Summer Tree Diseases to Watch for

Chelsi Abbott, technical advisor for the Davey Institute, talks about common tree disease, how you can spot them and what can be done to treat them. 
 
In this episode we cover:

• Fire blight (0:33) 
• Vascular welt diseases (2:27)
• Apple scab (4:28)
• Anthracnose (5:58)
• Tar spot (7:30)
• Breeding diseases out (9:35)
• How far spores can spread (10:25)
• Dutch elm disease (11:42)
• How Chelsi came to study plant pathology (12:48)
• Beech leaf disease (14:25)
• Trees Chelsi suggests planting in the future (14:57)
• What Chelsi enjoys about her job (18:13)

To find your local Davey office, check out our find a local office page to search by zip code.

To learn more about fire blight, apple scab and anthracnose, read our blog, How to Spot, Identify and Combat Leaf Disease on Trees.
To learn more about the right time to prune, read our blog, Can You Prune or Cut Tree Limbs in Summer?
To learn more about tar spots, read our blog, Why are There Brown or Black Spots on My Maple Leaves?

Connect with Davey Tree on social media:
Twitter: @DaveyTree
Facebook: @DaveyTree
Instagram: @daveytree
YouTube: The Davey Tree Expert Company
LinkedIn: The Davey Tree Expert Company

Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!

Transcript

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Doug Oster: Welcome to the Davey Tree Expert Company's Podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborist share advice on seasonal tree care, how to make your trees thrive, arborist's favorite trees and much, much more. Tune in every Thursday to learn more because here at the Talking Trees podcast, we know trees are the answer.

This week, I'm joined again by Chelsi Abbott. She's a technical adviser and education specialist for the Davie Institute. She's based in Chicago, and today we're talking all about diseases. The first one I want to talk about, Chelsea, is something called fire blight because that sounds really bad to me.

Chelsi Abbott: It is really bad. Your assumption is correct.

Doug: What is fire blight? What kind of trees are affected by fire blight?

Chelsea: Fire blight, first of all, it's actually caused by a bacteria. It's a bacterial infection mostly getting on trees in the ornamental family, so things like crab apples, serviceberries, pears, those kinds of things.

Doug: What does it look like?

Chelsea: The name is very apt. That's one thing you should know about scientists who were not very creative. It's called fire blight because it does look like the trees have gone through a little bit of a fire. They look burnt, they have a very blackened appearance. Then the branches will actually start to curl and cup over.

Doug: Is there hope for a tree that has fire blight?

Chelsea: There is, just depends on how much fire blight it has. Usually, what I recommend is pruning it out. Then they'll have to be some treatments. You'll definitely need to consult an arborist when dealing with fire blight.

Doug: Yes, if you see something that looks like that on your tree, call an arborist right away from Davey Tree, have them come take a look at it, and then we can go from there. There's never any way to really deal with a disease like that, unless you have somebody on the ground. Right?

Chelsea: Yes, it's going to require a couple years usually to get under management if even possible. Like I said, sometimes when we have to prune it out, it's almost too infected that we would be losing quite a large amount of trees which are large amount of the tree. It almost might be more detrimental just deal with it that way.

Doug: This time of the year, what kind of other things are we looking at as far as diseases on trees?

Chelsea: This time of year, you'll start to see symptoms, mostly of the vascular wilts. Now vascular wilts usually are fungal. I would say the most popular well well-known ones would be like Dutch elm disease and oak wilt. The reason why you see the symptoms from those diseases is because they are inside the vascular system. They're kind of clogging it. When there's drought, it makes those symptoms worse and that's when they sort of show up.

That looks very much like orange bronzy foliage up in the canopy, one branch here and there. It's actually a symptom we call flagging because it looks like a little orange flag is stuck into the tree.

Doug: You don't have to tell me about oak wilt because I've been affected by it in my property and we're working on it.

Chelsea: Oh, yes.

Doug: When you have an entire forest of oak trees, there's only so much you can do.

Chelsea: Yes, just like fire blight, the vascular wilts like oak wilt and Dutch elm disease, they need a pretty quick response and you do need an arborist with that one as well.

Doug: Dutch elm disease, now that's been around for a long, long time, right? Is it the same with oak wilt? Has it been around for a long time too, or?

Chelsea: Oak wilt's been around for a long time as well. They don't really know where oak wilt came from. It just kind of showed up. They assume that it's an invasive but they don't know where. The really big thing with Dutch elm disease versus oak wilt is they're pretty regional. They mostly just get around via the route graph, so tree to tree. They will actually sort of mesh their root systems elm to elm, oak to oak. Also, they get around by little beetles flying around, which is why you've probably heard the recommendation not to prune elms or oaks during the summer months because we're really trying to mitigate the transfer of that fungus.

Doug: Since we're talking about my property, now let's go to crab apples.

Chelsea: Yes, crab apples those lovely guys.

Doug: For me, it's, oh, it just went out of my head. What happens to crab apples, or apple scab, apple scab?

Chelsea: Oh, yes. I was about to say plenty. Plenty happens to them. Yes, the major one is a fungal foliar disease. We've talked about a bacteria. We've talked about a fungus that gets inside the vascular system with oak wilt and Dutch elm disease. Now we can talk about apple scab which is only attacking the leaves and then the fruit of the crab apple. That's more of an external sort of pathogen and treatment is still required, but it's not as aggressive as some of our vascular pathogens like fire blight or oak wilt.

Doug: With my crab apple, it always depends on the season as to how it's affected. If you have a really wet cool season, it will defoliate the plant.

Chelsea: Oh, yes.

Doug: If it's not too bad, then I'll lose a few leaves and the tree will look okay.

Chelsea: I always tell everyone, anybody that I'm teaching about diseases or anything like that, fungi love moisture. They like it when it's nice and cool and humid. If we get some rain going on, it's the perfect condition. If we ever really dry spring, which I'm not sure if you had, but we definitely did not have a dry spring here in Chicago, but if we did, we don't tend to see a lot of our foliar diseases. This year was very rainy for us. We're getting sometimes even diseases we haven't seen, like anthracnose come out of the woodworks because it was just super rainy.

Doug: Tell me about that one. What does that affect, and what does it look like?

Chelsea: Anthracnose is another foliar fungal disease. It gets on quite a few different hosts. Most commonly would be things like oaks. There's an anthracnose for maples, there's an anthracnose for ash, they're all very host-specific, but it can get on quite a few different hosts. The major one that we're concerned about are sycamores and dogwoods, though, because they could actually do quite a bit of damage because they also cause a bit of a canker.

What they look like the leaf spots because foliar fungal diseases cause leaf spots are sort of around the margin or the edge of the leaf and then they create a V pattern into the midrib or the middle vein of the leaf. Then they can also cause cankering, which are like wounds on the branches that can cause the tree to die back.

Doug: Each different species would be treated differently. Is that correct?

Chelsea: Yes. Unless it's been a super rainy year, and the tree has otherwise been stressed out by many things, we usually only recommend management on sycamores and dogwoods. They would both be managed once managed through a fungal or fungicide injection. One of them is managed by a contact or a fungicide that we spray on the leaves.

Doug: What else is on your mind when you're thinking about summer diseases for trees?

Chelsea: Especially if you're in the Midwest, we are coming up on our what I call the late season as foliar diseases, things like or oak blight, tar spot, which I would say is the most common one people will see because they're big black spots, usually on maples. Those will start to show up in the next couple of weeks or so. It's important to keep in mind that those late season diseases like tar spot and bur oak blight, they can weaken the tree. However, they're a lot less harmful than our early season ones because really the trees defoliating a little bit sooner than it normally would have.

Doug: We've touched on it a little bit about what to do if you have a problem like this. I guess it's just call your certified arborist, your Davey certified arborist, and you've got to see it. Tar spot, you're going to know what tar spot is, but still, you need an expert there to see how bad the tar spot is to see if you do need treatment. It's just important if somebody knows what they're doing to look at these trees in person.

Chelsea: Oh, yes, absolutely. There are a couple of things as a homeowner, that can help some of these management. We'll come in as professionals with the chemicals, but especially if we're talking foliar diseases, so things like tar spot or apple scab, we do usually recommend to clean up the leaves underneath the tree because that's where these diseases will overwinter. It can perpetuate them but it will have a very small effect but it might help, especially in years where we're having really large amounts of infections.

We can also recommend pruning the canopy to increase airflow, so that will therefore reduce the amount of humidity inside there which can again, exasperate diseases. There's a couple of cultural things that we can do to pair up with the chemical management.

Doug: Like in the case of a crab apple, if I'm thinking about putting a new one in, is part of the newer breeding trying to breed disease out?

Chelsea: Yes, there are a couple, I would think commercially available cultivars of crab apples that have some tolerance or resistance to apple scab. The thing with that though, is that it's never foolproof. We don't have anything that's 100% resistant to a lot of these diseases. Like you said, it's going to be pretty weather-dependent, but usually, we are trying to offer cultivars that don't have this. For example, they came in with the London plane trees because of the sycamore anthracnose, but the tolerance wear off and now the London plane trees are getting anthracnose. It's a forever battle, for sure.

Doug: In my case, for my dogwoods, it's not a big stand of dogwoods, it's one here, one there. I'm hoping that that's going to be a positive for me because I love my dogwoods and I don't want them to get that disease.

Chelsea: Unfortunately, spores can travel pretty far. It's a cool fungal disease mostly because if you're a burgeoning diagnostician, it's impossible to get wrong. It's called rust. I was using it as an example to explain to people how far spores can travel. This disease, they thought, "We'll eradicate it by removing all of this host," but then they found out that the spores of this rust could actually fly up from Mexico. Spores can really get around. They travel through wind and rain splash, and since they're so micro, they're just teeny tiny, they can get blown pretty far distances.

Doug: Well, there goes that theory.

Chelsea: That's why we always recommend not to plant monocultures. If you've got one here or there, then that tree will be infected, unfortunately, but if it does go down, then at least it's just 1 versus 10 trees.

Doug: I wanted to ask you about Dutch elm disease. Has there been any progress made on like an elm that would be resistant? Where are we with that?

Chelsea: Again, not anything that's commercially available, but I have read here and there that there are some-- A lot of research obviously is going into this. I don't have anything concrete, but I have talked to people who say that they're working on it.

Doug: Just like the chestnut tree.

Chelsea: Exactly. We're still working on it. It's a slow science.

Doug: Sure. You can imagine, it's not like a tomato where every season you could-- With a tree, you have to wait years to see if it's affected by the disease.

Chelsea: No, that's the number one thing where it takes 10 to 15 years sometimes to actually get results from using any kind of study with trees because you have to wait until they mature. That's like three or four different graduate students, too. It's quite turned over.

Doug: Tell me a little bit about how you got into this?

Chelsea: Into my job?

Doug: Into your obvious love of science and these diseases. When you say, "It's a really cool disease," that's somebody who's really into it.

Chelsea: Yes. I am a plant pathologist by training. That's what I have my advanced degree in. I would say I'm a gigantic nerd for fungi and bacteria, for sure. Actually, I always loved plants. Ever since I was little, I knew I wanted to work with them, but I didn't quite know what. When I was looking into graduate school, I read a bunch of papers and a bunch of different botany-centric disciplines, and plant pathology was the only one that didn't put me to sleep because graduate school is a lot of reading papers. I was like, "Well, that seems like the best shot for me."

Doug: Are other diseases that you're studying and thinking about have been here already or are there things that were worried about in the future, there are things that can come from other places? What are you thinking about from a scientific angle?

Chelsea: I'm always looking out for new oak diseases, mostly because, unfortunately, we're dealing with in North America, something called oak decline, which is all of the oaks are really struggling from a combination of environmental and second disease issues. I'm really always looking for the new thing, to jump onto them. There's also a lot of other ones that are cool, but I don't know what the likelihood is that they get established here. The beech leaf disease is something that I've always gotten my ear to because at this time, we don't fully understand it, so it's like watching pathology happen in real time.

We think it's caused by a nematode, which is a tiny little microscopic worm, but we're not 100% sure because we don't know how it gets there, how it spreads from beech to beech. That's something that I'm just, as a plant pathologist, I'm a little bit nerdy about even though it's bad because it's causing a lot of damage.

Doug: Try and make me feel better about this because, listen, let me just lay out this to you. Oak decline, where I'm at, we've lost all our ash trees. I look back into history and the chestnut is gone, most of our elms are gone. Make me feel better.

Chelsea: The oaks, it's an arrow to the heart on that one because who doesn't love a beautiful stately oak? A thing that I always often at times tell people is, it is natural for things to perish. Usually, what I like to do instead of talking about the tree that's in clear stages of decline, is I like to think about, what can we plant in the future. I can't make you feel better about the oaks declining, but I can tell you what to put there instead. [laughs]

Doug: Let me hear it.

Chelsea: Depending on where you're at, usually, if you're going to plant an oak, I tend to recommend to plant oaks that are from a little bit more southern location than what you're currently at, because unfortunately, that's where the weather is going to, or you can plant something that's just in generally not common in your area. I would say take a look around, see what the monocultures are, and try not to plant any of those things.

Doug: As I'm losing my oaks, what I'm trying to do, and you tell me if I'm right or wrong, I'm looking basically mostly native trees. I'm in the Mid-Atlantic region, Pittsburgh specifically, so it's American horn beam sourwood. In the forest itself, there's sassafras, there's hickory, but I want more diversity because it was, and still is, mostly oaks, but we're hoping that just a driveway will be the thing that's going to stop the roots from reaching each other, but who knows, the beetle could-

Chelsea: There could be a storm then the beetle visits that. Absolutely.

Doug: That's what I'm trying to do.

Chelsea: Again, with diseases in particular, unfortunately, there's no hacks that you can really do. That's why I do recommend just calling someone onto your site, getting a handle on what's going on, but then also asking them, "Hey, what's our plan moving forward if this tree does go? What would you recommend?" Typically, they will have a good handle on what they've seen doing well and maybe something that's not-- Typically, arborists don't recommend things that are super planted because they don't want to create our own monocultures. That's what I would always ask, always ask what's the next step, which is usually planting something fun and new.

Doug: I'm basically keeping Davey in business with my forest of oaks and hemlocks, hemlock woolly adelgid. It's one thing after another, but like you said, this is part of an evolution of how things go, and we'll see how it all plays out. Tell me, before I let you go, what you enjoy most about your job?

Chelsea: Oh, educating, 100%. I'm huge into not only educating arborists, which is part of my job, but I love educating people who just own trees who don't have a background in science. Anyone who owns a tree, they're interested in it, and they love to learn about it. They love to learn how to care for it, what to do. They're usually a very engaged audience. It's really all about educating anybody and everybody.

Doug: Well, I was educated, our listeners were educated.

Chelsea: Cool. Then I'm done for today.

Doug: Thank you, Chelsea. Thanks again for visiting with me. I always love talking to you and learn something every time. Thanks again.

Chelsea: Absolutely. Thank you for having me.

Doug: I learned a lot there. I hope you enjoyed hearing from Chelsea as much as I did. Now, tune in every Thursday to the Talking Trees podcast from the Davey Tree expert company. I am your host, Doug Oster. Do me a favor, subscribe to the podcast so that you'll never miss a show. Next week, we're diving deep into summer lawn care. Our expert has lots of tips for getting your grass to look great. As always, we'd like to remind you on the Talking Trees podcast, trees are the answer.

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