The Connecticut Agricultural Experiment Station – Office of Aquatic Invasive Species (CAES-OAIS) and the Lower Connecticut River Valley Council of Governments (RiverCOG) are leading a demonstration project to determine the effectiveness of herbicides registered for aquatic use by the U.S. Environmental Protection Agency to safely reduce and control the spread of hydrilla. The project is in partnership with the U.S. Army Corps of Engineers and its Engineer Research and Development Center’s (ERDC) Aquatic Plant Control Research Program.
The project and research began in 2023, to guide operational scale field demonstrations of herbicide efficacy in 2024. Additional field demonstrations are being planned for 2025.
How will hydrilla be treated?
The U.S. Army Corps of Engineers developed site-specific aquatic herbicide treatment plans for five selected sites in the Connecticut River in the summer of 2024. There are several safe, well understood, and effective herbicides that are available for use.
The hydrilla treatment should have minimal-to-no impact to recreation in the Connecticut River. Other than when contractors are on-site carrying out treatment where some restricted public access may be needed, no long-term closures or restricted access is currently anticipated with this work. Regarding fishing, the treatment is expected to have minimal to no effects on fishing or to fishing access.
Where will the demonstration project occur?
The five demonstration sites selected for aquatic herbicide demonstrations in 2024 were Keeney Cove, Portland Boat Works, Chapman Pond, Chester Boat Basin, and Selden Cove. Phenology sites used for collecting samples and studying hydrilla growth characteristics were at sites located in Deep River, Mattabesset River, Selden Cove, and Selden Creek. Additional demonstration sites added in 2025 are under review, and final selection of these additional sites will be confirmed as funding and permitting will allow.
Diquat is a fast-acting, non-selective herbicide used to control a variety of submerged or floating weeds in ponds and other aquatic environments. It works by interfering with photosynthesis and is rapidly absorbed by plants.
A search of the internet found no incidence of Diquat causing cancer in humans. Diquat is not considered teratogenic, carcinogenic, or mutagenic; that is, it produces no birth abnormalities, cancers, or spontaneous changes in genes. Diquat is an important herbicide not only because of its extremely low environmental impact, but also because of its phenomenal herbicidal effects.
Laboratory tests indicate walleye are the fish most sensitive to Diquat, displaying toxic symptoms when confined in water treated with Diquat at label application rates. Other game and panfish (e.g. northern pike, bass, and bluegills) are apparently not affected at these application rates.
A recent concern in Connecticut:
The USACE is conducting research to develop a safe treatment plan that controls hydrilla while also meeting project goals, and proposes using herbicides including Diquat dibromide, dipotassium salt of endothall, and florpyrauxifen-benzyl, individually or in combination. The spraying is planned to occur after July 4th to protect the anadromous fish spawning season.
There have been reports and social media campaigns raising awareness about plans to use Diquat Dibromide to control invasive weeds like hydrilla in several rivers and lakes, including: Lower Connecticut River area, Chester Creek, Hamburg Cove, Selden Creek, Salmon River, Deep River, and Lake Pocotopaug.
One such Facebook petition request post by Chris Webby stated: “There’s a plan in place to spray lakes and rivers all over Connecticut with a highly toxic chemical called Diquat after the 4th of July. Their reasoning is to combat an invasive weed called hydrilla, but other states that this chemical has been used in paint a grim picture of what the results would be. There’s other ways to combat hydrilla. The spraying needs to be stopped.”
Concerns include the toxicity of Diquat to wildlife and aquatic ecosystems, as well as potential risks to human health. It should be noted that Diquat is banned in Europe.
Project Manager Keith Hannon, U.S. Army Corps of Engineers, New England District:
“The threat of this strain [of Hydrilla] to the Connecticut River’s natural ecology are real, and include degradation of river habitat and water quality, and harm to native plants and animals. Additionally, the strain could affect the local economy through the loss of waterway navigability and fishing, lowering of property values, and increase in flood risk. …The USACE’s researchers and scientists are dedicated to protecting public health and the environment and use only herbicide products that are approved by the U.S. Environmental Protection Agency and the Connecticut Department of Energy and Environmental Protection (CT DEEP). … Application of any aquatic herbicide product is closely monitored and regulated by both federal and state agencies to ensure that they are safe for humans and the environment.”
The Aquatic Permit program, administered by the Connecticut Department of Energy and Environmental Protection’s (DEEP), Bureau of Materials Management and Compliance Assurance, regulates the use of chemicals proposed for introduction into the waters of the state, whether public or private, for control of aquatic organisms. These organisms are usually aquatic weeds or algae, but could include mosquitoes or unwanted fish. Applications are evaluated for the potential of causing unreasonable adverse effects to human health or the environment. Only chemicals registered for aquatic sites may be used.
DEEP claims that Diquat is a great aquatic weed killer that controls floating and submerged weeds in ponds and around docks. Diquat is highly concentrated and is quickly absorbed by plants.
Report any sightings of the strain to the state of Connecticut or the Connecticut River Conservancy. You can learn more about ERDC and the USACE’s efforts to eradicate Hydrilla.
For a tutorial on hydrilla and the work being done by various organizations please go to:
Sources: DEEP; Lake Restoration Inc.; Wisconsin Department of Natural Resources; Diquat Chemical Fact Sheet – NOAA (National Oceanic and Atmospheric Administration); United States Army Core of Engineers (USACE); Beth Gosselin, Chief, Public Affairs, U.S. Army Corps of Engineers, New England District; Department of Energy and Environmental Protection
Barbara Heimlich spent 35 years as Vice President of Program Management and Research for Paragon Development, an international consulting firm, where she was responsible for new product and business development. She is the Features Reporter for the Stratford Crier.
Has RFK JR been advised of what is happening?