Many Italian ryegrass populations in Oregon are resistant to more than oneherbicide; therefore, the resistance patterns of these populations must bedetermined to identify alternative herbicides for management. Two suspectedresistant Italian ryegrass populations (R2 and R4) survived flufenacet plusmetribuzin applications under typical winter wheat production conditions.Populations R2 and R4 were resistant to clethodim, pinoxaden, quizalofop,mesosulfuron-methyl, flufenacet, but not to acetochlor, dimethenamid-p,metolachlor, pyroxasulfone, imazapyr, sulfometuron, or glyphosate. R4 wasresistant to diuron, but R2 was not. The estimated flufenacet doses requiredfor 50% growth reduction (GR50) were 438 g ai ha−1(R2) and 308 g ai ha−1 (R4). Both populations were controlled bypyroxasulfone at rates greater than 15 g ai ha−1. An Asp-2078-Glysubstitution in the ACCase gene was found in both populations, while anIle-2041-Asn was found only in the R4 population. A Ser-264-Gly substitutionin psbA gene was found in the R4 population. Thesemutations previously have been reported to provide resistance to ACCase andphotosynthetic inhibitors, respectively. No resistance mutations wereidentified in the acetolactate synthase (ALS) gene of either population. Theaddition of the P450 inhibitor, chlorpyrifos, increased the injury resultingfrom mesosulfuron-methyl on both resistant populations providing indirectevidence that the ALS resistance may be metabolic. Multipleherbicide-resistant Italian ryegrass populations were identified in thisstudy with both target site and nontarget site based mechanisms likelyinvolved. However, several herbicides were identified includingpyroxasulfone, a herbicide in the same group as flufenacet, which could beused to control these two populations.