Emerald Ash Borer

The emerald ash borer (EAB), Agrilus planipennis, is an invasive insect that attacks and kills ash trees (Fraxinus spp.). White fringe trees (Chionanthus virginicus) and cultivated olive (Olea europaea) are also at risk.

EAB was first discovered in the U.S. in 2002 in southeastern Michigan. In the two decades following this discovery, EAB has spread rapidly in all directions, infesting much of the Midwest and East Coast. The first observance of EAB on the West Coast occurred in June 2022, in Forest Grove, Oregon.

 Learn how to identify the EAB.

State EAB link:  https://oregon-eab-geo.hub.arcgis.com/pages/identify#destination2 

Watch this informative video: What is EAB and Where is it found?

Many trees in Oregon are ash trees. Oregon ash (Fraxinus latifolia) is an important native tree that grows along rivers, streams, and throughout the Willamette Valley. Many other types of ash trees are commonly planted throughout communities – in yards, parks, and along streets.  

All species of ash in Oregon are susceptible to EAB. EAB adults lay their eggs on ash trees, and after hatching, the larvae burrow under the bark to feed on the tree, eventually cutting off its supply of water and nutrients. Once an ash tree becomes infested, the tree will die over the course of three to seven years.

Ash trees play a critical role in Lake Oswego's urban forest. Not only do they contribute to the aesthetic value of neighborhoods, they also provide 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. 

In addition, as ash trees die, they become extremely brittle and can be hazardous to people, property, and infrastructure. Removal of EAB infested trees can be costly.

Learn how to identify ash trees.

• State EAB link:  https://oregon-eab-geo.hub.arcgis.com/pages/identify#destination1 
• OSU Extension link: https://extension.oregonstate.edu/gallery/recognizing-ash-trees-oregon-w...

There are no known methods to eradicate EAB.  However, it is possible to slow the spread of EAB.

While the loss of our ash trees is inevitable, identifying infestations early and slowing the spread will give communities time to plan to mitigate the economic and ecological impacts of the pest.

The most up-to-date information is available on the Oregon EAB Map. 

State EAB link:  https://oregon-eab-geo.hub.arcgis.com/pages/survey-monitoring 

Of the City’s total tree canopy coverage, 20% is on publicly-owned or managed property (which includes parks, natural areas and public rights-of-way). The remaining 80% is on private property.

The City is implementing practices to best manage and slow the loss of trees on the publicly-owned or managed property. Slowing the spread of the EAB gives us more time to prepare for its arrival, reduces high costs related to the removal or treatment of infested trees, and helps protect our urban forest.

The City has been preparing for EAB’s arrival since 2023 and is working closely with state and local partners. 

For key actions, visit:   www.lakeoswego.city/emerald-ash-borer/what-city-doing    

Preemptive ash tree removal and replacement is safer and more cost-effective than waiting until trees become hazardous. This approach allows the City to control the timing of removals, avoid emergency response costs and risks, and provide more time to establish healthy replacement trees. While preemptive removal will cause canopy loss, it allows the City to manage that loss gradually and replant in advance. Waiting until ash trees become hazardous risks a larger, sudden loss of canopy, along with higher removal costs and greater risk to public safety.

About 80% of the City’s tree canopy is located on private property. 

While the City is preparing to slow the spread of the EAB and protect our urban forest on publicly-owned or managed property (which includes parks, natural areas and public rights-of-way), we are encouraging residents to take steps to best manage trees on their property. Property owners are responsible for the care and maintenance of trees located on their property. 

Here are a few things you can do to help:

• Learn more about the EAB
• Determine if you have an ash tree on your property
• Work with an ISA-Certified Arborist
• Properly care for your ash trees
• Avoid moving firewood
• Help detect and report EAB

Details can be found at:  www.lakeoswego.city/emerald-ash-borer/what-you-can-do      

Even though it's inevitable that EAB will spread in Oregon, containing it for as long as possible gives communities like ours more time to prepare.

Insecticide treatment is an incredibly effective option for both keeping ash trees alive and saving money. Mature trees provide many financial benefits such as reducing energy costs by providing shade and insulation, reducing flood risk, and improving human health by filtering air pollution. These benefits are lost when large trees have to be cut down. If your tree has lost less than 30% of its canopy consult with an ISA Certified Arborist on treatment options to protect the tree. Read more about insecticide treatments.

State EAB link: https://oregon-eab-geo.hub.arcgis.com/pages/eab-management#treatment