Weed management in wide- and narrow-row glyphosate resistant soybean

Field experiments were conducted in 1996 and 1997 at East Lansing, MI, to e valuate weed management programs in soybean [Glycine max (L.) Merr.] plante d in 30 in, and 7.5 in. rows. Efficacy of glyphosate applied alone, with am monium sulfate (AMS), flumiclorac, or imazethapyr was compared with preemer gence and postemergence weed management programs used in nontransgenic soyb ean. Glyphosate provided consistent weed control in wide- and narrow-row so ybean in both years. Common ragweed (Ambrosia artemisiifolia L.) and velvet leaf (Abutilon theophrasti Medicus) control decreased when flumiclorac was tank mixed with glyphosate compared with glyphosate alone in wide-row soybe an. Weed control was usually greater in narrow- than in wide-row soybean fo r treatments without glyphosate. Soybean yield with most herbicide treatmen ts equaled the weed-free control in narrow-rows, and gross margins for soyb ean planted in narrow-rows were greater than wide-rows. Yield in wide-row s oybeans was reduced compared with the weed-free control with all treatments except glyphosate, glyphosate + AMS, or glyphosate + imazethapyr Glyphosat e and glyphosate + AMS had the greatest gross margins for both years.