Glyphosate-Resistant Giant Ragweed Competition and Control in Mid-South Cotton

Giant ragweed has been primarily considered a weed of floodplains, fence rows, and ditch banks, but in more recent years has become an issue in agronomic crops across the United States.  Previous work determined that giant ragweed was one of the most competitive weeds in corn and soybean and can reduce yields with low populations of giant ragweed.  However, little is known about the effects of giant ragweed in cotton.  Therefore a field study was conducted in 2011 and 2012 to demonstrate the effect of giant ragweed on cotton maturity, lint yield, and fiber quality.  Giant ragweed densities were 0, 1, 2, 4, 8, and 16 weeds per 4 row by 30 ft. plot.  Plots were maintained weed free throughout the growing season.  Cotton heights, node above cracked boll ratings, lint yield, and fiber quality characteristics were assessed.  The objectives of this study were to determine if giant ragweed would reduce cotton height, delay maturity, reduce yield, and fiber quality at each of these populations. 

GR giant ragweed was first confirmed in 2007 in Tennessee and has continued to become more problematic throughout this region.  Few control options are available for control of GR giant ragweed in cotton.  Glufosinate is one of the more effective control options for GR giant ragweed; however, this herbicide can only be applied to glufosinate-tolerant varieties.  Therefore, field studies were conducted in 2009, 2010, and 2011 to determine control options for GR giant ragweed in cotton.  Pyrithiobac, trifloxysulfuron, and fluometuron were utilized and applied in combination with glyphosate or glufosinate.  All applications were applied once at either the 1-lf or 5-lf cotton stage, with the exception of a glufosinate followed by glufosinate application.  The objectives of this study were to determine cotton response to herbicide applications, GR giant ragweed control, and lint yield.