March 20, 2019 — With winter nearing its close, we’re entering spring cleaning season. In suburban yards, post-winter cleanup usually entails picking up a few fallen branches. However, for many rural properties, more substantial work is needed thanks to winter storms. As Oregon’s Department of Forestry has warned, fallen firs create ideal conditions for outbreaks of Douglas fir beetles.
Native to Oregon, Douglas fir beetles are usually present in our forests in low numbers, but populations can rise substantially under certain conditions.
These small, dark-colored beetles live beneath trees’ outer bark and can be quite destructive. Their feeding on a tree’s interior tissues creates networks of tunnels that eventually kill the tree by disrupting its nutrient flow. Beetles can also bring in harmful fungi that contribute to the tree’s demise.
After overwintering under the bark, fir beetles emerge in April and fly off to colonize new trees. Outward signs of infestation include the fir’s needles yellowing and then turning brown.
Healthy trees can generally fend off pests by producing chemicals that act as natural pesticides or resinous pitch that repels insects.
However, stressed or damaged trees, like those toppled in storms, have compromised defenses and are more easily colonized. Thus, removing this winter’s fallen trees before the beetles’ spring emergence is important for preventing an outbreak.
Additionally, if the trees are cut into firewood, stacking it in a sunny location, away from living trees, and covering it with clear plastic will help kill any beetles already in residence.
Other methods of beetle control involve using chemicals. Initially, commercial insecticides were the go-to approach, but this was costly and often logistically difficult. More recent methods use the beetles’ own biology against them. Initially, when beetles arrive at a tree, they emit natural chemicals (pheromones) that attract other beetles.
Later, to prevent overcrowding, they stop producing attractants and begin producing pheromones that act as a “no vacancy” sign to keep other beetles away.
Both types of pheromone can be made in laboratories and used in beetle control. Traps can be baited with attractant pheromones to lure beetles into a certain area and packets of repellent pheromone can be placed throughout a stand of trees to create a beetle exclusion zone.
So, anyone procrastinating about spring clean-up on their property should keep in mind the clock is ticking on beetle emergence.
Don’t let the beetles get to your trees before you do.