When You Have an Outbreak

Heavy defoliation of Subalpine fir and Engelmann spruce caused by western spruce budworm infestation.

If you've confirmed you have a western spruce budworm outbreak, you have options. Outbreaks tend to be cyclical and rarely kill trees, so one option is doing nothing. Multiple years of defoliation can sometimes kill young trees. You can also spray trees if you don't like the way they look when they've been attacked.

  • Chemical insecticide. Some insecticides, including carbaryl, are effective against western spruce budworms. You can spray individual trees from the ground.
  • Bacterial insecticide. Bacillus thuringiensis, or Bt, is a spray of naturally occurring bacteria that kills caterpillars without otherwise damaging the environment.
  • Do nothing. The western spruce budworm tends to follow a natural cycle, where it might be active for several years in a row, then quiet for a while. If you prefer, you can just wait out the outbreaks.

A local extension agent or forester can help you decide what to do about western spruce budworms on your land.

Good forest management can keep your woodlands productive and healthy for generations to come.


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