Skip to main content

Frequently Asked Questions

What is the EAB?

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?

Why should I be concerned?

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.

Are there plans to eradicate EAB?

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.

Where has EAB been found in Oregon?

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 

What is the City doing?

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    

Why the City is preemptively removing ash trees, why not just leave them and remove when they become hazardous?

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.

What can I do to slow the EAB’s spread?

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.

Are there ways to save ash trees? Do any insecticides work against EAB?

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 

When is the best time to inject ash trees with insecticides?

The ideal EAB trunk injection window in Oregon is mid-May through mid-June, after trees have fully leafed out but before the eggs hatch. Injections require the tree to be actively moving water and nutrients to properly distribute the insecticide throughout the canopy. 

  • Spring (Mid-May to June): The most optimal time to inject. The tree is actively transpiring, ensuring rapid uptake and distribution before the damaging larval stage begins. 
  • Summer (July to August): This is when larvae begin feeding actively. Injections are still effective, though slightly less efficient due to summer heat stress. 
  • Fall (September to October): Can be used for active infestations, but tree uptake slows down. It is generally recommended to stick to spring/summer for best results. 
  • Winter: Injections should not be performed because the tree is dormant and not actively transporting fluids.

How do I find a certified arborist?

You can find an ISA-Certified Arborist at: https://certificates.directory.isa-arbor.com  

A certified arborist can assess your trees and help you decide how best to manage them.

Do I need a permit to remove a tree? 

The City of Lake Oswego requires tree removal permits for trees 6” in diameter at breast height (DBH) or larger. If you would like to request removal of a tree 6” DBH or larger, please visit the City's tree website - www.lakeoswego.city/trees - for applications, or contact Planning staff at [email protected] or 503-635-0290 for assistance.

The City Council approved updates to the City’s Tree Code. As part of this update, the City has created a new low-cost, over-the-counter tree removal permit for EAB-susceptible ash trees (a permit is required for ash trees 6 inches or larger in diameter at breast height). The permit allows property owners to proactively remove ash trees before an infestation occurs or remove trees that become infested. These updates go into effect October 1, 2026. 

Why is the City removing ash trees that have not yet been infested?

First, it’s helpful to understand how EAB impacts ash trees. Unlike elms, oaks, and maples, ash trees use a thin ring of conducting tissue to supply water from the roots to the entire tree. When ash trees become infested with EAB, the larvae damage these functional water pipes as they chew just beneath the bark inside trunks and branches. This internal structure damage makes the trees extremely brittle, making the trees hazardous and unsafe for arborists to climb or remove. 

Removal cost vary significantly per-tree based on current health, size, location, and amount of debris hauled off. Street-side trees and trees within a park with easy access, such as Foothills Park, will be much less expensive to remove than a tree in a hard-to-access natural area. Trees with significant decline (structural damage) take longer to cut and may require specialized equipment such as mechanical lifts, bucket trucks, or cranes to complete the removals safely resulting in increased costs.

Investing public resources in proactive management strategies – such as removing ash trees before they become infested and structurally compromised – is typically safer and more cost-effective than waiting to remove them after an EAB infestation.

To improve safety and reduce future costs, the City has begun proactively removing ash trees identified as hazardous by an ISA Certified Arborist.

Will the City be replacing the ash trees they remove? 

As part of the EAB Readiness & Response Plan, the City will replace unhealthy and small ash trees in City parks with new tree species that are not vulnerable to this pest. You may see impacts to parks as the ash trees are removed. These trees will be replanted, though the planting location may vary.  

Healthy ash trees continue to provide benefits, including cooling our neighborhoods during summer heat, cleaning our air, and making our city beautiful. 

Why will some infested trees not be removed or treated in natural areas?

In natural areas both active and passive management is needed. Leaving standing dead ash may be the most realistic and cost-effective option. This “do nothing” strategy may be appropriate for trees in low-risk areas away from infrastructure, housing and other structures, and high-use spaces.

Why shouldn’t I move firewood? What does it mean to “Buy it where you burn it?”

Moving firewood is the primary way that EAB and other invasive forest pests spread. Even though EAB only attacks living ash trees, the larvae and pupae can stay living in wood for up to 2 years after a tree has been cut down. If infested firewood is brought to a campsite and then left unburned onsite, EAB adults can emerge in the spring and begin infesting ash trees in a new area. This is why it's extremely important to purchase or collect firewood within 10 miles of where you plan to burn it. Learn more at www.dontmovefirewood.org

Another option is to buy certified heat-treated firewood, where wood is heated by a certified facility at 160°F for at least 60 minutes. After treatment, firewood will no longer contain wood-boring pests like EAB. In Oregon, certified heat-treated firewood is often sold in bundles at grocery stores - just be sure to read the label carefully. "Kiln dried" is not a defined industry term; best practice is to directly ask wood producers if their kiln drying methods reach this temperature standard.

Are there restrictions on moving wood?

Yes. The Oregon Department of Agriculture (ODA) has established a permanent quarantine covering the infested counties, prohibiting the movement of ash, white fringe, and olive plant materials (including firewood) outside those areas. 

ODA Link:  https://www.oregon.gov/oda/ippm/survey-treatment/pages/emerald-ash-borer... 

What is EAB quarantine?

Oregon Department of Agriculture (ODA) regulates invasive pest quarantines in the state. In December 2022, ODA enacted its first county-wide EAB quarantine in Oregon, and has updated its boundaries as infestations are confirmed in new counties. The quarantine limits movement of ash, olive, and white fringetree wood or live trees without proper treatment. When EAB is confirmed in a new county, the quarantine automatically updates to include the entirety of the new county. To learn more and see if you live in a quarantined county, read about the quarantine.

State EAB Link: https://oregon-eab-geo.hub.arcgis.com/pages/quarantine 

ODA Link: https://www.oregon.gov/oda/ippm/survey-treatment/pages/emerald-ash-borer... 

What should I do if I see an ash tree that I think might be infested with EAB?

If you suspect you have an ash tree with EAB, please report sightings using the Oregon Invasive Species Hotline or by calling 1-866-INVADER.

If you own or manage a tree that you are concerned about, call an ISA-Certified Arborist for a consultation.

Oregon Invasive Species Online Hotline:  https://oregoninvasiveshotline.org/

Find an ISA-Certified Arborist:  https://certificates.directory.isa-arbor.com  

Before reporting: 

Printed from https://www.lakeoswego.city/emerald-ash-borer/frequently-asked-questions/

Share:E-mailFacebook (opens in a new tab)X (opens in a new tab)LinkedIn (opens in a new tab)Nextdoor (opens in a new tab)