£ CIRCULAR 926, U. S. DEPARTMENT OF AGRICULTURE 



mologists as well as the insecticide industry. This problem has 

 been intensified during recent years, particularly in southern 

 California, by the widespread use of the new organic insecticides 

 for the control of soil-inhabiting insects such as wireworms and 

 other root feeders. In 1949 an experiment was begun in Ventura 

 County to determine the effect of repeated soil applications of 

 aldrin, chlordane, toxaphene, and ethylene dibromide on vegetable 

 crops grown in treated plots. The results obtained during the first 



3 years of the experiment are presented in this circular. 



REVIEW OF LITERATURE 



Allen and coworkers (l) 4 and Foster (3) have published exten- 

 sive reviews of the literature on the effect of soil applications of 

 insecticides on the growth and yield of crops. Recently Simkover 

 and Shenefelt (5) reported that root nodulation on black locust 

 seedlings was not affected by soil applications of 10 pounds of 

 chlordane and sufficient technical BHC to give 1 pound of the 

 gamma isomer per acre. Tied j ens (6) discussed the effect of insec- 

 ticide-fertilizer mixtures on soil insects, as well as their phytotoxic 

 and off-flavor effects on crops, and stated that workers in Kansas 

 had found that aldrin in dosages as high as 100 pounds per acre 

 caused no objectionable flavor. Preliminary experiments on the 

 toxicity of cumulative residues in the soil to plant and animal life 

 have been reported by Gould and Hamstead (J+). 



GENERAL PROCEDURE 



The studies in California were conducted on the farm of J. Lau- 

 bacher, about 1 mile west of Oxnard. The soil consisted of Yolo 

 fine sandy loam, which had been planted to lima beans for many 

 years and to alfalfa for 3 years prior to these experiments. To 

 prevent the test insecticides from affecting plant growth and yield 

 by controlling wireworms and nematodes, these pests were con- 

 trolled on the entire site by fumigation with ethylene dibromide on 

 March 8 following thorough cultivation of the soil. No insecticides 

 other than f umigants had ever been used either on the crops or in 

 the soil. 



Experimental Method 



Each insecticide was tested in six randomized blocks containing 

 plots 21 by 160 feet, or approximately y 1H acre. To expedite plant- 

 ing and harvesting, roadways were established the entire length of 

 the site on both sides and between blocks 2 and 3 and blocks 4 and 

 5. The plots adjoined each other, but no crops were planted within 



4 feet of the borders (fig. 1). The entire site was prepared for 

 planting on March 8, 1949, prior to fumigation, and on March 14 

 it was furrowed and irrigated. 



* Italic figures in parentheses refer to Literature cited, page 19. 



