LAUSR

Abstract Rush skeletonweed is emerging as a regionally important weed of winter wheat production in eastern Washington. Field studies were conducted during the 2016 and 2017 crop years to evaluate several auxin herbicides applied at two seasonal timings (fall or spring) for control of rush skeletonweed in winter wheat. Clopyralid (210 g ae ha-1) provided >90% visual control of rush skeletonweed in both years of the study and aminopyralid (10 g ae ha-1) provided >80% visual control. Aminocyclopyrachlor, dicamba, and 2,4-D provided <55% control of rush skeletonweed. Season of application did not meaningfully affect efficacy of any herbicide tested. Wheat yields were reduced by 39 to 69% compared to the non-treated check when aminocyclopyrachlor was applied in the spring. Clopyralid is an effective option for control of rush skeletonweed in Pacific Northwest winter wheat. Nomenclature: Aminocyclopyrachlor; aminopyralid; clopyralid; dicamba; 2,4-D; rush skeletonweed, Chondrilla juncea L.; wheat, Triticum aestivum L.