Management of Palmer Amaranth (Amaranthus palmeri) in Second-Generation Glyphosate-Resistant Cotton

Max A. Batla, J. Wayne Keeling, Peter A. Dotray


Field experiments were conducted in 2005 and 2006 to evaluate glyphosate timings and use of residual herbicides to control Palmer amaranth (Amaranthus palmeri S. Wats.) in second-generation glyphosate-resistant cotton (Gossypium hirsutum L.).  Glyphosate treatments based on timing were used, in addition to preplant incorporated and postemergence-topical residual herbicides, to determine effective Palmer amaranth management systems.  In 2005, complete control (100%) of Palmer amaranth was achieved across all glyphosate postemergence-topical systems.  Less than complete control (94 to 98%) was observed with postemergence-directed glyphosate-resistant systems either with or without trifluralin preplant incorporated compared to second-generation glyphosate-resistant postemergence-topical systems.  In 2006, similar Palmer amaranth control (95 to 99%) was observed across all second-generation glyphosate-resistant systems following trifluralin preplant incorporated and no benefit was observed from pyrithiobac or S-metolachlor tank-mixed with glyphosate.  When trifluralin was not used, pyrithiobac or S-metolachlor tank-mixed with glyphosate early postemergence-topical followed by glyphosate improved control compared to glyphosate alone.  Delaying early-season glyphosate applications did not reduce cotton lint yield; however, when no glyphosate was used cotton yields were reduced.


Amaranthus palmeri S. Wats.; glyphosate; Gossypium hirsutum L.; palmer amaranth; residual herbicides; roundup ready flex cotton; weed management systems

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