Testing aerially applied Orthene for control of larch casebearer.

Abstract

Orthene was tested in a randomized block experiment to determine efficacy against larch casebearer. Needlemining larval populations were sprayed in September 1976 by helicopter with 0.5 lb Orthene/gal water/acre (560 g a.i/9.3 l/ha). Spray deposit was sampled with Kromekote cards. Plot mean larval populations, spray deposit, and defoliation index were analyzed to detect significant differences among treatments by using twoway analyses of variance. Larval populations were reduced an average of 92.1 percent on the nine treated plots and an average of 40.5 percent on the three check plots. Defoliation index averaged light on treated plots and heavy on check plots the following spring. Percent parasitization of casebearing larvae by native parasitoids was higher on treated plots than on check plots the following spring. No operational spraying of casebearer should be done with Orthene in areas where parasitoids have been introduced, however, until the effect on introduced parasitoids is known.

Citation

Hard, John S.; Meso, Stanley; Haskett, Michael. 1979. Testing aerially applied Orthene for control of larch casebearer. Res. Paper. PSW-138. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture. 6p