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Emerald ash borer infestation confirmed in Walla Walla County, threatening local trees
Washington officials have confirmed the state’s first documented emerald ash borer infestation in trees, at a Walla Walla County property. The invasive beetle can kill ash trees, and state agencies are urging residents to stop planting them and report suspected sightings.
A Walla Walla County homeowner’s green ash tree has become the first tree in Washington confirmed to be infested by emerald ash borer, an invasive beetle that has killed tens of millions of ash trees across the United States.
Arborist Isaac Long found small, D-shaped exit holes while examining the struggling tree in September. He took a branch sample to Washington State University’s Walla Walla extension office. State Department of Agriculture staff later inspected the site, found pale larvae in several trees and sent specimens to the U.S. Department of Agriculture, which confirmed the species.
The infested tree has since been removed. The state is urging residents not to plant ash trees as the pest spreads.
Emerald ash borer adults are about half an inch long and metallic green. The beetles lay eggs under tree bark; after hatching, larvae tunnel through the wood and can damage the tree’s vascular system, eventually killing it. The adults emerge through the distinctive D-shaped holes.
The insect, native to Asia, was first identified in the United States in Michigan in 2002. A beetle was reported on a windshield in the Vancouver area in August, but the Walla Walla County discovery is the state’s first confirmed infestation in trees.
“Once emerald ash borer has been detected, it’s only a matter of time before you see large-scale mortality of ash on the landscape,” said Zeima Kassahun, an urban and community forestry specialist with the Washington State Department of Natural Resources.
The beetle often spreads when people move infested wood. Washington enacted a firewood quarantine earlier this year, though Kassahun said the insect can also spread on its own.
The threat extends beyond lumber and neighborhood shade trees. Oregon ash is the Pacific Northwest’s only native ash species and grows along waterways, where it supports birds and insects and helps maintain healthy riparian areas. Ash trees also hold cultural significance for Indigenous communities.
The Department of Natural Resources’ Urban and Community Forestry Program can advise landowners on preserving some ash trees or buying time to replace them. Officials caution that dead ash trees become more brittle over time and can become more hazardous to remove.
Residents can report suspected emerald ash borer sightings at invasivespecies.wa.gov, by emailing invasivespeciesinfo@rco.wa.gov or through the Washington Invasives app. The agriculture department says specimens can be placed in a plastic bag and frozen.