Response of johnsongrass (Sorghum halepense) and imidazolinone-resistant corn (Zea mays) to AC 263,222

Field studies were conducted in 1992 and 1993 to evaluate AC 263,222 applie d postemergence (POST) alone and as a mixture with atrazine or bentazon for weed control in imidazolinone-resistant corn. Nicosulfuron alone and nicos ulfuron plus atrazine were also evaluated, Herbicide treatments were applie d following surface-banded applications of two insecticides, carbofuran or terbufos at planting. Crop sensitivity to POST herbicides, corn yield, and weed control was not affected by insecticide treatments. AC 263,222 at 36 a nd 72 g ai/ha controlled rhizomatous johnsongrass 88 and 99%, respectively, which was equivalent to nicosulfuron applied alone or with atrazine. AC 26 3,222 at 72 g/ha controlled large crabgrass 99% and redroot pigweed 100%, a nd this level of control exceeded that obtained with nicosulfuron alone. AC 263,222 at 72 g/ha controlled sicklepod and morningglory species 99 and 98 %, respectively. Nicosulfuron alone or with atrazine controlled these two s pecies less than AC 263,222 at 72 g/ha. Addition of bentazon or atrazine to AC 263,222 did not improve control of any species compared with the higher rate of AC 263,222 at 72 g/ha applied alone. Corn yield increased over the untreated control when POST herbicide(s) were applied, but there were no d ifferences in yield among herbicide treatments.