One of North America’s most destructive bugs arrives in Oregon, but mostly seen as a threat to ash trees in Willamette Valley

By ALEX BAUMHARDT/Oregon Capital Chronicle

A Portland biologist recently found an iridescent bug with the potential to wipe out Oregon’s ash trees, marking the first sighting on the West Coast.

The Oregon Department of Agriculture confirmed Monday that emerald ash borers, an invasive beetle whose larvae kill ash trees by burrowing into their bark, were discovered near a parking lot in Forest Grove about 25 miles west of Portland. They have destroyed ash trees across the country but this is the first time they’ve been spotted west of Colorado.

The beetles pose a major threat to forests which could be turned into grasslands and shrublands without native ash trees.

The Emerald Ash Borer Information Network, a consortium of scientists from universities and state and federal natural resource departments, has called it North America’s most destructive forest pest.

The group said the beetles have killed hundreds of millions of ash trees in 36 states and have the potential to cause local extinctions of the trees if they aren’t stopped. Researchers from the U.S. Forest Service estimate that the beetles will eventually decimate ash trees throughout most of North America. They say it’s possible that some could survive in places where in winter temperatures plunge to –22 degrees Fahrenheit.

The Oregon Invasive Species Council – made up of representatives from the state’s natural resource agencies, the Confederated Tribes of the Umatilla Indian Reservation, Oregon State University, Portland State University and various conservation groups – has had a plan since 2021 to confront the beetles. The state Department of Agriculture and Forest Service, which are also represented on the council, have launched a response based on those strategies, according to the state agriculture officials. They did not respond to questions about their response by Monday evening.

Oregon’s first sighting

The emerald ash borers in Oregon were discovered by Dominic Maze, an invasive species biologist for the city of Portland, who was picking his kids up from a summer camp in Forest Grove on June 30, according to an Agriculture Department news release. While waiting, he noticed ailing ash trees near the parking lot, with telltale holes in the shape of a “D” that are made by the beetles to lay their larvae.

In the release, Maze said he felt ill when he saw one, knowing how destructive they can be.

“I felt like I was going to throw up,” he said.

He alerted the Oregon Department of Forestry’s Forest Health Unit, which sent an entomologist to the site. She collected an adult beetle sample and sent it to the state Agriculture Department, where two invasive species specialists confirmed it was an emerald ash borer.

Emerald ash borers are about a half-inch long with a metallic green body. They are native to several Asian countries, where they have natural predators and typically do not kill native ash trees. In the United States, the beetles were first discovered in southeast Michigan in 2002. Studies indicate they likely arrived up to a decade earlier in packing material from international cargo, experts said.

In 2013, the U.S. Department of Agriculture banned interstate movement of ash wood and trees to curtail the infestation but in early January 2021, the agency lifted that ban. This was to shift resources towards helping states with management and containment, rather than enforcement, the department said in its announcement.

There are currently no federal restrictions on selling ash firewood, trees or other wood items from states where the beetles have spread. Although the Oregon Department of Agriculture can impose its own prohibitions, it has not done so. Other states, including Connecticut, have established quarantine areas to control their spread.

Major threat to Willamette Valley

Oregon is home to 10 species of ash trees, but just one – Oregon ash – is native to the Pacific Northwest. It can grow to 75 feet and live 250 years. It is mainly found in the Willamette Valley, especially in riparian zones along rivers and streams.

According to Oregon Department of Forestry maps, the bulk of the valley is at high risk of an infestation, with fewer than 10 high-risk areas in the rest of the state.

Many ash species are found in cities, where they have been planted in parks, around homes and along streets. Ash tree bark is distinctive for having a diamond pattern, and it has five to nine leaflets per leaf stock.

Any area with dense ash tree populations is susceptible to the emerald ash borer. The larvae are the most destructive. They feed on the inner bark of ash trees, making it difficult for the trees to transport water and nutrients, ultimately killing them.

The beetles do not attack any other tree species, according to the network.

The loss of Oregon ash trees would lead to the spread of invasive plants in many riparian zones, and that would cause once-forested areas to become shrub and grasslands, according to the Invasive Species Council. Native Oregon ash trees could be completely wiped out if the spread of the beetles is not stopped.

Nursery industry could be affected

The beetles have cost cities, property owners, plant and tree nurseries and forest industries hundreds of millions of dollars in lost products and eradication costs during the last 20 years, the information network said.

There are about 40 nurseries in Oregon that sell ash trees. The beetle could have a major effect on the nursery industry, Oregon’s leading agricultural sector, with just over $1 billion in sales annually. Oregon exports few ash tree wood or products, however.

The Oregon Invasive Species Council’s plan for eradicating emerald ash borers hinges largely on the hope that the bugs have not been in the state unseen for long. Eradication depends on catching them within about four years.

To do that, scientists will be tracking sightings of the beetles and mapping any infected areas. They can then remove infected or unhealthy ash trees that are vulnerable to infection, use insecticides and debark some trees by taking away the infected layer and destroying the larvae. The Agriculture Department could also enact quarantines, halting the sale of wood products and nursery trees from areas where the beetles have spread.

The Department of Forestry has established a collection of Oregon Ash Tree seeds for nursery cultivation and local restoration projects for the future. The seeds could be used to replant areas where trees have been eradicated due to infestations. Oregon also could use parasitic wasps that prey on emerald ash borer larvae when released, according to the council’s  plan. Several states have tried that but had limited success.