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Weed Management in Roundup Ready Flex Cotton in Arizona

William B. McCloskey, Kwame O. Adu-Tutu, and T. Vint Hicks


Experiments were conducted in 2002 and 2003 at the University of Arizona Maricopa Agricultural Center to evaluate the tolerance of RR Flex cotton to topical Roundup Weathermax (glyphosate) applications and to study weed management programs in RR Flex cotton. RR Flex cotton demonstrated excellent tolerance to glyphosate as measured by pollen viability and yield. The presence of the RR gene did not affect the yield of genotype pairs that were identical except for the presence or absence of the RR Flex genetic construct. In the weed management study, delaying the first topical glyphosate application resulted in larger, more difficult to control weeds and reduced cotton yield by allowing greater early season competition between weeds and cotton. The best weed control programs included early (1 to 2 leaf growth stage) topical applications at rates greater than 0.75 lb ae/A and a second Roundup application after the first post‑planting irrigation (10 node growth stage). The data also suggested that there may be significant value in making a layby, directed-broadcast application that includes a residual herbicide such as Caparol (prometryn) at layby.

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Document last modified 04/27/04