Effect of row spacing and herbicide application timing on weed control and grain yield in corn (Zea mays)

Field experiments were conducted from 1997 to 1999 at the University of Minnesota Southern Research and Outreach Center in Waseca to evaluate the (1) effect of corn row spacing oil grass and broadleaf weed species density and height, (2) optimal herbicide application timing in narrow- and wide-row systems, and (3) corn grain yield response to row spacing and herbicide application timing. Corti was planted in 51- and 76-cm row spacings. Within each row-spacing treatment, there were five herbicide application timings: a formulated mixture of acetochlor plus atrazine applied preemergence or a formulated mixture of imazethapyr and imazapyr tank-mixed with bromoxynil applied postemergence at 5-, 10, 20-, or 30-cm giant foxtail plant height. Reducing the row spacing in corn from 76 to 51 cm did not influence early-season weed emergence or growth. Similarly, late-season weed density and growth were not influenced by row spacing except in 1997. But corn grain yield increased when corn was planted in narrow rows compared with wide rows ill 2 out of 3 yr when averaged over herbicide application treatments. Herbicide application timing had a significant effect on late-season weed density and grain yield. But there was no interaction between herbicide application timing and row spacing on grain yield. Potential increases in crop competitiveness resulting from narrow-row corn did not appear to affect weed density or growth in this study.