparatus and degree of atomization desired have been
conducted. Tests of equipment indicate that, as compared with the standard
spray method, the concentrated .spray method covers areas more quickly and
requires less equipment, labor, insecticide, and expense.
A detailed .study of dusts, ordinary sprays, concentrated spray mix-
tures, and residues was made in the laboratory and field, and methods of
preparing concentrated spray mixtures of many of the more important insecti-
cides and fungicides were developed.
The addition of v/eak bordeaux mixture to either concentrated spray or
ordinary spray concentrations containing lead arsenate or calcium arsenate
considerably reduced the injury to susceptible plants. A copperas-lime mix-
ture (4 parts of FeSOi.THzO to 1 part of hydrated lime) practically elimin-
ated foliage injury caused by lead arsenate. Concentrated spray mixtures
greatly reduced injury, since they contained very little or no wetting agent
and water, and the residue was coated with certain oils or other adhesives.
This protected l^oth the residue and the plant, so that calcium arsenate,
cryolite, certain oils, and other materials were less phytotoxic.
When lead arsenate was applied in standard spray concentrations to
woodland trees 40 to 90 feet tall, from 42 to 65 percent of the insecti-
cide fell to the ground. The first inch of rain removed 68 percent of the
leaf deposit if no adhesive was used, or 35 percent if fish oil was added.
When applied in ordinary spray mixtures, lead arsenate adhered better than
all other com.mon insecticides except lime-sulfur and bordeaux mixture.
Concentrated spray mixtures can be made to adhere better than ordinary
spray concentrations. A heavier initial deposit of insecticide was obtained
per unit of area, owing to the absence of drippage and run-off. The use of
drying oils or semidrying plant oils in concentrated sprays greatly increased
the adherence of the spray residues, so that a considerable portion of the
initial deposit was present on the foliage after 3 months of weathering, in-
cluding 16 to 18 inches of rain.
21 -
Concentrated spray mixtures were superior to dusts. They gave a much
heavier deposit, with better adherence, less drift, and no loss by wind, re-
quired less insecticide, and could be applied during periods of the day when
there was too much wind for dusting. When lead arsenate dust was applied
from the air, from 4 to 10 percent of the insecticide applied was present on
the foliage after an average of 10 days of weathering. When applied from the
ground under favorable dusting conditions, an average of 15 percent of the
insecticide applied was on the foliage after 10 days of weathering, as com-
pared with approximately 75 percent in the case of concentrated spray. Lead
arsenate dust adhered better than all other common insecticidal dusts. Drift,
air currents around the leaves, wind after treatment, and rain caused low
dust deposits.
When various organic insecticides, such as derris, derris extract, and
nicotine, were applied in concentrated form it was possible to ccat the
insecticidal agent sufficiently to reduce greatly the deterioration caused
by light, air, and moisture.
Excellent coverage and adherence on wet foliage resulted from con-
centrated sprays applied either before, during, or following rain.
Tests indicate that many insecticides may be stored safely as con-
centrated spray mixtures for long periods of time. This should permit the
marketing and use of ready-made mixtures, and thus avoid the difficulties
often encountered by growers in weighing, measuring, and mixing insecticidal
materials.
Figure 1. — A, Nozzle for use in applying concentrated spray
with ordinary ground equipment. It consists of a brass
shell with a hole I/50 to I/I6 inch, or 0.5 to 1.6 milli-
meters, in the smaller end, a hollow screw with a hole near
the center, and a large brass cap for holding the shell and
screw in place,
B, Large brass cap containing the shell and screw which can
be screwed to ordinary extension rods. The short rod shown
has the nozzle coupling attached at an angle of A5° for treat-
ing leading shoots of pine trees with a solid cone type of
spray.
UBRARY
OTATE PLANT BOARO
Figure 2, — Rhododendron leaves sprayed with concentrated
spray mixtiires applied by a knapsack sprayer. The spray
deposit was exposed to 2 years of weathering, and during
this time 80 inches of rain fell.
Figure 3« — Leaves collected, after A. 8 inches of rain, from
trees sprayed with a concentrated spray mixture applied hy
a paint spray gun outfit.
iiiiiMiiiiiail
Figure U» — ^Paint spray outfit used for applying concentre tes,
Figure 5. — A paint spray
girn nozzle used with
the apparatus of
figure U*
Figure 6. — Low-growing trees
being treated with concen-
trates, applied by a paint
spray gun outfit.
SAYBOLT VISCOSITY AT 72 F.
L.A.= LEAD ARSENATE CbRAND A.) W.- WATER
SPREADER- ALKYLPHENYBENZENESULPHONIC ACID
80-
.01 .02 .03 .04 .05 .06 .07
POUNDS OF SPREADER PER POUND OF L.A.
Figure 7. — Viscosity chart, showing the rate of flow of
lead arsenate concentrates through an aperture of 1.76
millimeters (0.07 inch) at the usual field spraying
temperature .
O.S.= ORDINARY SPRAY CONCENTRATION OF 3 POUNDS INSECTICIDE TO 100 GALLONS OF WATER.
C.S.= CONCENTRATED SPRAY MIXTURE.
L.A.= LEAD ARSENATE.
W.= WIND 2 TO 10 MILES PER HOUR.
C.= NO WIND BEFORE FIRST LEAF COLLECTION
F.a= FISH OIL.
Q = PERCENTAGE OF TOTAL MATERIAL DEPOSITED ON GROUND.
^ = PERCENTAGE OF TOTAL MATERIAL REMOVED BY I INCH OF RAIN.
m = PERCENTAGE OF TOTAL MATERIAL REMAINING AFTER I INCH OF RAIN.
COLUMN NO.
12 3 4 5
100
90
O
u
3 80
Q-
<
TO-
GO
50
40
,66
f^;
42
137.71
©
I LA SPRAY n
L.A. DUST I I L.A. SPRAY + F.0.
NO STICKER
LA. - F.O.
•WATER 1-4-3
10
20
30
40
50
60
- 80
90
C.
O.S.
O.S
C.S.
Figure 8. — Comparison of the influence of rain, wind, and
other physical factors on the loss of insecticide TJhen
applied as a dust, an ordinary spray concentration, and
a concentrated spray mixture.
UNIVERSITY OF FLORIDA
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3 1262 09224 7609