Emerald ash borer
Agrilus planipennis
10 host plants
Last updated
Quick Reference
Emerald ash borer Adult emergence typically begins around 1763 GDD₃₂. As of April 7, 2026, Puget Sound stations range from 1148.6 to 1272.6 GDD₃₂, approximately 490 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 7, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,273 | Pre-season | Adult emergence | 490 |
| Seattle / UW | 1,253 | Pre-season | Adult emergence | 510 |
| Kent / Auburn | 1,206 | Pre-season | Adult emergence | 557 |
| Olympia / Tumwater | 1,192 | Pre-season | Adult emergence | 571 |
| Bellingham / Whatcom | 1,178 | Pre-season | Adult emergence | 585 |
| Tacoma / Puyallup | 1,162 | Pre-season | Adult emergence | 601 |
| Sequim / Rain Shadow | 1,149 | Pre-season | Adult emergence | 614 |
GDD source: UMD IPMnet Pest Predictive Calendar (Gill & Klick). Base 50°F, mid-Atlantic climate. Converted to GDD₃₂ for Western WA. About GDD₃₂ →
Monitoring & Action
Purple prism traps baited with (Z)-3-hexenol (green leaf volatile) and (3Z)-lactone (Manuka oil), hung 6-10 m high in ash canopy. Visual inspection for D-shaped exit holes (3-4 mm), S-shaped galleries under bark, crown dieback, bark splitting, epicormic sprouting, and bark blonding from woodpecker foraging. Biosurveillance via smoky-winged beetle bandit wasp (Cerceris fumipennis) where populations occur. (UMass Extension; USDA APHIS)
No formal action threshold for landscape trees. Any confirmed detection warrants immediate assessment of all ash within the area. For high-value trees, preventive treatment is recommended within 15 miles of a confirmed detection. (UMass Extension)
Larvae feed in serpentine, S-shaped galleries in the phloem and outer sapwood, disrupting nutrient and water transport. Canopy dieback begins at the crown and progresses downward. Epicormic sprouting (water sprouts) on trunk and major limbs. D-shaped adult exit holes approximately 3-4 mm across are diagnostic. Bark splitting exposes larval galleries. Increased woodpecker activity causes bark 'blonding' as birds forage for larvae. Small trees die within 1-2 years of infestation; larger trees in 3-4 years. Mortality approaches 99% in untreated ash populations within 6-10 years of EAB arrival in a region. (UMass Extension; USDA Forest Service)
Cultural Controls
- Do not move ash firewood or untreated ash wood products
- Avoid planting Fraxinus species in new installations
- Maintain tree vigor through proper irrigation and avoid wounding
- Remove and destroy confirmed infested trees promptly
Not yet detected in Washington state as of April 2026. First detected on the West Coast in Forest Grove, Oregon (Washington County) on June 30, 2022. As of January 2026, Oregon quarantine covers five counties: Washington, Yamhill, Marion, Clackamas, and Multnomah (Portland confirmed September 2025). Spread modeling by WSU/ODA/BLM projects arrival in Washington within approximately 2 years of 2025 estimates. Oregon ash (F. latifolia) is the primary native host at risk in the Puget Sound lowlands, common along riparian corridors and wetland margins. GDD conversion: 421 GDD₅₀ = ~1763 GDD₃₂; Kent reaches this threshold around May 15-27 (5-year average ~May 20). Emergence timing not field-validated for PNW.