Glyphosate–resistant Russian-thistle was identified in Washington in 2015. Other weeds resistant to glyphosate have been identified in the state in recent years, including prickly lettuce, horseweed, kochia, and Italian ryegrass. Many people think that herbicide resistance is a recent phenomenon associated with the overuse of glyphosate-resistant crops, but as a recent article released by the Weed Science Society of America states, herbicide-resistant weeds predate glyphosate-resistant crops by 40 years.
The use of glyphosate-resistant crops (there are no glyphosate-resistant wheat varieties) is very limited in the dryland crop production systems of Eastern Washington and yet herbicide-resistant weeds are a growing concern for many Washington wheat farmers. Resistant weeds can evolve whenever a single approach to weed management is used repeatedly, whether that approach is chemical, mechanical, or cultural. A diverse, integrated approach to weed management is the first line of defense against herbicide-resistant weeds.
Washington wheat growers who suspect that they may have developed a weed that is resistant to an herbicide may want to submit a sample to the WSU Resistance Testing Program.
For questions contact Drew Lyon (firstname.lastname@example.org or 509-335-2961) or Ian Burke (email@example.com or 509-335-2858), who are Weed Scientists at Washington State University in Pullman.