Emerald Ash Borer in Parks & Recreation

The City’s Planning Department has an in-depth webpage devoted to information regarding Emerald Ash Borer (EAB and trees on private property.)  Click here to be connected to that page.

Emerald Ash Borer: A Growing Threat to Our Urban Forests

The Parks & Recreation Department is taking proactive steps to stay ahead of the Emerald Ash Borer (EAB) infestation. The Emerald Ash Borer, Agrilus planipennis, is a highly destructive beetle that targets ash trees. It was initially discovered in the U.S. in 2002 in southwestern Michigan, and was first detected in 2022 in Oregon. While and emerald ash borer infestation has not yet been discovered in Lake Oswego, it has been detected in Clackamas County as well as several surrounding counties. These counties are currently under quarantine. Quarantine prohibits materials from all plant parts of ash (Fraxinus spp.), white fringetree, and olive trees from movement outside these counties – tree materials must remain within quarantine counties. Wood waste must be processed and disposed of accordingly.

What Are We Doing in Lake Oswego Parks & Natural Areas

Tree Inventory: The City recently completed an ash tree inventory within City owned park properties to assess the vulnerability of local ash trees and develop a pest management plan.

Preventative Treatments: In 2023, 28 ash trees in Foothills Park were treated as a precautionary measure against EAB with more treatments coming as EAB is identified within Lake Oswego.

Public Education: Ongoing workshops, articles, videos, and outreach events are being offered to educate residents on how to identify ash trees and signs of EAB infestation.

Monitoring & Training: The Parks Department, in collaboration with Oregon Department of Forestry, is regularly monitoring EAB traps across the city. Staff are also receiving specialized training on pest detection and management strategies.

Land Management: Parks Department staff are part of the Department of Forestry’s taskforce to create a collaborative outreach and management strategy for informing the public and following best management practices for removal of infested ash trees and replacement of lost canopy.

Why It Matters

Ash trees play a critical role in Lake Oswego's urban forest, providing shade, habitat, and erosion control, particularly in riparian zones (wetlands and stream corridors). An EAB infestation could devastate these vital ecosystems, leading to a loss of tree canopy, increased invasive plant growth, and diminished habitat for local wildlife. We are looking into ways to slow the loss of trees, along with replanting with other tree species. Once EAB arrives in an area, it cannot be eradicated – which means it doesn’t go away. For more information visit Oregon’s Department of Forestry’s website: Oregon-EAB.

What Should You Do?

Don’t move Firewood: The spread of EAB is largely due to the movement of infested firewood. Buy firewood locally (within 5 miles) and avoid transporting it to another site.

Stay advised on current quarantine and response updates on Oregon’s Department of Forestry EAB informational website, Oregon-EAB.

Report Suspicious Trees: If you suspect EAB or notice tree symptoms like crown thinning or bark splitting, report it to the Oregon Invasive Species Online Hotline.

For a printable information sheet, click here!