Aquatic Herbicides Are Only Effective Weapon Against Milfoil Plants

Published October 1, 2009

“It’s been a bad year for milfoil on Minnesota lakes—except on Grays Bay and Phelps Bay on Lake Minnetonka,” KSTP Eyewitness News 5 in Minneapolis-St. Paul reported recently.

The reason for the Grays Bay and Phelps Bay exceptions? “In May 2008, [a] contractor applied herbicide across the bays. Now more than a year later, the results are promising.”

“So far this year, they seem to have good control” of the milfoil in the areas that were sprayed, Minnesota’s Aquatic Invasive Species Coordinator Chip Welling told KSTP. “You can find one or two plants, but basically it’s gone. This is exactly what we’ve been trying to accomplish.”

Environmental Devastation

Eurasian milfoil, often used as a decorative plant in freshwater aquariums, is not native to North America. Once released into the environment, it aggressively takes over ponds, lakes, and slow-moving rivers and streams, forming a dense mat of vegetation that chokes out native plant and animal life.

Infestations often become so severe that fish die off, swimming becomes impossible, and a rancid odor of rotting vegetation permeates the surrounding air.

Effective Control

Environmental activist groups often oppose the use of aquatic herbicides to treat the aggressive milfoil, fearing the chemical will harm native plants and aquatic animals along with the milfoil.

In community after community, however, residents report aquatic herbicides effectively target only the aggressive milfoil while doing no harm to other plants and animals.

Massachusetts, Idaho Successes

In the Idaho resort community at Lake Coeur d’Alene, state officials recently noticed areas of milfoil infestation in some of the lakes and streams that feed the lake. The early results of aquatic herbicide treatment have been promising.

Massachusetts residents report similar results.

Sandra Brennan has lived on the North Pond shore of Lake Cochituate, in the greater Boston area, for more than 20 years, but in recent years she has been unable to swim in the lake because of the milfoil infestation. In June of this year, local communities contracted with a private company to treat the lake with aquatic herbicides. By July, nearly all the milfoil was gone, while native plants and animals remained unaffected.

“Within a few days the [milfoil] died and fell to the bottom,” Brennan told The MetroWest Daily News.

Brennan reports the native species of plants and animals are not only unharmed by the aquatic herbicide treatment but are actively thriving now that they have their natural environment back.

Even the fishing in the lake has improved, according to local resident Linwood Bradford, the article reported.

Alternatives Ineffective

Communities that have listened to environmental activist groups and tried more expensive treatment methods, such as hand pulling or mechanically harvesting milfoil, have been much less successful at battling the invasive weed.

The Maine Department of Environmental Protection hired divers last year to pull milfoil from Salmon Lake, but they report more than twice as much milfoil this year.

“We’re finding more plants on each dive,” John McPhedran, invasive aquatic plants specialist for the Maine DEP, told the Kennebec Morning Sentinel. “As a staff, we feel we need to apply herbicide to the cove in order to achieve our goal, to prevent the plant from spreading. We’re not going to get it with mechanical control.”

Competing Strategies

In upstate New York, the Finger Lakes communities of Cazenovia and Skaneateles are also battling milfoil infestations, but they’re using competing approaches. Cazenovia is using aquatic herbicides while Skaneateles has hired divers to pull the weeds by hand.

Aquatic herbicides will cost Cazenovia $450,000, versus an estimated $17 million to pull the weeds by hand. After Cazenovia Lake was treated with herbicides in June, residents resumed normal lake activities by early July. In Skaneateles Lake, it will likely take four years to remove the milfoil by hand.

“Early treatment with aquatic herbicides has time and again proven to be an effective and economical means of combating invasive milfoil,” said Jim Skillen, manager of formulator issues for Responsible Industry for a Sound Environment.

“Just as important as the economical benefits, the Environmental Protection Agency has determined that properly applied aquatic herbicides are safe for humans and the environment,” Skillen added.

James M. Taylor ([email protected]) is a senior fellow of The Heartland Institute and managing editor of Environment & Climate News.