Emerald ash borer

Near Adult emergence

Agrilus planipennis

10 host plants

Last updated

Data Maturity Structured

This profile synthesizes data from multiple published sources. Expert field review is in progress.

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.

— Chris Welch, ISA Certified Arborist

Quick Reference

Order
Coleoptera
Type
borer
Host Plants
10
GDD₃₂ Adult emergence
1,763
Indicator: Red horsechestnut first bloom
Peak Activity
Late May through July for adult activity (mid-Atlantic timing; PNW emergence ...
Damage Severity
lethal

Emerald ash borer Adult emergence typically begins around 1763 GDD₃₂. As of April 28, 2026, Puget Sound stations range from 1536.6 to 1694.7 GDD₃₂, approximately 68 units before the expected threshold.

Regional Season Tracker

GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 28, 2026
Station GDD₃₂ Current Stage Next To Go
Issaquah / East King 1,695 Pre-season Adult emergence 68
Seattle / UW 1,654 Pre-season Adult emergence 109
Kent / Auburn 1,644 Pre-season Adult emergence 119
Olympia / Tumwater 1,603 Pre-season Adult emergence 160
Bellingham / Whatcom 1,591 Pre-season Adult emergence 172
Tacoma / Puyallup 1,572 Pre-season Adult emergence 191
Sequim / Rain Shadow 1,537 Pre-season Adult emergence 226
Extrapolated

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

How to Monitor

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)

When to Act

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)

What Damage Looks Like

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)

Fraxinus americana White Ash, American Ash Fraxinus angustifolia Narrow-leaved Ash Fraxinus anomala Singleleaf Ash, Dwarf Ash Fraxinus excelsior Euopean Ash, Common Ash Fraxinus latifolia Oregon Ash Fraxinus ornus Flowering Ash Fraxinus oxycarpa Fraxinus oxycarpa Fraxinus pennsylvanica Green Ash Fraxinus quadrangulata Blue Ash Fraxinus sieboldiana Siebold Ash, Japanese Flowering Ash, Chinese Flowering Ash

Sources & References

Primary: UMass Extension Landscape, Nursery & Urban Forestry Program — Insect & Mite Guide: Agrilus planipennis