An invasive, tree-killing pest has made its way to Portland, spelling trouble for the many ash trees that cool residential neighborhoods on hot summer days.
On Wednesday, Oregon forestry officials announced the discovery of an emerald ash borer infestation in the Hazelwood neighborhood in Northeast Portland, in the parking lot of the David Douglas Aquatic Center. The affected trees will need to be removed.
The emerald ash borer is an iridescent green beetle that made its way to the U.S. from Asia in 2002, first decimating ash trees across the Midwest. Many tree experts say it’s not a matter of if, but when Oregon’s ash trees endure a similar fate. Forestry officials say Oregon will lose 99% of its ash trees to this pest in time.
“We’re going to see a massive change in our ecosystems in our urban forest because of this beetle,” said Matt Mills, Oregon Department of Forestry emerald ash borer specialist, at a press conference Wednesday morning.
Oregon has its own native ash tree, the Oregon ash, which is prevalent across the state, namely around low-lying lakes, streams and rivers. Biologists worry that losing Oregon ash trees will make waterways more vulnerable in the face of climate change.
Higher temperatures can degrade water quality in many ways — including increasing bacterial and algal growth, decreasing oxygen levels, and changing overall chemical profiles. That could make drinking water treatment more expensive, and it could kill fish. It could also increase flooding, as trees help prevent soil erosion.
Residential neighborhoods also rely on native and other ash species for shade. Portland, like many large metropolitan areas across the country, has experienced a shrinking tree canopy, particularly in lower income areas.
The emerald ash borer was first discovered in Oregon’s Willamette Valley in 2022. It has so far shown up in Washington, Marion, Yamhill and Clackamas counties. Those counties, and now Multnomah County, are under a state quarantine that prohibits people from moving ash, white fringe or olive tree plants, wood or green waste.
“We want to give those other parts of Oregon as much time as possible to prepare,” said Cody Holthouse, pest prevention program manager for the Oregon Department of Agriculture. “And so if we can limit the movement of green waste and firewood, we strongly, strongly encourage that.”
Oregon is the only West Coast state to discover the emerald ash borer within its trees. The beetle has yet to infest Washington, Idaho or California.
After the pest was discovered in Oregon, forestry officials installed a network of about 300 emerald ash borer traps, mostly in the Willamette Valley, to help detect infestations. The traps are large, purple cardboard rectangles, coated in pheromones and a sticky glue, which are strung high up in tree canopies.
This summer alone, officials found five more infestations across the valley. Holthouse said he expects emerald ash borers to continue spreading at an accelerating pace, as they did across the Midwest and East Coast, killing ash trees along the way. At this rate, ash trees could go the way of the American chestnut, dwindling to the point of near extinction.
What you can do
People should avoid moving firewood or woody debris more than 10 miles from where they collect it, Oregon forestry officials advise. Moving firewood from one area to another, like between counties or even between cities, can spread tree pests and diseases. That is likely how the emerald ash borer made its way to Oregon.
Oregonians can also take some proactive steps to help slow the spread of the emerald ash borer.
Landowners and homeowners should first determine if they have any ash trees on their properties. If they do, they should look for signs of an emerald ash borer infestation, or call a certified arborist for an assessment. Signs could include thinning or dead branches and yellowing leaves. When taking a closer look at tree bark, property owners might find tiny D-shaped holes. Underneath the bark, they might see serpentine boring tracks.
Those were the signs that helped a local arborist identify the infestation at the David Douglas Aquatic Center.
“When I came closer to the tree, I started looking for some D-shaped exit holes, which fortunately was possible for such short, small trees,” Peter van Oss of Teragan & Associates said. “And I did find a D-shaped exit hole that was about the size of a ballpoint pen tip.”
He reported the finding to the Oregon Invasive Species Hotline. Oregonians who find similar emerald ash borer damage can do the same by calling 1-866-INVADER (1-866-468-2337) or reporting it online.
Two other types of trees, white fringe and olive, might also succumb to an emerald ash borer infestation — bad news for Oregon’s olive farmers. Oregon State University researchers are still determining what that damage might look like.
“Research is ongoing,” Holthouse said. “We don’t fully understand what kind of host olive is for emerald ash borer, but right now, anecdotally, it looks like kind of a secondary host.”
If landowners find ash trees on their properties, but no signs of an infestation, they can take preventative action by replacing those trees, or by treating them with a pesticide every two-to-three years.
“This is an environmentally friendly treatment,” said Jen Cairo, Portland city forester. “It is injected into the trees, not sprayed or drenched into the soil. And it is fine for pollinators, animals, people and other vegetation.”
That work needs to be done by a certified arborist. Oregon doesn’t currently offer state financial assistance to people who cannot afford these services.
This story comes to you from the Northwest News Network, a collaboration between public media organizations in Oregon and Washington.
