Atrazine provides effective control of many small and large seeded broadleaf weeds, as well as some grass weed species, in numerous grass crops such as corn. In Wisconsin, the use of atrazine is prohibited in areas where atrazine total chlorinated residues were once found in concentrations greater than 3 parts per billion in drinking water wells. Glyphosate-resistant weeds, confirmed in 32 states, continue to be a major threat to corn and soybean production across the Nation and Wisconsin. In Wisconsin, a population of both giant ragweed (Ambrosia trifida) and horseweed (Conyza canadensis) has been confirmed to be resistant to glyphosate (Stoltenberg et al. 2012; Recker et al. 2013). 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). A pro-active survey of late-season weed escapes in corn and soybean fields was conducted throughout Wisconsin in 2012 and 2013. The objective of the late-season weed escape survey was to compare weed community composition in different types of management, including previous atrazine use, as well as identify areas where glyphosate-resistant weeds may first appear.
Soil Science Extension
University of Wisconsin Madison