Unit ad States Department of Agriculture
Agricultural Research Administrat ion
Beau of Xxtonclogy r-nd Plant qu-rantine
F~UM4WIQN OF DtYr SPRAYS AND DUBT$.Y
D.Chishol.m, Division of Insecticide Investiat ions
connctio with the intensive studies of' the insecticidal proper4,osof VT 1-tichloro-2, 2-bis(p-chloropheny1) etharne), which have been
Ati46 y lan wokes, methods of formulation of sprays and dusts have
rocejd mu t atnion. Such experim-,ents have been conducted largely
laboatoy ad small field-plot conditions.
'Oheicaly ureDDTI m,-elts at 108.50-1090C. :wvo grades of comercial
todut ae aailble, one known as "technical DITTI1 specified to have a e in pont ot ower then 880, and "DIE, purified,"~ specified to have
m~ltng oin ofat least 1030. The former has found use in louse
owder, ~ moqiolrvicide, -and in general ag ,ricultur). axperimentatin;
Ue a r i inened for use in aerosol bombs.
%).DT~ha benused in water susppnsions, solutions, emulsions, dusts,
The last-namred have been. discussed elsewhere, but the
atio ofthe other types of mixtures is pTEsnnted in this paper.
W ATnO SUSPM SIONIT
Watr uspensions are divided into three classes those resulting
qM te mxin of finely ground DDT (ground. either dry or wet) with water,
resltig from the dilution with xater of a solution of DDT in a wate-misibl organic solvent, and those obtained by mixing diluents or coated with DD~T with water.
I/Ths pperwas reud at the- joint meetings of the American Associ"x~~~~ sto fEooi rtonolo~ists and the ':ntomologi-cal Society of America
ett, NowYor Y. Dec. 13-14, 1944. lNuch of the information presclnted .11"Ve otaiedthr~ough corrosponder.nce with State ezpcrineat station invest~gaors nd for sveral Divisions of this Bureau.
Since technical DDr softens considrably below 880C., and is not free flowing, it is necessary, when dry-grinding this compound, to mix it with a diluent such as calcite, talc, or pyrophyllite. Care must b exercised during grinding to avoid overheating the mill. Mixtures containing up to 50 percent of DDT rmay be prepared in. this way. Iixtures of higher DDT content do not have desirable physical properties and are extremely difficult to grind.
Several commercial products containing various proportions of DT, wetting agent, and diluent have been tested. One containing 10 percent of DDT has a surface mean particle diameter (determined by the air-prm ation method, which does not necessarily reflect the particle size of t DDT) of 5 microns, as compared with 44 microns, the diameter of the openings in a U. S. No. 325 sieve. Another mixture containing 50 perce of DDT, which w-as micronized, had a surface mean article diaeter of
-.8 microns. Since DDT is known to be an effective contact inse the use of sr all particles might be expected to give a more uniform distribution with a consequent improvement of insecticidal properties with certEin insects. This is borne out by the increase in efficiency against larvae of the codling moth (Carpocapsa pomonella L.) when the p- ticle size is 4 to 5 microns as compared with 8 to 9 microns. On the o;ter hand, DDT deposits on glass plates have been observed to decras in weight by an average of 5 to 10 percent during five successive 16-ho expnosures to direct sunlight. Since rate of loss is directly relad t the area of the exposed surface, extremely fine particles with their large specific areas may not be desirable if effectiveness over long periods of time in direct sunlight is reouircd.
Mixtures containing as much as 10 percent of DDT with pyrophyllite can be wetted with water and under some conditions used as sprays. For general purposes, best results are obtained through the use of a surface active agent to provide uniform wetting and dispersion of the DD1 and adequate wetting of the sprayed surfaces without excessive run-off. Fixtures have beon prepared by incorporating the surface-active agent before grinding. While this method has certain advantages with refern to ease of preparation, it has the disadvantage of making it impossible to vary the concentration of DDT without also changing the physical properties of the spray mixture and thus affecting the quantity of DDTI deposited and the resistance of the residue to weathering. Since DDT studies are largely in the preliminary stage, both variables should b controlled by the investigator,in order to insure a rmximum of spray deposit and of distribution on specific types of foliage. This can be accomplished by the use of various amounts of surface-active agents.
Thefolowngwettin ei~ sticking agents have been upe4 with DDT
djj ert ixtres Sap powder, not to nc,-c d I percent of' the D~-,;
isaera popretry coIi:4.puda2 in amounts. ras. ing from 0.1 to 0.5 pcr4; -' atm prth DT;materia of thentu~ of' fish glue at the rate of
bund:-disovad in I pint of' wcter, por pound of DDT; and soybean flour
gt'he ateof1/2 pound pe pound of DDET. Ins crder to insure complete "Vettng f heDDT and to elimwinate egglomerates,. it is best to prepare.
pase fon he DD-dili-ent mixti~e, the wet~iing_ agent and enough water
(abot 1 /2 pnts per pound of' mixture) to give a. fairl~y hecvy paste,
TM4,past =ybe f urtbev dilut ed end ada.ed to the spray t nkc.
Spveal pray mixtures have been used which contain oil emlsion~s
d-SiceDDT i.s pr'efersntiay wettsd by oil, it is imiportant. to
%,ue: heproerratio' of' oil tXo DDT. If a large proportiOo o a quicklorakig eulion is used, oil-'ccated DDT may collect onl the surface of I ,t"e pi~y itrp, in curdy inassc-s. 0i1e nethod of' overcoming this diff't-,Vlty0,nist in diluting the Emulsion ~Aha glue solution lbef'ore adding
te DT.A finula consisting of 2 pounds of a 50:50 mixture of' DXYT ad P Fophylit or alcite, 1 quart of' smer Qd. e-mulsion, 1 pint of fish93,' e oluion(pepar .. at the rate of 1 pound of semiliquid glue per
J~4.o ae),and 100 gallons Of 7ater has beenfud obists
Tecone ent rat i on of the fish-glue solution ma~y be reduced, to
/4:pund er allon of water.
Wet g inin is conducted in the usual manner in a ball mill. A
1rotin agntin the proportions previously mntiozwed in connection w'.ith
ary grundmitures may be added previous to ,' rincding. M,-ixtures prepared
this w yae been reported to produce heavy spray deposits. They
hbv th diadvant~ige common to paste products in tha:t they tend to
DDTmaybe dissolved in we'*ter-miiscible, solvents such a~s methyl,
'ihl, disopropyl a1001v48s and acetone~ When these solutions are
_ouedino e-r, the DDT~ is thrown out of solution. h W ~seo
'-,rom1.5pocent solutions in the alcohols is finely divided and. may be
kep in usonsiozi with moderate agitation. That dispersed from acetone
'S ins frmsa gunwiy mass at first but later becomes crystal1.inee
E/T.s compounds include Orvus-W.a. (sodium salt of' lauryl sulfate), (soiumsalt of laury. pulfute), Vuataol OS (sodium salt of 'alkl npthelenesulfonic acid), Tw,%een 20 (a modified sorbitan iaono' A~re), reet (sodium monasult'onate of monob tyldiphenyl), and
Iinw (wterrs-u lubl sodium sulfonate of petr um hydrocarbons).
This objectionable feature may be overcome by adding a surface-active agent to the solution before mixing with water. One of the formulas used consists of 24 grams of DDT, 24 grams of Triton X-100 (polyethylene glycol phenylisooctyl ether), and acetone to make 100 mL., which is equivalent to 2 pounds of DDT per gallon of solution. On addition to water the DDT is dispersed as droplets of the guinmy material nontioned above, which becomes crystalline and settles out in this form on standing. The extent to which the DDT is dispersed and the time required for crystallizati and settling to take place are influenced by the proportion of surfaceactive agent in the acetone solution. Since this preparation is unstable, it should be used shortly after mixing and with moderate agitation.
Solutions of DDT in organic solvents have been used for spraying the interiors of barns for the control of flies and for impregnating fabrics fbr the control of clothes moths. From 1 to 5 grams of DDT per 100 ml. of a petroleum fraction has been used for the first purpose, and a 1 percent solution of DDT in a volatile solvent such as xylee or acetone for the second. The solvent and concentration of DDT selected depend upon the insect to be controlled. Since technical DDT often contains some insoluble material, it nay be necessary to filter the solution before use.
Emulsions of solutions of DDT in various solvents which are either substantially insoluble in water or only-slightly soluble have been used by several investigators. In order to avoid precipitation, water-miscible solvents should not be used for this purpose. For the same reason, if the solvent is appreciably soluble in water, allowance should be made for this when diluting such emulsions. For example, emulsions of DDTethylene dichloride solutions have been used, but in some cases enough precipitate was deposited in the tank to clog the screen. To overcome this difficulty it would be necessary to adjust the concentrations of both materials in the emulsion to provide for enough ethylene dichloride to saturate the water plus the amount required to keep the DDT in solution.
Consideration should be given to the proportions and types of
emulsifiers used. Since DDT is effective against many insects on contact, large proportions of the emulsifier may result in inferior control due to the coating of the DD~T deposit by the emulsifier upon evaporation o the water and solvent. For this reason and also to prevent excessive
run-off, it appears desirable to use only enough emulsifier to produce an emulsion which on dilution gives a spray with proper wetting quali.
;",.-SjWbiv-sigaorshee rtprtsed that emul~sions are more effective for "i isetsthen speions, others have suggested that costs ar~e K, A,, siv, ad thers have ncoutered difficulties ase mentioned above.
Twotyes of emulion have been used (1) those in wh~ichi the D~r is
ina-oltilc nlet such as Xyleneq and (2) those in which
vin s disolved in a eletiv"2ely nonivolatile solvent, such as petro,Lva ol. W th firt, typ DDT crystals axe distributed on the sprayed
,,41 wfte uonevaporation of the solvent, and with the second type the '',-sp#L-ye source oate4 44th the solution on evaporation of the water.
Tvoforula of the first typE are as follow s: (1) DDT 24 grams,,
ito B196 a phthaico glyoercl elkyl. resin) 3 grams, xylene to melko
41,0-a. ( ) DT24 -frams, Naee91ial. ITSF sodiumm alkyl aryl. sul fonate) 12 PButl Clloolve (.butyl. ether of ethylene glycol) 10 ml., zylene
1*4zaae 00 l. hese stock mixtures contain DDT at the rate of 2 pounds
'galon.They are best diluted to form emulsions by being added to 1I
OZg~ol~esof water, vigorously agitated, end then diluted with the
4 -;Oaade3 ofthe water.
AAexal of the second type is DDT 3 grams, mineral oil 75 ml., zkI-A gam and water~ 25 ml, The DDT~ is diasolved in the oil,
Ot4 ths sluton is emulsified on addition to a solution of the Gardinl
,in he-wter tiring the mixture vigorously me-anwhile. The volume of
_Op~dat vries with the amount of air incorporated during emulsifiction,
theweghtofDDT per gallon of spray mixture is to be controlled
t 4q.dsege, should be calculated on ths basis of the volume of
p~rouct.The original proportions are equivalent to approximately
4,piund f DT per gallon of emulsion. The solubility of DDTYI in 100) ml.
'~ ~ I "iiea i t 27-3000. (80-860F.) ranges from 4 grams for Deobasc
11 efied eroe0) to 10) grams for No. 2 fuel 9oi.. Solubility in spcci.fic N" la r gads of oil at the minimum, tem,..perature to be, encountered should dtermnedprior to emulsification. Emulsions of this typo should be
.,oo water preparation.
Polens other' then those mentionEd above, alone or in mixtures, as
adiferent proportions of the same or othcr surface-,active agents, VY bemore4esirable for the preparation of emulsions to be used for
goiic uroses. It is suggested that prcliminary batches of spray
ure b prepared and the physical propcrti -s observed before tests
P 4ae wih tnscots.
Dus mxtures have, in general, bzen preparc& by nixcing diluenta, OW~has probyllite,, talc, and walnut-~shell flour, with finely ground mitues Dusts containing as much~ as 10 percent of Dflt are 4
sufficitntly free-flowing for certain dusting purposes. On the other handl dusts containing from 1 to 3 percent have better physical properties nd have given good results. If the dust is prepared from a 50:50 mixtnauro care is required to obtain uniform distribution, as this mixture has a tendency to agglomerate in an ordinary dry mixer. Uniforaity might be accomplished by passing it through a hamer mill or brushing through a series of screens.
Diluents such as pyrophyllite, talc, or walnut-shell flourmay be coated or impregnated with DDT by dissolving it in a volatile solvent such as benzene or acetone, wetting the diluent with the solution, allowing the solvent to evaporate, and grinding the product. Fairly large batches may be prepared by spreading the diluent on a clean, hard surface and applying the DDT solution in successive portions from a sprinkling can. The mass should be remixed with a shovel after each sprinkling and then at intervals until all the solvent has evaporated. Only enough solvent should be used to dampen the diluent uniformly. Trial batches using the solvent without DDT will establish the proper proportions. The product should be ground to eliminate coarse agglomerates. A hamer mill is preferable for this purpose. Products containing more than 10 percent of DDT are liable to be difficult to grind.
Another method of impregnation used consisted in dissolving 2 pounds of DDT in 3 pounds of Velsicol AR-50 (alkylated naphthalenes) and ipregnating 45 pounds of Pyrax ABB (pyrophyllite) with this solution in a. ball mll. The resulting mixture was then added to another 50 pounds of Pyrex ABB and run through a brush mixer.
The compatibility of DDT with other insecticides, fungicides, and accessory materials has been studied from both the chemical and biological viewpoints. Whil6 DDT is a rather stable compound by itself, in alcoholic solution it readily reacts with alkalies with the loss of 1 mole of hydrochloric acid per mole of DDT and the formation of 1-dichloro-2,-bis (p-chlorophenyl) ethylene. This compound, which is comparatively inert as an insecticide, is also formed at temperatures above the melting point of DDT in the presence of certain catalysts. Of the compounds which may be present in small amounts in accessory materials, iron and iron oxides, chromium, and anhydrous ferric, aluminum, and chromic chlorides are known to be active in this respect. Of this group the anhydrous chlorides are the most active. Ferric and chromic chlorides may be formed by the action of DDT on the metals themselves. Accessory materials such as kaolin, fuller's earth, bentonite, and some samples of talc and Pyrax ABB have shown definite catalytic activity. Other samples of talc and Pyrax AB as well a4 calcium oxide and hydrated lime, are substantially inactive*
P~ri gren, clcimarsenate, and lead arsenate sh1-owed no catal~ytic action.
Wit 1)j?(.,3u itur 0.04 moale, and with sulfur 0.0? mole of bydrochloriq
tol wee ot-i~ne4 per Tmole of DDT. Pure nieotiine. in courion with
strrsl bai- itrogen.-bearing com~pounds, reacts with DTin the sae
Most f te olvts used with DDYT tead to inhibit cata V.tic
Th~e notable exceptions are n .ptha1 ene 2T d -.Ls nitro- and
chici~1 ro-rnen 9-dichlorobezzene tile ~ :cuof ferric
DD as shoi to oncur at r0C1Ym lies 6 ctolcum fracoil cyclobexanone, xylene, cnd VeszlAH-60 (alikylated
na *hleneei empletely or substantially inhibit the. catalytic.
reatio ofanhdrus ferric chloride.
Whie i ha been shcwn that many compounds acting as catalysts at
bigtt~.Ampe atu will decompose. MT, it is possible that under field
-coi~iion deomposition may nct take place or that Thel red.iction may be
t~o zow s cbave little influence On insecticidal viaue ef DDT.
4paetl, ever, spray mixtures containing only ~o~en~which do
dea oseDDT or which act as inhibitors in th,,e _"1Lioatry would be
q ,fiin under field conditions. Tests to dezorrn thLi~otac
th~e eacins under field conditions would be iii ordei-.
tests have bee-n made to determine the effectiveness of
spvaysconaiing DDTI and other material,. such as bc~rdeaux mixture, sulfur,
U, aulsins, ermate (ferric dirrethyl dithiocarbaate) and various
,,Ao- ,essrymaerials. These sprays have beer, used successfully with no
4. ~t~ltytofoiae except in a few cases where reepeated applications were
i' Te edition of lime-sulfur, bordeaux nuixture, and sulfur has been
to edcethe period of effectiveness. ,!hether this was due to
Ae'.0Mpoitonto inseQticidally inert~ compounds, ot to the physical masking 46t~he DT n the deposits has not been established. Since DDT~ is a 410'tactpoion and its deposits are not~ peirinant in direct seunlight, it
sugge tbtat, in addition to normal mechsiial ioss, part of the
d nsecticidal value may be due to the loss of' DDT from the surface
-mixd dposits end the masking of the remainder within the deposits&
T~~url cnstituents, such as apple wax, may also influence insecticidal
DESIRABILITY OF' AL ON STXADARD OF COTARISON
Cosieble variation has been fo~md in the results obtained with tVi difrent parts of the country even whe--n used to combat the sae
,tnsect speie. It i s therefore very desirable to include in each set of
-__tess, igansta given insect, material from a cormion source of the sam
'Torulaton*In this way pert of the variation in results 'Would be
tlitnaedo could be roore readily interpreted.
UNIVERSITY OF FLORIDA 3 1262 09230 3816