Scientists put herbicide in the CT River. Why it’s ‘like conquering a monster’ in the waterway

The verdict is in on year one of the effort to eradicate hydrilla, the pernicious, choking, aquatic weed that has exploded across the lower Connecticut River in less than a decade: Success so far, but more work ahead.

A year ago, when Joe Standart looked out over Selden Cove from his three century old farm house in Hadlyme, it was so choked from the bottom to the surface by an acre-sized raft of weed that he couldn’t move his boat through it.

“It looked like you could walk across the cove,” Standart said. “It was that solid.”

In August, after four years of study by invasive aquatic plant experts at the Connecticut Agricultural Experiment Station , scientists at the U.S. Army Corps of Engineers began the experimental application of a variety of herbicides at selected spots on the river below Hartford. There have been stunning results, according to those who live by or depend on the river for their livelihoods.

“It just disappeared,” Standart said. “We feel great about it. The arrival of the hydrilla was terrifying because, in the beginning, we had no sense of recourse, of a way to get rid of it. It seemed that we were fated to lose the cove, that it was going to be totally overrun.”

Across the river, Bob Petzold, who owns Chester Boat Basin , said he saw similar results.

“To be honest with you, in July I was getting nervous,” Petzold said. “We were scheduled for the middle of August for the treatment. And by July the hydrilla was growing so fast and getting so thick down there, I said to my marina manager, ‘I don’t know if we can wait that long. We may have to hire a contractor.’ We did a little remediation ourselves just to open up some pathways.

“But they did that treatment in August and I would say that within a week, we were noticing a huge difference. And within two weeks it was almost non-existent,” he said.

Months of post treatment monitoring

There is no disagreement that the effort to exterminate the incredibly robust invasive weed succeeded, at least over the short term, in spots like Hadlyme and Chester. But while positive, the result was less striking in different kinds of river conditions elsewhere.

There are big stakes in the success of hydrilla eradication for a river system that, in 70 years, has been transformed from western New England’s septic system to what the Nature Conservancy now calls “one of the world’s last great places.” The 200 miles of river and tributaries below Springfield contribute $1 billion a year to the state economy and the river’s cultural, recreational, aesthetic and real estate values are worth hundreds of millions of dollars more.

There are tens of millions of dollars of boats in marinas along the river and tens of millions of dollars more on the water any weekend. It is an underappreciated place of spectacular visitas: Granite ledges separate hundred-acre marshes where snowy egrets wade and osprey nest in piles of twigs atop drowned maples.

The hydrilla infesting the river is an especially robust and genetically unique strain believed to have arrived in Connecticut from Asia as a decorative aquarium plant. Although hydrilla has been a problem for decades in the south, the unique plant first spotted in the river in Glastonbury in 2016 has proven to be far more virulent.

It was named Connecticut River Hydrilla after a genetic analysis produced no matches anywhere else in the world.

With its explosive growth and the absence locally of anything that eats or kills it, the weed is changing the river ecosystem and that presents a threat to important fish species like menhaden and the big birds near the top of the food chain that have repopulated the river.

The largely successful eradication work this summer was based on application by the Army Corps of a variety of herbicides at five sites along the river from Glastonbury to Hadlyme. The sites were chosen based on variations in tidal and river flow characteristics.

The timing of herbicide application — late July to mid-August — was based on a window that balanced periods in the hydrilla growth cycle that left it most vulnerable against the need to avoid any chemical application that could affect the life cycle of important native plant or animal species, such as herring. And in addition to killing hydrilla, a program goal, according to the Army Corps, is to avoid killing native plant species, such as eelgrass.

Members of the U.S. Army Corps of Engineers check on the hydrilla before adding dye to measure flow in the Connecticut River at the Parker Point in Chester location on Wednesday, Oct. 2, 2024. (Aaron Flaum/Hartford Courant)

Preliminary results showed the herbicides essentially removed hydrilla in partially enclosed parts of the river with low flow rates, Keeney Cove in Glastonbury, where Connecticut River Hydrilla was first found; Chapman Pond in East Haddam, Selden Cove in Hadlyme and Chester Boat Basin.

The results of application at Portland Boat Works , located on a straight, fast flowing stretch of river in Portland, were less successful. The herbicide had some effect, but nothing like that at the enclosed application sites.

“The Portland site, like other mainstem river sites, are going to be the most challenging because you need that contact time with herbicide,” Keith Hannon, Connecticut River project manager for the Army Corps said. “So it is tough when the river is just pushing it away as soon as you put it in.”

“I think we can all definitely agree that the treatments were successful,” he said. “But there are other things we are monitoring, months of post treatment monitoring. So we are going out monthly to do assessments and to do surveys of the plants that are still growing there.”

‘Like conquering a monster’

Although early study results are promising, state and federal scientists it will take much more work to determine how best to control hydrilla or even if it can be effectively controlled.

One thing that will be closely monitored is what effect the herbicide has on the weeds’ extraordinary capacity to reproduce. The plant’s long, vine-like arms produce buds called turions, which eventually break off, drift and settle in the river sediment where they produce new plants the following year.

Although the herbicide appears to have killed off what can be seen of the hydrilla from the surface, its effect on turions buried in sediment has yet to be seen. It is hoped by the scientists that successive herbicide applications will lead to successively decreasing turion production.

One goal of herbicide application is to hit the hydrilla at a point in its growth cycle when turion development is vulnerable. But that can conflict with the need to protect other species of plants and animals.

The state agricultural experiment station and its recently created invasive aquatic plant program have been studying invasive hydrilla’s exceptional resilience for years and the Army Corps has based its work in part of the research.

Jeremiah Foley, a plant scientist with the station, said the muck at the bottom of a portion of the river he examined last week in Deep River is shockingly thick with turions.

“The data so far seems to show over a 10-fold increase in the number of turions formed compared to the other species that have historically been in the U.S.,” he said. “It is unbelievably thick back there, hundreds and hundreds of turions from a square meter of bottom.

What gets done next year on the effort to control hydrilla will almost certainly depend on funding and the effort so far has been expensive. The herbicide which appears to have been successful in treating 60-acre Chapman Pond cost about $700,000, according to people involved in the application.

The cost could come down significantly, if comparable but cheaper products are approved for use by Connecticut, they said.

“You can’t do this on the cheap,” said U.S. Sen. Richard Blumenthal, D-Conn. “If the stuff works, it will be a really good investment. In the long run it will save money. This species is in fact invasive, nature didn’t intend for it to be there. So from an environmental standpoint, if you think about saving the planet, it is kind of the right thing to do. It is morally imperative, not just economically and recreationally.”

Blumenthal’s may be the biggest financial backer of hydrilla eradication. He has succeeded in directing tens of millions of dollars to the Army Corps research effort and said he is involved in expanding a federal fund that will support the work when, as will eventually happen, the Corps moves on and the expensive business of controlling hydrilla shifts to state and local governments, regional groups, nonprofits and businesses.

“This stuff has presented seemingly insuperable difficulties in the past,” he said. “It is kind of like conquering a monster that seemed absolutely invulnerable. This treatment seems to work. We are keeping our fingers crossed.”

Most of the work identifying, plotting and tracking Connecticut River Hydrilla was done by the agricultural station’s invasive aquatic plant program, which was created in response to the infestation. Gregory Bugbee, who directs the invasive program composed of a handful of people and a couple of skiffs, welcomed the addition of the Army Corps, with its far greater budget and manpower.

Bugbee said much about the new, local hydrilla species remains a mystery, like why it seems to have stopped moving north at the Massachusetts border. He said it won’t move south of Essex because it can’t survive in saltwater.

The local hydrilla, once confined to the Connecticut River, has spread to ten Connecticut lakes and ponds, transported from river to lake by fishermen who fail to wash down their boats and trailers after a day on the water.

Bugbee’s office recently began an inspection of every boat launch in the state for signs of further spread.

“On the lakes, we’ve really only scratched the surface,” he said. “There’s a good chance we will find it in other places.”

The farther hydrilla disseminates, the more control efforts will cost. If responsibility falls on small towns with jurisdiction over lakes and ponds, the costs could be prohibitive, according to a variety of officials.

The goal of the Army Corp hopes to finish its work in the near future by sharing its recommendations for controlling hydrilla with state and local officials, who will have to assume the associated costs.

But the corps has a 50-50 matching grant program that could help qualifying state, local or non profit organizations cut costs.

“We have already approached the U.S. Army Corps of Engineers to get them to reserve some more money,” Blumenthal said. “The Army Corps of Engineers ought to have money for a program like this in a navigable waterway like the Connecticut River. And in other places where it affects navigable waterways. So I think it can be viewed broadly.”