PLANT RESPONSES TO INSECTICIDES IN THE SOIL 31 



and cabbage were followed by lima beans, snap beans, and sweet 

 corn. 



Manure will be applied to the appropriate sub-blocks at 2- or 

 3-year intervals and lime as may be necessary to establish and 

 maintain definite difference in soil reaction between the split plots. 

 Soil reaction in 1949 averaged 5.0 on the no-lime plots, 5.2 on the 

 limed plots. Ten tons of manure per acre were applied in 1947 

 and 20 tons in 1949. By withholding lime from the low-lime plots 

 or adding small amounts, and by adding further quantities care- 

 fully to the high-lime plots the desired differences in pH can be 

 gradually produced. Meanwhile, dependable data on the effects of 

 DDT levels alone are being obtained. The experimental value of 

 this field in relation to effects of DDT is expected to increase for 

 many years. 



No chlorinated hydrocarbons have been or will be used to con- 

 trol insects in these experiments. Rotenone and ryania insecti- 

 cides only have been used. No fungicides have been used. 



Results 



Table 12 presents the results of the 1948 and 1949 crops from 

 the DDT field plots. 



Of the cereals tested the Abruzzi and the Rosen varieties of rye 

 are by far the most sensitive to DDT. As little as 25 pounds per 

 acre of DDT produced a small but significant depression in the 

 yield of the full-grown but not ripe and dry plants; 100 pounds 

 significantly depressed the yields of ripe, dry straw plus grain. 

 During the fall and winter of 1948 the rye plants on the 100- and 

 200-pound plots were of a slightly abnormal color, with a tinge of 

 faint purplish red. The smaller size of the plants on the heavy 

 treatments was easily evident to the eye during most of their 

 development. 



There was no significant effect of the DDT on growth of either 

 of the two varieties of wheat or of Fulghum or Oklahoma oats. 

 Lee oats was significantly depressed in yield at 100 and 200 pounds 

 of DDT. Sunrise barley was not injured, but Wong barley ap- 

 peared somewhat sensitive. 



Lima beans were somewhat sensitive and snap beans highly 

 sensitive to the DDT treatments in both 1948 and 1949, the depres- 

 sion of growth appearing somewhat greater in the latter year. 

 In the 200-pound treatment the weights of lima bean plants with- 

 out pods were reduced significantly below those of the control 

 plots, but pod yields were not. Both plant weight and pod yield 

 of Stringless Black Valentine snap beans were markedly reduced 

 by amounts of DDT of 100 pounds per acre or more. In the 200- 

 pound plots pod yields were only about one-half to one-third as 

 large as the yields of the controls. As with lima beans, the effects 

 of the DDT at the several levels were as serious in 1949 as they 

 were in 1948 in these tests. 



The potato showed no significant differences in yield of tubers 

 due to the soil treatments with DDT. Other data indicate that 

 this potato variety is relatively tolerant to considerable amounts 



