WOODBURN, OR -- An invasive bug deadly to Oregon's native ash trees appears to be spreading. Emerald Ash Borer first appeared in Oregon two years ago, in Forest Grove. Three new infestations were reported in just the past month.

"This is really a difficult, a really difficult invasive pest to control, even under the best of circumstances," says Oregon Department of Forestry's Lilah Gonen. "We were always expecting Emerald Ash Borer to expand beyond Washington County, so none of this is unexpected." What is a surprise, says Gonen, is the seemingly sudden addition of two counties and a third awaiting confirmation. "The Marion County infestation, and by association, also the as-yet-unconfirmed Clackamas County infestation, they appear that they might be a complex of possibly a single large infestation along the Marion and Clackamas county border." Gonen says traps collected a large concentration of mature EAB, "We’re also seeing pretty advanced tree mortality, so trees that are already dead or dying and very close to death. And relatively high concentrations of those dead trees, and in streamside, creekside areas." The area is quite remote and difficult to access, which means the infestation could have have been growing undetected for years, "It’s totally possible that this one was before the Forest Grove infestation. And that the Forest Grove infestation started as a satellite of the Marion County. Or, it could be that these are actually two separate introductions." The other detection is in Yamhill County, and is likely an extension of the Forest Grove infestation discovered in 2022. 

Gonen says it’s critical people don’t haul wood and trees across county lines, "The primary mode that it spreads, so far as an invasive, has been by hitching a ride on firewood, on woody debris, on woodpacking materials, things like that." Oregon’s Department of Agriculture is also working out details of an expanded quarantine, to limit the movement of tree materials, including nursery stock.

Oregon ash is a native shade tree popular along urban streets. In natural areas, it protects streambanks and fish habitat. EAB can destroy entire stands and infestations have been devastating in other states. Gonen says, "The number one concern with Emerald Ash Borer is that we won’t be able to get ahead of it."