A BIG OLD copper beech tree is a focal point of my garden, and each time I look out the window at it admiringly these days, I feel the same love and gratitude I always have for its grandeur, but also a deepening twinge of worry. These are increasingly tough times for beeches, both European ones like my copper beech, and on a far bigger environmental scale, the precious native beech trees of our Eastern North American forests.

I’m joined for this podcast by Beth Brantley of Bartlett Tree Research Laboratories, who’s speaking July 18 on the future of beeches at the annual in-person and virtual Woody Plant Conference at Scott Arboretum at Swarthmore College.

Beth, whose doctorate is in plant pathology, is the Northeast Research Scientist with Bartlett Tree Research Laboratories, providing support to Bartlett Tree Experts’ regional offices; conducting arbor culture research; and sharing her knowledge through teaching and presentations. Beech leaf disease, one of the newer challenges facing beech trees today, is a particular interest of Beth’s, and she told me more about that and other pest and pathogen pressures facing these important trees. (Above, striping from beech leaf disease evident in beech leaves; photo from Bartlett website.)

Read along as you listen to the June 30, 2025 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify (and browse my archive of podcasts here).

beeches under pressure, with beth brantley

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Margaret Roach: Welcome Beth. How are you?

Beth Brantley: Well, hey, thank you, Margaret. I’m doing well today. How about yourself?

Margaret: I’m O.K. I’m worried about beeches.

Beth: Could you tell me a little bit more about your tree, your beech tree, Margaret, and your relationship with that tree?

Margaret: Sure, absolutely I could. I planted it almost 40 years ago, dragged it as a young tree up a hill and planted it in a field, on axis from key windows in my house, and I’ve stared at it every day since as it’s grown and grown into this majestic, giant creature. And then in the forests not far away are lots of other beeches.

And I guess the thing about it is that I have over the years of being a gardener and then a garden writer and so forth, heard the story of many different trees in trouble, one by one: the woolly adelgid and the hemlocks years ago and continuing. And I hear about oak wilt, and emerald ash borer and oh my goodness. So yeah, so I have a strong relationship with the tree. I can see it as we’re speaking right now, and it’s my companion [laughter]. It’s not in trouble right now, but I worry because I have seen ones elsewhere, not so far away that are.

Beth: Well, I appreciate that story and those connections, Margaret and indeed our beech trees are in trouble. And I will preface this by saying that I have the good fortune of working for a company that is based and grounded in science and safety, and it is our mission to keep trees healthy. And at the end of the day, all living organisms should have that opportunity to be kept healthy.

And as I think about your planted beech tree, I would share with you that my husband and I own 30 acres of mostly beech forest, which is also in trouble. And it’s not just beech leaf disease, that’s a problem in our forests, but all the other players that come to the table, including beech bark disease, and some other native pests and pathogens. But with beech leaf disease in particular, Margaret, neither of these trees, European beech nor American beech, have co-evolved with this foliar-feeding nematode. And I think that’s our greatest challenge with science and with research is how do we approach this really novel, what we call a pathosystem in these woody plants, our majestic beech trees. And what would you like to know today, Margaret, that I can share with you? [Above, leaves of American beech, Fagus grandiflora; photo from Wikimedia Commons by Dcrjsr.]

Margaret: Well, I think to set the scene for listeners who may not know what’s going on with beeches, there are sort of multiple things. Some of them have been around longer. I think beech leaf disease, what it was discovered in Ohio around 2012ish maybe, I think.

Beth: Correct.

Margaret: So that’s relatively new, but it’s already spread quite quickly, I think. But there were already other—and you just alluded to some—there were already other pressures on beeches. So just a little bit of what are the multiple stressors that beeches face, and are they all the European and the native beeches, or do some only target one or the other species?

Beth: Yeah, great question. So some do both and some are definitely host-specific. And I think I’ll start with your tree, with European beech, and talk about how the challenges that we see with European beech, especially the older trees, Margaret, on the historic estates that dot the Northeastern United States.

Trees in many ways are like people. They just become more susceptible to some of the challenges that present. There are wood-decay pathogens that we may not know about in an older tree until we see a fungal fruiting structure, for example, or a fruiting structure in general. There is a root rot disease caused by Phytopthora, which is not a fungus, but it’s a fungus-like organism that attacks roots of both European and American beech.

But I’m thinking about your beech tree, Margaret, on your property right now. It’s only 40. It’s in the prime of its life really [laughter], a young adult.

Margaret: It’s a babe [laughter].

Beth: And so your tree, given the right conditions, should be healthy and thriving. And I’ll talk about those cultural conditions in a moment. But back to the pressures: Your European beech actually has a woolly beech aphid that is specific, host-specific to European beech. It doesn’t feed on American beech. It’s kind of fun and fascinating, interesting, that it found its native host here in America. But then there are woolly beech aphids that do attack American beech. And these are stressors more than anything.

And then just a whole host… Beech are—I don’t want to use the word sickly in the wrong way. But they are subject to, how about this: They’re subject to or prone to several insects and diseases along with mites as well. So lots and lots of problems. And then American beech in our forests, the beech bark disease, which is a fascinating complex between scale insects that feed on bark and create little wounds, and then fungi spores that find those little wounds in the bark and colonize. So sort of a cool complex from a pathological perspective, but that can render mortality in the more susceptible individuals in our forest trees. So just so many to choose from. [Above: Woolly beech aphid on European copper beech leaf; photo from Wikimedia by Gailhampshire.]

Margaret: Yeah. And the thing about the beech leaf disease, the more recent one: What happened is a couple of years ago went to, you were just talking about these sort of historic gardens and so forth, and they have these majestic weeping beeches and things like that that were put in a century or more ago. And these greatest estates, many of them are now public gardens, and they’re losing them—they’re losing those older trees in a lot of cases.

And I was at one, and it’s surrounded by beech forest, native beech forest, so it’s the worst combination of things. So they’re vulnerable in two ways, to their natural lands as well as their ornamental foundations, their architecture, so to speak, of the garden. And that was where I first learned about beech leaf disease. And when you first see it, it’s kind of fascinating and eye-catching. And I use those terms very in quotes because obviously it’s insidious and horrifying, but at first it’s like, “Ooh, what’s that?” Do you know what I mean?

Beth: I do. I do completely. And the best way to identify it is looking up to towards light, towards the sun, and looking at the leaves from the underside, Margaret. And you see that damage that was caused by the nematodes feeding in the buds, in those little primordial leaves over winter, all of that damage was already done. And those leaves unfurl in the springtime with the damage that to me, I like to call them zebra stripes, so that darkened tissue in between the veins of the beech leaves. So easiest to see, looking up through that crown of the tree to see that stripe. [Photo looking up into infected beech canopy from Bartlett website.]

Margaret: Oh, so they did the damage before the leaf opens, so they don’t get inside the leaf layers or whatever like a leaf miner would. They’ve actually done the damage that shows in the leaf once it expands; they’ve done the damage when it was curled up before it expanded.

Beth: Exactly.

Margaret: Oh, I didn’t understand. O.K.

Beth: Yes. And that’s a really important thing I think for folks to know, that the damage is already done, the leaves emerge, and now it’s up to the beech tree to decide: does it retain that leaf Margaret and try to photosynthesize effectively with these damaged cells, or does it drop the leaves and push out a new flush?

And by this time of year, so you and I are speaking at the end of June, healthy trees are often pushing a new flush, dropping those old damaged leaves. So we tend to see sort of a light, green floppy set of leaves at the ends of these twigs that show no symptoms. And all of those other leaves are already on the ground. They’ve dropped them.

And I share this Margaret, because that’s really, you’ve got to think about it as a true depletion of stored energy. The tree stores these carbohydrates for so many reasons: defense, for growth, for reproduction. But now they’ve got to use up the gas in the tank to push out new leaves. So all of this comes at a cost to these trees. And at some point there is no more gas in the tank, no more stored energy reserves. And the trees really become susceptible to all of the late-comers to the, what I call the mortality spiral into the death party. For example, ambrosia beetles. That’s sort of the final nail in the coffin when you see those little pencil protrusions at the base of a beech tree of sawdust from these beetles that really have just come to clean up the party because the tree is dead.

Margaret: Right. So lots of things going on. And so you were talking about my tree, if it’s 40 years old; well, it’s older because it probably say it was 10 years old when I got it or something. But at any rate, it’s in the prime of its life. Maybe it has more resilience than a tree at a historic estate that was already 100 years old and whatever. But is that what we’re going to do? How are we going to tackle this, or are we tackling this beech leaf disease? Is it that we’re trying to fight this nematode, or are we trying to instill more resilience in the trees, or what’s the tactic for this?

Beth: Sure. Great question. And the good news is there are solutions, and we’ll address this again within the space of your tree. Let’s start with the tree itself. Let’s talk about building resilience for the tree and keeping the tree itself healthy. In my vision, Margaret, every beech tree that’s planted on a property would have a mulch bed all the way out extending all the way out to the edges of the furthest-reaching branches. And we call that the drip line affectionately [laughter]. Sure. So if you put that sort of umbrella on top of a tree, it’s where the edges of the umbrella would be.

And having that layer of mulch provides so many benefits for your tree, and any tree—it doesn’t have to be a beech tree. But first and foremost, it helps retain water. It acts really functionally as a blanket retaining the water in the soil. It prevents lawnmower damage to exposed roots and to the trunks of trees. And it also provides nutrients—organisms break down that woody material and pull those nutrients into the soil profile, so that our beech roots and other tree roots can access them. So I’m really a tremendous fan of mulch.

And we’ve had such a wet spring, Margaret, in the Northeast, so I’m not too worried about water going into this growing season. But certainly if we enter another really hot dry spell like we had last autumn, for example, and as part of the summer last year, we have to be mindful about providing all of our trees with adequate moisture. And I’m a fan of drip irrigation. I’m a tremendous fan of soil moisture meters that you can buy at your local box store or order online, or even just simply stick your finger in the soil as far down as it can go, and does it feel moist?

And I think those two things for me—just the mulch and proper water for the soil, for the roots—are my top two go-tos when I think of cultural amenities that we can provide for all of our trees. And again, for your beech tree in particular.

Margaret: Now we’re keeping the mulch away from trunk, I’m assuming, but we’re mulching out to the extent of the drip line.

Beth: Correct. Right, to the extent as far as his branches grow. Absolutely. Yeah. Please, please keep that mulch away from the trunk.

You want to have that nice exposed what we call a flare, where the trunk starts to taper into those roots.

So I am also a fan of understanding soil health, and for me, it’s soil nutrition, so submitting soil samples for nutrient analysis and making sure that your tree is really receiving everything that it needs. I think this is really important. And especially on some of our landscapes, Margaret, where we have turf going all the way up to the base of a tree. I see this quite often in my travels, and it kind of breaks my heart. The turf roots are going to get the water before the beech roots are, and they’re also going to take nutrients away from our tree roots. So just being mindful that we can do a lot of things for the health of the tree.

There are also potassium polyphosphites that are available, and another tree company, Davey Tree Research, that group has done a really excellent job showcasing how polyphosphites have helped to build resilience in beech trees subjected to beech leaf disease, to the nematodes. But keep in mind that these amendments, so these soil amendments, are really targeting helping the trees and not controlling the nematodes.

Margaret: Right, right. So it is to boost the resilience. It’s not to kill the pest, so to speak.

Beth: Correct. And I’m a strong advocate. That’s part of our health program for beech trees and for all trees, Margaret. I believe that we should all be doing all we can to promote health for these trees.

Margaret: The historic landscape that I talked to you about that I saw that surrounded by native beech forest, that they’re following, I think it was University of Connecticut guidelines actually, that did recommend the potassium polyphosphite fertilizer products and so forth. And they’ve been using those, and that was the direction they’ve been going. And just what you’re saying, other soil-health, soil-improving kind of tactics.

Just one quick question. Mulch: Are you using arborist chips, or any particular kind—is it a coarse-textured mulch? Any recommendations there?

Beth: Yeah, great question. If you have access, I prefer to find a composted landscape mulch.

Margaret: Something that’s been aged already.

Beth: So landscape wood bark mulch is an excellent material. I like that coarse material. So again, an excellent substrate to use, just as long as there’s some nutritional value to it. I’m not a fan of the ground-up pallets in the standard diet [laughter].

Margaret: Not industrial waste.

Beth: Yeah, we can do better.

Margaret: So where did this nematode come from? Do we know? I think I read that we think it’s non-native, but we’re not sure. And I don’t know if that’s the latest or not. And how does it spread? Do we know anything about the vectors of its spread or-?

Beth: Yes. Yes, we do. So this is a subspecies of a nematode in Japan, and a group of researchers went to Japan last year, and what they found is that Litylenchus the genus of the nematode that this Litylenchus in Japan attacks the native beech trees and it causes symptoms, but it doesn’t cause mortality. So there’s some co-evolution.

And through genetic analysis, we’ve identified this as a subspecies, but since our trees nor the European beech have co-evolved with it, there is no inherent resistance for our trees. And what this does provide is perhaps a glimmer of hope for some opportunities with genetics to utilize the Asiatic beech species as we do our best to conserve the beech tree in America, and eventually in Europe as well. That’s the origin of the nematode, is Japan. As far as spread, it’s really quite fascinating. This stayed quiet from 2012 to about 2018. It was just confined to Northwestern Pennsylvania, and into that southeastern Ohio corner. And it really didn’t do much. We didn’t hear about it. It was sort of off everyone’s radar. And part of the long-distance transfer, Margaret, was through the nursery trade.

Margaret: That’s what I figured.

Beth: Nurseries were growing European beech and in areas where American beech forest, just as you have described, were infested, and the transport of these, for example, over to Long Island and in through the Northeast, did the long-distance movement of these nematodes, again on nursery stock.

But they also, there are 10,000 nematodes in a single leaf, and they move in the wind, they move in the rain, they spread just gradual movement by birds, by mammals, by insects. So there are many, many different ways that the nematode is getting around. Even by, perhaps by people if we brush up against a leaf or a twig when they are moving from infested leaves to the buds, which is going to happen later on in the summertime and in early autumn. So lots of spread, but mostly by wind. That’s how we’re getting a lot of this spread. And again, just keep in mind 10,000 of these in a single leaf and you can just imagine how many are in a single tree, a mature tree.

So I want to circle back to what we can do for our trees in terms of managing the nematode populations.

Margaret: Definitely. Yes. Yes.

Beth: So we have really two wonderful options right now. Both are pesticides with what are called nematicidal properties. They kill nematodes. And one is a foliar application of an active ingredient called Fluopyram. And the other is a systemic injection of an active ingredient called thiabendazole. And I’ll provide you, Margaret, with two scientific papers that document the science behind these recommendations [here and here]. And again, working for a science-backed company; I cannot provide recommendations unless this has been vetted through the scientific community, and they have in these peer-reviewed journal articles.

And again, every tree is an individual, so we make recommendations on a case-by-case basis. I would encourage the listeners to reach out to a certified arborist, so an ISA-certified arborist, International Society of Arboriculture, for recommendations for their beech trees. And these are the two active ingredients that, again, the scientific community, the arboriculture community is promoting. And you mentioned the UConn references. I would also encourage listeners to look at the University of Massachusetts recommendations. [Beech leaf disease photo, above, by Matthew Border of Bartlett via Bugwood.org.]

Margaret: That’s the other one I’ve been reading, yes. The garden I was talking about that I visited, they are in, they’re on the border of Connecticut, so they probably consulted with the university that was nearest to them.

Beth: And I’ll also provide you a technical report that is available from Bartlett Tree Experts. We’re happy to share knowledge; that’s our goal. We want everyone to have healthy trees so we can assess trees, Margaret, one tree at a time, and we’re looking at other conditions of health as we make recommendations to treat for beech leaf disease. The foliar-spray applications are annual, and the systemic injections in the root flare are good for two years. But not every tree is a candidate for either of those, and we’re not going to do both [laughter]. You’re going to do one or the other.

Margaret: And the polyphosphites, is that a regular thing?

Beth: And we recommend twice a year, so beginning and end of the growing season. And that’s for all trees.

Margaret: It’s a lot, and again, the beech forest is such an important forest and part of our forest community in the Eastern United States, and such a supplier of sustenance for so many creatures and so forth. You said you and your husband have 30 acres of it. It’s a big deal, so I wanted to hear more about it and get more information.

Now in the last minute, I’m just going to shout out to people that if they want to learn more, they could attend your talk at the Woody Plant Conference at Scott Arboretum virtually or in person July 18th. Again, it’s going to be online as well. And there’s lots of other topics from invasive woody plants, to fruit-bearing woody plants, to all kinds of good topics on the program.

I’m very glad to connect because as I said, it’s just been trickling into my brain and it was time for me to start learning more about it, to dig a little deeper. So far, my tree’s looking happy, but you never know;  you never know.

Beth: So Margaret, I also want to give people a little bit of good news as well. We are just implementing research projects. I have the pleasure to work with Dr. Andrew Loyd and Dr. Matt Borden, also plant pathologists, but we are just launching into some forest-level research, looking at combining injections with removing some competing trees in two locations in Pennsylvania and in Rhode Island. So stay tuned. I’m not saying we have the answer, but we’re trying.

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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 15th year in March 2024. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the June 30, 2025 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify (and browse my archive of podcasts here).