Single and sequential applications of dicamba for the control of glyphosate-resistant common ragweed in glyphosate- and dicamba-resistant soybean

Confirmation of glyphosate-resistant (GR) weeds in southwestern Ontario has led to a change in weed management practices, particularly in soybean. Registered soil-applied herbicides have been identified that have activity on GR common ragweed; however, due to the long emergence period of common ragweed, additional postemergence options are required. The recent development of glyphosate- and dicamba-resistant soybean (Roundup Ready Xtend soybean) allows for the preplant and postemergence application of dicamba. Three field studies were conducted in Ontario, Canada, in a field with confirmed GR common ragweed. Glyphosate-resistant common ragweed interference resulted in 75% yield loss in soybean compared with the weed-free check. At 4 wk after application, dicamba tank-mixed with glyphosate applied preplant only, postemergence only, or preplant followed by postemergence controlled GR common ragweed up to 94%, 87%, and 99%, respectively. The availability of dicamba for use in glyphosate- and dicamba-resistant soybean will provide an additional mode of action for weed management in soybean.