Douglas-Fir Tussock Moth Ground Spray Tests, 1974

To find a replacement for DDT for control of the Douglas-fir tussock moth ground tests of 15 insecticides were conducted between June 21 and July 10′74 on the Wallowa-Whitman National Forest in northeastern Oregon. Each material was applied at 3 different rates, following recommendations solicited from the manufacturers. Each dosage tested was replicated on 3 randomly selected pairs of trees 15-25 ft high. Applications were made at a rate equal to 1 gal/acre using a backpack mistblower with a Beecomist Model 150 with wettable powder sleeve which gave a droplet size (VMD) of approximately 100 for oil based and 250 for water based sprays. Spraying took 5 days to complete, on each day 3 pairs of trees were randomly selected from those to be treated and set aside as checks. Population estimates were made at 1 day before spraying and 3 intervals after spraying by sampling 3, 18-inch branches from each tree. Populations were expressed as number of larvae per 1000 in of branch surface. Application was made primarily against first and second instar larvae.