If you own an ash tree in Washington, Yamhill, Marion, Clackamas or Multnomah County, use this winter to decide between treating it next spring and removing it before April 1. Oregon’s quarantine asks owners to cut ash only from October 1 to March 31, and a tree that is still healthy gives you both options; a tree that is already thinning gives you one.
Where emerald ash borer is in Oregon now
The Oregon Department of Agriculture confirmed the first West Coast emerald ash borer in Forest Grove on June 30, 2022. By the September 2026 Oregon Department of Forestry bulletin, finds had been confirmed in Washington, Yamhill, Marion, Clackamas and Multnomah counties, including 2026 detections in Tualatin, Newberg, Silverton, Beaverton, south and north Salem, Bethany Lake Park, the Banks-Vernonia State Trail, East Portland, Hazeldale Park in Aloha, and the Jackson Bottom Wetlands Preserve near Hillsboro on July 27.
The beetle has also crossed the Columbia. The Washington Invasive Species Council reports a specimen found August 3, 2026 in Hazel Dell, unincorporated Clark County near Vancouver, confirmed by WSDA and USDA APHIS on August 19. Clark County owners should read emerald ash borer in Washington.
- Quarantine counties: Washington, Yamhill, Marion, Clackamas and Multnomah (OAR 603-052-1075).
- ODA cutting window for ash, including branches and stumps: October 1 to March 31.
- Treatment: emamectin benzoate injection after spring leaf-out, repeated every 2–3 years (OSU EM 9607).
- Over about 20–30% canopy loss, treatment is generally not recommended (OSU; ODF).
- Penalty for moving regulated ash out of the quarantine: up to $10,000 (ORS 570.995).
Why the decision happens in winter
Adult beetles fly in the warm months. ODF’s fact sheet puts adult emergence in May through July, and the ODA quarantine flyer asks owners to avoid felling ash, including branches and stumps, from April 1 to September 30. Pruning and removal belong in the October 1 to March 31 window, when no adults are flying to carry larvae out of fresh wood.
Treatment runs on the opposite calendar. OSU Extension’s EM 9607 rates emamectin benzoate the most effective option, protective for up to three years, applied in mid to late spring after leaf-out by a licensed applicator because it is a restricted-use pesticide. So a winter decision either books a removal before April 1 or books an applicator for May.
Check the tree before the leaves are gone
Look at the crown in October while there are still leaves to judge. ODF and OSU list the signs:
- Thinning and dieback that starts at the top of the crown.
- Clumps of sprouts along the trunk and large limbs.
- Woodpecker flecking: patches of lighter bark where birds have chipped in to reach larvae.
- D-shaped exit holes about an eighth of an inch across.
- S-shaped galleries under loose bark.
ODF notes it can take three to four years after infestation before a tree visibly declines, so a tree that looks fine within a few miles of a find may already carry larvae. Report suspected finds to the Oregon Invasive Species Online Hotline or 1-866-INVADER with a photo.
Treat, remove or wait
- Healthy ash, 6 inches or more in diameter, that you value. ODF’s 2024 treatment sheet names these as the trees most worth treating and suggests starting when EAB is within 15 miles; Salem, Portland, Hillsboro and Beaverton are all inside that distance now. Book the injection for spring.
- Healthy ash, but you will not commit to repeat treatment. OSU Extension says removing a live ash is less expensive and more predictable than removing a dead one. Remove it this winter while the wood is sound.
- More than 20–30% of the canopy already gone. OSU puts the cutoff at 20%, ODF at 30%. Treatment is unlikely to save it, and dead ash turns brittle. Remove before April 1; see dead tree removal for how crews handle a declining tree.
- Small ash of no special value. Remove and replant with a non-host from OSU’s EM 9396, such as red alder, Oregon white oak or black hawthorn on wet sites.
ODF’s sheet also notes that yearly soil drenches of imidacloprid or dinotefuran have not prevented significant canopy decline. The full comparison is on emerald ash borer in Oregon.
What happens to the wood
Inside the five counties, raw ash logs and firewood can stay put. To leave, regulated ash material needs an ODA compliance agreement or must be processed: chipped to 1 inch or smaller, kiln-dried and debarked with an inch of wood removed, or heat-treated to 160°F at the core for 60 minutes. Hardwood firewood of every species is regulated, because a stack of maple often hides ash. ODF also lists burial under at least 12 inches of soil.
Burning is mostly off the table in the metro core. Domestic burning is banned year-round inside the Portland-area boundaries in OAR 340-264-0120, -0130 and -0140, and in much of the rest of those three counties yard debris may be burned only March 1 to June 15 and October 1 to December 15; see Oregon yard debris burning rules. Ask the crew which disposal route they use before the job starts.
Permits and who does the work
A dying ash is the easy permit case in most cities. In Portland, private trees 12 inches in diameter and larger are regulated under City Code 11.40; a dead, dying or dangerous tree gets a Type A permit with no public notice, and removal permit applications have been free since July 1, 2025. Street trees need a permit at any size. Salem regulates only significant trees, 30 inches and larger for most species. Other cities are on Oregon tree removal permits.
Any business removing or pruning your ash in Oregon must hold a Construction Contractors Board or Landscape Contractors Board license (ORS 701.005, ORS 671.525), and an injection must be done by a licensed pesticide applicator. How to check a license is on Oregon tree service license lookup.
A short plan for this winter
- Confirm the tree is ash, using the identification pages in ODF’s fact sheet and OSU’s EAB resources.
- Rate the crown now: under 20% loss, 20–30%, or more.
- Decide by January: treat in spring, or remove before April 1.
- If removing, get the permit and agree on chip size and disposal in writing.
- Replant with a non-host species in spring.
Sources
- Oregon Department of Agriculture, Emerald ash borer, checked 2026-10-02.
- ODA, Permanent EAB quarantine flyer (OAR 603-052-1075; ORS 570.995), checked 2026-10-02.
- ODF, Oregon Tree Health Threats Bulletin, September 2026; August 2026, checked 2026-10-02.
- Washington Invasive Species Council, Emerald ash borer (updated Sept 17, 2026), checked 2026-10-02.
- ODF, Emerald ash borer fact sheet, checked 2026-10-02.
- ODF, EAB treatment fact sheet (2024), checked 2026-10-02.
- OSU Extension EM 9607, What to do about emerald ash borer; OSU Extension, Should we treat ash trees for emerald ash borer?, checked 2026-10-02.
- OSU Extension, Emerald ash borer resources, checked 2026-10-02.
- OSU Extension EM 9396, Alternatives to ash in western Oregon, checked 2026-10-02.
- ODF, What to do with ash wood under the EAB quarantine, checked 2026-10-02.
- Oregon DEQ, Open burning (OAR 340-264), checked 2026-10-02.
- City of Portland, Tree removal and replanting permits (PCC 11.40); City of Salem, Tree removal on your property (SRC 808), checked 2026-10-02.
- ORS 701.005(5)(e); Oregon Landscape Contractors Board, checked 2026-10-02.
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