Selection and performance of weed management systems in cotton (Gossypium hirsutum) utilizing conventional and herbicide tolerant crop varieties

Field trials were conducted to evaluate standard, bromoxynil resistant, and glyphosate tolerant cotton management systems. Smooth pigweed, common cocklebur, entireleaf morningglory, and large crabgrass were controlled >90% by all weed control programs. Goosegrass was controlled greater than 97% by all programs that included a soil-applied herbicide or a late post-directed application of cyanazine + MSMA. Red sprangletop control was at least 93% in all systems that included a soil-applied herbicide. The total postemergence (POST) treatment of glyphosate followed by (fb) glyphosate in glyphosate tolerant cotton controlled goosegrass and red sprangletop 80 to 82% at 8 to 10 wk after planting. Red sprangletop control in the total POST system of glyphosate fb cyanazine + MSMA was poor (33%).;Lint yields obtained from weed free checks were similar for each of the three varieties. With the exception of bromoxynil early POST fb cyanazine + MSMA, lint yields were similar for all systems that included soil-applied herbicide(s) or two applications of glyphosate. Lint yields in the glyphosate tolerant systems that included a soil-applied herbicide were 130 kg/ha greater than the bromoxynil system. Lint yield from the bromoxynil system was equivalent to both standard programs and the total POST programs in glyphosate tolerant cotton.;Net returns were highest for the pendimethalin fb glyphosate fb glyphosate program, but was not different from the total POST program of glyphosate fb glyphosate or pendimethalin + fluometuron fb glyphosate fb cyanazine + MSMA. The addition of soil-applied herbicides to the total POST glyphsate fb cyanazine + MSMA increased net return. However, no increase in net return was obtained by the addition of pendimethalin to the total POST glyphosate fb glyphosate program. Net returns following the pyrithiobac standard system and the bromoxynil system were significantly lower than those obtained from glyphosate systems.;A cotton variety decision aid model was created using weed control efficacy information reported on herbicide labels and in university extension publications. The decision aid utilizes a "decision tree" approach where the cotton variety is selected to optimize weed control, minimize herbicide resistance development, and maximize farmer profitability.