Field experiments were conducted to determine the occurrence and the extent of interaction among four soil-applied organophosphate insecticides and the sulfonylurea herbicide nicosulfuron applied POST to corn. Nicosulfuron was damaging to corn when the crop was planted with terbufos, phorate, or fonofos applied into the open furrow. Terbufos was the most damaging and also caused damage when applied as a 17-cm band prior to or after closing the furrow, with or without incorporation. Phytotoxic symptoms appeared within 3 d of application of nicosulfuron and damage increased as the rate was increased from 53 g ai/ha to 140 g ai/ha. However, despite severe damage of up to 50% recorded in some terbufos combinations, all plants had completely recovered within 4 wk and none of the treatments had any effect on grain yield or crop maturity. No damage resulted from nicosulfuron when corn was planted with the insecticide chlorpyrifos. Efficacy data of nicosulfuron on the main weeds present are also reported.
