Weed control programs in drilled glyphosate-resistant soybean

Field studies were conducted in 19-cm-row soybean during 1997 and 1998 to e valuate the rate and timing of glyphosate applications applied alone at 0.4 2 and 0.63 kg ae/ha and with other herbicides to glyphosate-resistant soybe an in terms of weed control, soybean yield, and net return. Weed species in cluded barnyardgrass, hemp sesbania, pitted morningglory, and prickly sida. Among glyphosate-alone weed control programs, sequential applications gene rally provided the highest and most consistent control of all species evalu ated (above 90% for broadleaf species). Glyphosate applied in combination w ith selective postemergence (POST) herbicides or following soil-applied her bicides controlled most species comparable to sequential glyphosate applica tions. Most herbicide programs, except for single glyphosate applications, were, comparable to sequential glyphosate applications in terms of soybean yield and net return and ranged from 2,221 to 2,827 kg/ha and $410.28 to $5 49.60/ha. Depending on the year, either one or two glyphosate applications were needed for adequate weed control in programs with a soil-applied herbi cide. Glyphosate rate affected neither weed control, yield, nor net return. Depending on a producer's management style and weed spectrum, weed control programs with glyphosate alone, in combination with another POST herbicide , or following soil-applied herbicides are all viable options in drilled gl yphosate-resistant soybean.