Presence and distribution of ALS-resistant Kochia scoparia (L.) Schrad. in the Bighorn Basin of Wyoming

This research was designed to collect data on the presence and distribution of acetolactate synthase (ALS)-resistant Kochia scoparia in the Big Horn Basin of Wyoming. The Big Horn Basin is contained within Bighorn, Hot Springs, Park, and Washakie counties. The sites were located and assessed in a three-step process consisting of visual observation of probable field sites, GPS data collection and laboratory experiments for confirmation of ALS herbicide resistance. Results were analyzed using chi-square. The results indicated that 8.9% and 21.6% of all seed tested was ALS resistant in 2001 and 2002, respectively. Furthermore, 12 and 24 sites in 2001 and 2002, exhibited resistance of 40 and 33 sites respectively. The percent resistant seed at these sites averaged 11.8 in 2001 and 27.8 in 2002. These data indicate that ALS-resistant kochia is widespread and increasing in size in the Bighorn Basin of Wyoming.