SALEM, Ore. – The February 2021 ice storm brought down lots of large-diameter Douglas-fir (greater than 10 inches diameter at breast height), creating the potential for an outbreak of the native Douglas-fir beetle (DFB). Landowners have until the end of March to head off an outbreak, according to forest insect scientist Christine Buhl with the Oregon Department of Forestry.
Buhl, an entomologist, says stands with pre-existing stress from drought, root disease, etc., 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 1 to 3 years before collapsing on their own,” says Buhl. “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 and/or application of MCH repellant before April 2021. “MCH anti-aggregation pheromone is effective, inexpensive, and sold as a general use pesticide online,” says Buhl. “But MCH won’t work for trees that have already been infested. So landowners need to act before an outbreak gets going.”
Douglas-fir beetle: https://www.oregon.gov/odf/Documents/forestbenefits/Douglas-fir-beetle.pdf
Storm damage management: https://www.oregon.gov/odf/Documents/forestbenefits/Storms_2017.pdf