CORVALLIS, Ore. — Emerald ash borer is now confirmed in Portland and at new sites elsewhere in northwest Oregon.
EAB was verified in late August on green ash at a David Douglas School District site in East Portland after samples sent to a federal lab came back positive; Multnomah County is now under quarantine to slow human-assisted spread.
The Oregon Department of Agriculture’s permanent quarantine currently covers five counties. Moving ash, white fringe or olive wood outside these counties is prohibited.
- Clackamas
- Marion
- Multnomah
- Washington
- Yamhill
This summer, EAB was also detected at Hazeldale Park near Beaverton, at Killin Wetlands near Banks, near the town of Yamhill, southeast of Oregon City and on BLM land near Scotts Mills — all within the quarantine zone.
Portland’s new Emerald Ash Borer Response Plan prioritizes systemic injection (emamectin benzoate) for high-value public ash in low-canopy neighborhoods and removal of poorly sited or declining ash as resources allow. About 9,700 ash street trees (roughly 4%) are at risk citywide; use the city’s Tree Inventory Map to see ash near you.
A new model from ODA, Washington State University and the U.S. Bureau of Land Management projects likely natural spread across the Pacific Northwest — possibly reaching Washington within two years, the lower Willamette Valley in about 10 years and Southern Oregon in about 20, not accounting for human transport.
Don’t remove healthy ash preemptively
Dave Shaw, retired forest health specialist with the Oregon State University Extension Service, advises against cutting down healthy ash unless EAB is nearby or confirmed on your tree. It could be years before emerald ash borers find your tree, Shaw said, which then take several years to die after being infested.
Observations from the eastern United States, where the beetle was first detected in 2002, suggest that trees in areas where the infestation has started take longer to die than in areas where the insect is well-established.
But once EAB is confirmed in a tree, remove it before it becomes a hazard.
The insect has destroyed over 100 million ash trees in the eastern United States. Research is underway in many areas of the country to find a biological or chemical application to halt emerald ash borer, but so far there’s no cure for a tree infested by the beetle. It can take up to six years for the tree to die, but eventually it will be killed, Shaw said.
Homeowners have the option of using a systemic pesticide to keep the insects at bay, but once the beetles arrive, pesticides won’t kill them, Shaw said. And applications are expensive and must be repeated every two to three years, he said, comparing the use of chemicals to using a Band-Aid.
“If you just have one tree and can afford it and don’t mind the pesticides, they are available, but the most effective treatments must be applied by licensed professionals and both the product, and the labor add up quickly,” he said.
If a homeowner or woodland owner chooses to use a pesticide, a list can be found in the Extension article What to do about emerald ash borer: Recommendations for tree protection in EAB-infested areas.
Symptoms to watch for
- Thinning or dying canopy
- Sucker shoots on trunk or at the base
- D-shaped exit holes in bark
- Splitting bark and S-shaped galleries under bark
- Rows of small peck holes from sapsuckers
- Adult beetles visible in summer
Report possible finds to the Oregon Invasive Species Hotline and consult the statewide EAB trap web map for current detections.
Choose replacement trees
Heather Stoven, OSU Extension horticulturist, said the first thing to think about is “right tree, right place.” Choose wisely by considering your site’s sun exposure, soil, nearby structures and overhead power lines. Ask local nursery professionals or Master Gardener volunteers for help. If planting in a parking strip, obtain a city permit.
Mid-size shade trees to consider (hardiness varies by species/cultivar and site):
- Dogwood (Cornus)
- Ginkgo
- Hornbeam (Carpinus)
- Magnolia
- Maple (Acer)
- Oak (Quercus)
- Snowbell (Styrax)
- Tupelo (Nyssa)
- Yellowwood (Cladrastis)
- Zelkova
For detailed information, visit Alternatives to Ash in Western Oregon: With a Critical Tree Under Threat, These Options Can Help Fill Habitat Niche.
Stay informed
OSU Extension Emerald ash borer resources include photos of the beetle and articles on protecting trees, identifying ash trees, FAQs, alternatives to ash in their native habitat and more.
City and state partners continue monitoring and management, including targeted removals, trap trees and biological control releases where appropriate. Check local updates before making decisions, and avoid moving firewood across county lines.
Previously titled Don’t cut down that ash tree just yet – Oregon won’t see full effect of emerald ash borer for years
