'Most Destructive And Costliest Forest Pest Ever' Found In Oregon

Forestry officials in Oregon said Monday that an invasive beetle known for decimating ash trees throughout North America and Europe was recently discovered west of Portland.

The Oregon Department of Forestry said the iridescent green emerald ash borer (EAB) is considered the most destructive forest pest in North America and had been detected in 34 other states before it was discovered in Forest Grove on June 30.

Officials said it's the first discovery of the insect on the West Coast. The beetle is believed to have come from Asia through Canada to the U.S. about 20 years ago.

The insects have killed up to 99% of the ash trees in some North American locations. Years of attack by the invasive beetle species have decimated Connecticut's population of ash trees, for example.

The emerald ash borer was discovered in Oregon by Dominic Maze, an invasive species biologist for the City of Portland. He was waiting outside a summer camp in Forest Grove to pick up his children when he noticed several ash trees with D-shaped exit holes in their bark, state officials said.

He recognized the holes as a sign of the emerald ash borer and then spotted the beetles. He called the Oregon Department of Forestry and an entomologist and two other invasive species specialists confirmed the invasion.

"It's an ecologically vital tree as it shades water, keeping it cooler for fish," Wyatt Williams, the Oregon Department of Forestry's invasive species specialist, said. "The roots stabilize streambanks, reducing erosion. And lots of animals, birds and insects eat the seeds and leaves. Losing it will likely have a huge impact on those ecosystems."

The infested trees in Forest Grove were cut down and chipped within 48 hours of the discovery.

"Since it was first found in the Detroit, Michigan area back in 2002, EAB has become the most destructive and costliest forest pest ever to invade North America," Williams said.

In 2021, the Oregon Invasive Species Council finalized the Emerald Ash Borer Readiness and Response Plan for Oregon to guide the state in its response.

The Oregon Department of Forestry has already collected seeds from Oregon ash trees across the state to try and preserve as much of the tree's genetic diversity as possible. Researchers will test the seeds to see if any have resistance to ash borers and if so, they may be able to breed resistance into local strains and replant them.

Oregonians, cities and towns should consider removing ash trees that are already in poor health or growing in spaces too small for them, and remove ash trees from approved street tree lists, officials said. Portland has already removed it from trees it plants in the city.

"Starting to steadily replace ash will spread out the costs and impacts better than waiting for a massive dieoff," said Scott Altenhoff, Oregon Department of Forestry's Urban and Community Forestry Assistance program manager. "Fortunately, there are many alternative tree species, including Oregon white oak, incense cedar and Chinese pistache, that might be more heat and drought resistant than ash".

According to the Oregon Department of Forestry, the ash borers are native to eastern Asia, including far eastern Russia, China, Mongolia, Japan, Taiwan and the Korean Peninsula. The pest was likely introduced to the Great Lakes area through international shipping of infested solid-wood material, the department said.

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