Cankerworm Control in Shelterbelts, Walhalla, North Dakota, 1976

Each insecticide was applied from the air to 1 of 6 one-half mile long single row belts. There were approximately 100 yds between belts. Pre-treatment larval counts were made from two randomly selected twigs on each side of 6 trees along each belt on June 2. Twig samples were taken at eye level and approximately 20 ft above ground level. Larvae were in the 1st to the 3rd instar and averaged 48.9 larvae/2 ft twig. There were approximately 2 spring cankerworms to 1 fall cankerworm. Treatments were applied June 3. Post-treatment larval counts were similarly made one week later. The materials were applied with 44, D-7 nozzles at 40 psi and 115 mph. Three gals of water/acre were applied. Wind speed at application was 5-10 mph, and measurable and prolonged rainfall occurred during the period between application and post-treatment larval counts. Data consisted of % reduction in cankerworms between pre- and post-treatment counts. No reduction in cankerworms was assumed when post-treatment counts were equal to or greater than pre-treatment counts. The arcsin transformation was applied to the data. Treatments were compared with a series of “t” tests for paired comparisons.