Western Spruce Budworm

Stand heavily infested by western spruce budworm

Western spruce budworm is the most destructive defoliating insect affecting conifers in Montana and the most important forest pest second only to mountain pine beetle.  Spruce budworm primarily affect douglas-fir trees, but also attack other conifer species when population levels are high.  Several management options are available to reduce damage caused by spruce budworm.  The most effective option available to reduce spruce budworm damage is to alter the forest stand condition by thinning the stand.  The goal, when thinning to reduce spruce budworm damage, is to convert the stand from a multi-layered to a single layered canopy.  This exposes dispersing spruce budworm to natural predators and improves vigor of leave trees allowing them to more effectively recover from damage caused by the budworm.  In certain situations where budworm damage is severe pesticide application may be warranted.  Several chemicals are labeled for application on forest stand and individual trees to reduce spruce budworm populations.  The 2 chemicals we recommend are either BTK and Carbaryl.  BTK is the preferred chemical to apply as it is a naturally occurring bacteria (Bacillus thuringiensis) which attacks only insects found in the spruce budworm family and is safe to use near water.  Spraying targeted at the forest stand level is usually applied aerially from either an airplane or helicopter, and individual trees are usually sprayed from the ground using a truck mounted sprayer.  Contact us if you believe western spruce budworm is negatively effecting trees on your property.

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