Forest managers can avoid serious impacts from spruce budworm using the following forest management practices:
- Harvest spruce when stands approach rotation age, generally between from 60 and 90 years. The rotation age for balsam fir-dominated stands is less than that of spruce, ranging from 45-50 years in dry upland sites and 65-70 in wet lowland sites.
- Commercially thin younger white spruce stands before outbreaks (evaluate spruce stands for thinning at about 30 years of age). Do not thin during outbreaks or periods of excessive drought.
- If possible, avoid leaving mature balsam fir and white spruce trees as residual wildlife trees after final harvests. Residual budworm hosts can promote quicker budworm population increases and serve as a source of caterpillars that drop down on strands of silk and feed on seedlings and saplings. If only spruce and fir trees are present, leave clusters rather than isolated trees for wildlife habitat and seed sources.
- Promote a higher percentage of spruce over fir, the budworm's preferred host, to reduce future impacts of spruce budworms. Promoting other tree species will further reduce the budworm's impact. Lower balsam fir prices means that insecticide spraying in large stands is probably not economical. Spruce budworm generally affects an area for five to eight consecutive years, and firs begin to die after three to five consecutive years of significant defoliation. Consider final harvest for any spruce-fir stands that have sustained two consecutive years of budworm defoliation. Harvesting a site after two consecutive years will maximize site restoration potential and timber value.
You can spray high-value yard and woodlot trees with Bacillus thuringiensis variety kurstaki (Btk), a microbial insecticide that kills caterpillars that eat it. However, spruce budworm begins feeding at the tops of trees, so effective Btk application that reaches upper foliage can be difficult for homeowners. For assistance in treating your trees, you can search a list for commercially licensed pesticide applicators in your county.
Because spraying pesticides is expensive in terms of both time and labor, keeping trees healthy with proper watering, mulching, thinning, and root protection is your best defense against most insect and disease damage, including spruce budworm.
Other Sources of Information
United States Forest Service Forest Insect and Disease Leaflet – Spruce Budworm
Eastern spruce budworm - UMN Extension
Spruce budworm - Government of Canada