The emerald ash borer (EAB) is one of the most destructive tree pests in North America, and it’s been steadily moving toward the Pacific Northwest: it has now been confirmed in Oregon and British Columbia, both within range of Washington State. According to Washington State University’s Urban Forest Health Lab, while EAB hasn’t yet been confirmed in Washington, state and regional agencies are actively monitoring for it, and Seattle-area homeowners with ash trees should know what to watch for.

What Is the Emerald Ash Borer?

The emerald ash borer is a small, metallic-green beetle whose larvae tunnel under the bark of ash trees, cutting off the tree’s ability to move water and nutrients. Left untreated, an infestation is typically fatal to the tree within a few years.

Do You Have Ash Trees?

Ash trees are less common in Pacific Northwest landscapes than maples, firs, and cedars, but they do appear in older neighborhoods and as street trees in parts of Seattle and the Eastside. If you’re not sure whether a tree on your property is an ash, a certified arborist can identify it during a routine visit.

Early Warning Signs

• Thinning or dying canopy, often starting at the top of the tree
• D-shaped exit holes in the bark, about 1/8 inch wide
• Vertical bark splits
• Increased woodpecker activity, as birds feed on larvae under the bark
• Sprouting growth low on the trunk (epicormic shoots)

What Homeowners Can Do Now

Because EAB hasn’t been confirmed in Washington yet, there’s no need for alarm, but early awareness matters, since infestations are far easier to manage when caught early. If you have ash trees, it’s worth having them checked periodically as part of routine tree health maintenance. Suspected sightings should be reported directly to the Washington Invasive Species Council, which coordinates the state’s monitoring and response efforts, rather than assumed to be another pest.

How Emerald Arbor Care Can Help

Our arborists can identify ash trees on your property, monitor for early signs of pest and disease pressure, and build a tree health maintenance plan suited to your landscape. Learn more about our tree health services or call (206) 558-2814 to schedule an assessment.

Sources: WSU Urban Forest Health Lab, Washington State University; Washington Invasive Species Council.