Dipel (R) was applied by helicopter to three blocks of Douglasfir and Engelmann spruce infested with Choristoneura occidentalis Free., in southwestern Montana. Dosage was 1 pound (7.2 Bill) in 2 gallons of water/acre (453 g in 7.5 t/0.4 ha). A commercial surfactant, Bio-film (R) was added at the rate of 16 oz./100 gal. (453 g/378.5 £) of spray. Rhodamine B extra S dye was added at the rate of 1.25 g/i. Dipel was applied to mainly third and fourth instar budworm. Mortality, corrected by covariance analysis, at 21-day postspray counts indicated an average of 50.4 percent control. Additional mortality further reduced the population to an estimated 4.4 budworm/100 buds compared to 12 budworm/100 buds in check blocks. Foliage protection was 5.6 percent. Significant parasite population disruptions occurred following spray application.