ODF: Downed trees create potential for Douglas fir beetle outbreak

SALEM — The Oregon Department of Forestry reports that the February 2021 ice storm brought down numerous large-diameter Douglas fir — defined as greater than 10 inches in diameter at breast height — to create the potential for an outbreak of the native Douglas-fir beetle.

Christine Buhl, forest insect scientist with ODF said landowners have until the end of March to head off an outbreak. Buhl, an entomologist, says stands with pre-existing stress from drought, root disease and so on are more at risk for a beetle outbreak.

An orange, sawdust-like powder on the bark of downed Douglas fir is a sign beetles have moved in and are preparing to lay eggs.

“Outbreaks tend to last one to three years before collapsing on their own,” Buhl said in a press release. “But during that time beetles can move from downed wood to healthy Douglas fir trees nearby, weakening or killing them.”

Treatment includes removal of damaged material or application of MCH repellant before April.

“MCH anti-aggregation pheromone is effective, inexpensive and sold as a general use pesticide online,” Buhl said. “But MCH won’t work for trees that have already been infested. So landowners need to act before an outbreak gets going.”

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