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1 October 2013 Giant Ragweed (Ambrosia trifida) Competition in Cotton
Kelly A. Barnett, Lawrence E. Steckel
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Glyphosate-resistant (GR) weeds, including giant ragweed, are among the most challenging weeds for growers to control in cotton. A field study was conducted in 2011 and 2012 to determine the competitiveness of giant ragweed with densities of 0, 0.1, 0.2, 0.4, 0.8, or 1.6 plants m−1 of row. Early in the growing season, giant ragweed competition with densities of at least 0.8 plants m−1 row reduced cotton height compared with the weed-free control. Based on node above white flower (NAWF) and node above cracked boll (NACB) data, a delay in cotton maturity was observed for treatments with giant ragweed present at a density of 1.6 m−1 of cotton row for NAWF and 0.8 m−1 or 1.6 m−1 of row for NACB. Lint yield losses of 50% were estimated for cotton with rows growing along side of giant ragweed at a density of 0.26 plants m−1 row. Cotton in rows located 140 cm away from giant ragweed required an estimated 1.85 plants m−1 row to reduce yield by 50%. These data suggest that giant ragweed sphere of influence was at least 1 m wide. Cotton fiber quality was not affected by giant ragweed at any density. Giant ragweed is a highly competitive weed in cotton, even at low densities, and efforts should be implemented to control giant ragweed early in the season to prevent cotton yield loss.

Nomenclature: Cotton, Gossypium hirsutum L., giant ragweed, Ambrosia trifida L., glyphosate resistant, GR.

Weed Science Society of America
Kelly A. Barnett and Lawrence E. Steckel "Giant Ragweed (Ambrosia trifida) Competition in Cotton," Weed Science 61(4), 543-548, (1 October 2013).
Received: 25 October 2012; Accepted: 1 May 2013; Published: 1 October 2013

giant ragweed
Glyphosate resistance
Herbicide resistance
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