Abstract The Orthene 75S water-soluble powder formulation of acephate was applied with and without the addition of Nalcotrol 1 (a viscoelastic antidrift additive used at 9 fluid oz/100 gallons of mix) at the rate of 0.094 lb ai/acre to 350 acre plots of mixed grasses approximately 25 miles northeast of Vernal, Utah on July 28 and 29. Both treatments were applied in water at one quart of fluid/acre at 40 psi with a Piper Brave, PA 36-350 PC turbo charged airfract using (18) 8002 nozzles rotated 30° aft. Application speed was 120 mph at a height of 50-300 ft because of surrounding mountainous terrain. The swath width was 60 ft. Pre and post application densities of grasshoppers were ascertained by counting grasshoppers in (40) 0.1m2 rings at 10 randomly selected locations within each treatment. At each site rings were separated from each other by at least 5 yards. Pre treatment counts were taken 24 hr prior to treatment and post treatment counts were conducted 4 and 10 days following application. Rings were left in place throughout the test. The above species were in the 4th instar through adult stages of development and comprised 95% of the grasshopper population: Camnulapellucida (Scudder) 75%, Melanoplussanguinipes (Fab.) 8.7% and M. bivittatus (say) 11.5%. Precount densities ranged from 15.00 to 93.75 grasshoppers/m2 and averaged 47.25 grasshoppers/m2 in the orthene plus Nalcotrol plot. The orthene only plot exhibited densities which ranged from 7.25 to 45.25 grasshoppers/m2 and averaged 19.53/m2. Data were recorded as % mortality and the arc sine transformation was used to analyze the effectiveness of the treatments by using at test of significance for treatment mortalities at each post count time Interval. Forty sweeps were taken at each density sample location to determine species frequency.