Emerald ash borer
Adult emergence ActiveAgrilus planipennis
10 host plants
Last updated
Quick Reference
Emerald ash borer Adult emergence typically begins around 1763 GDD₃₂. As of May 23, 2026, all seven Puget Sound stations have passed this threshold (2149.6–2365.5 GDD₃₂), so Adult emergence is likely underway across the lowlands.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of May 23, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,366 | Adult emergence | — | — |
| Kent / Auburn | 2,343 | Adult emergence | — | — |
| Seattle / UW | 2,303 | Adult emergence | — | — |
| Olympia / Tumwater | 2,267 | Adult emergence | — | — |
| Tacoma / Puyallup | 2,233 | Adult emergence | — | — |
| Bellingham / Whatcom | 2,230 | Adult emergence | — | — |
| Sequim / Rain Shadow | 2,150 | Adult emergence | — | — |
Source: Multiple sources, all base 50°F: UMD IPMnet 421 GDD₅₀ (mid-Atlantic); UMass 450-550 GDD₅₀ (March 1 start); Brown-Rytlewski & Wilson (2004) 471-584 GDD₅₀ first emergence, 584-705 peak (Michigan field data); Barker et al. (2023) DDRP model validated ±7 days. Profile uses 421 (UMD) as conservative first-emergence threshold. 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. Preventive treatment is the standard arboricultural protocol for high-value trees 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 USDA APHIS; Oregon Department of Agriculture
- Avoid planting Fraxinus species in new installations OSU Extension; WSU DNR Urban Forestry
- Maintain tree vigor through proper irrigation and avoid wounding UMass Extension
- Remove and destroy confirmed infested trees promptly Oregon Department of Agriculture
Host Plants (10)
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. Green ash (F. pennsylvanica) is widely planted as a street and park tree across the PNW. Oregon seed conservation efforts underway (OSU Extension). European ash specimens planted in PNW landscapes face dual-threat monitoring needs (EAB + ash dieback).
— Chris Welch, ISA Certified Arborist
Sources & References
Primary: UMass Extension Landscape, Nursery & Urban Forestry Program — Insect & Mite Guide: Agrilus planipennis
- Barker et al. (2023). An integrative phenology and climatic suitability model for emerald ash borer. Frontiers in Insect Science 3:1239173.
- UMD Extension IPMnet Pest Predictive Calendar (Gill & Klick) — GDD₅₀ emergence threshold: 421
- Oregon Department of Agriculture — Emerald Ash Borer Program.
- OSU Extension — Emerald ash borer in Oregon: what to do now, and what to plant next.
- OSU Extension — What to do about emerald ash borer (EM 9607).
- OSU Extension — New detections of emerald ash borer signal plan is working.
- WSU DNR Urban & Community Forestry — Preparing for Emerald Ash Borer in Washington State
- PNW Gardeners Handbook — EAB first detected Forest Grove, OR, June 2022