Noctua pronuba Linnaeus, 1758 (Lepidoptera: Noctuidae), the yellow underwing moth, was recently introduced into western North America. Blacklight traps at multiple sites in eastern Washington State indicate two broad periods of moth flight. A spring flight was evident in May and June, and a late season flight was evident from late August into October. Noctua pronuba moths were captured also in traps baited with acetic acid plus 3-methyl-1-butanol, but not in traps baited with acetic acid or 3-methyl-1-butanol alone. This chemical combination is thought to be a feeding attractant for many noctuid moths and may be useful for monitoring N. pronuba. The seasonal pattern of moths captured in traps baited with this chemical lure was similar to the pattern seen with blacklight traps.