Herbicide resistance in weeds is an increasing problem for farmers in the Pacific Northwest. Wheat and barley growers find themselves losing previously effective herbicide options for the control of Italian ryegrass, downy brome or cheatgrass, wild oat, Russian thistle, prickly lettuce, and mayweed chamomile or dog fennel. Much of this resistance is the result of target-site resistance, where a single gene mutation results in a binding site/protein change that results in the herbicide no longer being able to bind to the target site and allowing the weed to grow and reproduce in the presence of the herbicide.
However, in recent years, a more complicated form of herbicide resistance is emerging: non-target-site resistance. Metabolic resistance is one type of non-target-site resistance that is particularly concerning because it can result in plants developing resistance to specific or multiple herbicide groups without any previous exposure to those herbicides. This makes managing metabolic resistance difficult by the traditional practice of mixing or rotating the use of effective herbicide modes of action. Greater than 80% of newly identified resistance in Italian ryegrass and downy brome from Eastern Washington is the result of non-target-site resistance. To learn more about non-target-site resistance, read my recent post on the Weeders of the West forum. Additional information about herbicide resistance can be found on the Herbicide Resistance Resources page of the WSU Wheat and Small Grains website.
For questions or comments, contact Drew Lyon via email at drew.lyon@wsu.edu or phone at 509-335-2961.