3 Lake Minnetonka bays to get a dose of invasive-weed killer

Sometime this week, when the water temperature reaches 53 degrees, two invasive plant species in Lake Minnetonka will encounter a nasty surprise: herbicides.

The Lake Minnetonka Association now has the plan, permits and funding to treat three of the lake's bays with two liquid herbicides meant to control Eurasian water milfoil and curly-leaf pondweed.

The plants -- milfoil in particular -- are the bane of many a boater's existence. "Those weeds get so thick they practically stop the engine," said Wally Krake, who has lived on the lake for 10 years.

The project is the most expansive chemical treatment on the lake in decades. And it's possible because lakeshore owners ponied up.

Treating the three bays -- Carman, Grays and Phelps -- could cost between $180,000 and $190,000, said Dick Osgood, the association's president.

The state Department of Natural Resources gave a $25,000 grant, the Lake Minnetonka Conservation District $30,000 and a group of cities $24,000. Lakeshore owners paid the rest.

Once milfoil enters a lake, as it did on Lake Minnetonka in 1987, it can never be eradicated. But experts say the treatments will temporarily reduce the plants, as evidenced by a 2006 test on small portions of the bays.

"Those effects have not been as well-documented," said Chip Welling, the DNR's milfoil expert. "So the monitoring [the U.S. Army Corps of Engineers] will be doing after the treatments will help us determine whether these are realistic goals."

Since 1989, the Lake Minnetonka Conservation District has run a milfoil harvesting program. People on large floating harvesters spend the summer pulling mats of milfoil from 500 acres of the lake. But that will be suspended this year in the three bays being treated with herbicides.

There are trade-offs to both approaches, Welling said. Herbicides are effective over large areas, are selective and might control the invasive species for longer.

Mechanical harvesting's effects are immediate, more effective in cutting through channels and can be done without a permit from the DNR.

Often, lakeshore residents resist using chemicals on the lake. For example, homeowners on Christmas Lake, which has a great deal of milfoil, debated whether to treat the lake with herbicides.

The Lake Vegetation Management Plan (online at www.startribune.com/a4339) guides eradication efforts. It calls for five years of chemical treatments.

"The first two or three years are the most expensive and most extensive," Osgood said. "After that, we'll be doing more maintenance -- spot treatments that are smaller in scale."

How effective the treatments will be and how long the results will last are not certain, Welling said.

"These treatments are expensive, and they're not something that you do once and solve the problem," he said. "It remains to be seen how much money people on the lake will be willing to contribute long-term."