Weed Management in Enhanced Glyphosate-Resistant Cotton

Brandon L. Joy, J. Wayne Keeling, Peter A. Dotray

Abstract


Field experiments were conducted in 2003 and 2004 to evaluate glyphosate rates and timings on control of Palmer amaranth, devil’s-claw, ivyleaf morningglory, and silverleaf nightshade in enhanced glyphosate-resistant cotton.  Treatments based on cotton growth stage (CS) were compared to as-needed (ASN) treatments based on weed population and size.  Palmer amaranth, devil’s-claw, and silverleaf nightshade were controlled (> 90%) with postemergence (POST) treatments based on CS or ASN applications in both years.  These weeds were controlled with glyphosate at 0.75 lb ae/A and no benefit was observed with an increased glyphosate rate.  Ivyleaf morningglory control, in both years, improved with increased glyphosate rates to 1.5 lb ae/A.  When the first application was delayed to 11-leaf cotton, three glyphosate applications at 1.5 lb ae/A were required to achieve control.  Ivyleaf morningglory in 2003 was controlled with four glyphosate applications applied ASN beginning at two-leaf cotton and ending with the last treatment applied at 20-leaf cotton.  In 2004 with increased rainfall and weed pressure, five applications of glyphosate at 1.5 lb ae/A were required for effective control (> 90%). 


Keywords


Amaranthus palmeri S. Wats.; cotton; devil's-claw; glyphosate rates; glyphosate timing; Gossypium hirsutum L.; Ipomoea hederacea (L.) Jacq.; ivyleaf morning glory; Palmer amaranth; Proboscidea louisianica (Mill.) Thellung; silverleaf nightshad

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