Emerald ash borer (EAB) is a tiny green beetle from eastern Asia that is having a devastating impact on ash trees in North America, including northwest Oregon. Across the U.S., millions of ash trees have been killed by the larvae of this pest. The larvae eat tissues under the bark, eventually killing infested trees.

First found in Oregon in 2022 at a school in Forest Grove, this summer the beetle showed up in traps in six new areas. Five of the sites were within the existing EAB quarantine boundary.

A trap was placed this summer at a sixth site in Multnomah County after Peter Van Oss, a private arborist with Teragan and Associates, noticed an ailing green ash tree in the parking lot of the David Douglas Aquatics Center in the Hazelwood-Mill Park area. Van Oss suspected it might be infested with EAB and alerted officials.

City and state officials then inspected the tree Van Oss had reported and saw signs of EAB infestation, such as dieback at the top and serpentine gallery marks under the bark. A single adult insect was trapped and sent to the United States Department of Agriculture, specifically to the Animal Plant Health Inspection Service’s Plant Pathogen Confirmatory Diagnostics Laboratory in Maryland, which confirmed it was EAB.

The other new sites where EAB was found this summer are:

Hazeldale Park about a mile west of Beaverton
Killin Wetlands Nature Park near Banks in western Washington County
Five miles northwest of the town of Yamhill in Yamhill County
Three miles southeast of Oregon City in Clackamas County
Bureau of Land Management-administered land east of Scotts Mills in Clackamas County

“The pattern of spread in the eastern U.S. has been that populations at first increase slowly and the rate of natural spread is slow,” said Cody Holthouse, Manager of the Oregon Dept. of Agriculture’s Insect Pest Prevention and Management Program. “But within a few years there is a rapid build-up in the population and it spreads in all directions at a faster pace. That’s exactly what we’re starting to see with these detections.”

Holthouse said EAB is about half an inch in length and is hard to spot with the naked eye. It is not strongly attracted to traps, making early detections in novel locations difficult. “Finding one in a trap usually means there are quite a few already in that area,” he said.

Holthouse said the discovery in southeast Portland puts all of Multnomah County into the EAB quarantine zone. Other quarantined counties include Clackamas, Washington, Marion, and Yamhill counties.

“Quarantine is designed to prevent humans from spreading EAB by limiting movement of firewood or any other plant materials from ash, olive or white fringetree (Chionanthus virginicus),” said Holthouse.

A full list of quarantine regulations can be found here.

The City of Portland has been preparing for EAB’s arrival for years. It removed ash trees from its list of approved street trees in 2019. It completed a comprehensive response plan for dealing with EAB earlier this summer.

"Our approach to managing Portland’s urban canopy is rooted in community stewardship, science and long-term resilience," says City Forester Jenn Cairo. "By working with Portlanders to inventory trees and educate folks about best practices, and intentionally planting a diverse range of tree species, we’re building a more adaptable canopy, one that’s better equipped to withstand threats like the Emerald Ash Borer and other invasive pests. This proactive strategy helps safeguard the health of our urban forest for generations to come."

For the past few summers, the Oregon Dept. of Forestry (ODF), in collaboration with the USDA Animal and Plant Health Inspection Service, made sticky purple traps available to numerous public land managers and soil and water conservation districts that agreed to place and monitor the traps.

“Traps contain a lure and are checked periodically during the summer when adult EAB are flying. It was in those traps that the beetles were found,” said ODF Invasive Species Specialist Wyatt Williams.

While it’s possible EAB could turn up in more traps when they are checked in September, Williams said most adults will have finished their short life cycle, laid their eggs, and died by October or November.

“At that point, further spread is almost entirely by humans moving firewood,” said Williams. “That’s why it’s recommended you buy or cut firewood within 10 miles of where you plan to burn it.”

Public agencies in Washington County, where EAB was first detected three years ago, have been preparing for its spread beyond Forest Grove. For example:

Beaverton is protecting nearly 500 ash street trees in good condition by injecting them with emamectin benzoate. This systemic insecticide has proven very effective at preventing infestation by EAB while being safe for humans, pets, and wildlife, including pollinators.
Hillsboro is conducting a tree inventory of public and right-of-way trees. This data will help locate ash tree populations and inform the city’s EAB response plan. To protect its ash trees, Hillsboro will also be treating approximately 500 healthy public ash trees along the western and southern city boundary. This will create a buffer zone from current outbreaks as a phase one response plan.

Outside Washington County:

Salem has been treating high-value public ash trees to protect them ahead of EAB’s arrival.
Keizer, with help from ODF, is inventorying its street trees to find how many are ash.
Portland recently completed its EAB response plan, which among other things involves the treatment of public trees in good condition in low-canopy neighborhoods, and the pre-emptive removal of ash trees in poor condition to spread the cost out over several years.

What you can do

If you think you’ve seen an emerald ash borer, ODF and ODA ask that you first make sure it’s not a common look-alike bug.

“You can find a good description and photos comparing EAB to other common insects in Oregon that are also green in color at OregonEAB.com,” said ODF EAB Specialist Kat Bethea. “If you can capture the beetle in a jar or other container that’s ideal, but at least try and take a clear, close-up photo. This helps us identify the insect in question much more easily.”

Bethea said people suspecting they’ve found EAB should report it over the phone to 1-866-INVADER or online at https://oregoninvasiveshotline.org/reports/create. Attaching a clear photo is important. Bethea said people who know they have an ash tree and notice a decline should report it the same way.

“Any ash tree can be infested, including native Oregon ash as well as non-native street, park and yard trees. Signs of infestation include thinning and yellowing leaves, bark splitting, D-shaped holes in the tree bark, and shoots from buds on the trunk or branches,” said Bethea.

Matt Mills, who is also an EAB Specialist with ODF, said, “You can find whether or not you’re in an EAB-infested area or close to one by checking an online map we’ve created. It shows the five counties where firewood from hardwood trees cannot be removed. That quarantine also covers any part of ash, olive or white fringetree (Chionanthus virginicus).”

People who want to protect their ash trees before they become infested should consider the same treatment Beaverton and Salem are using to protect their public ash trees. “The insecticide is injected at the base of the trunk and gets taken up into the tree canopy and is quite effective at protecting the tree from both adults and larvae,” said Mills.

Mills said treatments must be done before trees are damaged and repeated every two or three years by a licensed pesticide applicator.

“That’s why we recommend only treating high-value trees in good condition,” he said. “Ash trees planted in the wrong place to reach their mature size, such as under powerlines, should be removed as time and funds permit and replaced with species that aren’t susceptible to EAB.”

Homeowners might also consider replacing young ash trees while they are still small and starting over by planting a species that is not susceptible to EAB. “This gets new tree canopy jump-started in urban areas where ash trees will be lost if not treated,” Mills said.

Source: Oregon Department of Agriculture

Mike Jones