Herbicides Part of Life and Death for R.I. Ponds

By TIM FAULKNER/ecoRI News staff

Why are so many Rhode Island lakes and ponds infested with invasive plants? Boaters and fishermen typically introduce alien plant life as stowaways in water and as fragments on waders, boots and fishing gear, according the state Department of Environmental Management (DEM). Once established, these invasive plants spread, flowing downstream to other bodies of water.

In fact, early 60 percent of the state’s lakes have at least one invasive species, according to DEM.

But the damage is not all caused by visiting fishermen and boaters. Lakes and ponds without public access also take in fast-growing plants through birds, wildlife, aquariums, water gardens and landscaping. Arnold Pond in Coventry and Hundred Acre Pond in South Kingstown likely got their infestations of Brazilian elodea from the dumping of an aquarium tank in the pond.

There are several ways to curtail or get rid of invasive plants: hand pulling, harvest wheels, divers using vacuums (suction harvesting), nets and barriers, and herbicides. Installing blankets to block sunlight are expensive but effective for small infestations.

Between 50 to 60 applications for herbicide treatment are approved annually by the DEM for lakes and ponds across the state. Most are requested by a lake association; others by a municipality or individual. Once approved, the applicant hires an outside vendor to apply the chemicals.

Herbicides have both financial and environmental costs. Treatments cost between $300 and $1,000 an acre. Harsh chemicals such as 2,4-D and glyphosate are often used.

The June 17 treatment on some 10 acres of water along the shoreline of Hundred Acre Pond used two types of pesticides: flumioxazin and diquat. It was the third treatment in three years and the fourth in more than a decade. Hundred Acre Pond also lies downstream from turf farms, and fertilizers from the farms are suspected of running into the pond to feed plant life.

Diquat is non-selective, meaning it kills more than the targeted invasive plants. In the confusing world of pesticide databases, diquat is considered an acute toxin by the Pesticide Action Network; the Environmental Protection Agency (EPA) relies on a 1985 report from the Chevron Chemical Co. to offer a mystifying assessment of the chemical. Other groups consider flumioxazin and diquat toxic to mammals and fish.

Kace Quinn, who lives near Hundred Acre Pond, said the first pesticide three years ago coincided with a sharp drop in smallmouth bass, pike and pickerel throughout the pond. "I haven't caught anything besides sunfish in years," he said. "I'm sorry to say that the fishing spots around the pond that my family has been using for generations are completely empty.”

Bass, especially, are having trouble making beds on the shore side, he said. Quinn suspects that pesticides and herbicides have caused the fish to decline. “It's a shame that my kids will never have the same experiences I have had in this cherished location," he said.

Elizaberth Herron, program director for the University of Rhode Island's Watershed Watch, said herbicide treatments have become more regulated and effective since the state began requiring the use of licensed applicators. Certain herbicides destroy some plants better than others, and the timing of the application is important, she said.

“In some cases there aren’t a lot other methods available,” Herron said. “You don’t want to be use herbicides in every lake all the time but in certain cases they can be very effective.”

The DEM and several state groups such as the Rhode Island Natural History Survey and Save The Lakes have built an effective campaign to monitor invasive plants and the health of the state’s lakes, ponds, rivers and streams.

Every New England state, except Rhode Island, runs a boat-ramp monitoring program requiring boaters to clean their boats before entering the water. Instead, Save The Lakes organizes volunteers to oversee the boat inspection program.

Maintaining a balance between boating, fishing and swimming and a lack of natural predators to stop invasive plants often makes herbicide use a necessity, according to officials.

"All it takes is a little piece of weed on a boat to introduce something to the lake," Save The Lakes president Judy Colaluca said. Doing nothing, she said, is not an option with invasive plants, otherwise the lake or pond can fill in. "Once it's gone, it's gone."