Dreaded invasive ash borer reaches Marion, Clackamas counties

The scourge of the invasive emerald ash borer has reached the Woodburn area.

Officials from the Oregon Department of Agriculture and Oregon Department of Forestry announced that in Marion County, five beetles, indicating a “significant population,” were found in traps along the Pudding River south of Woodburn and west of Mount Angel, the release said.

“Given the trees did not show any signs of damage, we would not have known about this site for some time if not for the traps,” a specialist said.

Marion is the fourth county where the emerald ash borer has been found in the state, joining discoveries in Yamhill and Clackamas counties recently. The discoveries were confirmed by a USDA laboratory.

Contractor first to spot menace recently

Meanwhile, a contract worker for Portland General Electric, who had recently undergone Oregon Department of Agriculture training in identifying the pest, reported spotting the beetle in the Elliott Prairie area, east of Woodburn in Clackamas County, in mid-July after he noticed the tree canopy declining.

An Oregon Department of Forestry invasive species specialist who visited the site in early August found evidence that EAB larvae had been feeding on Oregon ash, all but killing several trees. The specialist also discovered signs of infestation along Butte Creek in Mount Angel and south of Hubbard, with declining canopies and the D-shaped exit holes indicative of when the beetles have tunneled out of the trees.

“The extent of dieback suggests that EAB may have been present for a number of years at the site but went unnoticed given the difficult access and dense vegetation, which includes a mix of oak and conifers,” the ODF specialist said.

In Yamhill County, an adult beetle of the invasive species was found about seven miles south of Gaston in one of 197 traps deployed by the ODF and the U.S. Department of Agriculture in the Willamette Valley.

The beetle was first discovered in Oregon near Forest Grove in late 2022 after initially migrating from Asia to the United States two decades ago.

Small but deadly for Oregon ash trees

Described in ODA literature as a small, metallic-green beetle native to eastern Asia, the EAB was first discovered in the United States in Michigan in 2002. Since then the beetle is responsible for killing tens of millions of ash trees across the eastern United States, with a death rates for the trees at nearly 100%.

The beetles spell the doom of the trees by burrowing into their bark, “causing canopy dieback and, ultimately, tree death,” an ODA release said. “The half inch beetle is often challenging to detect, especially in newly infested trees. Signs of infestation include thinning and yellowing leaves, bark splitting, D-shaped holes in the tree bark, and basal shoots.”

Agencies face a stiff task in attempting to eradicate the pest

“No state has been able to eradicate EAB, so since its first detection in Forest Grove, we have expected it to eventually show up in new parts of Oregon,” Cody Holthouse, ODA compliance and regulatory manager, said in the release. “That’s why folks from collaborating agencies have been methodically surveying for the insect, setting out traps beyond the known infestation area and training people to know the signs and symptoms of infestation. That definitely helps us learn where the insect is spreading.”

Holthouse, chairman of the state’s Interagency EAB Task Force, said the ODA will soon conduct intensive searches in areas around the outbreaks in Marion and Clackamas counties to determine if the beetle has enlarged its territory. He added that the agencies are unsure if the sighting near Gaston indicates a spread from the original Forest Grove site or were introduced in another fashion.

“The pest often travels in loads of firewood transported by people, so (new introduction) is quite possible,” he said.

The ODA is considering implementing a quarantine of wood that would restrict the movement of several tree materials from the ash, olive and white fringe tree wood varieties.

“That quarantine restricts the movement of several tree materials, including but not limited to logs, green lumber, nursery stock, scion wood, bud wood, chips, mulch, stumps, roots, branches and firewood of hardwood species,” Holthouse said. “We want to protect the rest of Oregon for as long as possible to give communities more time to prepare.”

Washington County is already under a permanent quarantine to slow the spread of emerald ash borers.

To slow further spread of the beetle, the ODA and ODF are recommending Oregonians buy firewood near where they intend to burn it and avoid taking firewood more than 10 miles from where it was cut.

For more information on EAB and an up-to-date list of resources, visit ODA.direct/EAB . Suspected EAB infestations can be reported over the phone at 1-866-INVADER or online at oregoninvasiveshotline.org .