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

Abstract

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.