Drier Weather Brings In Tree-Killing Bark Beetles

Drought conditions allow bark beetles to thrive, according to the Dept. of Forestry—and trees can suffer as a result.

Posted: May 2, 2018 2:37 PM
Updated: May 2, 2018 2:38 PM

SALEM, Ore. — With drought conditions already anticipated in Klamath County, the Oregon Department of Forestry (ODF) is forecasting dry conditions across the state—thanks to a warm end to last summer and an unseasonably dry winter.

Drought alone can kill trees, but the ODF warns against "secondary attacks" from bark beetles over the summer.

“Above average temperatures this spring mean beetles may come out sooner than normal. If this happens, beetles may attack trees sooner than usual,” said ODF Entomologist Christine Buhl.

According to ODF, most varieties of bark beetle are a normal part of a healthy ecosystem. The beetles will naturally target and kill the sick or less vigorous trees that compete with healthier trees. However, dry or drought conditions can stress even healthy trees—leaving them vulnerable to attack by bark beetle populations that then grow out of hand.


ODF encourages tree and forest owners to watch for telltale drought symptoms—dead tops, dead branches, thinning canopies and stressed cone crops. They encourage that concerned citizens consult with an arborist or forester to brainstorm methods to keep healthy trees alive in spite of low precipitation.

Steps the public can take might include removing some less-healthy trees or weeds to allow the remaining trees to get enough food and water during dry spells. ODF says to avoid fertilizing and planting less drought-tolerant trees such as the Douglas fir in areas historically domanted by more drought-tolerant trees like oak or pine.

After the 2012-2015 drought, the ODF reports, Oregon had one good year of rain. However, it takes much longer than that in favorable conditions for trees to recover. After a long, hot summer and a dry winter, Oregon soils are not as saturated as ODF officials anticipated.

“Given the recent drought and below average rain and snow this winter, trees will likely be drought-stressed this season - unless precipitation boosts back to normal levels,” Buhl said. “What we need is a longer, lighter rain to allow trees time to soak up the water.”

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