Weed control with reduced rates of imazaquin and imazethapyr in no-till narrow-row soybean (Glycine max)

Jeffrey S. Dilbeck Michael S. DeFelice J. Andrew Kendig Department of Agronomy, University of Missouri, Columbia, MO 65211 Field studies were conducted at three locations in 1993 and 1994 to evaluate weed control and crop response to metolachlor plus combinations of 0.5 X and 1 x label rates of imazaquin applied preplant and imazethapyr applied early postemergence or postemergence in no-till narrow-row soybean production. Giant foxtail, common ragweed, common cocklebur, and large crabgrass population reductions were greater with sequential preplant metolachlor plus imazaquin followed by early postemergence or postemergence imazethapyr than with preplant metolachlor plus imazaquin or early postemergence/postemergence imazethapyr alone. Ivyleaf morningglory was not effectively controlled by any herbicide program. Pennsylvania smartweed populations were reduced with all herbicide treatments. Soybean yields with treatments utilizing 0.5 X rates were usually equal to 1 X rates if imazethapyr was applied early postemergence or postemergence. Net income with reduced herbicide rates was equal to full-label rates and provided no greater risk to net income.