Earlier this summer, an invasive species called Japanese Stiltgrass was spotted in Rock County.
Scientists are now asking the public to help prevent the invasive grass from spreading across the state.
Until recently, Stiltgrass had only appeared in Wisconsin once in an isolated infestation in La Crosse County in 2020 that the Department of Natural Resources is still working to eradicate.
Mark Renz is a University of Wisconsin-Madison Extension weed specialist and professor in the Department of Plant and Agroecosystem Sciences. He says the non-native annual grass is newer to Wisconsin, but has been detected in the eastern and southern U.S., including Illinois, for several years.
Renz spoke with Lake Effect’s Xcaret Nuñez about how to identify Japanese Stiltgrass and what to do if you find it.
This interview has been edited for length and clarity.
What's the recent status update on confirmed cases of Japanese Stiltgrass?
We had an initial report in one property just east of Beloit and since then, we've created an alert and asked woodland and forestry owners and people who just frequent these areas to be on the lookout for this invasive annual grass called Japanese Stiltgrass. We've gotten many reports — two of those have turned out to be positive reports of new infestations, one in the southwest part of the state and one in the southeast part of the state. So that's the bad news.
But it's actually good news, because these populations were only about 30 by 30 square feet, so those property owners should be easily able to eradicate those populations before they spread further. And they were found before they were really causing any impact whatsoever in those forests.
For folks who have never heard of Japanese stiltgrass, why is this particular invasive grass a problem? How does it damage forests?
It's kind of an interesting scenario. So I like to use the analogy that this is very similar in many ways to crabgrass in your lawn. It's an annual grass that grows from seed every year and dies. But what's unique about this plant isthat it can grow in shaded environments and shaded conditions underneath forests and on the edges of forests. It also produces a lot more biomass, and that biomass tends to climb on top of other vegetation, suppresses it and dominates the understory. So you get mats of this annual grass.
So we have data that clearly shows that the understory of native plants and wildlife is impacted by having this new species that's not native to our system. But what's even scarier is that biomass that sits there, that mat of annual grass, dries out over winter, and it changes fire frequency, or, more importantly, fire intensity. So it can really cause some dramatic shifts in that ecosystem, potentially causing additional harm to nearby urban environments if it's invaded, and it even changes some of the stuff that's happening below ground and the nutrient relationships.
So it's really impactful. This has been present in the southern part of the US for decades, so we've been on the alert for it for many years, but the best way to prevent this impact is to identify it right when it establishes and get rid of it before it spreads.
How can people identify stiltgrass?
It's really a hard plant to identify, because all grasses look alike, and even trained botanists can struggle with this. I'll preface this by saying you really should look at some of our resources to help you with identification — we have videos and fact sheets.
Essentially what you're looking for is a low-growing grass that has a relatively short leaf, and that leaf has a very distinct midrib that's white in the middle of it. And this grass, if it gets big enough, can actually grow on top of other vegetation, kind of like a vine. If you look at the base of that annual grass, you will see roots that come out as nodes near the ground, but above the ground, and those [nodes] kind of look like stilts, and that's where it gets its name, Japanese stiltgrass.
I understand that stiltgrass also flowers in September. What does it look like when it flowers?
It does not have a showy flower like we typically think of — it has more of a grass-like flower because it's wind-pollinated. Actually, what makes this plant so aggressive is it produces flowers that don't need to be pollinated to produce seed. So it has a special type of flowers that allows it to rapidly produce seeds. So that's our goal with management: If we can prevent seed production, we can win this battle. The good news is we're far enough north that it doesn't start to produce seed until the middle of September, so we can still detect things now, get rid of it before seed is produced, and protect our forests from further spread.
Can this invasive species still be managed or removed after it flowers?
When it’s in the process of flowering… we're usually using techniques where we're trying to collect the flowers so the seed doesn't go back into the soil.
Once that seed is in the soil, we've lost that round of the battle. But usually what we're trying to do is alter our tactics and try to encourage that seed to germinate, and when it germinates, we want to actively control it before it produces flowers and seeds the next year.
The good news is the seed does not persist very long in the soil. Research has shown that anywhere from two to three years is the seed longevity [for Japanese stiltgrass]. So if you have an invaded forest, if you prevent seed production for three consecutive years, you should eradicate that population as long as no seed is coming into that environment from outside sources.
What are some ways that people can help prevent the spread of any invasive species?
There are two pieces of advice that are really simple. Number one: Learn how to identify some of the common invasive species that are in areas that you visit, because knowledge of where they are will then make you aware of how they spread.
The other, probably more important thing, is whenever you go to a site, when you're getting ready to leave that site, just take a moment to clean off any mud or debris on yourself, your vehicle, or your equipment, before going to another location. What we find is 90% of the time it's accidental spread of these populations, not knowingly, because it was contaminated in something else that was delivered.
What to do if you find Japanese stiltgrass
- Take close-up photos of the grass as well as mid-range and zoomed-out photos that show the landscape.
- Write down the location, habitat, size and density of the infestation.
- Contact one of these experts to help confirm identification:
- UW Extension Forestry: email forestry@extension.wisc.edu or call Working Lands Forestry Educator Tony Johnson at 608-386-8900.
- Wisconsin DNR: email invasive.species@wisconsin.gov.
- If the infestation is confirmed, UW Extension Forestry will help you come up with a control plan based on the site details and level of infestation
You can learn more about Japanese stiltgrass by visiting the Renz Weed Science website. You can also stay up to date on the latest status of Japanese stiltgrass in Wisconsin on the UW-Madison Division of Extension website.
