POSTEMERGENCE HERBICIDE APPLICATION TIMING EFFECTS ON ANNUAL GRASS CONTROL AND CORN (ZEA-MAYS) GRAIN-YIELD

Giant foxtail, woolly cupgrass, and wild-prose miller infest millions of hectares of land devoted to corn production in the midwestern U.S. Control of these species and effects on corn grain yield were evaluate d at various timings using POST applications of nicosulfuron vs. appli cations of various PRE herbicides at 17 locations across the midwester n U.S. in 1992 and 1993. Nicosulfuron applied to 5 to 10 cm giant foxt ail and woolly cupgrass provided greater control than that observed wi th selected PRE herbicides. Giant foxtail control with nicosulfuron av eraged 88%, and control of woolly cupgrass averaged 77% across all sit es. Nicosulfuron, applied to 5 to 10 cm wild-prose miller, provided a level of control similar to chat of selected PRE herbicides. Corn grai n yield was greater when giant foxtail was controlled POST with nicosu lfuron vs. PRE control with selected soil-applied herbicides. Corn gra in yields were similar when nicosulfuron was applied POST to 5 to 10 c m woolly cupgrass or wild-prose millet vs. PRE control of these grass weeds. Across a broad range of geographical locations, nicosulfuron, a pplied POST to 5 to 10 cm tall grass, provided greater or similar leve ls of weed control vs. the selected PRE herbicides, with no deleteriou s effect on grain yield.