The potential increase of glyphosate-resistant weeds is a major threat to corn and soybean production across the nation and in Wisconsin. There are 14 glyphosate-resistant weeds confirmed in the United States, five of which occur in states that border Wisconsin (Heap 2012). A southern Wisconsin population of giant ragweed (Ambrosia trifida L.) was confirmed to be glyphosate-resistant and announced at this conference one year ago (Stoltenberg et al. 2012). Additionally, a different Wisconsin population of giant ragweed was also recently confirmed as resistant to cloransulam-methyl3 . Integrated weed management tactics, including the use of multiple effective modes-of-action (MOA) against troublesome weeds are important to delay the onset of glyphosate resistance (Norsworthy et al. 2012). Identifying geographies that may be most vulnerable to glyphosate resistance development could help direct attention and pro-active resistance management tactics before wide-scale control failures occur (Davis et al. 2008). The objective of the late-season weed escape survey is to identify areas of Wisconsin for potential shifts to weeds that are more difficult to control with glyphosate and areas where glyphosate resistant weeds may first appear.
Soil Science Extension
University of Wisconsin Madison