Western Spruce Budworm
Western spruce budworm is the most widely distributed forest defoliator in western North America.
Budworms have a one-year life cycle and are actually a small moth at full maturity. Here in the West, there can be severe infestations in healthy Douglas-fir, white fir and spruce.
Symptoms of Infestation
Evidence of western spruce budworm can be observed year-round. Dead branches or sparse foliage may indicate feeding during previous years. Budworms have the potential to consume all new growth on the host tree. During outbreaks of three or more successive years, trees may die. Budworms create ideal conditions for other insect and disease invasions.
CSFS Forest Entomologist Dr. Dan West produced an Esri Story Map for the 2021 Forest Health Report, which offers users an interactive way to find out about forest conditions and insect activity in their area.
- Budworm populations can be substantially reduced with chemical insecticides. Large forested areas can be aerially sprayed for short-term protection, and individual trees can be sprayed using ground equipment. (Always carefully read and follow all label instructions before applying insecticides.)
- Promoting tree vigor through silvicultural methods such as thinning or promoting mixed-tree stands will help reduce the risks of an infestation.
- Generally, budworm populations are kept under control by a combination of predators, parasites, climatic conditions or insufficient food supplies.