New Weeds from the South

New Weeds from the South

Part of Ep. 2104 Climate Change for Gardeners

Climate change means new and stronger weeds. University of Wisconsin-Extension weed specialist Mark Renz shows how climate change will turn some of our existing weeds such as Canada thistle into super weeds. Plus, a look at some new weed threats from the south.

Premiere date: May 22, 2013

TRANSCRIPT+
Wisc Gardener Transcript: 

Shelley Ryan:

We are at the UW-Madison Arboretum probably not in one of their favorite spots because we are surrounded by Canada thistle. I am with Extension Weed Specialist Mark Renz to talk about Canada thistle, and why it seems to be one of the few things that's happy about climate change.

 

Mark Renz:

This plant is really truly a unique plant. Not many people get excited about weeds but I'm one of them.

 

Shelley Ryan:

Yeah, this is not thrilling me here!

 

Mark Renz:

This plant is one of the few plants we have a lot of information about how climate change has already affected it and probably will affect it in the future. Research shows what's really unique about this plant, and has documented that as CO2 levels increase we're getting more above ground and below ground growth. More shoots and roots.

 

Shelley Ryan:

Oh, goody.

 

Mark Renz:

So, that's really the problem. In addition, that research has looked at management and it looks like that's going to become more difficult because of more shoots and more root growth.

 

Shelley Ryan:

Standard practice is Roundup, for many people because this is a real bear to get rid of.

 

Mark Renz:

Actually, that's what the research evaluated was the use of glyphosate, the active ingredient in Roundup. What they found is that it was less effective at controlling the plant. It killed the same amount of root tissue it typically would. There was just so much more root tissue.

 

Shelley Ryan:

So, more of the plant, less effective. What does that do for organic gardeners who are trying to, I assume, just pull it?

 

Mark Renz:

They're left with pulling, mechanical management, physical management, mowing. It's really difficult, really a struggle. A lot of our organic growers, and I know of one or two that have actually gone out of business because Canada thistle is so difficult to manage. We don't recommend composting it, which many of them try to do because this perennial root that we're holding in our hands can actually resprout and reroot and cause an invasion in that population to exist. Really a difficult plant to manage. We know it's a problem in urban areas as well as Ag lands, and also natural areas like this. It's really a problem.

 

Shelley Ryan:

Just about everywhere. Are there other weeds that are happy about climate change?

 

Mark Renz:

A lot of our weeds, unfortunately are gonna probably do better from climate change. Two that I'd like to highlight would be garlic mustard and wild parsnip. Recently, we've had an early warm up in the spring some really erratic behavior. It seems like garlic mustard really took advantage of that. Populations just blossomed this year. It's really dominant in the south, and spreading north. It's probably going to spread even farther to the north. We're seeing it in full sun habitats where we haven't seen it in those areas in the past.

 

Shelley Ryan:

Right, it used to be shade mostly.

 

Mark Renz:

Wild parsnip is another one that's spreading rapidly in the east and the north. We know this from the south, and need to be on the lookout. Those are probably going to be players in the future.

 

Shelley Ryan:

What about buckthorn? That's one that's a pain for me.

 

Mark Renz:

Buckthorn, I kind of say we've already lost the war.

 

Shelley Ryan:

Great.

 

Mark Renz:

It really has these huge massive thickets. A couple areas are relatively free of buckthorn but that one really does well in our environment. It's up north of us, and to the south of us. It's going to continue to really thrive as our climate changes.

 

Shelley Ryan:

You guys are going to have to change your maps entirely because everything's going to spread.

 

Mark Renz:

Right, and that's one of our concerns. In our lab, one of the things we do we do predict a modeling to predict where these spread. One of the big tools we look at is that climate changes, we're going to have to redo all our maps and so that's a lot more work we're going to have to do!

 

Shelley Ryan:

These are weeds that are already here in Wisconsin and most of us are somewhat familiar with some of these. Are there new weeds that we might not even know are coming?

 

Mark Renz:

There's actually two I want to highlight. We're most concerned about the weeds coming from the south. They come in from the north and the south, usually. From the south, the first one we're concerned about is a plant called kudzu, or the plant that ate the south.

 

Shelley Ryan:

I've heard of it, yes.

 

Mark Renz:

It's close to the Wisconsin border, just south of Chicago. We're concerned about it moving in there. It's been documented in Canada as well as to the south of us. It's probably a matter of time before we get that one. We're really actively looking for that plant.

 

Shelley Ryan:

You said two.

 

Mark Renz:

The other one we're concerned about is Japanese stiltgrass. It's an annual grass, like crabgrass in our gardens. But instead of growing in full sun it grows in shady conditions like understories of forests and creates a canopy of just grass in that understory displacing the native plants. Animals don't like it and don't do as well in that habitat. Also, it's changing the soil ecosystem and potentially the fire disturbance regime.

 

Shelley Ryan:

Increase of fires, because of this dried grass as an understory, basically.

 

Mark Renz:

It dries out right about now, and there's much more fuel than would typically be in many of our systems and so we might get forests burning much more frequently.

 

Shelley Ryan:

So, all sorts of problems. What do we do? I mean, I'm hearing gloom and doom. Is there anything we as gardeners and homeowners can do?

 

Mark Renz:

I think there are. I'd like to point out, one, educate yourself.

 

Shelley Ryan:

Okay, know your enemy.

 

Mark Renz:

We have lots of resources in Extension and DNR and others have resources to help with identification.

 

Shelley Ryan:

We'll have a link to your website to help with that.

 

Mark Renz:

That would be wonderful. So know what those are. Then if you think you might see something, tell someone.

 

Shelley Ryan:

Okay, don't keep it a secret.

 

Mark Renz:

Right, a County Agent, someone from DNR some other person that can get the word out so we can go in and try and conduct some management on an early detection basis. If you're wrong, that's okay. We'd rather have that information be wrong than have you not share that information.

 

Shelley Ryan:

Rather than have kudzu be the vine that ate the north. Thanks, Mark. Sure, my pleasure.

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