Emerald ash borer, an invasive pest, has been discovered in three more counties this summer, according to the Oregon Department of Agriculture and the Oregon Department of Forestry.

The beetles have been confirmed in Marion and Yamhill counties.

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A third site on the border of Clackamas and Marion counties is believed to harbor emerald ash borer, but the state needs to confirm the identity of the insects with the USDA Animal Plant Health Inspection Service laboratory in Maryland.

Jeff Stone, Oregon Association of Nurseries executive director, said the problem was concerning because there’s no answer other than trying to slow the progress of the “insidious” pest.

“Some people think it’s been here for a little bit. It’s just a matter of time before, unfortunately, it spreads,” Stone added.

He believed many Oregon nurseries have pivoted away from ash, white fringe and olive trees susceptible to the pest.

“People have started reducing the number they have in production and moving on to other trees or more disease resistant trees,” Stone said.

About the pest

Emerald ash borer, a small, metallic-green beetle native to eastern Asia, was first found in the U.S. in Michigan in 2002.

Since then, it’s killed millions of ash trees across the eastern U.S., with death rates up to 99%.

“You can’t ship ash there. The borer is just waiting for it,” Stone said.

The beetle’s larvae burrow into the bark of ash trees, causing canopy dieback and ultimately tree death.

“If you cut in the middle of the tree where an emerald ash borer has been, that whole tree is wrecked,” Stone said.

The half-inch beetle is often challenging to detect, especially in newly infested trees.

Signs of infestation include thinning and yellowing leaves, bark splitting, D-shaped holes in the tree bark and basal shoots.

Monitoring the spread

Emerald ash borer was first detected in Forest Grove, Ore. in June 2022, and that area is now heavily infested.

Since then, authorities have set out about 200 traps to monitor the pest in the Willamette Valley.

They’re also searching areas surrounding the infestations in Marion and Clackamas counties to find out whether the bug shows up further out.

The Yamhill County site, in the area of Gaston, Ore., could represent a spread from Forest Grove, which is only seven miles away. Emerald ash borer often travels in loads of firewood transported by people.

Quarantine details

A quarantine was already in place for Washington County, and that now applies to the newly confirmed areas of Yamhill and Marion counties, said an ODA spokeswoman.

That quarantine restricts the movement of ash, olive and white fringe tree wood, as well as other materials from those species.

“We want to protect the rest of Oregon for as long as possible to give communities more time to prepare,” said Cody Holthouse, ODA compliance and regulatory manager, and chairman of the state’s interagency emerald ash borer task force.

Holthouse urged Oregonians to buy firewood near where they intend to burn it and avoid taking firewood more than 10 miles from where it was cut.

Stone said nurseries will work closely with ODA and do the right thing.

“Oregon has a stellar reputation for cleanliness of plants and trees. Nobody wants to get lax and ruin that reputation,” Stone added.