PITTSFIELD -- An application of herbicides to control Pontoosuc Lake weeds will focus Tuesday on about 230 acres of the waterbody close to shorelines in both Pittsfield and Lanesborough.
The application at sites evenly distributed between the two communities will require closing the lake to recreational purposes until Wednesday morning, officials said, followed by restrictions on lake water use for 10 days.
Annual herbicide treatments, similar to those also done at Onota Lake, Cheshire Lake, Richmond Pond and other water bodies in Berkshire County, aim to control invasive nuisance weed species like Eurasian watermilfoil, according to James McGrath, Pittsfield's Park and Open Space Program manager.
The herbicide will be applied under a multiyear contract by Aquatic Control Technology Inc. of Sutton, McGrath said. The annual cost is $20,000, split between the communities.
June applications are an attempt to schedule treatments before the peak summer season, McGrath said, and also to attack the milfoil and other annual weed species before they mature. The herbicide used "works very rapidly" upon contact with the weeds, McGrath said.
Volunteers with Friends of Pontoosuc Lake have conducted a preliminary survey of weed growth this year and will perform post-treatment surveys shortly afterward and in late August, said the group's president, Lee Hague of Lanesborough.
Since the weeds won't grow in deeper waters where little or no sunlight reaches, the herbicides are applied along docking, swimming or other areas of the lakeshore. If allowed to grow, the weeds could interfere with boats and swimmers.
McGrath said herbicide treatments have been applied annually since a mechanical weed harvesting program shut down seven years ago. The harvesting equipment, which originally was purchased by the former county government and later came under control of the city, had aged, he said. For that and other reasons, the herbicide program replaced it.
The herbicide to be used, Diquat, is approved for the use by the federal Environmental Protection Agency, McGrath said, and conservation commissions in the communities have reviewed the annual program. The effort is part of a long-range management plan for the lake, which also includes winter lake draw-down events every three years to expose shoreline weeds to the cold.
"We are trying to control the weeds in place or reduce them and encourage the native plants to help keep it in check," McGrath said.
Hague said a half-dozen volunteers with the Friends of Pontoosuc Lake will do an informal survey of the effect on lake weeds after the application and a more extensive survey in late August using weed rakes and an underwater camera. A pontoon boat is used, he said, and group members check weed growth, the species distribution and other factors at 20 to 30 points in the lake.
Locations are plotted with GPS equipment, Hague said, and records of growth recorded.
"We are trying to compare it year to year," he said.
The invasive nuisance weeds have been the milfoil, curley-leaf pondweed and more recently European naiad, Hague said. The naiad, which matures more slowly and is not as vulnerable to the herbicides in early June could pose a problem for the program in the near future. Hague said planners might have to consider a second application in the season to attack the naiad, which has been moving into areas previously dominated by the milfoil and curley-leaf pondweed.
The entire lake will be closed to all uses, including, swimming, fishing and boating, on the day of treatment. These uses may resume on Wednesday morning, June 11.
Use of the lake water for irrigation (watering lawns, gardens or plants of any kind) is prohibited for 10 days post treatment. Use of the lake water for drinking and watering livestock is also prohibited for 10 days.
Posters warning of these temporary water use restrictions will be posted around the lake shoreline. For more information about the program, call (413) 499-9344.
To reach Jim Therrien:
or (413) 496-6247.
On Twitter: @BE_therrien.