Todd Gaines, CSU Associate Professor of Weed Science
We conducted a survey of eastern Colorado for winter annual grass weeds in wheat. We found no resistance in the samples to quizalofop (Aggressor herbicide in CoAXium) as expected since CoAXium wheat hadn’t yet been introduced, and we found that mostly all the samples were sensitive to imazamox (Clearfield wheat and Beyond herbicide), except for a couple of samples in Weld county. In those samples, we found feral rye resistant to imazamox. Two populations had target site mutations in the ALS gene. A third population had enhanced metabolism of the herbicide. All three populations were collected based on grower and crop consultant observations and concerns about potential resistance, and were not part of the random survey. Growers should monitor feral rye after imazamox application for efficacy and consider submitting samples for resistance testing.