The Goldendale Sentinel - Headlines & History since 1879

By Andrew Christiansen

Stressed firs increase vulnerability



Contributed WHAT"S KILLING THE TREES?: Conservationists are concerned about what is happening to Douglas firs in the area.

The effects of the 2015 drought is presenting its effects on Klickitat County trees this spring. Residents of the county have been noticing that Douglas fir trees appear to be dying at an alarming rate. According to Dan Lennon, Landowner Assistance Forester with DNR, Douglas firs are especially vulnerable because most of the county is outside ideal habitat for the trees. "Poor soils, heat and lack of moisture," says Lennon put Douglas firs at risk.

The situation has created a further problem as stressed trees attract insects that are attracted to chemicals exuded by the trees as they deteriorate.

One of those insects is the Douglas fir beetle, which can attack in swarms, says Washington State University Regional Extension Specialist Stephen Van Vleet. "Damage from the beetles shows up in patches of dying trees," says Van Vleet.

This is particularly the case on the west side of the county, says Lennon. "Storm damage from three years ago along the highway 141 corridor has attracted Douglas fir beetle." Lennon says that while beetles are present around Goldendale, he doesn't see large numbers and attributes most of the local damage to the drought. But, one would expect to find a variety of boring type insects in damaged trees, including Douglas fir beetle in Douglas firs that are stressed.

Unfortunately, the solution to the problem for Douglas firs is not simple. "Thinning stands helps eliminate competition, but it is a catch-22 for Doug firs because the thinning opens up the canopy and creates more heat at the base of the tree, which accelerates the damage," says Lennon. "The pitch of trees is the natural insecticide. When trees are under drought stress or stress due to overcrowding, they don't have enough flow of pitch to fight off boring insects," says Lennon.

Van Vleet says that when Douglas fir beetles attack, there isn't much you can do to stop it. "Treatment with insecticides isn't effective because the timing has to be precise and it takes a contact insecticide that will kill everything, good and bad and still may have variable results due to the hard shell on the beetle." Van Vleet says a repellent may be useful in some situations.

Home owners can check into using a repellent by contacting Lennon. "It would be something to consider for a valuable landscape tree or some tree that has some special significance," says Lennon. "If someone had a commercial farm they might consider some repellent on parts of the plantation, otherwise, it isn't very effective in general settings and does nothing to repel other types of beetles or ips common to this area."

Van Vleet advises people bring suspect insects to the Extension Office for positive identification. "There are other insects, for instance a sawyer beetle that can come in after trees have been damaged."

The bottom line is that forest health is the most effective management of the problem. Most trees are attacked by disease and insects when they become stressed, so while you may find a certain pest present, the underlying cause is likely environmental. Dead trees should be removed in the fall and burned. Don't leave slash piles for very long on the ground. With the burn ban in effect June 1, it is better to leave dead trees standing right now and wait to cut them down and burn them in the fall. Plant trees that are best adapted to the environment, which means trees that can endure wide temperature swings under semi-arid conditions for central and eastern Klickitat County.


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