What to Know About the Emerald Ash Borer

The Emerald Ash Borer (EAB), a species of invasive insects that target and decimates ash trees, was spotted in Oregon last year for the first time according to Oregon State University researchers. Oregon is host to several ash tree species, including the native Oregon ash. EAB has killed over 100 million ash trees in the eastern United States since it’s first detection in 2002, according to Forest Grove’s municipal website.

Oregon State University hosted a webinar to educate the public about EAB, teaching physical appearance, warning signs, and prevention of this prevalent pest.

Alex Gorman, the Assistant Professor of Practice at the Forestry and Natural Resources Extension in Columbia, Washington, and Yamhill Counties.

EAB originated in eastern Asia, around China, North and South Korea, and Japan. Gorman said it likely made its way over in untreated packaging like a pallet or a box.

According to the webinar, EAB was first detected in the United States in 2002, around Detroit, Michigan. In 2013, EAB was detected in Colorado, and by 2022 it had reached 36 states. The pest, which has an up to 95% tree mortality rate (sometimes higher) and has already killed hundreds of millions of trees since the 1990s, has never successfully been eradicated.

Then, in June 2022 the first West Coast EAB case was detected in Forest Grove, Ore. There was a false alarm in Newberg, Ore.

Since EAB is so new to the Pacific Northwest, Gorman said they are monitoring to see how the insect reacts in a more moderate climate than where they were initially found in the midwest.

“Maybe we’ll be the first ones, here in Oregon, to have a successful eradication campaign,” Gorman said. “But, so far in the last two decades we have not.”

How to Identify an Ash Tree

With a wide variety of tree species in the Pacific Northwest, and specifically the Willamette Valley, picking an ash tree from a lineup can prove difficult.

However, according to Oregon State University, “Ashes are easy to identify because they’re one of the few groups of trees whose leaves are both opposite and pinnately compound — that is, a complete leaf is composed of a single stalk with multiple leaflets arising along that stalk; and pairs of complete leaves arise oppositely from one another on the branch.”

In layman’s terms: ash tree branches have stalks with leaves on opposite sides of one stalk, forming a mirror image if you sliced the stalk half. Ash seeds look like little canoe paddles, which the tree drops in the fall (ash trees are deciduous).

For more information on identifying ash trees, visit Oregon State University’s online identification resource.

How to Identify an EAB Infestation

An emerald ash borer is 1/4 inch to 1/2 inch long, and 1/8 inch wide — it can comfortably fit on a dime. It’s a bright green color with an almost metallic sheen.

“The adult insect is an objectively beautiful insect,” Gorman said. “It’s unfortunate it’s such a pest.”

The EAB larvae live for one to two years in the tree layers just below the bark to feed. Once they reach their adult phase, they chew a “telltale D-shaped exit hole” in the tree bark. After they chew their way out of the tree, they fly to the next tree and repeat the process.

There are a few symptoms that could signal an EAB infestation.

• Canopy Thinning and Dieback: if an ash tree is losing leaves and “looks a little sad”, that’s an early sign that there may be some sort of pest, and potentially EAB.
• Epicormic Sprouting: this is a stress response from a tree as its canopy thins where it starts shooting branches from the base of its tree.
• Woodpecker Damage: Woodpeckers will actually work harder to find EAB larvae in the sapwood. They’ll flake off the bark until they find the larvae, which they wouldn’t do unless there was a real reward.

Oregon State University suggests you start with their EAB guide if you suspect an EAB infestation, as the insect is commonly mistaken for other insects.

How To Avoid Spread of EAB

Gorman said there are several ways to slow the spread of EAB throughout the county and state. The first one is increasingly relevant as camping season has arrived:

“It’s just a good rule of thumb to not transport fire wood very far,” he said. “And, especially with EAB, we’re asking please do not move [wood products] very far at all, and try to move in the winter when things are asleep.”

Early detection and reporting are also essential steps.

“The terrifying thing about EAB is their sense of smell, we’ll call it,” Gorman said.

EAB will smell when trees have been cut down, and they’ll be encouraged to fly further to find another forest to infest. So, clear cutting to control the spread wont work.

What to Do If You Think You’ve Identified an Emerald Ash Borer Infestation

If you think you’ve found an EAB infestation, you can confirm your sighting and report it on Oregon’s Invasive Species Hotline. The site also has a list of common EAB lookalikes to help accurate reporting.

A huge thanks to Oregon State University for sharing information about the Emerald Ash Borer.