Two years into a five-year test of herbicides to control Eurasian water milfoil on Lake Minnetonka, results are so encouraging that more shoreline property owners are asking for the chemical treatment in their bays.

After seeing the weed fade away this year on Grays Bay and Phelps Bay, residents of Gideons Bay and St. Albans Bay are trying to raise money for milfoil treatments next summer.

"There's a ton of interest,'' said Dick Osgood, executive director of the Lake Minnetonka Association, which started the weed control program on Grays Bay, Phelps Bay and Carman Bay in 2008, with the approval of the state Department of Natural Resources and the Lake Minnetonka Conservation District.

"Overall, the treatments did reduce Eurasian water milfoil quite effectively,'' said Chip Welling, coordinator of the DNR's program for dealing with aquatic invasive species.

Welling said that the chemical used has been found safe and effective by the federal Environmental Protection Agency. If it is used properly, "we know we can control [milfoil].''

The question is how native plants will bear up under the chemicals and how long the milfoil control will last, he said. "That has a bearing on how much future treatments are going to cost, and that has a bearing on whether people will undertake them or not.''

The U.S. Army Corps of Engineers intends to answer those questions with its continuing study of the chemical application in Lake Minnetonka, Welling said.

So far, corps monitoring shows that while the treatment killed the milfoil, it appeared to have no strong effect on most native plants, although some water lilies died, Welling said. Next summer, the goal will be to prevent that from happening.

A key reason to control milfoil is to promote the growth of native plants that provide habitat for fish and wildlife and improve water quality, Welling said. Water lilies are native plants.

After limited success with the herbicide in 2008, Carman Bay was dropped from the treatment program. In 2009, adjusting for better results, the association switched from a liquid that diluted too rapidly to a granular herbicide that maintained contact with the plants longer, Osgood said. The treatment also focused exclusively on milfoil and not on curly leaf pond weed, as it had the previous year, he said.

Grays Bay and Phelps Bay property owners were so happy with the second-year results that they are "ready to go again next year,'' Osgood said.

Lake Minnetonka has 42 bays. Residents of Gideons Bay and St. Albans Bay are trying to come up with $79,000 and $55,000, respectively, to combat the weeds, which continually heap up on their shoreline.

"It's an eyesore,'' said Gideons Bay homeowner Bob Tenner. "It clogs up the boats. It's bad for other native species. No one wants to swim in it. It's a big chore that takes the fun out of living on the lake.''

The cost of the treatment is hefty, and 65 percent of the money must be raised by shoreline property owners, with the rest coming from the DNR and other government agencies. The costs to individual property owners are determined bay by bay, but most fall in a range of $250 to $1,000 per property per year, Osgood said.

In the first two years, treatment in Grays Bay cost $67,000 and $65,000. Next year it will cost an estimated $56,000. In Phelps, the treatment cost $61,000 in 2009, $60,000 this year, and is estimated at $68,000 next year.

Although the two bays were "milfoil-free'' this summer, controlling milfoil is like controlling dandelions -- "it's a maintenance program'' year after year, Osgood said. But as the water weed is controlled, the cost should drop, he said. "We are expecting that the fifth year should be about 25 percent of the first year's cost, and that will be about maintenance level.''

The chemical used has been formulated to mimic a plant hormone, Osgood said. Plants take it in and "grow themselves to death.''

The EPA has found that it has no measurable effect on animals or humans, breaks down in sunlight and lingers in the water for about 30 days, Osgood said. During that time, however, water from the treated area should not be used to water lawns or gardens. Laurie Blake • 612-673-1711