Visitors to a wetland in summer may encounter a sea of tall plants teeming with soft, purple flowers. They may look pretty, but they could be the invasive purple loosestrife (Lythrum salicaria), an introduced aquatic plant that is harming native wetlands.
Introduced invasive plants, including purple loosestrife, reed canary grass (Phalaris arundinacea), and common reed or phragmites (Phragmites australis), are outcompeting native wetland plants, degrading the ecosystem, and making it difficult for native flora and fauna to thrive. A non-native cattail (Typha sp.), which hybridizes with a native cattail, also is disturbing wetlands.
A recent study showed that invasive plants cover more than 40 percent of randomly selected wetlands in Illinois, according to Thomas J. Benson, research associate professor at the University of Illinois Urbana-Champaign. Benson specializes in habitat management and wildlife ecology.
“Invasive plants often outcompete native species, leading to declines in native plant and animal populations as well as other negative consequences for ecosystems, including change in hydrology and soil composition,” he says.
Phragmites, for example, is really hard on turtles, according to Janice Gilbert, executive director of the Invasive Phragmites Control Centre and a wetland ecologist for the Great Lakes Region. The turtles crawl into a phragmites-laden environment, can’t find their way out, run out of food sources and energy, and then they die, she explains.
Professionals and volunteers are working to lessen the impact of aquatic invasives as part of their wetland restoration projects.
“It’s an uphill battle dealing with these plants,” says Katie Kucera, lead ecologist at the Wetlands Initiative. “It takes a lot of work and can feel a little disheartening,” she admits. “But year after year, we see small wins; we see native species return to the wetlands and coming back to breed. That shows what we’re doing is working.”
The arsenal to combat invasive aquatics includes restoring natural hydrology, performing controlled burns, harvesting the non-natives, introducing insects that eat the plants, targeting specific areas with herbicides and planting native species that thrive in wetlands. “It’s a multi-tiered approach,” Kucera says.
The Wetlands Initiative has been working in the Lake Calumet region to stifle the growth of reed canary grass, phragmites and cattails. That work is restoring sedge meadows and marshes that once thrived there.
The European native reed canary grass, sold to farmers to plant in hay meadows and wet pastures, spreads quickly. “It grows early in the spring, flowering before many native sedges and grasses in wetlands,” Kucera says. “While it primarily grows in wet areas, it can survive dry periods and continue to spread.”
To keep reed canary grass in check, the Wetlands Initiative staff removes seed heads from the invasive plant and also treats it with grass-specific herbicides early in the spring before it has a chance to flower and before other native species emerge. “Using grass-specific herbicide protects native forbs and sedges,” Kucera adds.
Keeping phragmites from overtaking a wetland can be even more daunting.
“Phragmites is likely the single most damaging species in the Calumet region and is still present across the Chicago region, from roadside ditches to disturbed natural areas,” Kucera says. “In certain places where it’s too deep, reed canary grass doesn’t grow well, but phragmites can do it all. It’s along every highway, every road. It creates runners 15 to 20 feet long trying to spread.”
The Phragmites Adaptive Management Framework, coordinated through the Great Lakes Commission, provides resources to managers and supports researchers studying the most effective treatment methods for the plant.
These include installing water-control structures, which the Wetlands Initiative has done in the Calumet region. “That allows us to raise the levels to drown out invasive species, which we can then cut below the water level, or to lower the levels to allow the native seed bank hidden below to emerge,” she explains. Targeted herbiciding also is important in controlling phragmites, and often has to be done for several consecutive years before native species can be planted.
To reduce the amount of hybrid and non-native cattails, the Wetlands Initiative drives along the plants with what’s called a Marsh Master. The cattails get pushed below the water line, which makes it more difficult for them to grow. The Marsh Master reduces the need to herbicide the cattails.
Their work in the Calumet region is returning it to what it was before settlement: a complex of sedge meadows, hemi-marshes and other wetlands. According to Kucera, in the past several years, bird species that once bred at Calumet have returned to nest.
Native bulrushes and sedges planted there are now prospering and providing shelter and food for animals. “We see a lot of amphibians at the Calumet sites,” she adds. “Recently, while planting wetland plugs, we were finding toads and baby frogs everywhere.”
The Wetlands Initiative also actively cuts down purple loosestrife, a European native once sold as an ornamental plant to the U.S. and Canada. The decaying leaves release tannins into the soil, which may harm American toads, which find it difficult to breed in those conditions, Kucera explains.
Purple loosestrife is responding to biological control, an innovative idea in which insects that eat the plant are introduced to the landscape. “Many sites where the biological control beetles are present see a decrease in purple loosestrife,” Kucera confirms.
Recently, the Girl Scouts of Northern Illinois raised and released beetles into a wetland infiltrated by the loosestrife. “I think it’s cool, Girl Scouts are taking an interest in managing ecosystems in this way,” Kucera says, adding that no herbicides are used where beetles have been released.
Where purple loosestrife and other invasive wetland plants such as phragmites are removed, native plants such as rosemallow and swamp milkweed can be planted, depending on the site, she says.
Kucera recommends visiting some of the wetlands that have been restored by removing invasives and introducing more native plants. These include Indian Ridge Marsh Park, located off Torrence Avenue, south of Trumbull Park: and Big Marsh Park, located near the Ford Calumet Environmental Learning Center.
“Seeing a stand of invasive plants like phragmites makes you feel as if you’ve lost something,” Kucera says. On the other hand, she says seeing a thriving wetland teeming with wildlife after removing invasive plants is like finding a lost treasure.
Sheryl DeVore has written six books on science, health and nature, as well as nature, health and environment stories for national and regional publications. She is co-author of an upcoming book, Birds of the Midwest, to be published by Timber Press. Learn more at SherylDeVore.WordPress.com.
SIDEBAR
Lake and Pond Invaders
Managers of open-water lakes and ponds are combating Eurasian watermilfoil (Myriophyllum spicatum), likely introduced through the aquarium trade. It forms thick mats in shallow areas, blocking sunlight and killing aquatic plants needed by underwater species for food and shelter. It also affects recreational activities such as fishing and swimming. Among other techniques, the plant is harvested with special aquatic equipment at places such as the Chicago Botanic Garden.
Hydrilla (Hydrilla verticillata), an invasive aquatic plant, was discovered in waterways in Lake County in 2019 and in DuPage County in 2024. A Hydrilla Task Force has helped keep these invasions at bay. Hydrilla is one of the most aggressive aquatic invasive plants in North America, disrupting fish habitat and water movement, according to the North American Invasive Species Management Association.
How to Help
Boaters and hikers can help stifle the spread of invasive aquatic plants. Check boats, trailers and gear for attached plants before entering the water. Remove mud, debris and aquatic plants from equipment and discard away from water sources. Before hiking trails around wetlands and lakes, clean debris, mud and plants from boots and dispose of them away from water sources.
Volunteer to help remove invasive aquatic plants at local nature preserves. Report sightings of invasive plants and learn about new ones at the Illinois Invasive Species Council.
