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

Field experiments were conducted in 1996 and 1997 at East Lansing, MI, to evaluate weed management programs in soybean [Glycine max (L.) Merr.] planted in 30 in, and 7.5 in. rows. Efficacy of glyphosate applied alone, with ammonium sulfate (AMS), flumiclorac, or imazethapyr was compared with preemergence and postemergence weed management programs used in nontransgenic soybean. Glyphosate provided consistent weed control in wide- and narrow-row soybean in both years. Common ragweed (Ambrosia artemisiifolia L.) and velvetleaf (Abutilon theophrasti Medicus) control decreased when flumiclorac was tank mixed with glyphosate compared with glyphosate alone in wide-row soybean. Weed control was usually greater in narrow- than in wide-row soybean for treatments without glyphosate. Soybean yield with most herbicide treatments equaled the weed-free control in narrow-rows, and gross margins for soybean planted in narrow-rows were greater than wide-rows. Yield in wide-row soybeans was reduced compared with the weed-free control with all treatments except glyphosate, glyphosate + AMS, or glyphosate + imazethapyr Glyphosate and glyphosate + AMS had the greatest gross margins for both years.