The battle to protect Minnesota lakes from invasive species just got more complicated after researchers on Lake Minnetonka discovered that a certain kind of watermilfoil is more resistant to herbicide treatments and becoming more abundant.
In a study using cutting-edge genetic screening techniques, researchers found that hybrid watermilfoil — a cross between the invasive Eurasian watermilfoil and Minnesota's native northern watermilfoil — is actually more dense in areas treated with herbicides.
The study results, released Wednesday, show that the hybrid plant has more tolerance to treatments like herbicide that kill off Eurasian milfoil, and is more abundant in Lake Minnetonka than expected.
"It's another thing we need to be concerned about, but now we can get a handle on it," said Ray Newman, fisheries professor at the University of Minnesota.
Swimmers and boaters likely are very familiar with milfoil, which forms thick mats of vegetation and was discovered in Lake Minnetonka in 1987.
Since then it's spread across the state, altering ecosystems by displacing native plants. It can be controlled by herbicides or mechanically by a harvester or cutter.
"Some lakes haven't been seeing success and don't know why," said Eric Fieldseth, the Minnehaha Creek Watershed District's aquatic invasive species program manager. "You may have to vary your treatment depending on what you have."
The study, which was done by the U, the watershed district and Montana State University, is one of the first in-depth examinations in Minnesota of hybrid watermilfoil.
Researchers now plan to expand the study.
Funded by $35,000 from Hennepin County, the 2015 and 2016 tests were done on Minnetonka and Christmas Lake.
"It's an eye-opener to folks," Fieldseth said.
Researchers say it shows that groups fighting the spread of invasive species need to know the plants' genetic makeup. It may not be a "one-size-fits-all" approach. The study found that there are multiple genotypes of watermilfoil.
"Hopefully, it helps folks manage [invasive species] more efficiently and sustainably and have better results," Fieldseth said.
Lake Minnetonka, the epicenter for boating in the Twin Cities, has become a hub of new research on aquatic invasive species.
Another county-funded study last summer used low doses of a copper-based pesticide to kill off zebra mussel larvae (called veligers), the first study of its kind in the state or nation. And U researchers, along with a marina owner and boat manufacturer, are looking at how boat designs could reduce the amount of water left on boats, such as live wells.