Emerald Ash Borer Infests Ash Trees in Washington

The invasive beetle, which has killed 100 million trees nationwide, is now confirmed in Walla Walla County.

Updated on Oct. 29, 2026 in Botany

Emerald Ash Borer Infests Ash Trees in Washington

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The emerald ash borer, an invasive insect responsible for the loss of over 100 million trees nationwide, has officially reached Washington. Infestations are now confirmed in Walla Walla County following an initial detection near Vancouver in August 2026.

Why it matters

This arrival threatens to decimate native Oregon ash populations and other true ash species across Washington, with potential community canopy losses reaching 90 percent without intervention.

The emerald ash borer has resulted in the destruction of 100 million ash trees across the U.S. Experts project that local communities could see up to 90 percent of their ash populations eliminated by the invasive beetle.

The players

Emerald ash borer

An invasive coleopteran insect that has killed more than 100 million ash trees in the United States.

Oregon ash

A native Pacific Northwest deciduous tree species that is highly vulnerable to emerald ash borer infestation.

The details

The emerald ash borer is a wood-boring beetle that targets native North American ash species, including the Oregon ash common in the Pacific Northwest. Adult beetles feed on ash leaves, but it is the larvae that cause mortality by tunneling into the tree's vascular tissue, specifically the phloem—the layer that transports sugars from the leaves to the roots—effectively girdling and killing the host tree.

August 2026: Emerald ash borer first detected near Vancouver.

The Tech Race

The arrival of the insect in Washington state follows a multi-decade pattern established by the U.S. Department of Agriculture's national emerald ash borer response programs. Washington's situation now mirrors the trajectory of eastern states that have struggled for years to mitigate the beetle's ecological impact.

Property owners and land managers with ash trees should monitor for signs of infestation, as nearly all true ash species are at risk of total loss. Local authorities will likely initiate management protocols as the beetle continues to spread from the confirmed sites in Walla Walla County.

The takeaway

The invasion of the emerald ash borer signals a long-term threat to the state's canopy structure. Residents should track updates from the Washington state Department of Agriculture regarding quarantine zones and tree disposal guidelines.