PITTSFIELD, Mass. — How does Pittsfield keep its lakes from being overtaken by weeds? Specifically, Eurasian milfoil. 

This was one of the many topics covered during the inaugural Lake Management Commission on Thursday. Both Onota and Pontoosuc Lakes were treated last month; 218 acres of Onota were treated with ProcellaCor on June 23, and 53 acres of Pontoosuc were treated with Diquat on June 17. 

Before 2021, Diquat, a contact herbicide, was used on Onota Lake. In 2022, Pittsfield invested $220,000 for a 260-acre treatment with a new systemic herbicide, ProcellaCOR, that specifically targets milfoil.

Control had been pretty decent for about 2 1/2 years, and there were spot treatments in 2024. In 2025, only about 15 acres could be treated. 

"We're targeting Eurasian milfoil. That's really the concern and not only at Onota Lake, but the other lakes that are in our region," Parks, Open Space, and Natural Resources Manager James McGrath said. 

"We followed up with annual spot treatments in 2023 and 2024, but we were finding that, in the initial application, the concentrations were a little bit lower than they perhaps should have been, and we were learning a lot about ProcellaCOR and its efficacy, and also some of its limitations."

"Last summer in 2025, there were some budget constraints, and we saw milfoil really growing to some really nuisance levels. We did a very small treatment in 2025, and really, we were looking to 2026 to be the year where we really had to do something." 

ProcellaCor specifically targets species like water milfoil and is classified as "reduced-risk" by the U.S. Environmental Protection Agency, though it is more expensive. 

Last year, about 220 acres of very dense milfoil were found, primarily in the center and northern parts of the lake. A color-coded map from June, displayed at the meeting, shows one long, dense area on the North side of the lake and three dense areas on the southern side.