Invasive emerald ash borer now found in multiple counties in the Willamette Valley

On Monday, the Oregon Department of Forestry confirmed that the emerald ash borer has been discovered in three new counties in the Willamette Valley. In the past month, the invasive pest was caught in traps set in Marion and Yamhill counties, and is also suspected of being in neighboring Clackamas County, pending confirmation by the U.S. Department of Agriculture.

The highly destructive beetle, which is native to Asia, has killed over 100 million ash trees nationwide since it first appeared in the U.S. over 20 years ago. The state’s agriculture and forestry departments quickly mobilized to contain it when it was first spotted in Oregon in Forest Grove in Washington County two years ago. Those efforts included issuing a quarantine that’s now permanent to prevent the movement of firewood and other plant materials out of the county made from ash, white fringe and olive trees. State crews have also removed infested ash trees and have been treating healthy trees with insecticide near infestation sites. Lilah Gonen is a community assistance forester and the emerald ash borer coordinator for ODF. They join us to talk about the state’s efforts to slow the spread of emerald ash borer and the threat it poses to native Oregon ash trees.

The following transcript was created by a computer and edited by a volunteer:

Geoff Norcross:  From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Geoff Norcross. When the emerald ash borer was first discovered in Washington County Oregon two years ago, the [Oregon] Department [of] Forestry (ODF) knew they weren’t going to eradicate it. The best they could hope for was to slow the spread. Make no mistake, the spread is happening. This summer, the ODF announced that it had found the destructive forest pest in three more counties across the Willamette Valley: Yamhill, Marion and Clackamas. We wanted to see if this is actually a win. The agency took big steps after the first emerald ash borer was discovered, including a quarantine of tree materials out of Washington County. Would the spread of the invasive pest have been worse without those measures?

For answers we’re turning to Lilah Gonen. Lilah is the emerald ash borer coordinator for the Oregon Department of Forestry and Lilah joins us now. Lilah, welcome to Think Out Loud. It’s good to have you.

Lilah Gonen:  Thanks for having me.

Norcross:  Can you first describe how this pest attacks and kills ash trees?

Gonen:  Yes. So the emerald ash borer is a wood boring beetle. It’s native to Northeast Asia and it’s been present in North America for over 20 years now. It’s been killing ash trees in the Midwest and the East Coast. And we now have it here in Oregon. And it’s actually the larvae of the beetle that do the bulk of the damage to the trees.

The adult beetles lay their eggs on the bark. The larvae hatch from those eggs and they burrow into the inner bark layer of the tree. And they feed on the vascular tissue which disrupts the flow of water and carbohydrates up and down the stem of the tree. And over the span of about five years or so, they will actually completely girdle the tree and kill it all from the inside out.

Norcross:  What do you mean “girdle” the tree?

Gonen:  Girdling is a tree work term where you can actually, if you cut the bark in a ring around a tree, that will eventually kill it because you’re disrupting that flow of water and nutrients up and down. And so the larvae are actually girdling the tree from the inside by cutting away that vascular tissue underneath the bark.

Norcross:  When a tree has been infected with the emerald ash borer larvae, can it be saved?

Gonen:  In the early stages of an infestation, yes, you can possibly save a tree, but you would have to know that emerald ash borer is present. You can actually inject trees with a systemic insecticide. This is usually done prophylactically, sort of preventatively, to prevent an EAB infestation. But in the very early stages, if you know that EAB is present in a tree before you’ve lost 30% or so of your canopy cover, you can possibly save the tree using this systemic injection.

Norcross:  I like that you use a shorthand for this creature. You call it the EAB. Now you’re so familiar with it, right?

Gonen:  Yes, that’s the industry term.

Norcross: How did it get here?

Gonen:  In short, we don’t really know. But EAB does spread mostly through infested wood material that people move around, through shipping or because they’re camping and they’re taking firewood with them. We don’t know for sure exactly how it landed here in Oregon. But likely it was from somebody moving infested firewood from somewhere in the Midwest or East coast where EAB is prolific and endemic. That’s likely how it arrived here, sometime in the early 2020s or late 2010s.

Norcross:  You mentioned the Midwest and the East Coast have a long history with this particular animal. Is there just something about our native trees compared to ash trees in those areas of the country in terms of how vulnerable they are to the EAB, or the difficulty in protecting them?

Gonen:  So, pretty much all ash trees that are native to North America and to Europe are susceptible to emerald ash borer infestation and are susceptible to being killed entirely. There are actually native ash trees in Northeast Asia where emerald ash borer co-evolved. And those trees actually do have a conferred genetic resistance to emerald ash borer. They’ve co-evolved with each other. They live side by side. EAB tends to only infest dead and dying trees and it acts as a nutrient cycler in the ecosystem there.

But here, where our ash trees have not co-evolved with emerald ash borer, they do not have that conferred resistance. And about 99%-plus of those trees will eventually succumb and die if they are infested with emerald ash borer and not first treated with a systemic insecticide.

Norcross:  OK. So we first, as I mentioned, learned that EAB was here in 2022 in Forest Grove, in Washington County. Now, we know it’s not just there. When did you first become aware that it was no longer confined to just Washington [County]?

Gonen:  So I personally learned only about two weeks ago. And things have moved pretty quickly since then. We had three distinct moments that occurred this summer that all happened sort of clustered around the same time. First, we had an emerald ash borer adult show up in a trap in Northern Yamhill County, about seven miles south of the known infested area in Forest Grove. That is something that we expected to see.

We’ve been putting out traps around the state for many years now. This year, we put out about 200 traps, surveillance traps, about seven miles or so outside the infested area. That was something that we were expecting to happen at some point. So that was confirmed by the USDA, that adult beetle was confirmed last week. We now know, yes, that we have at least one beetle that showed up in Northern Yamhill County.

The Marion County and Clackamas County situation is a little bit of a different story. We had, in late July, early August, the same situation, where we went to go check on a surveillance trap. We found five adult beetles in one of those traps. Now, that’s really significant because these traps are actually not particularly effective at attracting emerald ash borer to them. They really only will catch EAB adult beetles in them if they happen to be incidentally flying around. So catching five adults in a single trap was an indicator that there was probably a dense population nearby.

Norcross:  A lot of EAB in Yamhill?

Gonen:  This is in Marion County. And then we also received a report through the Oregon Invasive Species Hotline, around that same time, from a utility worker who had actually been recently trained by the Oregon Department of Agriculture on how to identify emerald ash borers. And he had sent in a report from nearby Clackamas County of what he believed to be an infested tree.

Since then, we have been doing visual surveys throughout this county line area between Marion and Clackamas County, and finding trees that are severely infested with emerald ash borer. We already have seen some pretty significant decline in mortality along the Pudding River watershed area, just east of Woodburn. And it’s sort of existing on this county line area between Marion and Clackamas County. So far, we’ve only officially confirmed emerald ash borer in Marion County. Those adult beetles that we found in a trap were sent over to the USDA and they officially confirmed that yes, they are EAB. And we just sent some samples from Clackamas County into the USDA, and we expect to get a confirmation about that soon.

Norcross:  Why do you need federal confirmation that you actually have the EAB? You know what it is.

Gonen:  We do know what it is, but we do receive federal money. We do receive federal resources from the USDA to help us in managing emerald ash borer. So we do need their confirmation before they open up those coffers to us.

Norcross:  There was a quarantine in place in Washington County. No wood products in or out. It was temporary. It was made permanent. What happened? Why did the EAB jump the quarantine?

Gonen:  That’s a very good question. It’s something that we were always expecting to happen. Something that’s really important to know about emerald ash borer is that there’s no known eradication method for it on the landscape. Our management strategy always, from the very beginning, was to contain it for as long as possible to give communities time to prepare. But we never deluded ourselves into believing that the emerald ash borer was not going to jump beyond county lines. Typically, they don’t fly very far. They’ll only fly maybe to the next tree or even stay on the same tree year to year. But every now and then you do get an adult beetle that will fly multiple miles to scout out a new tree. So that’s likely what we saw in Yamhill County.

The Marion County and Clackamas County situation is a little bit different. We actually think that it could be a separate introduction, that came maybe even before the forest grove infestation. It’s looking like we’re seeing some pretty widespread mortality there, which is indicating that that infestation could be on the order of five to 10 years old. We really don’t know yet. We have to do a lot more investigation and research before we can confirm that. But it’s entirely possible, again, because people come to Oregon to camp, they bring firewood with them, people move down woody material around all the time. It’s entirely possible that emerald ash borer could have multiple introductions into the state of Oregon.

Norcross:  Sounds a little inevitable.

Gonen:  Unfortunately, it is and it’s a good cautionary tale, not only for us in the state of Oregon, but pretty much every other state that emerald ash borer has not yet been confirmed.

Norcross:  Are there any?

Gonen:  Oh, there’s plenty of states. So far emerald ash borer hasn’t been confirmed in Washington. It has not been confirmed in California. It has not been confirmed in Idaho. In fact, we’re the only western state where emerald ash borer has been confirmed. It has also been confirmed in British Columbia. So it really does stand to reason that there’s likely populations that have just not gone detected yet throughout the rest of the West.

Norcross: What are the tell tale signs that a tree has been infested?

Gonen:  So first, you always want to just be looking out for just general signs of decline in mortality in your ash trees. So that’s gonna look like canopy loss. That’s gonna look like epicormic shoots, which is when the tree starts putting out these little water shoots at the base of the trunk or in the middle of the stem.

Norcross:  And we say canopy loss, [meaning], no leaves at the top?

Gonen:  Exactly. That means you’re losing leaves in the summertime when you would not be expecting to be losing leaves on your tree. Unfortunately, these are really just general signs of stress in a tree. So they’re never gonna be particularly diagnostic for emerald ash borer or for any other pest or disease. So you want to look a little bit more closely. Out east, they started to see that woodpeckers began to learn that emerald ash borer larvae were infesting ash trees. They really love eating the live larvae in the trees. So woodpeckers will start to fleck the outer bark away and you’ll actually see this blonding pattern as the outer bark has been flecked off by woodpeckers. And you also can see woodpecker drill holes. So woodpeckers are a lot of times a really good early surveillance strategy when looking out for EAB.

You also wanna be looking for splits in the bark. As the EAB larvae eat away at that inner bark, the bark will actually begin to pull away from the main stem of the tree and will crack. And sometimes you can even find the larval galleries, these S-shaped galleries, underneath those bark splits, if you peel them away with a knife. And finally, you wanna be on the lookout for D-shaped exit holes. When the adult beetles emerge from the tree, after the larvae have pupated and become adults in the springtime, they will leave these very distinctly D-shaped holes in the trunk of the tree. They can be in any orientation. They’re about an eighth of an inch or so wide and they’re very clean lines. And once you see a D-shaped exit hole in an ash tree, it’s absolutely an emerald ash borer infestation. There’s pretty much nothing else in Oregon that will leave those exit holes in an ash tree.

Norcross:  And if I see those signs, what do I do?

Gonen:  You can take photos and make a report to the Oregon Invasive Species hotline. There’s both a phone number and a website that you can make those reports to. We also recommend that anybody who has ash trees on their property, who’s responsible for managing ash trees, first learn how to identify an ash tree, both in an urban area and a natural area. Because we do have native ash trees here in Oregon. Call a certified arborist, an ISA-certified arborist. We’re really encouraging people to seek professional tree care support to help in managing and coming up with a plan for their ash trees on their property.

Norcross:  Last year we spoke with Cody Holthouse from the Oregon Department of Agriculture about other initiatives to keep it in Washington County which, it turns out, didn’t exactly work. But one of the strategies was introducing a wasp which is a natural predator of the emerald ash borer. Can you give us an update on that and its effectiveness?

Gonen:  Since 2007 or so, the USDA has been in charge of managing a biocontrol program for emerald ash borers throughout the U.S. And when EAB was confirmed in Washington County, ODA has been working alongside the USDA on this biocontrol program. So they have these parasitic wasps that are also native to Northeast Asia that have also co-evolved with EAB. These wasps lay their eggs either on EAB larvae or EAB eggs depending on the species. And they parasitize them and they kill them, basically from the inside out. They are highly specific to EAB. They will not really infest or parasitize other insects. So they’re really quite safe to use from an ecological standpoint.

And ODA has been working for the past year or so on releasing a couple different species of these wasps in known infested areas in Forest Grove. It’s looking really promising. They’ve recently been able to recover multiple life stages of these wasps from the areas where they were released. So that gives us some evidence that they are able to establish in these areas and hopefully be able to, in the long-term, keep EAB populations lower than they otherwise would be.

Norcross:  We also talked about the quarantine that was in place in Washington County. Do you anticipate there’ll be similar ones in Yamhill, Marion and Clackamas?

Gonen:  I do believe that the quarantine automatically updates as soon as EAB is detected in a new county. The quarantine does automatically expand to those counties. So I believe that the quarantine has automatically already expanded to Yamhill and Marion counties, and will expand to Clackamas once it is officially confirmed there.

Norcross:  Can you speak to the challenges of enforcing a quarantine like that and the public’s willingness to go along?

Gonen:  It is difficult. We have many roads that go in and out of counties. Counties are also artificial boundaries and insects don’t necessarily respect those boundaries. So it really is about education and outreach, and really letting people know the importance of keeping wood waste material as contained as possible. If you’re gonna go camping and you need to buy firewood, try to buy it as close to that location as possible. Or buy kiln dried firewood if you can. It’s almost exclusively an outreach and education effort. The enforcement behind it, unfortunately, is very difficult. We can’t be standing on every county boundary and inspecting everybody’s cars for ash wood waste material.

Norcross:  It occurs to me we’ve been talking about this beetle as a threat to the Oregon native ash. But are there other species that are susceptible too?

Gonen:  There are a couple of other species. Yeah. So olive and white fringe trees are two other tree species in the same family as ash, in the olive and lilac family. We do have evidence that EAB will infest these couple of trees. In Oregon and the West Coast really, that is a concern when it comes to olive, especially if EAB does manage to make its way down into California. But our results are still somewhat inconclusive as to whether it prefers olive, or whether it’s more difficult for it to establish on olive trees. We really don’t know that yet. We know for sure though that ash is a much more prevalent tree on the landscape than either olive or fringe. And it absolutely prefers ash as its primary host over those other trees. So we’re really focusing our efforts primarily on ash trees.

Norcross:  How important is the Oregon ash tree to the ecosystem?

Gonen:  Oh, it’s extremely important. Oregon ash is a native tree. It’s prevalent, really, throughout the entire Willamette Valley. It’s a lowland riparian tree. That means that we find it in creeks, streams, wetlands, anywhere where it can grow really close to water. And this tree is really important in shading those waterways and keeping the temperatures cool, in promoting stream bank stability, helping with erosion control, and just the general cleanliness and quality of our waterways. This tree has really high cultural value for Indigenous populations here. This tree is a major component of the salmon life cycle, fish that are already threatened and endangered in our ecosystems.

So if we lose Oregon ash on the landscape, it’s really going to have some pretty major implications. And we’re already working with land managers across the state, and figuring out how to make that transition away from ash and into some other trees and shrubs that can hopefully somewhat mimic its place on the landscape.

Norcross:  I read that there are about 94,000 ash trees in Portland alone. What kind of die off could we see if the EAB moves into an area that has this high concentration of susceptible trees?

Gonen:  Oh yeah, it could be pretty major. And already, you can just go on Google and look at photos from the Midwest of before and after EAB has come into cities because it’s scorched earth. I mean, anywhere where you have a closed canopy of ash trees, whether it’s in a natural area or in an urban street, you could end up with basically a complete deforestation event. That’s why we’re trying to keep the populations as contained as possible and do this type of outreach. We’re working with municipalities all across the state and land managers all across the state to help them prepare and to start making the transition away from ash trees with, hopefully, as much time as possible before EAB arrives in their area.

Norcross:  Well, you’ve been tracking this very closely from other parts of the country, now here and now the spread here. Based on what you’ve seen, what do you think the infestation picture might look like five years from now?

Gonen:  That’s a good question. It really depends, I think, on how much we actively manage EAB. Unfortunately, out east, they were kind of the testing grounds for emerald ash borer. No one knew what it was or what its extent would be until it was already too late. So people out there weren’t really able to take proactive measures. And like I said,

it was quite scorched earth. Out here, we do have the benefit of some time, of resources, of research from our partners out in the Midwest and East Coast.

So, in five years, we might see it expand to other counties. But our hope is that with an infusion of education, outreach, resources, we’re able to keep the damage as contained as possible. And again, like I said, start making a transition away from ash trees and into our other palate of diverse trees, both in urban and natural ecosystems.

Norcross:  Lilah, thank you so much for this.

Gonen:  Great. Thank you for having me.

Norcross:  Lilah Gonen is a community assistance forester and the emerald ash borer coordinator for the Oregon Department of Forestry.

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