Spring has sprung, and the war wages on against the biggest threat to Washington County’s ash trees.
State and local agencies came together in April to slow the destruction of Oregon-native trees from emerald ash borers — an invasive beetle that has been deemed the most destructive pest in North America .
A total of 80 trees were removed in Forest Grove in April as part of a collaborative grant between the Oregon Department of Agriculture and Oregon Department of Forestry, and leaders are looking to take proactive steps before the pest rips through the state's viridescent groves.
Wednesday morning, April 24, withered branches came crashing down on Emily Street. In the surrounding neighborhood, faint depressions in the soil held remnants of trees that recently stood tall above homes.
“This is kind of a cautionary tale,” Lilah Gonen, community assistance forester, said. “This is a warning to let municipalities, land managers and homeowners around the state know that this is coming.”
The metallic-green beetles might be a half-inch long, but they’re a huge threat. Emerald ash borer larvae tunnel into trees and munch on the inner bark, disrupting their ability to transport water and nutrients. A tree typically dies within two to five years of an infestation.
Emerald ash borers have plagued the Eastern United States since their arrival in 2002, and alarms have been sounding in Oregon since the state had its first sighting in 2022 .
Max Ragozzino, an entomologist with the Oregon Department of Agriculture, explained how many of Forest Grove’s trees had been dealing with infestations for years by the time researchers detected the beetle, forcing removal throughout the city.
“We have only a few ways of detecting EAB, usually after it's been present at a site for a couple of years,” Ragozzino said. “It’s a hidden infestation, so we rely on the tree giving us signs of decline to show us that EAB is present.”
There are a few telltale signs that show if a tree is infested with the pest: thinning canopy, dying branches and splits along the bark. The most obvious indication is the D-shaped holes where the beetles exit the tree, but at only three-millimeters long, they can be hard to spot.
Emerald ash borers gravitates toward strained trees, Ragozzino explained, which researchers are using to pinpoint and isolate the problem.
“We've identified a handful of sites within Forest Grove, and we are girdling trees to stress them out and draw the emerald ash borer to those trees that later this summer we are going to destroy,” Ragozzino said.
Not past the point of no return
The vicious grinding of a wood chipper whirred throughout the street, as the blades broke down wood fed in by contractors. According to the Oregon Department of Forestry, it’s a necessary step to prevent the pests from flying off and finding a new home.
Adult emergence is estimated to begin around the first week of June this year, and officials are aiming to prevent the larvae from gaining wings to travel.
Over the past couple of years, agencies from all over have worked to combat the spread, from developing a wood-burning device to collecting seeds to preserve and study. Using the Slow Ash Mortality (SLAM) approach, researchers are throwing everything but the kitchen sink at the issue — removing trees and working to preserve what they can.
On Wednesday in Cornelius, Oregon Department of Forestry crews identified healthy urban ash trees in the area, with plans to inject non-infested trees with a specialized insecticide.
“This is an insecticide that we know from over 20 years of research from the Midwest is extremely effective at keeping trees alive from EAB, killing any emerald ash borer larvae that are located within the stem of the tree,” Gonen explained. “Because it's a systemic injection, it keeps all the insecticide within the tree.”
While it was too late for many trees in Forest Grove, Gonen noted how it’s not past the point of no return for other cities like Cornelius, where ash trees are still healthy.
“We’re able to inject most of the healthy trees in the town and hopefully keep them alive or slowly phase them out and remove them over time rather than have to remove a ton of trees all at once,” Gonen said. “It gives us an opportunity to kind of work on our own timeline instead of on the timeline of emerald ash borer.”
As officials continue to grapple with the issue, community members can do their part by not transporting firewood, which is a suspected culprit for how the insect made its way to Forest Grove.
Eggs are laid inside the tree bark, making it difficult to tell whether a tree is infected before chopping it for firewood and moving it across the state or country. In 2022, Washington County placed a quarantine that prohibited the removal of ash, olive and white fringe trees and tree materials to prevent the spread.
“The No. 1 thing that every single person can do to keep the spread of EAB and other forest pests limited is to not spread firewood,” Gonen said. "Leave firewood and downed woody material in place; don’t move it around. That is the number one way that EAB is vectored across the entire country.”
To learn more about invasive species or report a potential pest, visit oregoninvasiveshotline.org .
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