Western Spruce Budworm Control with Three Dosages of Orthene, 1976

Abstract

Abstract Orthene 75S (acephate) was applied at the rates of 1 lb a.i./gal/acre, 1/2 lb a.i./gal/acre, and 1/4 lb. a.i./gal/acre against 4th and 5th instar larvae of the western spruce budworm in the Targhee National Forest, Idaho, Jul 7 to 11′76. Orthene was mixed in water with no adjuvent except a dye for marking. Application was by a Hiller SL4 helicopter using Beecomist nozzles, flying at 45 mph, 50 ft above tree tops. Spray plots were about 100 acres in size and at 6500 to 7100 ft elevation. Three plots were treated at each dosage rate, with 3 additional plots left untreated as checks. Populations, expressed as larvae/100 buds, were determined 24 hr before spray and at 3 intervals afterward from 24 sample trees in each plot. Orthene is now being considered for operational use against the western spruce budworm at the rate of 1 lb a.i./acre. The results suggest that the population reductions achieved by the 1 lb/acre and 1/2 lb/acre rate did not differ significantly. Therefore, a dosage rate as low as 1/2 lb/acre may be almost as effective as 1 lb.