Giant ragweed resistance to glyphosate has been confirmed in several Midwest states, including the neighboring states of Minnesota and Iowa. In Minnesota as well as Ohio, giant ragweed has developed resistance to more than one herbicide mode of action (glyphosate and ALS inhibitors). In Wisconsin, we’ve identified three giant ragweed populations that are suspected of being resistant to glyphosate. Results of preliminary experiments on a giant ragweed population from southwest Wisconsin (Grant County) and a second population from southeast Wisconsin (Rock County) were reported at the 2011 Wisconsin Crop Management Conference. A third population of giant ragweed with suspected resistance to glyphosate was identified in south-central Wisconsin (Columbia County) in 2011. Seeds were collected from this giant ragweed population for investigation of resistance to glyphosate and other herbicide modes of action. The results of greenhouse experiments conducted over the last 12 months to more fully characterize the whole-plant response of the Grant County and Rock County populations to glyphosate will be presented.
Soil Science Extension
University of Wisconsin Madison