Pittsfield Treats Lakes for Eurasian Milfoil
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.
Using this information, the city contracted with Solitude Lake Management to establish a treatment zone, and 218 acres of the lake were treated on June 23. There were sign postings and public notification beforehand.
That treatment cost about $256,100, and the Lake Onota Preservation Commission contributed more than $46,100, bringing the city's obligation down to $210,000. Between free cash and the LOPA gift, the contract amount was met.
When you look at the contracted amount in relation to the acreage we treated, the systemic treatment of Onota in 2026 was valued at $1,175 per acre, McGrath reported, compared to the contact herbicide treatment at Pontoosuc that cost $144 per acre.
"So it's $1,000 more per acre to utilize the systemic chemical."
The permit for work at Onota Lake was originally issued in 2014; it has been extended multiple times and expires in 2029. The Natural Heritage & Endangered Species Program plan expires in 2027.
The Conservation Commission in June OK'd a request for Diquat treatment on 53 acres of Pontoosuc Lake with the same vendor. That three-year permit for herbicide treatment was issued in 2023 and extended through the Permit Extension Act to 2028.
Neither Onota nor Richmond Pond authorizes the use of Diquat.
Tags: herbicide, lakes, ponds, onota, Pontoosuc,
