On Wednesday, the Oregon Department of Forestry announced that the emerald ash borer has now been found in the Hazelwood neighborhood in East Portland and five other new sites in the north Willamette Valley. In addition to Portland, the highly invasive and destructive beetle has now been found near other urban areas in the region, including Beaverton, Banks and Oregon City. The Oregon Department of Agriculture said that the discovery of EAB in Portland has now put all of Multnomah County into the EAB quarantine zone, which also includes Washington, Yamhill, Marion and Clackamas counties.
Native to Asia, EAB was first detected in Oregon in 2022 at an elementary school in Forest Grove. Considered to be the most destructive forest pest in North America, EAB has killed over 100 million ash trees nationwide since its arrival in the U.S. more than 20 years ago.
Joining us to discuss the spread of EAB and how the public can help efforts to contain it are Cody Holthouse, manager of ODA’s Insect Pest Prevention and Management Program and City of Portland Forester Jenn Cairo.
Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. The Oregon Department of Forestry announced yesterday that the emerald ash borer has now been found in Portland and five other new sites in the Northern Willamette Valley. It’s the first time the invasive beetle’s been found in these particular locations. The emerald ash borer has been called the most destructive forest pest in North America, having killed over 100 million trees nationwide since its arrival in the U.S. more than 20 years ago.
Cody Holthouse is the manager of the Oregon Department of Agriculture’s Insect Pest Prevention and Management Program. Jenn Cairo is a City of Portland Forester. They both join us now. It’s good to have you both on Think Out Loud.
Jenn Cairo: Thank you, Dave.
Miller: So, Cody, first – can you just remind us where the emerald ash borer has been detected in the past and where these new sites are?
Cody Holthouse: Certainly. Yeah, so we had, in 2022, detection of emerald ash borer in Forest Grove, Oregon, and that’s where we put up an initial response plan and reacted to it. And then after some time working around that infestation, we realized in 2024 – with some help from other partners, we actually had someone report it from the public – that there was a secondary infestation over in Marion and Clackamas Counties, right on the border of those two counties, right along the Pudding River and the Butte Creek watersheds. And places that are nearby or places like Woodburn and Mount Angel are impacted as far as cities, but it’s more rural river locations that that area is in.
We actually found that that is an older infestation, judging by the galleries present in those trees …
Miller: The galleries?
Holthouse: Yeah, galleries being the larval chambers that are inside, under the bark. So when you peel the bark back, you can see where the larvae of EAB have been feeding. And that indicates to us, based on how many galleries we’re seeing there, that it’s been there probably up towards a decade or longer.
So those are the two major infestations we’ve been dealing with and then they’ve been radiating out from there, as you can imagine. So we’re putting out a lot of traps, a lot of people visually surveying around those locations, and indications that there’s a gradual kind of progression out from those two locations.
Miller: So that was before … and what about now, the big announcement yesterday, where were they found?
Holthouse: Yeah, so the big news right now is that we have detection at the David Douglas School District here in Portland – that’s Multnomah County. So that’s a huge progression, quite a jump we would say, from where it’s been in Marion, Clackamas, Yamhill, Washington counties. And so we’re trying to get a bearing on exactly how many are here, what the establishment looks like. But from what we can see at the green ash trees at the school district site in Portland, it does look like it’s been here for at least a season or two and we’re likely having to now catch up with just how established it is here in the city.
Miller: Is it fair to say that for you, it was just a matter of when this would happen, meaning sightings, detection in Portland, in Multnomah County, as opposed to if it would happen?
Holthouse: Yeah, it was just a matter of time, unfortunately. We knew, based on the level of establishment in Forest Grove and out in the Pudding River and Butte Creek watersheds, that it would keep moving. We were just hoping to slow it down. We’ve been working hard to try and limit its spread from those locations, but given precedence in the east coast of the U.S. as well as other invaded ranges, we know that this is a species that can move past management lines. So yeah, we did anticipate this movement to occur.
Miller: Jenn, as I understand it, the infested tree in Portland was identified in the parking lot of the David Douglas Aquatic Center. How was it found?
Cairo: The person who found its name is Peter van Oss and he is a local arborist with Teragan & Associates. And he was going to the school as part of his work to help them with a project there. As he explained it, when he pulled into the parking lot he noticed that the ash trees in the parking lot looked stressed. And thanks to Peter and his training, he took a closer look, saw the holes in the tree and the declining nature of the tree, and thought that it might be EAB and called the state’s hotline to report it.
Miller: This is an expert, then, who was experienced and saw this as opposed to, I don’t know, a passerby who had looked, say, at an Oregon Department of Agriculture website and made a guess. This is his job.
Cairo: That’s right.
Miller: Has the city been preparing for this day?
Cairo: Yes, we have. It’s unfortunate but not [un]expected that emerald ash borer is here, as Cody referenced. We’ve seen it across the eastern part of the country in the Midwest where millions and millions of trees have been lost. So our preparations have included several steps. We have had an inventory of our street and park property trees for a long time, so we know how many ash we have and where they are, for the most part. We’ve also developed an emerald ash borer response plan that’s online.
Some years ago, 2019, I believe, we removed ash as tree species options that can be planted with permits in the city. We participated with the Oregon Department of Agriculture, Oregon Department of Forestry and others in planting traps, placing traps around the city. We also did a field survey of, or [are] doing a field survey of ash trees in natural areas, so we know what to do there. And we have helped ODF and ODA host-free EAB detection trainings for a couple of years now.
Last but not least, just recently, we were able to remove or reduce most of the tree permit fees in Portland. So now, when a regulated ash needs to be treated or removed, there isn’t that cost barrier in place.
Miller: So, based on those surveys that you’ve done in recent years, how common are ash trees in Portland?
Cairo: Ash trees are fairly common. They are a significant part of Portland’s canopy. There are a total, at least 95,000 ash in the city. Most of those, roughly 72%, are located in our natural areas.
Miller: As opposed to, say, street trees in neighborhoods?
Cairo: That’s right, as opposed to street trees or trees in a developed park.
Miller: So what does that mean in terms of the way you think about this infestation? I mean, is that better news or worse news if there’s now an increasing likelihood that a lot of these trees could be killed?
Cairo: I think it’s all bad news, really. I will say that in natural areas where especially our native ash, the Oregon ash, fraxinus latifolia are … they’re a very important part of the ecosystem there. They usually are near waterways, riparian areas and provide a lot of shade to those waterways, including for fish like salmon, who rely on that cooler water. And of course, they’re a part of those ecosystems. So their loss there is really significant.
On the other hand, ash that are street trees, for a lot of folks, the tree in front of their house is their closest piece of nature. So that loss is significant.
Miller: Nature and shade.
Cairo: And shade, and better air quality, and having a connected and more livable neighborhood, and mental health – all of these things. There are many services we get from our urban trees.
I’ll mention too, Dave, the other thing is, if not addressed early, trees that are dead – all trees, not just ash – can become hazardous. So that’s especially important in streets and in developed parks. In the natural areas, if it’s, so to speak, on the back 40, that’s not an issue because there aren’t people or property there that might be damaged.
Miller: Cody, we heard from Jenn, the various actions that the city of Portland has taken over the last couple of years in preparation for this and ongoing efforts. And you were saying earlier that it’s a question of slowing down the spread as opposed to stopping it, because what you’ve seen on the East Coast and the kind of westward spread of this is that it seems inexorable. So, is there anything you can do to effectively stop this, or are we looking in the coming years or decades at the likely mass die-offs of ash trees all throughout Oregon?
Holthouse: Well, to speak to that, both are true. We’re gonna experience a massive fallout of ash in Oregon, but we can also slow it down effectively. So again, both things can be true. What we’re hoping to do is contain it to the areas that it is now and really just slow that expansion down. We know from looking at other situations in the East Coast that there’s this human factor, where we move firewood or we move our green waste and we transport that firewood to a friend’s house, say, in Washington State or California. And all of a sudden there’s a huge jump in that progression rather than a normal, quote unquote, “natural progression” of the beetle flying from tree to tree, if that makes sense.
Miller: That’s because there’s larvae, potentially, in those logs that people are moving?
Holthouse: Yeah, because you have that development of the larval instars of this beetle inside of the wood, if you take an actively infested tree, take it and chop it up, and then transport those pieces of firewood, say, across state lines, county lines, you may have an adult beetle then fully emerging out of that log a month later. That’s very possible and they’ve done a lot of research on this. Even logs that are submerged can even have successful emergence of a beetle. They’re very resilient and can emerge even in a dead and dying or transported piece.
Miller: That seems essentially invisible, but obviously we’re talking now because an arborist did see things that concerned him, he called authorities and they verified that in fact the EAB was in Multnomah County. What are the signs? I mean, what should people look for in trees, say, on their own curbs or in natural areas?
Holthouse: You can look for a canopy decline. If you notice that a few branches are flagging as dying or already dead, you might take a closer look. That might kind of hone your interest. And then as you’re getting a closer look at the tree, you might look for what we call blonding or these splotches of bark that have been kind of messed with by woodpeckers. Woodpeckers are looking for the larvae developing inside, so woodpeckers are a good indication of a heavy infestation. Also, you might look for the exit holes of the beetles, so there’s a D-shaped, a capital D-shaped exit hole that’s very telltale of this species on ash trees. So if you’re seeing that, very likely.
And then if you’re able to – you don’t want to do this just any tree, it should be one that you own and have permission over – you can peel back bark too and look for these S-shaped serpentine galleries that go just under the bark. And that’s that tell-tail kind of feeding pattern of their larvae as well. And there’ll also be bark splits or epicormic shoots, which are small shoots of the tree sending up, some people call them suckers, small little branches at the base of the tree. That’s the tree saying, oh boy, I’m getting cut off from nutrients. I’m gonna try to put out some lower branches to get some actual photosynthesis going.
Miller: Jenn, what’s gonna happen in the coming months or years if people look for this, find this, and call the city and say, “this tree on my block” or “in this natural area near me has an infestation.” What will happen?
Cairo: First, we’ll want them to call the state’s hotline, which is central for all of us. And what will happen if they think they have an infestation, their next step is to get someone knowledgeable to take a look at their tree with them, make sure it’s an ash, assess whether it does have EAB or not. Ideally, folks are gonna do that before they think there’s an issue. See if they have ash, which they can use the internet to see what kind of species they have. Get a certified, experienced arborist to come look at their ash trees.
If the trees are healthy and on the larger side, so bigger than six inches in diameter, the arborist might recommend to them that they can treat the tree to reduce the risk of infestation. And alternatively, if the tree’s not in good health or a smaller tree, they might want to remove it in advance and put another tree back that is not an ash, that is resistant to EAB.
Miller: Does this only affect ash trees? It is called the emerald ash borer, but is it hungry for other kinds of trees as well?
Cairo: It is ash, and also a white fringe tree, and also olive. We don’t have as many of those white fringe trees or olives in Portland. It is ash that is our main concern, but Cody might want to speak to the other two.
Holthouse: Yeah, I know that you could probably find white fringe tree in a nursery or something like that, potentially. That, I think, would be kind of more of a peripheral plant that people might buy, but it’s possible – something to be aware of if you are looking at a nursery at a new plant.
Olive, I will say, is on our radar. We’ve been working with Oregon State University on trying to get our kind of heads around what the risks are for the olive industry. It’s a small, budding industry here, but there are a few olive growers here in the Willamette Valley that we are working with, and trying to make sure and just keep an open line of communication on, because we’re not sure, again, what the risks are. The data says that it’s possible for EAB to do some development on olive, but it has also been established that it seems to be a subpar host. So again, we’re watching that really closely right now.
Miller: Cody and Jenn, thanks very much.
Cairo: Thank you.
Holthouse: Thank you.
Miller: Cody Holthouse is the manager of the Insect Pest Prevention and Management Program at the Oregon Department of Agriculture. Jenn Cairo is the City of Portland’s City Forester.
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