Emerald Ash Borer (EAB)

EAB was first noticed in Michigan in 2002. Scientists believe the insect had been present there since the early to mid-1990s. 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 on June 30, 2022, in Forest Grove, Oregon. At that time, the nearest known infestation was more than 1,200 miles away in Colorado. In 2024, additional infestations were found in Marion, Yamhill, and Clackamas Counties. 

In July 2025, a local arborist noticed that a green ash (Fraxinus pennsylvanica) tree in a parking lot in SE Portland’s Hazelwood neighborhood was showing early signs of decline consistent with EAB infestation. The arborist notified authorities through the OISC Hotline. The City of Portland then installed purple prism traps in the suspected tree to monitor for adult EAB activity. After a month of regular trap checks, an adult beetle was collected and sent to Oregon Department of Agriculture and USDA Animal Plant Health Inspection Service (APHIS) for confirmation. 

We don’t know exactly how long emerald ash borer has been in Portland but based on the condition of green ash trees in the vicinity, it is likely that this pest has been in the area for at least a year or two. It is extremely difficult to find signs of early infestation. It may be a year or longer before infested trees begin to show tell-tale signs of dieback. These early signs typically go unnoticed for another year or two. 

We know from years of experience in other states that EAB can naturally spread up to about 10 miles or so a year. But EAB can spread long distances when transported in firewood or living plants. That is why a quarantine has been placed on every county in Oregon whenever EAB is discovered in it. 

First, learn if any trees on your property are ash, olive, or white fringe trees – all are susceptible to EAB. You can use Portland’s Ash Tree Web Map to see all ash street trees and park trees. OSU has an online guide for how to identify ash trees here.

Next, look for signs and symptoms of EAB. Symptoms are changes in the tree that tell you it may be experiencing a problem. Symptoms can occur from EAB or from other stressors on the tree. Common symptoms are canopy decline, epicormic sprouts, bark splits, and woodpecker damage. A sign is the physical evidence of EAB and helps distinguish it from other stressors. Signs of EAB include D-shaped exit holes and S-shaped larval galleries. Other insects can also leave behind larval galleries, but EAB have a distinct S-shape.   

A Chemical Treatment Permit is required for street trees. Trees on private property do not need a chemical treatment permit. A Removal and Replanting Permit is required for private trees and street trees. If you're unsure if a permit is required, you can read more about permit requirements or contact Urban Forestry. 

Oregon Department of Forestry (ODF), Oregon Department of Agriculture, and community partners, including Portland, have been preparing for this event for years:

• In 2009, The Oregon Invasive Species Council launched a statewide assessment of invasive species. The City developed the City of Portland Terrestrial and Aquatic Invasive Animal Assessment. This document details the City's specific role in invasive animal management.
• In 2018, cooperating agencies developed Oregon’s EAB Readiness and Response Plan ODF provides ongoing education and guidance to cities and towns on best practice for slowing the spread of EAB.
• ODF has been collecting and saving Oregon ash seeds to preserve for future planting and also to test them for resistance to EAB.
• ODF has been setting traps across the state to monitor EAB spread.
• In 2019, City of Portland Urban Forestry removed ash species from Approved Street Tree Planting Lists.
• In 2020, Portland's Bureau of Environmental Services surveyed more than 250 properties in the Johnson Creek and Columbia Slough watersheds. This survey helps the City better understand the potential impact of emerald ash borer on our region's urban forest.
• In 2020, Portland City Council approved the Portland Invasive Species Strategy 2020–2030. This project charts a course for how the City and community address invasive species and their impacts. The strategy includes the emerald ash borer.
• Portland has ongoing inventories of park trees and street trees. This data provides us with an understanding of where public ash trees are located and potential impact. Tree inventories are important tools for forest management. By planting a diverse species of trees and avoiding overrepresentation of any tree type, we aim to reduce susceptibility to pests and pathogens.