Synthetic pheromone evaporated from controlled-release applicators substantially reduced the ability of male Douglas-fir tussock moths,Orgyia pseudotsugata(McDunnough), to locate females and mate in the field. Dosages of 0.05–5.0 mg/ha/day were tested; the 2 strongest treatments of 1.0 and 5.0 mg/ha/day were the most effective. The disruption effect was relatively greater with traps baited with live females than with traps baited with synthetic pheromone. Catches of males in traps increased with increased height of traps above the 1.5 m treatment level up to 18.3 m.