PLANT RESPONSES TO INSECTICIDES IN THE SOIL 21 



DDT for 400 pounds suggest that the effects of these two con- 

 stituents together are roughly equal to the sum of their separate 

 effects. 



Results With BHC 



Table 5 shows technical BHC to be outstandingly different from 

 DDT in three important respects when compared on a pound-for- 

 pound basis of total substance in the technical grade of the mate- 

 rials: (1) Technical BHC appears more harmful to germination 

 and stand than is DDT; (2) all crops tested appear to be seriously 

 injured by 200 pounds per acre or more of technical BHC, while 

 several crops appear to be relatively unaffected by that amount of 

 DDT; and (3) large amounts of BHC — 200 pounds per acre or 

 more — appear far more toxic to growth than corresponding 

 amounts of DDT. 



In these tests most of the cucurbits appeared very sensitive tc 

 technical BHC, the complete inhibition of a stand of plants of 

 some of them at the 400-pound level contributing largely to the 

 low average of all crops tested, at this level. Honey Dew musk- 

 melon is especially sensitive. 



DDT at 1,000 pounds per acre reduced the average growth of 

 sensitive crops little more than half and tolerant crops by no sig- 

 nificant amount. Technical BHC, however, at 400 pounds virtu- 

 ally eliminated all growth, and 200 pounds reduced it to a fourth 

 of the control on the average. Beans and cabbage may be less 

 sensitive than most crops, but the limited number of tests here 

 preclude close comparisons. 



The highly purified gamma isomer of BHC (not the commercial 

 grade of gamma BHC) in a separate set of tests appeared to have 

 no adverse effect upon germination and stand up to 400 pounds 

 per acre. Pound for pound, it appeared to be as toxic to young 

 plant growth, however, as did the technical form. On the average 

 of the limited tests made 100 pounds of pure gamma isomer re- 

 duced growth about 25 percent below the control, and the techni- 

 cal grades did the same. At 400 pounds, both forms reduced 

 growth to about 8 to 9 percent of the control. Beans and cabbage 

 appeared less sensitive than the other crops, although they too 

 were very hard-hit by rates of 200 pounds or more. 



Although the gamma isomer appears as toxic, pound for pound, 

 as the technical BHC, only about one-eighth as much of it needs 

 to be used to control most pests against which BHC is used. Un- 

 fortunately, these studies reveal nothing on the effect of BHC, 

 technical or gamma, upon the food or feed value or flavor and 

 taste of crops grown on soils containing appreciable quantities 

 of it. This problem has suddenly become a very pressing one. 

 These exploratory studies do, however, show that an accumulation 

 of 100 pounds per acre of technical BHC may be expected to re- 

 duce growth and yield of many crops significantly; at 200 pounds 

 per acre growth was reduced to only one-fourth of the control. 



Results With Chlordane 



Exploratory tests with chlordane ( 1,2,4,5,6, 7,8, 8-octachloro- 

 2,3,3a,4,7,7a-hexahydro-4,7-methanoindene) suggest that, except 



