Willenborg, C. J. and Dosdall, L. M. 2011. First report of redbacked cutworm damage to cow cockle [ Vaccaria hispanica(Mill.) Rauschert], a potential new crop for western Canada. Can. J. Plant Sci. 91: 425-428. We report the effects of redbacked cutworm Euxoa ochrogaster (Guenée) on cow cockle [Vaccaria hispanica (Mill.) Rauschert] plant height, seed yield, and 1000-seed weight (TSW). Euxoa ochrogaster damage to plots varied considerably among genotypes, with some genotypes exhibiting <10% damage and others >45%. Seed yield also varied significantly among genotypes and exhibited a strong linear relationship with the extent of E. ochrogaster damage. This is the first known report of any insect pest feeding on cow cockle. Results suggest that E. ochrogaster has the potential to cause significant losses in cow cockle crops.