Warning: Bronze Birch Borer and Emerald Ash Borer – Serious Threats to Trees in Western Washington

By Cody Cochran | Jan 2026

Hey PNW folks—if you have birch or ash trees on your property, this is a serious alert. Two invasive wood-boring pests, the Bronze Birch Borer (BBB) and the Emerald Ash Borer (EAB), are actively damaging and killing trees in western Washington. This isn't a distant threat; it's already claimed hundreds of trees and continues to spread in counties like Thurston, Lewis, King, and beyond. These beetles target stressed trees and can kill them in just a few years if left unchecked.

Bronze Birch Borer: Widespread and Deadly in Our Area

The Bronze Birch Borer is a metallic bronze beetle about 1/2 inch long that attacks birch trees, especially non-native varieties like European white birch. Adults lay eggs in bark cracks, and larvae tunnel under the bark, girdling the tree and blocking nutrient flow.

In western Washington, BBB is rampant and has killed hundreds of birches in Thurston, Lewis, and surrounding counties. It's not a question of "if" your birches will get hit—it's "when," particularly if they're stressed by drought, poor soil, or other factors common in our climate.

Early signs: Thinning or yellowing in the top canopy, branches dying back from the crown downward, bumpy ridges on bark, or D-shaped exit holes.

Emerald Ash Borer: Arriving and Expected to Explode

The Emerald Ash Borer is a bright green invasive beetle from Asia that's devastated millions of ash trees nationwide. Larvae create S-shaped galleries under the bark, girdling and killing the tree.

Though not as widespread as BBB yet, EAB has been detected in areas of Thurston County and nearby regions like Portland and Vancouver, BC. Experts expect it to become just as prevalent here soon, potentially wiping out untreated ash trees.

Watch for: Top-down dieback, bark splitting, D-shaped exit holes, woodpecker activity, or basal suckers.

How to Protect Your Trees: Prevention is Key

The best defense is keeping trees healthy with proper watering, mulching, and avoiding wounds—stressed trees are prime targets. But for reliable protection, preventive systemic treatments are essential, especially since infestations are hard to spot early.

At Wolberts, we offer preventive treatments to keep these pests from ever infesting your birches and ashes. We use professional trunk injections or soil injections to deliver protection directly into the tree's system.

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These treatments typically require just one application per year (depending on the product and tree size). Note: This isn't a one-and-done service—it must be repeated annually to maintain ongoing protection as the effects wear off.

Timing is ideal in late winter to early spring for best uptake as trees wake up, but we can perform injections effectively any time of year if needed.

Don't wait for symptoms—by then, it may be too late. Contact us for an inspection, preventive plan, or advice. We're here to help keep Western Washington's trees standing strong. Questions? Comment below or reach out!

Contact us today if you have questions or want a free estimate.