The western spruce budworm, Choristoneura occidentalis Freeman, is a major insect pest in Colorado. Host species for spruce budworm include Douglas and white fir, blue spruce, and Englemann spruce. In September, the insect is no longer feeding. The first instar larvae have moved into cracks and crevices under bark where they will remain throughout the winter. The larvae hibernate until the following spring when they feed on new needles and developing buds. Extensive feeding prevents food production for the tree. Damage can range from superficial/aesthetic to death of twigs, branches and tree tops during outbreaks. Defoliation also weakens the tree making it susceptible to bark beetles.
Management of spruce budworm includes the use of Bt products or carbaryl on high value trees. Timing of applications should be 2-3 weeks following bud break, somewhere around the middle of June depending on location.
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Updated Friday, April 19, 2013