Weed control and economies in nontransgenic and glyphosate-resistant soybean (Glycine max)

A study was conducted in 1996 and 1997 near Rohwer, AR, to evaluate weed control with standard herbicide programs in nontransgenic and glyphosate-resistant soybean (Glycine max) compared with glyphosate-based herbicide programs in glyphosate-resistant soybean. Total postemergence (POST) programs containing 0.84 kg ae/ha glyphosate 14 d after emergence (DAE) followed by 0.42 kg/ha at 42 DAE controlled pitted. and entireleaf morningglory (Ipomoea lacunosa and I. hederacea var. integriuscula) 80 to 83%. This control was lower than with any other weed control program in the study. All glyphosate containing herbicide programs controlled barnyardgrass (Echinochloa crus-galli) at least 94%. Soybean injury was 8% or less for all herbicide treatments except for 'Hartz 5088 Roundup Ready' treated with pendimethalin plus chlorimuron and metribuzin preplant incorporated (PPI) followed by glyphosate or acifluorfen plus bentazon 42 DAE. All weed control and soybean injury ratings were similar at 24 d after the 42 DAE application (DAA) when compared with the 10 DAA rating. Two weed control programs with 'Northrup King S-59-60' soybean using standard herbicide programs yielded 3,015 and 3,070 kg/ha, and net returns were $92.20/ha and $122.82/ha, respectively. Two production systems containing the Hartz 5088 Roundup Ready cultivar had positive net returns of $35.11/ha and $39.49/ha.