Can We Save Oregon Ash Trees?

By now you’ve likely heard that identification of the dreaded emerald ash borer (EAB) has been confirmed in Washington County, Oregon. The Oregon Department of Agriculture believes that the infestation has been in that county for at least three to five years. The outlook is grim.

Of northeastern Asian origin, the EAB is a small green beetle in the Buprestidae family which feeds on members of the olive family (Oleaceae), especially ash trees (Fraxinus species). Adults feed on leaves and females lay their eggs in bark crevices. Eggs hatch in seven to ten days and larvae burrow through bark to living tissues where they feed, eventually cutting off the flow of water and nutrients, which causes a slow death. Adults emerge in one to two years and typically travel only about a half mile afterwards.

In its native range, this beetle is typically not found in high numbers and does not cause significant damage to native trees. However, outside its native range it is extremely destructive to trees indigenous to North America or Europe.

The EAB is now considered to be the most destructive forest insect to ever invade North America. First detected in Michigan in 2002, it has spread through much of the U.S. (36 states and the District of Columbia). Though harmless to people and other animals, it has proven deadly to all ash species in North America, including the native Oregon ash (Fraxinus latifolia), naturally found west of the Cascades in southern British Columbia, Washington, Oregon, and northwestern California, as well as central California and the Sierra Nevada.

Spread throughout the country has been mainly by the movement of infested firewood, logs, chips, and nursery stock. Movement of emerald ash borers and their host material has been, until recently, regulated by the USDA under a federal domestic quarantine. The quarantine for emerald ash borer was repealed in January 2021.

The Oregon ash tree is currently relatively common and is a significant component of riparian forests; it is the only native ash tree in the Pacific Northwest. It is widely used for stream restoration due to its wide and spreading root system that stabilizes soil, controls sediment, and moderates stream temperatures. Widespread loss of these beautiful, long-lived trees will affect water quality (including higher stream temperatures) and change the wildlife species composition of their ecosystems, causing harmful effects on species dependent on those ecosystems.

How to help
Learn now to identify ash trees and trees that resemble them here.

If you have ash trees or know of some, familiarize yourself with the basic signs and symptoms of emerald ash borer. Reports may be made at

Also check out this article. Robert Haight, a Forest Service researcher in St. Paul, Minn., proposes a strategic approach which involves identifying beetle-infested ash trees before they show signs of damage. “One way, he says, involves searching for woodpeckers. The emerald ash borer hides its eggs in bark crevices and tunnels deeply within trees — invisible to humans, but not to woodpeckers. They pick at the tree’s bark, searching for tasty grubs.” So please keep an eye out for our friends, the woodpeckers, foraging on Oregon ash trees.

UPDATE February 2023: The Oregon Department of Forestry has collected 900,000 Oregon ash seeds; it hopes to find trees resistant to the borer in that collection. Read about it here.

More info and brochures:

Oregon’s Readiness and Response Plan:

Xerces Society:

© 2022 Eileen M. Stark

Leave a Reply

Your email address will not be published. Required fields are marked *