Problem Identifier Unit Screen//v.w/ RR Template

Problem Identifier Unit Screen//v.w/ RR Template Douglas Fir Tussock Moth

Problem
Much of the foliage is eaten, starting at the top of the tree and progressing downward. The entire tree may be defoliated in one season. Trees that lose most of their needles a second year are usually killed. Inch-long, hairy, gray or light brown caterpillars with black heads and tufts of orange hairs on their backs may be feeding on the needles.

Analysis
(Orgyia pseudotsugata)

Douglas fir tussock moth populations are cyclical. Every 7 to 10 years, forest populations build up to epidemic proportions. When this occurs, true firs, Douglas fir, spruce, pine, and larch may be completely defoliated. In cities, damaging numbers may be found every year. In mid- to late summer the hairy, wingless female moths lay their eggs in a frothy substance covered with a layer of hairlike scales. When the eggs hatch the following spring, the caterpillars begin feeding on the new needles at the top of the tree. As the younger foliage is devoured the caterpillars move downward, feeding on older needles. Large numbers of tan excrement pellets accumulate around the base of the tree. Since conifers do not replace their old needles, defoliated trees are often killed after two seasons. Less severely damaged trees may be killed later by bark beetles. In August, the caterpillars pupate to emerge as adults.

Solution
When you first notice damage or caterpillars in May or early June, spray with an insecticide containing acephate, carbaryl, or Bacillus thuringiensis (Bt). Repeat the spray 2 weeks later if damage continues.

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