The insecticide acephate (0.5-dimethyl acetyl phosphoramidothioate) was applied at 0.5, 1.0, and 1.5 lb A.I./gal (.058, 0.118, 0.179 kg/l.) in aqueous solution to individual Douglas-fir trees infested with western spruce budworm, Choristoneura occidentalis Freeman, larvae in central Washington using hand held ground application equipment. Application was made when larvae were in the needle mining – bud mining stage at rates ranging from 2.58 to 5.10 gal/acre (3.97 to 7.84 l./ha). For all three concentrations, mortality of larvae inside needles was 94–98% after 1 day compared with a check mortality of 18% and larval mortality inside buds was 99% after 1 day compared with 23% for the check. Regression analyses indicated that defoliation was positively correlated with the number of needles mined the current year and per cent punctured buds, and negatively correlated with larval mortality inside both needles and buds. The data suggest that when applied at the rates used, acephate has some type of systemic action and can provide foliage protection during the year of application.