2DIG2004_Wisconsin_Gardener_Dutch_Elm_Disease Transcript

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- The streets of most American cities used to be lined with gorgeous elm trees providing a lot of beautiful shade. Well, that's a thing of the past. I'm with UW-Extension Plant Pathologist Brian Huddleston to talk about why that's a thing of the past.

- Yeah, again, like you said, we used to have a lot of elm trees along the streets of America. And unfortunately, there was a fungal disease that came in. And, basically, it has killed most of the elms, certainly, in the eastern United States and certainly, here in the Madison area in Wisconsin, so...

- Decimated is a good word to use.

- Decimated is a great word to use for that. It's what's called a vascular wilt disease, which is some of the toughest ones to deal with. From a control standpoint, the fungus actually enters in, typically, into a tree through bark beetles that bring in the fungus. That colonizes the water-conducting tissue that's called the vascular tissue in the tree, and it blocks it off. So, any point above that, that point on the tree, will not get water from the root system.

- So, and vascular... You have an example that of the water being blocked off.

- Right, the water-conducting tissues run underneath the bark. And when this fungus infects the trees, it will cause a browning of that particular tissue. That's what I use as a visual cue when I'm doing a diagnostic in my clinic.

- Shelley: Well, where does Dutch elm come from? I mean, I think "Dutch" is the key word right there.

- Right. And that's more from the fact that it arrived in Europe before it arrived in the United States. And there was a lot of initial work that was done by the Dutch on the disease, but the fungus actually originates, people think, in Asia. And if you look at where there's resistance to the disease, it tends to be in Asiatic species of elms.

- Shelley: And this hit our American elms about when?

- Around the 1920s here in the United States, a little bit later here in Wisconsin because it took some time to travel from the East Coast into the middle part of the country.

- Well, we are walking along one of the many bike paths in Madison because there's some really good examples of this disease.

- That's right. People don't think there are a lot of elms left, but there are actually a lot of volunteers that have grown elm. And there's certainly a lot along this bike path. And some of the symptoms I've been seeing in the trees around here, the elm trees is flagging, which is an initial symptom where you tend to see individual branches start to die back usually...

- Shelley: So out at the outer edges like...

- Brian: Yeah, usually from the tip back, down towards the trunk. And oftentimes, that's where the bark beetles will enter into the tissue. They'll do some feeding, drop off the fungus there, and then it colonizes back into the main trunk. It'll eventually move down into the root system, colonize the entire tree, and then it'll do what it's done here which is kill the entire tree.

- Shelley: So when we see a tree in... Well, okay, when we see a tree that has flagging,

- Right.

- is there anything we can do to stop it at that point?

- Brian: Usually, at that point, it's a lost cause because...

- Really, even that early?

- Brian: Right, when you're seeing those visual cues, that usually means that the fungus is not only in the branch that you're looking at, but also way down in the trunk, which means that there's no real way to treat the tree. So we usually recommend removal in that particular case.

- Shelley: So there's no cure, basically.

- No cure. There are some preventative treatments. If you have, for example, a really nice showcase elm in your front yard that you want to try to protect, there are fungicide treatments that you would inject into the base of the tree.

- As a preventative.

- As a preventative. It helps prevent the tree

- Okay.

- from becoming infected. And these are not easy treatments to do. So you really need to get a certified arborist to come and do that.

- Okay.

- Once you have a symptomatic tree, it's an issue of removal. And if you have a cluster of trees, you've gotta be very careful to break what are called "root grafts." It's where the roots of various trees have fused together underground because the fungus can move from tree to tree that way.

- Shelley: So that tree's a hazard.

- That is a hazard, both from potentially moving to other elms in the area underground and also the insects that can move the fungus around, could revisit that tree, pick up the fungus, and then move on to other elms.

- Shelley: Okay. I mean, it's an inoculate right now. Basically, it can spread it even though it's deader than a doornail.

- That's right.

- Now, I live along a bike path as well. And on the bike path property are three trees with no bark whatsoever and their elms.

- Okay.

- Are they a hazard?

- I wouldn't worry about those because once the trees debark, lose their bark, then I would not expect the Dutch elm disease fungus to be active at that point.

- So they're just dead and ugly, but they're not something I'm gonna have to panic about.

- No, and actually, I would check around the base of those for morels because oftentimes you'd find morels growing at the base of dead elm trees.

- Okay, so they might be worth keeping around for a little while.

- Yes, for a little while.

- What about planting elm trees that are resistant?

- Definitely, that's an option. There are some very resistant varieties that are hybrids between American elms and Asiatic species of elms. They usually don't have the real nice vase form of an American...

- That beautiful shape, yeah.

- Yeah, they're more like a typical tree, but there are also true American elms that have been bred for resistance. There's an Independence elm, an American Liberty elm, a Valley Forge elm, the Princeton elm. There are several varieties that are available. I wouldn't grow a lot of those because even those elms, although they're resistant, they aren't immune which means they can get the disease.

- Shelley: So, take good care of them, maybe use the preventative treatment, and make sure they're not stressed because that just helps their resistance.

- That's right. And just make sure you're only planting one here or there, don't do a monoculture, like we used to, along our streets where it was all the same tree.

- Shelley: Which is why Elm Street no longer has any elms.

- Brian: That's true.

- Shelley: Okay, thanks, Brian.

- Brian: You're welcome. 

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