SOIL INSECTICIDE AND PLACEMENT INFLUENCE CORN (ZEA-MAYS) TOLERANCE TONICOSULFURON

Field experiments were conducted in 1991 and 1992 to evaluate corn tol erance to nicosulfuron following in-furrow or surface-band application s of seven soil-applied insecticides. The organophosphate insecticides evaluated included terbufos (15G and 20CR formulations), phorate, chl orpyrifos, fonofos, and DPX-43898, as well as the synthetic pyrethroid tefluthrin. Potential for a nicosulfuron/ insecticide interaction to injure corn was ranked as follows: terbufos 15G = phorate > terbufos 2 0CR > fonofos. Chlorpyrifos, DPX-43898, or tefluthrin followed by nico sulfuron caused no significant corn injury. Corn injury and yield redu ction were greater in corn treated in-furrow compared with surface-ban d. Soil moisture at nicosulfuron application was more influential in c ausing corn injury and loss of yield than growth stage of corn at nico sulfuron application. Nomenclature: Chlorpyrifos O,O-diethyl-O-3,5,6-t richloro-2-pyridyl phosphorothioate; DPX-43898 O-O-diethyl O-(1,2,2,2- tetrachloro-ethyl)phosphorothioate; fonofos O-ethyl S-phenyl ethylphos phonodithioate; nicosulfuron, xy-2-pyrimidinyl)amino]carbonyl]amino]su lfonyl]-N, N-dimethyl-3-pyridine-carboxamide; phorate O,O-diethyl S-[( ethylthio)methyl]phosphorodithioate; tefluthrin, 2,3,5,6-tetrafluoro-4 -methylphenyl)methyl-(1alpha, o-1-propenyl)-2,2-dimethylcyclopropaneca rboxylate; terbufos, S-[(tert-butylthio)methyl]-O,O-diethyl phosphorod ithioate; corn, Zea mays L. 'Pioneer 3394.'