Weed management and net returns with transgenic, herbicide-resistant, and nontransgenic cotton (Gossypium hirsutum)

Weed management systems were compared in bromoxynil-resistant, glyphosate-resistant, and nontransgenic cotton. A standard system of pendimethalin preplant incorporated (PPI), fluometuron preemergence (PRE), fluometuron plus MSMA early postemergence-directed (POST-DIR), and cyanazine plus MSMA late POST-DIR in combination with cultivation controlled broadleaf signal-grass, large crabgrass, common lambsquarters, jimsonweed, pitted morningglory, prickly sida, sicklepod, and smooth pigweed 98 to 100% late season. Weed control, cotton yield, and net returns were similar when pyrithiobac or bromoxynil plus MSMA postemergence (POST) replaced fluometuron plus MSMA POST-DIR. Fluometuron PRE had little to no effect in bromoxynil systems. Glyphosate POST to three- to four-leaf-stage cotton followed by cyanazine plus MSMA late POST-DIR and cultivation controlled weeds 96 to 100%. Glyphosate POST followed by glyphosate POST-DIR and cultivation controled pitted morningglory and large crabgrass 89 to 90% and other species at least 94%. Yields and net returns at one location were similar for glyphosate applied twice or glyphosate POST followed by cyanazine plus MSMA POST-DIR and the standard system. Pendimethalin plus fluometuron in glyphosate systems did not increase yield or net returns. At a location severely infested with large crabgrass, pendimethalin plus fluometuron in glyphosate systems increased yield 37 to 44% and net returns 85 to 108%, respectively, when glyphosate was applied to cotton at the three- to four-leaf stage, but not if glyphosate was applied to cotton at the one-leaf stage. Yield and net returns were similar when bromoxynil-resistant, glyphosate-resistant, and nontransgenic cotton were treated using the standard system.