Weed Control Alternatives in Very Early-Maturing Mississippi Soybean

Field experiments were conducted in 2000 and 2001 at Stoneville, MS to determine the most efficacious and economical weed control programs for MG III soybean and to determine the profitability of using a preharvest desiccant with this production system. The most consistent Johnsongrass and barnyardgrass control over years and rating periods occurred with herbicide programs that utilized sequential POST glyphosate applications or a POST glyphosate application following PRE herbicides. Late-season prickly sida control was at least 86% with all herbicide programs except POST programs chosen by MSU-HERB, a computer-based herbicide recommendation program. Greater than 90% hemp sesbania control 7 weeks after final POST application (WAFPA) was achieved with any program that included a POST herbicide. At least 71% pitted morningglory control 7 WAFPA was achieved in 2000 with all treatments. Rainfall contributed to heavy preharvest weed infestations in 2001 and greater than 70% pitted morningglory control was achieved only when residual herbicides were utilized. Soybean yield and net returns were generally not improved by using a preharvest desiccant in 2000 when moisture was limited following in-season herbicide applications and weed flushes at harvest were low. Soybean yield and net returns generally increased with the use of a preharvest desiccant in 2001. Residual herbicides reduced the need for preharvest desiccants in 2001. Sequential glyphosate tank mix programs with cloransulam + acifluorfen provided net returns equal to the best treatments regardless of year or preharvest desiccant.