Quarantine in Washington County aims to limit spread of invasive emerald ash borer

Last summer, an invasive and highly destructive forest pest was first spotted in Oregon at an elementary school in Forest Grove. Oregon is the first state on the West Coast and the 36th in the nation where the emerald ash borer has been detected. The small, shiny green beetle is native to Asia and has killed over a hundred million ash trees nationwide since its arrival in the U.S. roughly 20 years ago. In May, the Oregon Department of Agriculture reinstated a temporary quarantine on ash and white fringe tree products from Washington County, including untreated lumber, nursery stock, firewood and wood chips greater than one inch in size. The department also began releasing several species of wasps that are natural predators of emerald ash borers at tree locations where they’ve been observed. Cody Holthouse, manager of the Insect Pest Prevention & Management Program at the Oregon Department of Agriculture, joins us to talk about the quarantine and other efforts to combat the spread of emerald ash borer.

Note: This transcript was computer generated and edited by a volunteer.

Geoff Norcross: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Geoff Norcross. An internet search of the Emerald Ash Borer finds article after article from Kansas to Texas to Rhode Island saying “it’s here.” The small green beetle is an especially destructive invasive pest and when it gets into certain trees, namely Ash trees, it’ll kill them. The Emerald Ash Borer was first discovered in Oregon in June of last year in a tree in Forest Grove in Washington County. It was the first time the bug was found in any west coast state. Since then, tree managers have taken steps to stop the spread of the Emerald Ash Borer and we wanted to see how that’s going. Cody Holthouse is the manager of the Insect Pest Prevention and Management Program at the Oregon Department of Agriculture and he joins us now. Cody, welcome to Think Out Loud.

Cody Holthouse: Thanks for having me. Good to be here.

Norcross: When you got the news that the Emerald Ash Borer was found in that tree in Forest Grove, what first went through your mind?

Holthouse: Oh, man. Yeah, a lot of mixed emotion, but by and large, just really disappointed. I’m fairly new to Oregon and I’ve been in Utah before that and had been trained by my mentors there to look out for that beetle for many years. And so to get here in my new home and then, and find this beetle, it was very disappointing.

Norcross: Welcome to Oregon… Wasn’t there just a bit of inevitability about this though? I mean, seeing how it spread to other states, was it going to show up in Oregon at some point?

Holthouse: Yeah, we knew that there would be this push westward, from where it’s been establishing in the east over the last two decades. And so Oregon had actually spent some time writing up a response plan back in 2019, initiated that effort and that was the ODA and Oregon Department of Forestry that kind of pushed that and wanted to be prepared. So, yeah, we knew eventually it could happen. We were just hoping it might be a little slower to the uptake and also maybe we’d have more time in advance notice of other places happening in between. It was quite the jump between Colorado and Oregon, but that’s the nature of wood boring insects. That’s how it goes.

Norcross: How did it get here?

Holthouse: It’s a mixed bag of options. We don’t know, but likely it could be firewood… somebody took a truckload of firewood for a camping trip or something, could be nursery stock that was infested. There’s a variety of things. Unfortunately, we can’t nail it down. But, yeah, it likely human mediated, given the jump.

Norcross: Can you describe it in case we see it in the wild?

Holthouse: Yeah. I get a lot of people comment[ing] on the fact that it looks smaller than they’d expect. It’s 3/4 of an inch, half an inch, green metallic beetle. It’s in the metallic wood boring beetles family…

Norcross: So it’s a pretty good name.

Holthouse: Yeah, it is. I think a lot of people actually use beetles from this family as jewelry. You’ll see them as earrings or things like that. And so, yeah, beautiful iridescent green, the abdomen, which is kind of the body of the insect and the back end has kind of a cool orange-ish color to it as well, if you take the wings apart and look there.

Norcross: How does it attack trees?

Holthouse: Well, it’s a pretty interesting life cycle that you have to kind of understand and know how they’re attacking the tree. So the larvae develop after hatching from their egg, they bore into the wood, through the bark and the phloem, they feed there, develop…

Norcross: Phloem?

Holthouse: Yeah. So just as you pass through the bark of a tree, a lot of us have maybe heard about phloem and xylem, but phloem is where you get a lot of the transpiration of sugars and other nutrients up the outer rim of the tree, essentially just below the bark. And so EAB [Emerald Ash Borer] has evolved to go after that area of the tree and feed there. And so you get these kind of serpentine galleries as the EAB larvae develop in there, they just kind of work their way through that tissue feeding developing and they’ll eventually pupate there over winter and then emerge as an adult. And the adults actually feed on the leaves as they emerge and look for a mate.

Norcross: So they’re there for the sugar and then they move on to the rest of the tree?

Holthouse: Well, yeah, the sugars and other nutrients there in the phloem, and they usually start out [in the] upper canopy and they work their way down the branches to the trunk of the tree, kind of utilizing as much of that resource as possible. If they did it the opposite way, they’d cut off [the] supply of nutrients at the bottom of the tree and the tree would die a lot faster. And so they’re actually pretty interestingly evolved and that they’ll go after the canopy up where there’s sun touching the canopy usually, and they’ll be feeding there and then girdle branches as they go down. And that girdling, again, causes there to be a cessation of nutrient transfer to the rest of the branch.

Norcross: I understand that there are wood boring beetles that are actually beneficial to trees, and Ash trees specifically. What is different about these beetles and the way that they attack trees that are just so harsh and deadly?

Holthouse: It’s a really good question and we actually have a lot of different native Buprestids and other beetles that are wood boring beetles and by and large, a lot of those are feeding on either dying or dead trees, and they’re kind of helping that recycling of that carbon and other resources there in the tree, they’re breaking the tree down. That’s a very natural part of our ecosystems and wood borers are vital for that kind of nutrient cycling in our forests.

What makes this situation different is that the Emerald Ash Borer is going after a very healthy viable Ash tree and taking it in three to six years to complete mortality, and that’s not a very normal situation again. Most beetles that are native that we’re dealing with on the daily, are going after weakened trees that are on their way out, or have already died.

Norcross: Well, you say it happens in three to six years, but does it always happen? Is it inevitable that a tree that gets this beetle is going to die?

Holthouse: I think our 16 different native Ash species here in North America, there’s a varied story. You have a few exceptions to the rule, like Blue Ash that might show a little bit more resistance and resilience. But by and large, most of our native North American Ash are gonna be taking a hit, and I think it’s close to like 95-99% of all of our Ash are gonna be dead in three to six years.

Norcross: Wow.

Holthouse: That’s pretty certain.

Norcross: Does it have an appetite for other kinds of trees besides Ash?

Holthouse: Also a good question. We have noted, and I say we, that’s the scientific community, has noted White Fringe Tree and Olive are also susceptible. They’re not quite as desirable of a host as Ash, but we have noted that there’s development in those trees and you can get emergence of adults as well.

Norcross: How important are Ash trees to the Oregon economy? What are they good for?

Holthouse: By and large, we’re looking at the real intrinsic value of the forest around our riparian corridors and Ash acts as a really important shade property on our river systems. And so we’re looking at rivers that are sometimes dominated by Oregon Ash, our native species. If you lose that species, you have a real exposure to more sunlight and potentially changing of temperatures of the water below. The system will very likely change dramatically. And, again, because you’re losing 90% to 99% or all of the Ash in that area, it really wipes out that canopy and it’s more of a habitat loss.

As far as economics, we have the whole ornamental tree side of this to consider. I noticed as I walked in your building today, you have ornamental ash outside of this beautiful building. And so street trees are definitely at risk here and we could get into some numbers there, but each city has their own inventory of Ash trees or they should be working on that. And it becomes pretty clear that financial kind of hit very quickly.

Norcross: Is there a climate change element to this story? Are the trees stressed and thus more susceptible to infestation?

Holthouse: There is a component to that. Obviously, Emerald Ash Borer can attack a healthy tree or a stressed tree, but they are more attracted to a stressed tree. And those stressed trees emit volatiles, secondary compounds that are especially attractive to the adults as they’re going and looking for a host to lay eggs on. I think there’s research out there that says up to five times or even more attractive than a normal tree would be, those stressed trees. And that could be drought stress. In our situation where we’re looking to monitor for the pests, we actually will manipulate a tree by girdling it and creating a stress tree. And you can actually get information out of that stressed tree, which is really great as we’re trying to understand movement and patterns of where it’s going.

Norcross: So Cody, a year ago, almost exactly, this beetle was found in a tree in Forest Grove in Washington County. So what has happened since then?

Holthouse: Yeah, great question. So a lot of the national resource community has rallied around this detection. Since we really confirmed this species being here after June 30th, early July, we got to work on consulting our readiness plan that was written a few years ago to make sure we follow those guidelines that we’d put for ourselves and then forming a task force as well, that has, I think over 40 different agencies and local cooperator groups are involved in that. And that meets monthly. So the first or second Tuesday of every month, we have a big meeting with many different land managers, agencies at a state and federal level, where we’re discussing tactics and strategies as to how to keep monitoring for this insect, see where it’s moving, what industries it’s affecting. And those have been really, really helpful task force meetings.

The task force itself has several different, I think close to six now, different subcommittees that are all dedicated to different parts of this project. So I work with the survey and monitoring subcommittee. There’s a wood waste utilization committee, communications. We have one on best practices and management strategies, training, and then a steering committee as well, to kind of keep everything organized.

Norcross: There was an immediate quarantine that was put in place last year. What did that look like? And what did that mean for moving wood in and out of Washington County?

Holthouse: So the quarantine itself…we want to slow this species down as much as possible. And so if we can stop people from moving Ash trees, potted Ash plants, or maybe a downed Ash tree that just didn’t look great. So somebody’s had their arborist come and take it down. We really want to stop those kind of trees from moving outside of Washington County and inoculating a new county and spreading this pest through human beings. So that quarantine is really getting at stopping that physical movement that…

Norcross: We’re actually on the second quarantine – one expired and another one took its place. How is it different? How was the approach evolving?

Holthouse: So right now, the next one was enacted, I think just after May 16, it goes through November 11. And so we’re hoping this next temporary quarantine gives us just a little more time to continue preparing for our permanent rule, which will go out and kind of have a more indefinite phase of this quarantine. But these temporary quarantines allow us to kind of assess the situation, see how fast and quickly it’s moving. Are we accurate to which plants we’re including on this quarantine? Do we need to be more inclusive, less inclusive?

We’re really trying to tap into the industries and businesses that are affected by these decisions too. And we’re making all kinds of meetings with them and their leaders to try and make sure that when we do arrive at our permanent rule and hopefully after November 11, that it’s encompassing all the right materials and also not limiting business in such a way that we’re really limiting business. We wanna make sure we work with the community as best as possible.

Norcross: And what are you hearing from those business owners who are affected by these moves?

Holthouse: Mixed bag, of course. A lot of people [say] this is old news. Emerald Ash Borer has been moving across the United States now for the last two decades. And so a lot of people, especially in the ornamental nursery business are tuned into this story and they’ve had some time to react and to respond and have really, I think shrunk that market down quite a bit as far as selling ornamental Ash. We do have some industry growers that are making for a native Ash plantings. And so they have been impacted by this and haven’t been able to ship out their normal quota of Oregon Ash to other conservation projects, things that normally go on. And so I definitely there’s an impact here.

Norcross: Your team has also done something dramatic. They’ve been releasing different species of wasps that are native to Asia to eradicate the Emerald Ash Borer. Can you talk about that effort and how it’s going?

Holthouse: Yeah, the Biological Control Program here has been let out by Doctor Max Ragozzino and I really enjoyed working with him on this aspect of slowing this Ash mortality and a big part of that is enabling Mother Nature to really be a part of the story as much as possible. Like any invasive insect, they experience this release from natural enemy pressure.

The United States has been really keen on looking at what native parasitoid wasps are effective in Asia and trying to see if we might get those released here in North America. And that’s after lots of quarantined research on these different parasitoid wasps. Four different wasps, I believe, have been approved for release in the United States, three of which, the Spathius agrili, Tetrastichus planipennisi, and Oobius agrilihave been approved for release here in Oregon and we’ve already released several 100 of each of those three species here.

Oobius agrili is the egg parasitoid. So it actually goes after the egg stage of emerald ash borer and limits that life stage from developing, kills it and a wasp emerges and then Tetrastichus and Spathius both go after the larval stage of the beetle and they can have multiple progeny come out of just one beetle larvae. And so you get quite a numeric response from those two species in particular.

Norcross: We’ve heard time and again that when land managers will bring in a species to deal with another species, the cure can bring problems of its own. How are you ensuring that these wasps that you’re releasing into the wild aren’t going to bring their own problems?

Holthouse: Yes, that’s the right question to be asking. And we have plenty of situations where we have seen it go wrong. But luckily I get to kind of expound on years of research. And so we have many, many different scientists, entomologists across the nation who’ve been working on these three species that we ended up releasing for the last 10 years now and doing a lot of data on non-target effects, understanding their impact on, not just general Ash Borer, but what other beetles might be impacted. And we find it’s a very, very specific, narrow range. They are specific to the species and very little in the way of non-target effects.

So again, you’re never gonna get away with a solution to these problems that is scot free of any issue. But we feel pretty confident that these are the right wasps to be releasing at the right time.

Norcross: Given that this Emerald Ash Borer was found in Washington County and so far it seems to have been contained in Washington County, is that a win?

Holthouse: For now, we’re taking every win we can get. And I would consider it somewhat of a win. I think that if we hadn’t done any kind of quarantine and hadn’t talked about this and worked as a community here locally and as a state, I think there’s potential it could have moved faster than it has already. It’s just one truck load of firewood to really change the game. And so we’re hoping to really contain it there as long as possible. We know that inevitably, it’s probably gonna jump our line at any moment and show up in another area of Oregon or Washington. And that’s very possible. But right now we’re just kind of taking one day at a time.

Norcross: I live in Washington County. I don’t have any Ash or Olive or White Fringe on my property, I don’t think. What do I need to know? What do I need to be on the lookout for and what do I need to do?

Holthouse: So right now, a great thing is to establish whether or not you have Ash on your property. That’s a good first step – learn how to identify it. I think that’s easier said than done sometimes when you’re not “in the world of botany or entomology” every day. Understand what your risk is if you have Ash or White Fringe tree or Olive and then go after what you can do to be observant to take a look at the canopy. Do you notice the tree is in decline? Are there dead branches? Is that increasing as time goes by? Do you have epicormic shoots or little kind of suckering branches coming out of the base of the tree that indicates there might be an issue in the upper canopy. Do you see beetles on the tree? And if you do, take a look at them. Do you see ‘D’ shaped exit holes in the bark? Those are some things to start looking at.

But as we’re all considering our place in this story, if you are farther away from Forest Grove, for right now, tend to those Ash trees, if they’re healthy, do what you can to keep them healthy. There are options to prevent infestation. You can treat your tree if you feel it’s a heritage tree or provides shade value that you really don’t want to live without. The other idea too is nearby that tree, you might find another plot that’s got open sunlight and you plant a new tree that’s gonna potentially start to fill in the gap when eventually that Ash tree will probably go away down the line.

Norcross: I’m sure there are other invasive pests that your department is trying to control right now. What lessons are you learning from this experience with the Emerald Ash Borer that you could maybe apply to other wildlife?

Holthouse: You know what, really the silver lining in this whole EAB invasion is that we have come together as a state and as local cooperators. I can’t emphasize enough how much we’ve benefited from the local knowledge in Washington County. People that work at Clean Water Services, Oregon Metro, the Soil and Water Conservation Districts, they are the true heroes of the story. They knew the land, they knew what was at stake and they’ve been quick to respond and work with us and looking for this beetle and mitigating its negative impacts. And so for me, I think a lot of the connections around how to share knowledge and respond to an insect problem like this has just far reaching impacts on how we do things in the future. And I hope that it continues to guide us as we know how to build a team, how to form these surveys that we do, how we slow these kind of wood boring pests down. These are skills that we’ll use for many years going forward.

And I mean, I could give you a list that’s very long of other wood boring pests that Oregon has to worry about, namely Mediterranean Oak Borer is another one that has hit us in the last few years. So again, I think that’s a huge benefit here as well.

Norcross: Cody Holthouse. It was great to talk to you.

Holthouse: Thanks so much. Thanks for having me.

Norcross: Cody Holthouse is the manager of the Insect Pest Prevention and Management Program at the Oregon Department of Agriculture.

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