Thursday, November 16, 2006 - 8:15 AM

Management of Problematic Populations of Giant Ragweed in Glyphosate-Resistant Soybean in the Eastern Corn Belt: Part II.

Mark M. Loux1, Jeff Stachler1, William G. Johnson2, Andrew Westhoven2, Vince Davis2, and Greg Kruger2. (1) The Ohio State Univ, 2021 Coffey Rd, Columbus, OH 43210, (2) Purdue Univ, Lilly Hall of Life Sciences, 915 West State St, West Lafayette, IN 47907

Giant ragweed biotypes with reduced sensitivity to glyphosate were identified in greenhouse research at The Ohio State University and Purdue University in 2004 and 2005.  Field studies were conducted at five sites in Ohio and Indiana in 2006 to determine the most effective strategies to manage these biotypes in glyphosate-resistant soybeans.  The following factors were evaluated in these studies:  presence or absence of a preplant nonselective herbicide treatment and residual herbicides; and postemergence glyphosate application timing and rate.  Based on preliminary results, most effective management of these giant ragweed biotypes occurred when the field was treated with glyphosate and 2,4-D ester prior to planting, followed by: 1) two postemergence glyphosate applications; or 2) an initial postemergence application of fomesafen, and then a subsequent postemergence application of glyphosate.  Least effective management occurred where the field was not treated prior to planting, and the herbicide program consisted solely of postemergence glyphosate applications.  Giant ragweed plants survived an initial glyphosate treatment of 0.8 to 3.4 kg ae/ha, but a subsequent glyphosate treatment improved control of surviving plants.