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emerald ash borer on leaf

Emerald Ash Borer

Emerald ash borer (EAB) is an invasive beetle that infests and kills ash trees. EAB has killed hundreds of millions of trees across the United States. In 2022, EAB was confirmed in Oregon and it has since spread to Clackamas, Marion, Yamhill, and Multnomah counties.

EAB is now within 5 miles of Trillium Creek Park and up to 10 miles of the rest of North Clackamas Parks and Recreation District.

Impacts of EAB

Oregon ash (Fraxinus latifolia) is an important native tree that grows along rivers, streams, and wetlands in low-elevation areas. They are a critical source of shade, erosion control, pollution filtration, and wildlife habitat. According to an inventory taken in 2025, we have identified 915 ash trees of various sizes within North Clackamas Parks and Recreation District.

The mortality rate of infected ash trees is 100%, regardless of the tree’s health, age, or size. Once EAB arrives in an area, it cannot be eradicated—which means it doesn't go away. Losing ash trees in Oregon and the district will have impacts to local environment, economy, and public health.

Ash tree leaves and blue sky

How NCPRD is Handling EAB

Although the beetle will kill many ash trees in Oregon, there are steps we can take to slow its spread and reduce its impact. NCPRD has been actively working with local, state, and federal partners to prepare for the looming threat. We have developed an EAB Management Plan that prioritizes public safety in our parks and green spaces, while also mitigating canopy and shade loss.  The plan includes the following action items:

  1. Treatment: Protect suitable ash trees by treating with an injectable insecticide.
  2. Reduction & Replanting: Preemptively remove trees that pose high risk, and small or unhealthy ash trees that are not suitable for treatment. Replant trees, dependent on the park and location, through community volunteer events.
  3. Wood Disposal: Manage wood waste responsibly and proactively.
  4. Educate: Provide district residents with information relating to EAB and the resources available for mitigating its impact.  
EAB Management Plan

What you can do as an individual to avoid spreading EAB

Frequently Asked Questions

EAB spreads primarily through human-assisted movement, such as moving infested firewood and nursery stock. Movement of ash material out of a quarantined area is prohibited. EAB can also spread naturally through short-distance flight by adult beetles

EAB kills ash trees by their larvae tunneling in S-shaped galleries under the bark, cutting off the vital flow of water and nutrients (sap) between the roots and leaves, leading to canopy dieback and eventual death within a few years, even in healthy trees. This disruption starves the tree, causing it to decompose from the top down, with symptoms like thinning leaves and epicormic sprouts.  

EAB injection treatment involves drilling small holes near the base of an ash tree and injecting systemic insecticides directly into the tree's vascular system using specialized micro-injectors or pressurized capsules, allowing the pesticide to move up to the canopy to kill feeding larvae and adults. The insecticide travels with the tree's water, making the tree's tissues toxic to EAB larvae and adults.

Systemic insecticides that are injected directly into the tree are low-risk to pollinators. Research has shown that pesticide residues from systemic applications are not found in ash pollen. This is the safest tactic for pollinators while also effectively protecting the treated ash trees.

Treatment with systemic insecticides can be effective in protecting ash trees. However, this can be expensive and must be repeated every few years for the duration of the tree’s life. 

Emerald Ash Borer look-a-like diagram

Additional Resources

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Contact

For questions about the Emerald Ash Borer Management Plan, contact the Natural Resources Team at parks@ncprd.org.