Toxicological Studies on Cutworms. X. Laboratory and Field Microplot Studies on Effectiveness and Persistence of Some Experimental Insecticides Used to Control the Black Cutworm in Organic Soil12
Laboratory and field microplot tests were conducted to determine the effectiveness of some experimental insecticides in controlling Agrotis ipsilon (Hufnagel) attacking vegetables grown on organic soil. Primary screening tests in the laboratory with 12 insecticides indicated that 8 were more toxic by contact than DDT, and 4 as or more toxic than endrin to, 3rd-stage cutworms. Secondary laboratory screening tests done with 6 of the insecticides applied as EC formulations to the surface of moist and air-dry organic soil indicated that chlorpyrifos, leptophos, Stauffer N-2596 (S-(p-chloropheny1) O-ethyl ethylphosphonodithioate), and Bay 77049 (OO-diethyl O-(2-quinoxalinyl) phosphorothioate) were most promising. Microplot field trials, using plots seeded to onions and artificially infested with 4th-stage cutworms, indicated that leptophos was most effective > chlorpyrifos > N-2596 > DDT. Residues of all 3 experimental insecticides were moderately persistent in organic soil, but no residues were detected in onions harvested from the plots treated at the highest rate of insecticide application of 2.24 kg active ingredient per hectare. It was concluded that leptophos and chlorpyrifos warrant field testing on a larger scale for black cutworm control on organic soil.