Picea: Spruce Budworm

Problem
Needles on the ends of branches are chewed and webbed together. In mid-July the branch ends often turn reddish brown. Branches or the entire tree may die after 3 to 5 years of defoliation. Reddish brown caterpillars, 1¼ inches long, with yellow or white raised spots, are feeding on the needles.

Analysis
(Choristoneura species)

Spruce budworms are very destructive to ornamental spruce, fir, and Douglas fir, and may infest pine, larch, and hemlock. The budworm is cyclical. It comes and goes in epidemics 10 or more years apart. The moths are small (½ inch long) and grayish, with bands and spots of brown. The females lay pale green eggs in clusters on the needles in late July and August. The larvae that hatch from these eggs crawl to hiding places in the bark or in lichen mats; or they are blown by the wind to other trees, where they hide. The tiny larvae spin a silken case and hibernate there until spring. In May, when the weather warms, the caterpillars tunnel into needles. As they grow, they feed on opening buds; later they chew off needles and web them together. The larvae feed for about 5 weeks, pupate on twigs, and emerge as adults.

Solution
When the buds begin to grow, in late May, spray with an insecticide containing acephate or carbaryl, or use the biological insecticide Bacillus thuringiensis (Bt).