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Amid fire damage and drought, Oregon trees’ next nemesis: Bark beetles

Ponderosa pines show dieback caused by Ips beetles, which attack a wide variety of pines injured by fire or storms or weakened by drought
Oregon Dept. of Forestry
Ponderosa pines show dieback caused by Ips beetles, which attack a wide variety of pines injured by fire or storms or weakened by drought

Oregon Dept. of Forestry offers advice to landowners about native pests

SALEM, Ore. (KTVZ) – Many of the trees damaged by Oregon's Labor Day wildfires last year may face a new threat in the form of tree-killing beetles, which emerged in April, looking for new homes.

Oregon Department of Forestry Forest Entomologist Christine Buhl warns that fire-injured trees can attract bark beetles, which lay their eggs under the bark. When the larvae hatch, they begin feeding on the tree, destroying the tissues needed to send water from the roots to the needles and return nutrients.

The two main culprits, both of which are native to Oregon, are:

  • Douglas-fir beetle, which attacks and kills large-diameter Douglas-fir
  • Ips beetles, some of which are lethal to small-diameter pines, including ponderosa, lodgepole, sugar and western white pine, as well as introduced pines

“These two beetles do not attack trees that are already dead," Buhl said, "but they will readily go after living trees that have been weakened by drought, storms or by being scorched or partly charred in a wildfire.”

If enough fire-injured or drought-weakened trees are available, populations of either beetle can in a year or two build up enough numbers that they can overwhelm the defenses of a healthier tree.

“Not every fire-injured stand may experience an uptick in infestation, and not every infestation will spread to healthy trees,” Buhl points out. “But the likelihood is greater when otherwise healthy trees are already struggling due to prior stress, such as drought. This is especially true on poor sites with thin or compacted soils, sun-soaked south-facing slopes, or former farmlands converted to woodlots.”

Forest landowners concerned about beetles should look for brown frass – sawdust-like piles dug out of trees by the insects. Ips, however, tend to damage smaller diameter portions of pines (tops, branches), which can make it hard to recognize an infestation until treetops begin to die. By the time trees are dying, beetles may have moved on to other trees nearby so check those, advises Buhl. Infested trees will usually die within a year or less.

Landowners can remove beetle-infested trees early to reduce the risk of a larger outbreak, taking care in pine stands to burn or chip pine that’s 3 to 8 inches in diameter. “From April through September Ips beetles can infest pine slash. So if you can’t burn or chip slash it is best to wait till just after fire season in late October or November to limb up pine trees or conduct operations that create pine slash,” Buhl recommends.

She said landowners who want to forestall an outbreak of Douglas-fir beetle next spring might want to review their situation with a specialist (ODF stewardship forester, ODF entomologist, OSU Forestry Extension) to determine the health of their stand and infestation levels.

Based on the review, it might be recommended that they consider buying the beetle pheromone repellant MCH. If applied in March, MCH discourages this beetle from gathering and attacking trees en masse when they emerge in April from their winter homes.

For more information about insects that affect forest trees visit

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  1. We must all remember that three generations of Oregon loggers know more about forest health than scientists that have only been around the same amount of time. These loggers understand that fires do not happen in clear cuts when clear cutting is done in a responsible way. The responsible way led two many to get in the industry way before the environmentalists strapped themselves to trees and blocked trucks from getting to the goods. A “tragedy of the commons” happened in the early 80’s and the hippies were a but too late.

    1. So easy to blame others. Just like Russia and China want, a divided US is a weak US. Most mills closed and logging was reduced due to market demands, yeah capitalism. Why do you think the Warms Springs Mill closed? Not because of the hippies. We were cutting faster than the forests regrew and regenerated value, older tree are vastly more valuable than regen. No one wants the regen trees, the cost of cutting the regen rarely pencils.

      We are in fact having massive fires in large part because of all the clear cutting. Now all the forests are equal age, age diversity in forest builds resiliency, patchiness, and frequent small fires keep the ladder fuels reduced (thus all the control burns currently). Go to the historical society and look at the photos of our forests before we cut them. The tree spacing was far greater than now, there was much more diversity in age and forest structure. When a forest is the same age and has dense ladder fuels it burns easier. Now add drought and windstorms… bam massive fires.

    2. we must all use the brains we were born with – “fires don’t happen in clear cuts”? – you are hilarious! – “the goods”? – some people call them forests – dollar signs cloud your mind

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