Glyphosate Resistance and Tolerance in Italian Ryegrass (Lolium perenne spp multiflorum) : Termination Treatments, Cultivar, and Resistance Evaluation

Graduation date: 2016Annual ryegrass, or Italian ryegrass (Lolium perenne spp. multiflorum), has been the most stable, in terms of acres, grass produced for the past 25 years in Oregon. Increased interest in Italian ryegrass as a cover crop has increased demand for quality seed. Ideal Italian ryegrass cover crop cultivars are named cultivars, have winter hardiness and uniform germination, emergence, and growth to guarantee effective termination and reduce the potential for volunteer carryover. The typical method of cover crop termination is through chemical means with a non-selective herbicide or with tillage. In this study, nine termination treatments were used to determine effective treatments and explore potential differences in control between a diploid and a tetraploid cultivar. There was no difference in response based on ploidy level between the treatments. Glyphosate and glyphosate tank mixtures effectively controlled Italian ryegrass. A cultivar evaluation was also conducted to determine if there was a difference in response to glyphosate between ploidy levels. There was no difference in response to glyphosate due to ploidy level. Shikimate acid assays did suggest possible differences in the amount of glyphosate binding to EPSPS depending on the cultivar. An Italian ryegrass population (OR10) was found to be glyphosate resistant. Along with screening the OR10 suspected resistant population, samples collected from seed production fields were collected and screened. No glyphosate resistant populations were found