Laboratory Evaluation of New Insecticides for Control of Redbacked Cutworm Larvae1

Abstract

Sixteen insecticides were evaluated as oral toxicants for control of fifth-stage larvae of Euxoa ochrogaster (Guenee). Of eight pyrethroids, six were more toxic than endrin and all were more toxic than chlorpyrifos. Their order of toxicity was deltamethrin > FMC 26021 [(5-benzyl-3-furyl) methyl(+)- cis -2,2-dimethyl-3-(2-methyl-1-propenyl) cyclopropanecarboxylate] > permethrin > AC 222705 [(±) cyano(3-phenoxyphenol) methyl(±)-4-(difluromethoxy)-α-(1-methylethyl)-benzeneacetate] = cypermethrin > fenpropanate > endrin > fenvalerate > FMC 18739 [(5-benzyl-3-furyl) methyl(+)- trans -2,2-dimethyl-3-(2-methyl-1-propenyl) cycloyropanecarboxylate] > chlorpynfos. Deltamethrin was 13- and 29-fold more toxic than endrin and chlorpyrifos, respectively, and six other organophosphorus insecticides included in these tests varied from one-third to one-tenth as toxic as endrin. The pyrethroids were 1.4- to 6.6-fold more toxic as contact poisons, and all were more toxic than the standards, with deltamethrin 50- and 166-fold more toxic than endrin and chlorpyrifos, respectively. In greenhouse tests with mature sixth-stage larvae, deltamethrin gave the most effective control at 0.07 kg/ha. Permethrin gave better control as a foliar spray than when applied to bare soil. Cypermethrin and fenvalerate were less effective and would require rates in excess of 0.14 kg/ha. Endrin at 0.28 kg/ha gave equivalent control as a foliar or bare-soil treatment, whereas chlorpyrifos at 0.56 kg/ha was less effective and was unsatisfactory when applied to bare soil.