Emerald ash borer in Oregon

Where EAB is in Oregon

The Oregon Department of Agriculture confirmed the first West Coast EAB on June 30, 2022 in Forest Grove, Washington County. ODF’s EAB specialist calls the 2026 spread “to be expected” four or five years after a first detection.

The 2026 season used 426 traps placed by 40 cooperating agencies; EAB turned up in two (Silverton and Salem), with eight more detections made by other means. Every 2026 find sits inside the five-county quarantine.

The permanent quarantine: OAR 603-052-1075

ODA’s permanent EAB quarantine covers Washington, Yamhill, Marion, Clackamas and Multnomah counties. It regulates ash, olive and white fringetree in every form that can carry larvae, plus firewood of every hardwood species, because a stack of oak and maple rounds often hides ash.

Why the state rule is the one that counts

There is no longer a federal EAB quarantine. APHIS removed its domestic EAB quarantine regulations in 2020, and the final rule took effect on January 14, 2021. Since then, moving ash wood is governed by state rules, which in Oregon means ODA’s OAR 603-052-1075 above, not a federal permit.

APHIS’s program now concentrates on biological control, rearing and releasing stingless parasitoid wasps that attack EAB, along with detection surveys and public outreach. Its page (last modified April 23, 2026) counts EAB infestations in 38 states and the District of Columbia since the beetle was first found in North America in 2002, in southeast Michigan. APHIS’s point on spread applies directly to the Willamette Valley: the beetle flies on its own, but people carry it long distances in infested ash firewood, logs and nursery stock, so buy local or certified heat-treated firewood. APHIS takes questions at 1-866-322-4512; Oregon sightings still go to the Oregon Invasive Species Hotline below.

Why Oregon ash matters here

Oregon ash (Fraxinus latifolia) is the state’s only native ash and is highly susceptible to EAB. It grows below 2,000 feet, with 80 percent of the species below 1,000 feet, which is exactly where people live in the Willamette Valley. ODF calls it a key part of riparian forests and wetlands west of the Cascades, where it stabilizes soil, controls sediment and moderates stream temperature.

Portland alone has more than 95,000 ash trees: over 10,000 on streets and in parks, about 16,000 on private lots and roughly 68,000 in natural areas (ODF, August 2026). The USDA NRCS plant guide puts forest-grown Oregon ash at about 75 feet with trunks of 16 to 30 inches; open-grown trees are shorter and broader with large limbs. In a yard, that is a mid-size removal, not a small one.

If you replace an ash on a wet site, OSU Extension’s EM 9396 lists non-host alternatives that fill the same niche: red alder, white alder, black cottonwood, Oregon white oak, black hawthorn and several native willows for seasonally wet clay soils.

Signs of EAB on your tree

By the time a canopy looks thin, larvae have usually been feeding for years. ODF’s fact sheet says it can take three to four years before a tree starts to decline, and adults emerge May through July. Look for:

• D-shaped exit holes about one-eighth of an inch wide, flat on one side and rounded on the other.
• Serpentine (S-shaped) galleries under loose or split bark, from hundreds or thousands of larvae.
• Canopy thinning and dieback that begins in the upper crown and worsens each year.
• Epicormic shoots, clumps of sprouts along the trunk and big limbs, as the tree tries to replace lost crown.
• Woodpecker flecking, patches of lighter bark where birds have chipped away to reach larvae, plus loose bark.
• The adult beetle, metallic green and only about half an inch long; APHIS adds that the abdomen is coppery red and that adults live about three weeks, most active on warm, sunny days. Many green insects get mistaken for it; check ODF’s visual diagnosis guide before you report.

Report a suspected find through the Oregon Invasive Species Online Hotline (oregoninvasiveshotline.org) or 1-866-INVADER, with a photo. A certified arborist can tell EAB galleries from the native borers that only attack dying wood; see tree risk assessment for what that visit covers.

Treat or remove?

Injections work. OSU Extension’s EM 9607 rates emamectin benzoate (Arbormectin, Tree-age) as the most effective choice, protective for up to three years per treatment, applied in mid to late spring after leaf-out by a licensed applicator because it is a restricted-use pesticide. ODF’s September 2026 bulletin reports treated trees staying green in heavily infested regions while untreated ash nearby died.

The limits are the tree’s condition and your budget. OSU says trees with more than 20 percent canopy decline are generally not good candidates; ODF’s 2024 treatment sheet draws the line at 30 percent canopy loss and says healthy trees 6 inches in diameter and larger are the best candidates. Treatment “could cost hundreds of dollars and must be repeated every few years” (OSU); ODF figures a tree can be treated for about 20 years before the cumulative cost equals removing and replacing it.

ODF’s sheet adds that annual soil drenches of imidacloprid or dinotefuran have not prevented significant canopy decline, and cover sprays are among the least effective options.

Removing an ash inside the quarantine

ODA’s flyer asks you to avoid felling ash, including branches and stumps, from April 1 to September 30, and to do removal and pruning from October 1 to March 31 when adults are not flying. That puts ash removals in the same winter window as storm work, so book early; see dead tree removal for how crews handle brittle ash.

The wood has four legal destinations under the ODA flyer and ODF’s ash-wood guidance: stay inside the quarantine as logs or firewood; be chipped to 1 inch or smaller; be kiln-dried and debarked with 1 inch of wood removed, or heat-treated to 160°F for 60 minutes; or be buried under at least 12 inches of topsoil. Ask the crew which one they are using. Moving raw ash out of the five counties needs an ODA compliance agreement (eab@oda.oregon.gov, 503-986-4636).

Firewood: ODF says not to move it more than 30 miles from where it was cut. Backyard burning of yard debris is banned year-round inside the Portland metro boundaries set in OAR 340-264-0120, -0130 and -0140 (Clackamas, Multnomah and Washington counties), so chipping, not burning, is the practical route in the quarantine’s core; details in Oregon yard debris burning rules.

Permits still apply. In Portland, private trees 12 inches DBH and larger are regulated under Portland City Code 11.40; a dead, dying or dangerous tree gets a Type A permit with no public notice, and applications have been free since July 1, 2025. Street trees need a permit at any size. Other cities differ; see tree removal permits in Oregon.

Modeled estimate, not quotes (method): removing a 25–50 ft ash in Oregon models at $900–$1,800, and 50–80 ft at $1,800–$3,600, with chipping and haul-away but no stump; multiply by 1.25 within 10 ft of a structure. Stump grinding adds $150–$450 by diameter. Current figures are on tree removal cost.

What to do this season

1. Confirm it is ash. OSU’s gallery “Recognizing ash trees in Oregon, Washington and Northern California” shows the details.
2. Check the crown now. A thinning top, sprouts on the trunk and woodpecker work mean you are choosing a removal date, not a treatment.
3. Healthy and valuable? Book a licensed applicator for an emamectin benzoate injection next spring after leaf-out, then repeat every 2–3 years.
4. Removing? Schedule October through March, confirm the crew’s chip size and disposal plan, and get the permit if your city needs one.
5. Check the crew at the Oregon CCB or LCB license lookup; Oregon requires one or the other for tree removal.
6. Replant with a non-host from EM 9396 and water it through its first summers.

For removal options, start at tree removal. For the beetle across the river, see emerald ash borer in Washington; other pests are listed under pests and diseases.