Italian ryegrass (Lolium perenne L. spp. multiflorum [Lam.] Husnot), also known as ryegrass or annual ryegrass, is an introduced cool season, annual or biennial bunchgrass native to southern Europe. It is widely distributed and a troublesome weed of winter wheat cropping systems throughout the United States.
In the inland Pacific Northwest (PNW), Italian ryegrass is a problematic weed in areas receiving greater than about 16 inches of annual precipitation. Ryegrass plants readily cross-pollinate, resulting in populations with significant adaptive capacity that has contributed to the extensive development of herbicide-resistant biotypes. Italian ryegrass populations in the PNW have developed resistance to the ACCase inhibitors (Group 1), acetolactate synthase or ALS inhibitors (Group 2), glyphosate (Group 9), glutamine synthetase inhibitors (Group 10), and very long-chain fatty acid synthesis inhibitors (Group 15).
Widespread herbicide resistance in Italian ryegrass makes integrated weed management strategies critical for effective long-term management of this troublesome weed species. A new PNW Extension publication (PNW778), “Italian Ryegrass Management in Inland Pacific Northwest Dryland Cropping Systems”, discusses multiple control strategies that can be combined in various ways to build an integrated weed management plan for Italian ryegrass management in wheat-based cropping systems of the inland PNW.
If you have been struggling with the management of Italian ryegrass, check out PNW778. Additional publications and videos about Italian ryegrass, downy brome, feral rye, jointed goatgrass, Russian thistle, and more can be found on our Weed Resources Publications page.
For questions or comments, contact Drew Lyon via email at drew.lyon@wsu.edu or phone at 509-335-2961.