Info on Emerald Ash Borer in Parks & Recreation

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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) invasion, a highly destructive beetle that targets ash trees. EAB was first detected on the West Coast in Oregon in 2022 and has since been found in Clackamas, Washington, Yamhill, and Marion Counties, placing these areas under quarantine. While EAB has not yet been detected in Lake Oswego, the city is preparing for its potential spread.

What is an Emerald Ash Borer?

Emerald ash borer, Agrilus planipennis, is a beetle that was first discovered in the U.S. in 2002 in southeastern Michigan. It has since been detected in more than 30 states, including Oregon (Forest Grove), on June 30, 2022. This was the first confirmation of the invasive pest on the West Coast. 

While the emerald ash borer (EAB) has not been detected within the City of Lake Oswego, it has been detected in Clackamas County as well as Washington, Yamhill, and Marion Counties. These counties are currently under quarantine. Quarantine prohibits materials from all plant parts of ash (Fraxinus spp.), white fringetree (Chionanthus virginicus spp.), and olive (Olea spp.) trees from movement outside these counties. 

What We're Doing

Tree Inventory: The City is conducting a comprehensive tree inventory in parks and natural areas 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.
Public Education: Ongoing workshops and articles 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 the Clackamas County Soil and Water Conservation District, is regularly monitoring EAB traps across the city. Staff are also receiving specialized training on pest detection and management strategies.

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. 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 prevent loss of trees, along with replanting with other tree species.

How You Can Help

Take Care of Your Trees: Keep your ash trees healthy by watering them during dry months and mulching the base. Avoid pruning during peak EAB activity (April through October).
Don’t Move Firewood: The spread of EAB is largely due to the movement of infested firewood. Buy firewood locally and avoid transporting it across county lines.
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.

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