Emerald ash borer (EAB), a small but destructive invasive beetle that attacks ash trees, has now been detected in east Multnomah County. Since its arrival in the U.S. in 2002, EAB has killed millions of ash trees nationwide, and experts have long anticipated its spread to our region.
Oregon’s first confirmed detection was in 2022 in Forest Grove, and this summer the beetle was found in multiple new sites, including Portland’s Hazelwood neighborhood. The presence of thinning canopies and telltale larval galleries under the bark confirm that EAB is now a local threat—underscoring the need for awareness and action in Troutdale.
What is the emerald ash borer?
The emerald ash borer (EAB) is an invasive beetle native to Asia that specifically attacks ash trees. Its larvae tunnel under the bark, feeding on the tree’s inner tissues and disrupting the flow of water and nutrients. Over time, this damage weakens and kills the tree, often within just a few years of infestation.
What happens to ash trees when they are infested?
Early signs of infestation can be difficult to spot. They may include:
- Thinning or yellowing leaves
- Small D-shaped exit holes in the bark
- Splitting bark that may reveal S-shaped larval tunnels
- New shoots sprouting from the trunk or branches
As the infestation progresses, canopy dieback becomes more severe and spreads downward. Once these symptoms are visible, the tree has often been infested for several years.
Are there many ash trees in Troutdale?
While some streets and parks in the city do have ash trees, they make up only a small percentage of Troutdale’s overall tree canopy.
How can I identify ash trees?
- Leaves: Compound leaves with 5–11 oval leaflets, smooth or slightly toothed.
- Branching: Opposite pattern—branches, buds, and leaves grow directly across from each other.
- Seeds: Single-winged seeds (samaras), shaped like canoe paddles, often in clusters.
- Bark: Mature trees have a distinct diamond-shaped ridge pattern; younger trees have smoother gray bark.
Are any other trees susceptible?
While ash trees (Fraxinus spp.) are the primary host, EAB can also attack other members of the olive family (Oleaceae). White fringetree (Chionanthus virginicus) is known to be susceptible, and there is possible vulnerability in Chinese fringetree (Chionanthus retusus) and even olive (Olea europaea). Still, ash trees are by far the most at risk.
What can I do?
- Be careful with firewood: Buy or cut firewood within 10 miles of where you plan to burn it. Transporting firewood is one of the fastest ways invasive insects and diseases spread.
- Consider treatment: Systemic insecticides can protect ash trees if applied early by a licensed pesticide applicator. Treatments usually need to be repeated every 2–3 years. Severely infested trees often cannot be saved.
- Avoid summer pruning: Pruning can signal stress and make trees more attractive to pests. Try not to prune ash trees between May and September, when adult EAB beetles are most active.
- Choose alternatives: Ash trees have not been recommended for planting in Oregon for more than five years due to the EAB threat. If you have a young ash tree, consider replacing it with a different species.
How can I learn more about EAB?
Here are a list of state and local resources that provide more information:
- Emerald Ash Borer Resources - OSU Extension Service
- Emerald Ash Borer Information - City of Portland Urban Forestry
- Don't Move Firewood Campaign - Oregon Invasive Species Council
- Identification Guide - Oregon Department of Forestry
(Photo credit: David Cappaert, Bugwood.org)