Think Out Loud

New strain of hazelnut blight overcomes disease resistance in Oregon orchards

By Gemma DiCarlo (OPB)
March 15, 2024 4:45 p.m. Updated: March 22, 2024 7:31 p.m.

Broadcast: Friday, March 15

Barcelonas are the most common hazelnut tree, producing most of the nuts we buy in stores. Many survived Oregon's eastern filbert blight, which started to spread in the 1970s.

Barcelonas, pictured in this 2016 file photo, are the most common hazelnut tree, producing most of the nuts we buy in stores. Many survived Oregon's eastern filbert blight, which started to spread in the 1970s.

Jo Mancuso / OPB


Eastern filbert blight, a fungal pathogen that kills hazelnut trees, first made its way to the Northwest in the 1960s. Since then, farmers have managed the fungus by pruning infected trees and spraying orchards with fungicide. But the most successful intervention has been a disease-resistant cultivar that’s been bred into newer hazelnut varieties.

A new strain of the blight has overcome that disease resistance, however. As reported in the Capital Press, the strain originated in an Oregon orchard and now threatens thousands of acres of newer trees in the state.

Ken Johnson is a professor in the department of botany and plant pathology at Oregon State University. He joins us with more details on the new strain and what it could mean for Oregon’s multimillion-dollar hazelnut industry.

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

Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. Eastern filbert blight, a fungus that kills hazelnut trees, first made its way to the Northwest in the 1960s. Since then, farmers have managed the fungus by pruning and spraying infected trees. The most successful technique has been to plant a variety that’s resistant to the blight. But nature finds a way and as reported in the Capital Press, a new strain of the fungus that gets around that resistance was discovered recently in the Willamette Valley. It now threatens tens of thousands of acres of orchards. Ken Johnson is a professor in the department of botany and plant pathology at Oregon State University. He’s been studying this pathogen for decades now and he joins us. Ken Johnson, welcome.

Ken Johnson: Thanks, Dave. Nice to be here. Thank you for having me.

Miller: It’s great to have you on. What does this blight do to hazelnut trees?

Johnson: I guess the simplest analogy is something like a cancer. It gets in on a young shoot tip, but then sort of just progressively moves down the branch, killing the branch as it goes and producing new spores in that process. And then once you start to get those spores,

you get more infections in the same tree and then the whole tree gets kind of a blighted appearance from dying from the top down. You can still see a lot of the old orchards around the Portland area and you see old hazelnut orchards, they don’t look very good. That’s probably because of the plight.

Miller: What exactly have hazelnut growers done over the last number of decades now, in response?

Johnson: Well, the industry has expanded remarkably. I think when I started at OSU in 1988 there was about 25,000 acres and now it’s close to 90,000 acres. So the industry has really grown and much of what’s been planted that’s new are cultivars that came out of the Oregon State breeding program that have this resistance gene that is in the process of failing.

So resistance has sort of made eastern filbert blight go away. And now it’s going to come back. I don’t think the situation is as dire as it was when we first started working on it, but it’s going to be a new thing that has to be managed as we go forward.

Miller: Why isn’t it as dire now as before?

Johnson: Just the knowledge that we have. When I started on it in ‘88 we didn’t even know how it got in the tree. We didn’t know what kind of materials we could spray on the trees that would prevent infection. The tree size was about 30 feet tall and they are really hard to spray and many growers didn’t know how to spray. And then the new trees are going to top out about 12 to 13 feet so they’re much, much easier to spray and also to prune individually as the disease comes into the orchard.

Miller: What percentage do you think of active hazelnut orchards right now have the resistance gene that you said is now in the process of failing?

Johnson:  Well, I would say about 60% of the acreage that’s out there has the resistance gene in it that’s in the process of failing. The number of places that actually have the pathogen is very small and it’s centered around Woodburn. It’s really just one orchard where we feel like it’s where it started and there’s a hot spot out in the middle of that orchard. And then we found it moving out of that orchard and a couple other ones that were down downwind from that orchard. But there’s not a whole lot more than maybe a half a dozen orchards that have this strain in it right now.


Miller: Did growers that you’ve talked to over the years understand that at some point this might happen?

Johnson: That’s a tough one. I think that the local adaptation of an islet is always hard for people to grasp that concept.

Miller: What do you mean by the local adaptation of an islet?

Johnson: So that the fungus came. We believe the new strain was born here and it was just a chance mutant coming out of one of the orchards where these spores are being produced. And it got lucky and it found this orchard in Central Marion County. So we’ve done that with a genetic fingerprinting technique comparing it to islets in the Willamette Valley as opposed to where it’s native back in the Eastern United States. That kind of evolution. We there’s a lot of examples of it in agriculture, but it’s harder for people to grasp that. The industry was very concerned about another introduction coming from the eastern half of the United States where it was already known that OSU cultivars back in say New Jersey got eastern filbert light back there due to the genetic diversity that they have in the pathogen there. But so people were really focused on that, but people were less focused on the fact that it could actually happen locally through mutation in the local population.

Miller: So, is it good news or bad news or is that the wrong framing - the fact that you found out that this newly resistant strain is a local mutation as opposed to something that hitchhiked from New Jersey?

Johnson: That’s a really tough question to answer. I think it’s good news in the sense that it’s pretty similar to what we’ve already had and when we know what we already had, we sort of know our enemy. If another enemy came from the Eastern United States, would that one be really different? There’s a chance it could be. So I guess it’s good news that it’s a local one if it had to happen.

Miller: So, how much do you know at this point about how virulent this new strain is?

Johnson: Well, virulence is really complicated. And it depends on the cultivar that it’s on. That’s what I’m saying. I talked to somebody recently and I said, well, I would expect the virulence to be like it was on the older main cultivar which was called Barcelona. And I said, well, I would expect it to be like eastern filbert was on Barcelona. I don’t expect a big change other than that, other than it can now affect these infected trees that had or have the resistance gene in them.

Miller: Hearing you talk about all this, we’re talking about a fungus, not a virus, and we’re talking about hazelnut trees, not people, not humans,

Johnson: Right, right.

Miller: But I cannot help but think about our collective experience with COVID and with vaccines and the constant evolutionary game of mutations. And then the human biotech response, whether it is finding strains of trees that are resistant to the fungus or creating different versions of a vaccine. Has COVID changed the popular understanding of some of the work that you do?

Johnson: Well, I think we can talk about strains and the fact that strains evolve over time and people grasp that much more readily now after COVID. I think people kind of knew this kind of thing from a cold virus but probably didn’t give it that much thought. But with the close following of the molecular data on the COVID strains and things like that, people are much more informed about the ability of microbes to adapt to new situations. Yeah, I think you’re right about that.

Miller: Just yesterday, we talked about a very invasive species called Quagga mussel, which the invasive species coordinator for the state says it’s just a matter of time before it’s basically all throughout the Columbia River Basin. And once it gets there, you can’t get rid of it. Do you think about the spores on a relatively small area around Woodburn right now as the same, or do you think it’s possible to somehow eradicate them there and forestall the invasion?

Johnson: Yeah. Well, we talked about this quite a bit and I actually started working on this a couple of years ago before this breakout happened - like holy cow, the breakouts here. What we were trying to do is work on early diagnostics and being able to identify this situation as it came. And now we’re doing it in real time. But yeah, I do think that the situation that we have around Woodburn now really warrants really close monitoring. And I’m a proponent of it. Perhaps we can come up with the funding for one of these orchards [where] the disease is already too advanced in, that we somehow come up with some funding that we could just maybe replace that whole orchard and see if we can start fresh. I think we’re still at that opportunity.

Miller: You’ve been doing this since 1988 - 36 years now. Is there a part of you that is excited about this even though it represents a huge headache and maybe a big economic hit for a lot of farmers?

Johnson: So I was an instructor of introductory plant pathology for 36 years as well. And I’ve been talking about this kind of phenomenon for years and years. And the case-in-point is bananas right now. [They] are in this almost exact same boat, where there’s a new strain that’s attacking the export banana that many of us eat every day. So, yeah. And then to be standing in this orchard and knowing that this is probably the spot, the hot spot where this happened. I mean, there’s sort of a little bit of a professional thrill to that. I guess that’s not probably the proper way to say that, but it’s true.

Miller:  Ken Johnson, it was a pleasure talking with you.

Johnson: Thank you very much.

Miller: Ken Johnson is a professor in Oregon State University’s department of botany and plant pathology.

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