Résumé :
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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 ans severity of defoliation was calculated for the treated area and a st of four nested rings surrounding the treated area (0-0.5 mile, 0.5-1 mile, 1-2 miles, and 2-4 miles) for up to 8 years : 3 years prior to treatment, the year of treatment, and 4 years following treatment. Insecti ide 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 severity in treated and adjacent untreated areas was nearly identical dollowing treatment. For the perio from 1985 through 1992, defoliation patterns (including both extent and severity) following treatment were generally similar in treated and adjacent untreated areas.
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