A severe wind storm knocked down these ponderosa pines, which are now susceptible to pine engraver beetle. Photo: State of Idaho
Severe November and December wind and snow storms in Spokane and other areas could be causing more damage than you realize. By this spring, you may notice little piles of reddish bark dust around your trees. This is a sign that bark beetles are attacking the trunks and branches of your damaged trees.
When the weather warms up, bark beetles become active, infesting and feeding on the sugary inner bark of your uprooted or broken trees. Over just a few weeks, inside the damaged logs, these beetles can build up populations, which then attack and kill neighboring healthy trees.
The chief culprits are known as the pine engraver beetle and the Douglas-fir beetle.
Ponderosa pine and lodgepole pine trunks and branches that are larger than three inches in diameter can be infested by the pine engraver beetle. Pine engraver beetles that infest wind-thrown trees in April and May will lay eggs that develop into adults and emerge in June of the same year. Although beetles that emerge in June often continue to infest damaged trees, the next generation of beetles that emerges in August may attack adjacent healthy trees.
The Douglas-fir beetle infests Douglas-fir trunks that are larger than about 10 inches in diameter. These beetles’ offspring require a year to mature and could infest healthy Douglas-fir trees in spring of 2017.
Both types of bark beetle are highly attracted to the thick, moist, nutritious inner-bark tissue of trees that are recently wind-thrown or have broken tops, as well as logs.
How to minimize your chance for infestations
The best option to reduce beetle infestations is to interrupt the amount of moist inner bark tissue that is available for beetles to breed. Remove damaged trees by salvaging the larger timber and safely burning or chipping smaller material. Try to increase the rate at which the inner bark dries out by cutting green logs into smaller pieces, removing branches, dispersing the woody material in a sunny area.
Leaving damaged trees or logs in the shade or in small sheltered piles lengthens the time the inner bark is suitable beetle food and habitat; it also increases the chances that the wood will become infested.
DO NOT stack green firewood next to healthy standing trees. The idea is to reduce the number of places the damaging beetles have easy access to breed this spring, so high populations won’t develop and threaten remaining trees later.
If you own forestland and need advice about tree care, contact a DNR Region Office near you or the WSU Extension Office in your county.