Cory Mills and Craig Bednarz. Texas Tech University, PO Box 42122, Lubbock, TX 79409
Roundup Ready Flex (RRF) cotton, with enhanced glyphosate-resistance, is tolerant to topical applications of glyphosate from emergence to harvest. In 2006 multi-location studies were conducted with 6 RRF cotton varieties to determine the yield response and seed quality to late season topical applications of glyphosate. The field experiments were arranged in a split-split-plot design with location (5 locations, 3 in Arizona and 2 in Texas) as the main plot, application rate of glyphosate (2 rates of Roundup Weathermax, 1.125 and 2.25 lb ae/acre, respectively) as the subplot, and timing of application in terms of growth stages (first bloom, full bloom, first bloom+ full bloom, cracked boll, first + full bloom + cracked boll) as the subsubplot. The experimental results show that applications of glyphostae as high as 2.25 lb ae /acre and as late as the cracked boll stage did not affect cotton yield and seed quality in terms of the Cool-Warm Vigor Index Test (CWVI). These data show that RR Flex allows a wider window of application without the risk of yield or seed quality loss. This should allow producers greater flexibility in crop management without restricting glyphosate application to a narrow application window.
