Herbicide combinations for weed management in glyphosate-resistant soybean(Glycine max)

Field experiments were conducted in 1995 and 1996 at DeKalb and Urbana, IL, to evaluate weed management systems in glyphosate-resistant soybean plante d in rows 76 cm wide. These experiments compared weed control using preemer gence (PRE) herbicides followed by glyphosate or postemergence (POST) tank- mix combinations of glyphosate and acetolactate-synthase-inhibiting herbici des with glyphosate applied alone at 0.63 kg ae/ha in single or sequential applications. Overall, the use of a tank-mix partner or a PRE herbicide fol lowed by glyphosate improved weed control compared to a single application of glyphosate. However, weed control with these treatments was not better t han with sequential applications of glyphosate. Control of giant foxtail ex ceeded 90% for single applications of glyphosate except at DeKalb in 1995 w hen late emergence of giant foxtail occurred after POST applications had be en made. A PRE grass herbicide or a late postemergence (LPOST) application of glyphosate was necessary for season-long control of late-emerging giant foxtail. Tank-mixing glyphosate with imazethapyr, cloransulam-methyl, and C GA-277476 or applying glyphosate LPOST following these herbicides improved giant foxtail control compared with these herbicides applied alone. A singl e application of glyphosate controlled common lambsquarters 88% or greater in two of three trials. At Urbana in 1995, a single application of glyphosa te controlled common lambsquarters 78% compared to 88 to 96% control with P RE herbicides followed by glyphosate or sequential applications of glyphosa te. Velvetleaf control with a single application of glyphosate ranged from 55 to 78%. A PRE application of chlorimuron + metribuzin, cloransulam-methy l, or sulfentrazone followed by glyphosate POST, as well. as sequential app lications of glyphosate, consistently improved velvetleaf control compared to a single application of glyphosate. In some cases, adding glyphosate to a POST application of imazethapyr or CGA-277476 improved control of velvetl eaf but decreased velvetleaf control when added to cloransulam-methyl.