Spruce and Fir Damage

Question: I have seen damage on spruce and fir trees. What is damaging these trees?

Answer: There are two primary pests causing damage to spruce and fir trees, spruce budworm and douglas-fir tussock moth. Spruce budworms have damaged hundreds of thousands of acres of trees since 2009.

They usually have damaging cycles of three to four years, but they have had cycles of over 15 years. The larvae hatch in July and August and over winter under bark scales. Larvae emerge in April and May and move to the buds. Most of the damage is done to the new buds but with high populations may extend to older growth. Host trees, in Montana, are douglas-fir, spruce and grand fir. Landscape trees that are being damaged the most are Colorado blue spruce, Engelman spruce and any type of fir tree.

Tussock moth larvae have been damaging douglas-fir, grand fir and spruce in the forest. They are damaging all spruce and fir varieties in landscape trees.

Tussock moth larvae defoliate trees very quickly and usually will kill any part of the tree that is defoliated. Defoliation usually starts from the top down. Tussock moths over winter in the egg stage. Eggs hatch in late May, usually around bud break. These moths have a long larvae stage and can damage trees from May to August.

Note: Tussock moth caterpillars should not be handled because the hairs can cause a painful rash and some people have also had blisters from handling these caterpillars.

Control of both spruce budworm and tussock moth begin with monitoring your trees and spraying them when the pest is detected. If you are spraying your own trees, any product that is labeled to control caterpillars will work. There are many organic sprays that can control these pests.

Note: Do not use systemic soil applied insecticides for these pests because they are not effective on caterpillars.

Turfmaster Lawn & Tree Care, Inc. uses a long residual product and sprays spruce and fir trees before May 15th to prevent these pests. This spray also prevents white pine weevil and mites that have been damaging your evergreens.

Cold temperatures can affect both of these pests, so the mild winter may increase the potential for damage in 2012.

Note: If you are a fly fisherman, try using a spruce moth fly during June and July for the North, South and Middlefork of the Flathead rivers.