Postemergence Control of Annual Grasses and Corn (Zea mays) Tolerance Using DPX-79406

DPX-79406 was evaluated for POST annual grass weed control in both controlled environment and field experiments. In controlled environment experiments, green foxtail was most susceptible to DPX-79406; whereas yellow foxtail was least susceptible of the species evaluated. DPX-79406 at 12 g/ha completely controlled six leaf black-seeded proso millet, yellow foxtail, green foxtail, and barnyardgrass. In the field, DPX-79406 at 3.0 to 25.0 g/ha effectively controlled annual grass weeds without injury to three- to six-leaf corn. There was more variation in the effectiveness of DPX-79406 applied in the field. Early POST applications provided less weed control than the late application, especially for barnyardgrass, because of weeds emerging after application. As a result, higher doses were sometimes needed for effective control. In weed-free field trials at two sites in 1990 and 1991, corn tolerated doses up to 75 g/ha of DPX-79406 applied at the three- to six-leaf growth stage. However, doses as low as 18.8 g/ha applied at the six- to nine-leaf growth stage reduced grain yield. In 1991, corn tillering increases and height and yield reductions were related linearly to the dose of DPX-79406 applied during later growth stages. DPX-79406 should be applied early POST in order to avoid crop injury while providing effective weed control.