110 MISC. PUBLICATION 6 2 6, U. S. DEPT. OF AGRICULTURE 



APPENDIX 



DDT INSECTICIDES 



The discussion of insecticides in the 

 preceding pages has been confined to 

 well-known standard materials. In 1 940 

 DDT, an organic compound so called 

 from its generic name dichloro-di- 

 phenyl-trichloroethane, was discovered 

 by Swiss investigators to have remark- 

 able insecticidal properties. As a re- 

 sult of intensive research by the Bureau 

 of Entomology and Plant' Quarantine, 

 it was used effectively in various theaters 

 of war to control the body louse and 

 other important pests of man. DDT 

 is known to be effective against many 

 other insects, and further research may 

 show that it can be used on flowering 

 plants and shrubs in place of some of 

 the older insecticides. Experimental 

 work has not progressed sufficiently, 

 however, for detailed recommendations 

 to be issued for the use of DDT on most 

 of the flowering plants and shrubs 

 mentioned in this publication. 



DDT is one of the few chemicals 

 which acts both as a stomach poison 

 and a contact insecticide. It acts 

 chiefly in the latter capacity, causing a 

 paralysis of the nervous system. Af- 

 fected insects do not die quickly. In 

 fact, they may live for several hours, 

 or even days, after coming in contact 

 with the chemical, but they do not 

 recover. Another feature of DDT is 

 the persistence of the spray deposit, 

 which may make it particularly adapted 

 for the control of insect pests of the 

 flower garden. 



Technical DDT is a gray or cream- 

 colored waxy powder, sometimes rather 

 lumpy and sticky, which has a faint 

 floral odor. It is the basic material 

 from which various commercial in- 

 secticidal preparations are made, and 

 it is suitable for use as an insecticide 

 only when properly prepared. 



Commercial preparations containing 

 DDT are available in five general types: 

 (1) Dust mixtures to be applied as a 

 dust as purchased, (2) wettable powders 

 that will mix readily with water to 

 form suspensions for spraying, (3) 

 emulsions to be diluted with water and 

 applied as a spray, (4) solutions to be 

 applied without further dilution, and 

 (5) aerosols in containers or "bombs," 

 to be applied by opening a valve to 

 release the insecticide. 



The dust mixtures, the suspensions 

 produced from wettable powders, and 

 possibly the emulsions will be satisfac- 



tory for controlling insects on flowering 

 plants and shrubs. Experimental data 

 indicate that in these forms DDT will 

 probably be effective against ants, azalea 

 and other whiteflies, the boxwood leaf 

 miner, the cabbage looper, the eastern 

 tent caterpillar, the European corn 

 borer, the fall webworm, flea beetles, the 

 imported cabbageworm, the Japanese 

 beetle, leafhoppers, plant bugs, the rose 

 chafer, rose midge, spittle bugs, the 

 spruce budworm, and thrips. DDT is 

 not effective against mites and certain 

 aphids. 



It appears that dust mixtures con- 

 taining 3 to 5 percent or more of DDT 

 may be used against some of these in- 

 sects. When wettable powders are em- 

 ployed, a satisfactory dosage is 2 pounds 

 of the 50-percent powder, or 4 pounds 

 of the 25-percent powder, per 100 gal- 

 lons of water. Indications are that 

 these preparations will not injure the 

 woody shrubs, but they are known to 

 injure some of the garden vegetables, 

 such as squash. Before their use can be 

 recommended generally, it will be neces- 

 sary to test these preparations on each 

 flowering plant. 



In preliminary tests emulsions con- 

 taining 0.1 to 1 percent of DDT were 

 found to control azalea and other white- 

 flies, lace bugs, the boxwood leaf miner, 

 the eastern tent caterpillar, the fall web- 

 worm, the Japanese beetle, the rose 

 chafer, the spittle bug on pine, and the 

 spruce budworm. To avoid injury on 

 such plants as azalea and boxwood, low 

 strengths should be used. Since the 

 DDT content and formulation of the 

 commercial emulsion concentrates will 

 vary, and since emulsions may injure 

 tender plants, the directions furnished 

 by the manufacturer should be carefully 

 followed. 



For many insects the proper formula- 

 tion to use, the rate and time of applica- 

 tions, and whether or not DDT can be 

 expected to give more satisfactory 

 results than other available materials 

 have not yet been determined. Care 

 should be taken to apply no more than 

 the dosage recommended by the manu- 

 facturer. 



DDT wettable powders can also be 

 used with the fungicides ferric dimethyl- 

 dithiocarbamate, wettable sulfurs, fixed 

 copper, or bordeaux mixture provided it 

 is of low lime content. Since hydrated 



