TIMING OF TOTAL POSTEMERGENCE HERBICIDE APPLICATIONS TO MAXIMIZE WEED-CONTROL AND CORN (ZEA-MAYS) YIELD

Grass and broadleaf herbicides are available for effective, single-app lication total postemergence weed control in corn. Field experiments w ere conducted in 1992 and 1993 on sites with dense natural weed infest ations to determine the effects of weed interference prior to herbicid e application on corn yield. Nicosulfuron plus bromoxynil was applied at 5-, 10-, 15-, or 20-cm weed canopy heights in plots with or without weed interference. Crop injury was more severe when herbicides were a pplied to smaller corn. Herbicide applications made to 5-, 10-, or 15- cm tall weeds provided nearly complete weed control. Weed interference did not reduce corn height or grain yield when postemergence applicat ions were made to weeds 10 cm or less in height. Weed interference red uced corn height and grain yield in 1999 when applications were made t o 15-cm tall weeds even though weed control was nearly complete. Weed control was incomplete and corn height and grain yield were reduced wh en applications were delayed until weeds were 20 cm tall.