Bark beetles may attack trees damaged in winter storms

Friday March 20, 2020

News Release

March 20, 2020

Bark beetles may attack trees damaged in winter storms

(COEUR D’ALENE) – Damaging winter storms across northern Idaho this season mean forested areas are more susceptible to infestations of certain bark beetles this spring. In December and January, heavy, wet snow led to breakage in treetops and branches. Storms with strong winds toppled trees on several occasions, including this past weekend. Please see attached photos for examples.

Idaho Department of Lands (IDL) forest health officials want forest landowners to know that trees uprooted or broken in the storms can become infested by bark beetles as the weather warms. The beetles can build up populations in fresh, damaged logs and then attack and kill neighboring healthy trees. Dead trees do not pose a threat, only green trees that were damaged this past winter or spring are cause for concern. The following species are especially susceptible to bark beetle attack but taking certain steps can mitigate problems.

Pines and pine branches larger than three inches in diameter can be infested by the pine engraver beetle (Ips beetles). Pine engraver beetles infest and reproduce in wind-thrown trees and slash in April and May. Their offspring emerge in June, often attacking adjacent live pines.

Douglas-fir can be infested by the Douglas-fir beetle. Douglas-fir beetles infest large-diameter logs in spring, and their offspring emerge to attack new trees the following year (spring 2021). Large, fallen western larch are also attacked by Douglas-fir beetle, but live, standing larch are rarely attacked.

Engelmann spruce can be infested by the spruce beetle. Large-diameter logs are attacked, and offspring emerge one to two years later. Spruce beetles can attack ornamental species like Norway or blue spruce, but these are infrequent hosts.

The best option to reduce beetle infestations is to remove damaged trees. Otherwise, consider safely burning or chipping. Fresh chips should not be piled near live trees because their odors can be attractive to bark beetles in spring.

If damaged trees cannot be removed or destroyed, cut logs and branches into small pieces and spread them in a sunny area to hasten drying as soon as possible. Piled logs in shady areas are more likely to be infested. DO NOT stack green firewood next to live standing trees.

In pines, quick action is necessary since beetles can emerge from damaged pine materials this coming June. Large-diameter logs of Douglas-fir, western larch, and spruce will not pose a threat until spring 2021. If infested logs of these species are split for firewood by this summer, they will dry out in time and kill developing beetles before they emerge. These logs can also be removed, chipped, de-barked, or burned during the winter of 2020-2021.

More information on Idaho forest health is available here. IDL Private Forestry Specialists also are available in offices across the region to assist forest landowners. Information about landowner assistance is available here.


Robbie Johnson
Public Information Officer
Idaho Department of Lands
208-334-0236/ 208-908-1786
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