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Scientists say there's still time to save Minnesota from invasive wetland plant

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Frost covers common reeds (phragmites australis).
Phragmites, a fast-growing invasive grass, is spreading across Minnesota in wetlands and along lakes and rivers. Pictured here are frost-covered phragmites australis in a wetland in Hede-Bazouges, France.
Damien Meyer | AFP | Getty Images 2017

An invasive grass is spreading in wetlands across Minnesota, but scientists at the Minnesota Aquatic Invasive Species Research Center say there's still time to stop it in its tracks.

They want the state to get serious about invasive phragmites, an invasive strain of a native wetland grass that grows faster, taller and thicker than its native cousin.

"Invasive phragmites is sort of like native phragmites on steroids," said University of Minnesota professor Dan Larkin, a MAISRC scientist who studies aquatic ecology. 

Phragmites — which rhymes with Aphrodite's — can have a significant impact on wetlands if it spreads unchecked.   "For example, in coastal marsh systems over time, it can turn a wetland with a lot of good hydrologic connectivity into something that's more like a meadow," Larkin said. "It can really engineer the ecosystem."

MAISRC spent 18 months searching for phragmites in Minnesota, using field trips and crowd sourcing to identify about 400 populations of the invasive species across the state.The plant is already becoming a problem along the St. Louis River estuary near Duluth and in some wetlands around the Twin Cities, Larkin said. 

But most of the phragmites populations across the state are small — so far. 

"That's the stage at which control can be effective," Larkin said.

And that's why Larkin and his colleagues are urging a state committee to take action.

"We see this as a window of opportunity where we can target populations at this stage and nip them in the bud before they get much larger and we see the really negative ecological impacts that have happened elsewhere," Larkin said. 

Invasive phragmites is now classified as a restricted noxious weed in Minnesota, meaning it can't be sold in or imported to the state. 

MAISRC is petitioning Minnesota's Noxious Weed Advisory Committee to review that status and reclassify the fast-growing grass as a prohibited species. Once a species is deemed prohibited, it requires the state to pursue efforts to control or eradicate the plant. 

The committee advises the state agriculture commissioner on invasive plant species and regulated weeds. The Minnesota Department of Agriculture identifies 23 prohibited species on its noxious weed list. Fourteen of those species — including Palmer amaranth and Oriental bittersweet — are identified as those that must be eradicated, and nine of them — including the wild parsnip and the Canada thistle — are identified as species that must be controlled. 

The Noxious Weed Advisory Committee voted to put phragmites in its prohibited-control category in 2017. But Tom Landwehr, then-commissioner of the Department of Natural Resources, appealed that decision. He argued that while phragmites is invasive and a threat to wetlands, the state didn't have enough information about how widespread the invasive grass is. 

Because of DNR opposition, the state ag department decided not to list invasive phragmites as a prohibited species. 

MAISRC researchers have now collected data in an attempt to address those concerns. The DNR has reviewed the new information, but Heidi Wolf, who runs the agency's invasive species program, said it is not yet taking a position on whether phragmites should be prohibited.

Researchers found that 17 of Minnesota's 280 wastewater treatment facilities plant non-native phragmites in wastewater ponds. Because the grass grows so quickly and uses so much water, it's planted to separate wastewater solids from liquid. 

Larkin said it was once thought the plants did not spread easily by seed, and would be safe in contained ponds. But phragmites has proven otherwise, and the invasive has escaped wastewater plants. 

And like many invasives, phragmites is adaptable to human-caused changes in the environment.

"More salt, more nitrogen, more phosphorus," Larkin said. "It's really well-adapted to exploit those changes, and so where a lot of our native wetland flora might be harmed or not be able to benefit from the increases in nutrients, non native phragmites can take those resources and run with them, and grow really well."

MAISRC researchers are now assessing potential control methods — including herbicide applications and well-timed mowing — that could be used in various parts of the state, Larkin said.

"This is not a lost cause," he said. "We think this could be a real opportunity to do something positive with an invasive species."

The state Noxious Weed Advisory Committee meets Wednesday.