Emerald ash borers haven't been found in Southern Oregon yet, but Oregon State University assistant professor Dan Stark said it could take just one person transporting infested firewood to bring them to the region.
Since 2019, Stark has led the Oregon Forest Pest Detector program, which trains volunteers to identify trees and recognize the warning signs of invasive forest pests.
The program will relaunch this fall with an updated curriculum focused on emerald ash borers, which were first detected in Oregon in 2022.
"Early detection is really key to get into an area and do the best you can to manage those trees that might be already infested," Stark said.
Ash trees are common along the Rogue and Umpqua rivers, where they help keep streams cool by providing shade for fish and other wildlife.
After emerald ash borers infest a tree, they first feed in the canopy, making the damage difficult to spot. In many cases, infestations aren't detected until years after the beetles arrive.
As the insects spread, they tunnel beneath the bark and lay eggs in the tree's crevices. Their larvae feed on the tissue that carries water and nutrients, eventually killing the tree before moving on to another.
Jim Gersbach, a public affairs specialist with the Oregon Department of Forestry, said widespread ash tree losses could have lasting effects on streams and rivers. Without the trees' shade, waterways can warm, making them less suitable for fish and other wildlife.
He said losing ash trees could also create openings for invasive plants to take hold.
Stark said preventing emerald ash borers from becoming established is difficult because North American ash trees have little natural defense against the invasive beetle.
"That's what makes them so devastating," Stark said.
While experts expect emerald ash borers to continue spreading across Oregon, they say insecticides and the release of natural predators can help slow their advance.
Stark said one of the simplest ways people can help is by avoiding the transport of firewood. Because the beetles often hide inside dead or dying wood, moving firewood can unintentionally spread the pest.
"You wouldn't really know that your wood is infested, but they really love that wood that's dead or that's dying. That's the only time they could really attack it," Stark said.
Small, D-shaped holes in firewood can be a sign that adult emerald ash borers have emerged. To reduce the risk of spreading the insect, Stark recommends burning firewood within 10 miles of where it was purchased.
Adult emerald ash borers typically emerge from trees in Oregon in June, although this year they began emerging about a month earlier than expected. After mating, females lay their eggs later in the summer, typically between July and September. The larvae then spend the winter developing beneath the bark before emerging as adults the following spring or early summer.
Stark said increasingly mild winters also are helping the insects survive.
"We depend on that freeze or those cold temperatures to really knock them down and keep them out," Stark said.
Stark said climate change is creating more favorable conditions for emerald ash borers to reproduce, feed and spread.
