Spruce Budworm

Problem type: Insect

Name of problem: Spruce Budworm

Plant name(s): Balsam fir, white spruce, black spruce

Symptoms / Characteristics:
Young larvae use silk webbing to tie new shoots together and form a feeding tunnel or nest. The larvae are wasteful feeders and sometimes eat only the base of the needles and spin webbing around the remainder, causing the tree to look scorched as the foliage dries. Prolonged infestations may result in branch dieback and even plant death.

The spruce budworm, Choristoneura fumiferana, is a severe defoliator of North American conifers. During its 1-year life cycle, the spruce budworm goes through six larval phases, beginning in August and ending the following July, when the adult moth emerges. From early May to late June the larvae will feed on old needles as well as developing buds and new foliage. Buds are often destroyed before the new shoots even have a chance to expand. The young larvae are yellow with brown heads and are likely to be seen in May. Mature larvae cause the most damage and are likely to be seen during the first two weeks in June. They are reddish brown with black heads and are also characterized by two rows of white spots running lengthwise down their backs.

Control / Preventions:
Chemical insecticides are effective if they come in contact with, or are ingested by, the larvae. This presents a challenge because the larvae are often protected by the silk-webbed needles. Maximum spray efficiency is generally achieved between late May and mid June when new shoots begin to expand. Commonly used insecticides include dimethoate, malathion and trichloron. Biological insecticides such as Bacillus thuringiensis (Btk) and Mimic are also effective. Insecticides must only be applied according to manufacturers direction.