Frequency, distribution, and ploidy diversity of herbicide-resistant Italian ryegrass (<i>Lolium perenne</i> spp. <i>multiflorum</i>) populations of western Oregon

Abstract Italian ryegrass [ Lolium perenne L. spp. multiflorum (Lam.) Husnot] is one of the most troublesome weeds worldwide. also a grass seed crop cultivated on 50,000 ha in Oregon, where both diploid and tetraploid cultivars are grown. For this work, we will refer to species as multiflorum, since common names annual same species. A survey was conducted understand distribution frequency its susceptibility selected herbicides used control. The were clethodim, glufosinate, glyphosate, mesosulfuron-methyl (mesosulfuron), paraquat, pinoxaden, pyroxsulam, quizalofop-P-ethyl (quizalofop), pronamide, flufenacet + metribuzin, pyroxasulfone. ploidy levels populations tested. total 150 fields surveyed between 2017 2018, which 75 (50%) had present. Herbicide-resistant documented 88% collected. frequent resistances acetyl-CoA carboxylase (ACCase), acetolactate synthase (ALS), 5-enolpyruvylshikimate-3-phosphate (EPSPS) inhibitors, combinations thereof. Multiple resistance cross-resistance, found 75% populations, patterns resistance. Paraquat-resistant biotypes confirmed six orchard for first time Oregon. Herbicide spatially clustered, with cases northern part area. Populations resistant ALS ACCase inhibitors prevalent wheat ( Triticum aestivum L.) fields. positively correlated plant density. Tetraploid feral identified, but no herbicide documented. This diversity western Resistant present across area, indicating that problem widespread.