Oregon Ash Tree Near Tualatin River

Emerald Ash Borer in Oregon

July 27, 2022 By

The emerald ash borer (EAB) is an invasive insect that has decimated ash species across the United States and is considered the most destructive forest pest in America. It has now been spotted in Oregon.

The first confirmed sighting in June 2022 in Forest Grove, Oregon, has raised the alarm throughout the state. All ash species are vulnerable to the EAB, including urban landscaping ash and our native Oregon ash (Fraxinus latifolia). Oregon ash has the unique ability to thrive in the dense, wet soil of river and stream beds. This makes it a critical tree for the health of our rivers. The Oregon ash tree seen above grows high above the Tualatin river in Lake Oswego. Its roots stabilize the soil nearest the river, preventing erosion. The summer canopy shades the river, decreasing water temperature, and making the river more habitable for our native fish. The rivers of Oregon will suffer if Oregon ash is lost to EAB.

Oregon Ash Tree Leaves

The severe risk of the spread of EAB has prompted authorities to request the help of the public in reporting sightings of the pest in order to understand the range of the current infestation and the speed at which it spreads. Oregon ash can be easily identified by the long compound leaves that are divided into oblong leaflets that grow opposite from one another. Because the larvae of the EAB consume the cambium of the tree hidden beneath the bark, the first outward sign of the EAB infestation is after adult beetles emerge in late spring. The EAB is a ½ inch long metallic green beetle which leaves a distinctive 1/8 inch wide D-shaped exit wound on the ash tree bark when the adult emerges. You can learn more about their identification with this Oregon Department of Forestry Fact Sheet and report a sighting at the Oregon Invasive Species Council website.