Tussock moth infestation hits Inland Northwest

Tussock moths chewed their way across 68,000 acres of the Idaho Panhandle last summer, leaving behind red-topped trees.

The native pests primarily attack Douglas-fir trees, grand fir and subalpine fir trees. Aerial surveys indicate that the moth outbreak also affected 1,600 acres in eastern Spokane County and about 9,000 acres in the Blue Mountains of southeast Washington and northeast Oregon, according to the Washington Department of Natural Resources.

Tussock moth outbreaks typically peak in 10 year cycles. The outbreak in Spokane County will probably subside this year, but the Idaho Panhandle could see an increase in the number of acres affected, forest entomologists predict.

Tussock moth caterpillars feed on both old and new foliage. Though the trees appear dead, many survive if they can form buds that can last through the winter. However, repeat defoliation can stunt tree growth, cause top-kill and may make trees more susceptible to later attacks from bark beetles.

Outbreaks typically collapse within two to four years, due to a build up of natural enemies, including a viral disease. Birds and parasitic wasps also help keep tussock moth populations in check.

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Rich Landers

Rich Landers

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