The U.S. Army Corps of Engineers this week announced its intention to move forward with plans to use diquat and other chemical herbicides to combat a highly invasive strain of hydrilla along the Connecticut River.
Those plans ignited significant controversy earlier this summer when the Army Corps released an initial proposal to expand its use of herbicides at a dozen sites along the lower portion of the river.
While those plans were in fact part of a years-long effort to study the effectiveness of using herbicides to control hydrilla, they quickly became the subject of viral social media posts laden with inaccuracies and conspiracy theories about the government’s intentions. In particular, many of those posts focused one chemical included in Army Corps’ plans — diquat dibromide.
In an attempt to clear the air, officials extended the public comment period for the project until August and held both in-person and virtual events to answer questions from the press and the public.
On Wednesday, the Army Corps held an online meeting to announce an update to its plans.
Beginning on Aug. 19, officials said, they plan to apply herbicide treatments to Selden Cove in Lyme and the Chester Boat Basin. Only the Chester location will receive treatments of diquat combined with another herbicide, endothall, according to the Corps’ plans. Selden Cove will be treated with only endothall.
Both treatments are scheduled to last two days, concluding on Aug 20. If weather or field conditions prevent the project from moving forward on those days, alternative dates are available the following week. (One alternate location, Middletown’s Pameacha Pond, was also included in the Corps’ schedule.)
The decision to pare the number of treatment sites down from 12 to two was due to a lapse in federal funding available for the project, according to Keith Hannon, the project manager for the Army Corps’ New England District. Last year, the project received $5 million in funding from Congress.
In addition to the two sites selected for herbicide treatments, Hannon said officials also plan to continue a related series of hydrological studies using colorful dyes at a handful of spots along the river, including a new location in Agawam, Mass.
“We are limited in what we’re able to do this year,” Hannon said. “The dye studies do have a cost, but they’re cheaper, so we’re able to do those, and those will directly inform the study and future riverside applications.”
Those dye studies date back to 2023, when research scientists working with the Army Corps began using dyes to study the flow of water in areas afflicted by hydrilla to determine which herbicides to use in specific concentrations to avoid harming other native species of wildlife. Based on those results, the Army Corps first started applying herbicides, including diquat, at five areas along the river last summer.
In follow-up sampling at those locations, researchers recorded large declines in the amount of hydrilla, with minimal impacts to native plants, according to results shared at Wednesday’s meeting. This summer, however, the hydrilla has returned in Chester Boat Basin and, to a larger extent, in Selden Cove.
Among the concerns raised by members of the public at Wednesday’s meeting was the potential impact on swimmers at a children’s summer camp at Hamburg Cove, down river from the two treatment areas.
Anne Overstreet, the director of the U.S. Environmental Protection Agency’s Pesticide Re-Evaluation Division, said the agency did not find any information to justify those concerns during its most recent review of diquat in 2020.
“The bottom line is, if the labeled directions are being followed, there are no concerns from people swimming or coming into contact with water that’s been treated with diquat,” Overstreet said.
