Glyphosate-Resistant Giant Ragweed (Ambrosia trifida) Control in WideStrike® Flex Cotton

A field study was conducted in 2009, 2010, and 2011 on a grower's field with a known population of glyphosate-resistant giant ragweed to determine potential control options utilizing a WideStrike® cotton variety. Glyphosate-resistant giant ragweed control and cotton response to herbicide applications were both assessed. Few herbicide treatments provided greater than 80% control. Glufosinate followed by glufosinate was the only treatment that provided greater than 90% control at each assessment timing. Other effective treatments were glufosinate alone, glufosinate plus glyphosate, glyphosate plus pyrithiobac, and glufosinate plus fluometuron. Results from this study indicate that few of the studied herbicide treatments provide effective control of glyphosate-resistant giant ragweed without reducing yield in WideStrike cotton. Treatments that had the highest level of giant ragweed control at all ratings and also had the highest yield included glufosinate followed by glufosinate, glufosinate plus pyrithiobac, and glufosinate plus fluometuron at either rate. However, glufosinate followed by glufosinate was the only treatment that resulted in greater than 90% control of giant ragweed without reducing crop yield.