Evaluation of Douglas-fir tussock moth, Orgyia pseudotsugata, egg masses collected from an outbreak area in the lower Flathead Valley indicated that overall egg viability was relatively high, egg parasitism was low, and virus infestation averaged 7.1 percent northwest of Polson, 17.9 percent south of St. Ignatius, and 57.0 percent west of Ravalli. In the three areas, a total of 2,240 acres may be visibly defoliated in 1975, and light defoliation may be scattered over an additional 5,600 acres. The outbreak is expected to decline due to natural causes by the end of 1975.
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