Field experiments were conducted in 1988 and 1989 to (i) evaluate annual weed control with nicosulfuron applied at rates of 17 to 70 g ai/ha with several additives and (ii) evaluate annual weed control with nicosulfuron applied at rates of 17 to 105 g/ha at three corn growth stages. In 1988, in the adjuvant study, giant foxtail control increased linearly with no additive or with urea ammonium nitrate as the rate of nicosulfuron increased. Petroleum oil concentrate, nonionic surfactant, and a combination of either petroleum oil concentrate or nonionic surfactant with urea ammonium nitrate applied with nicosulfuron increased giant foxtail control to 90% or greater regardless of rate both years. Nicosulfuron at all rates with no additive and in combination with all additives controlled 93% or more of redroot pigweed and Pennsylvania smartweed both years. Corn grain yield was related to the level of giant foxtail control. In the rate by corn growth stage study, giant foxtail, redroot pigweed, and Pennsylvania smartweed control was 90% or greater regardless of nicosulfuron rate or application stage both years. Corn grain yield was related more to the duration of weed competition than the level of weed control with grain yield 8 to 12% lower with nicosulfuron applied at the V7 growth stage compared with the V3 or V5 growth stage.

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