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

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Black leg (caused by Plenodomus lingam and P. biglobosus) and chlorotic leaf spot (caused by Pyrenopeziza brassicae) are economically important fungal diseases of Brassicaceae crops. Surveys of seed fields and weed hosts were conducted to understand the distribution and prevalence of these diseases in Oregon after black leg and chlorotic leaf spot outbreaks occurred in Brassicaceae crops in 2014. Post-harvest black leg ratings for these diseases were conducted in 2015 and 2016 in seed fields of canola, forage rape, and turnip. Black leg incidence was greater in turnip (51%) compared to canola (29%) and forage rape (25%). The overall average disease incidence was greater on seed crops harvested in 2015 (46%) compared to crops harvested in 2016 (28%). A disease survey of wild Brassicaceae plants was conducted along Interstate 5 in Oregon. Brassicaceae weed population sites were identified and 40 sites were sampled for these diseases. Black leg and chlorotic leaf spot were present in 60% and 45%, respectively, of the sampled sites. Both species of Plenodomus were detected in weed populations with P. lingam being the predominant species recovered (95%). The northernmost sample site with black leg was found less than 32 km from the Oregon-Washington border, and southernmost site occurred within 32 km of the Oregon-California border. Chlorotic leaf spot was detected less than 32 km from Oregon-Washington border, whereas the southernmost detection was approximately 164 km from the Oregon-California border. Based on this study, infected crop residues and weed hosts may facilitate persistence and spread of these pathogens.

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