Effects of insecticide treatments on subsequent defoliation by western spruce budworm in Oregon and Washington: 1982-92.

Author This publication reports analyses involving pesticides. It does not contain recommendations for their use, nor does it imply that the uses discussed here have been registered. All uses of pesticides must be registered by appropriate State and Federal agencies before they can be recommended. CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers. Effects of insecticide treatments conducted in Oregon and Washington from 1982 through 1992 on subsequent defoliation by western spruce budworm (Choristoneura occidentalis Freeman) were evaluated by using aerial sketchmaps and a geographic information system. For each treatment, the extent and severity of defoliation was calculated for the treated area and a set of four nested rings surrounding the treated area (0-0.5 mile, 0.5-1 mile, 1-2 miles, and 24 miles) for up to 8 years: 3 years prior to treatment, the year of treatment, and 4 years following treatment. lnsecticide treatments applied in 1982 and 1983 coincided with reduced percentages of defoliation by western spruce budworm during the year following treatment. However, the percentage of defoliation usually returned to pretreatment levels by the second year, and defoliation severity in treated and adjacent untreated areas was nearly identical following treatment. For the period from 1985 through 1992, defoliation patterns (including both extent and severity) following treatment were generally similar in treated and adjacent untreated areas. Abstract This page was intentionally left blank. Western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera: Tortricidae), is commonly regarded as one of the most important defoliators of western coniferous forests (Fellin and Dewey 1982, Furniss and Carolin 1977, Johnson and Denton 1975). Defoliation by budworm larvae feeding primarily on developing buds and new foliage may lead to tree growth loss, topkill, and mortality (Van Sickle 1987). Over 2.1 million acres have been treated with insecticides to suppress western spruce budworm populations in Oregon and Washington since the current outbreaks began in 1980 (appendix A). The objective of this analysis was to answer several questions regarding the effectiveness of these treatments: What are the effects of treatment on defoliation extent and severity in subsequent years? How long do the treatment effects last? Is there any evidence that budworms from untreated areas invade adjacent treated areas after treatment? Answers to these questions would help …