Hydrilla, Herbicides, and Hype: What You Should Know

Invasive species outcompete native species for resources. This damages Connecticut’s biodiversity and habitat health. One particularly destructive invasive is called Hydrilla. Originating from Asia, Hydrilla is an aquatic invasive that has been ravaging Connecticut’s freshwater ecosystems since 2016. 

Hydrilla can grow up to an astounding one inch per day leading to dense mats up to several feet long. Not only does the plant grow with rapid speed but its ability to spread quickly exacerbates the problem. Hydrilla spreads not only through seeds, but also root buds (turions and tubers), and plant fragments, making it extremely hard to control. Fragments travel easily on boats, currents, and fishing gear, helping it spread quickly and widely.

​Beyond crowding out native species, Hydrilla presence leads to: 

• Kills fish by reducing oxygen in the water
• Slows or blocks water flow in lakes and reservoirs
• Disrupts feeding areas for birds and spawning spots for fish
• Lowers property values along the water
• Restricts areas available for swimming, fishing, and boating 
• Blocks boats and clogs waterways
• Gets tangled in boat motors
• Raises the risk of flooding by clogging water systems

Clearly, Hydrilla is a huge problem for Connecticut’s wildlife, rivers and people. The question is, how to stop and reverse its damage? 

One proposed method for managing invasive Hydrilla is manual removal. A recently developed tool, the Weedoo Environmental Work Boat, can cut Hydrilla up to five feet below the surface. While this solution is chemical-free, it can’t keep up with Hydrilla’s rapid growth and doesn’t address its ability to reproduce through underground tubers.

This summer, the Army Corps of Engineers has begun an experimental project to reduce the Hydrilla decimating Connecticut river habitats. After extensive research and project preparation, the U.S. Army Corps of Engineers selected a targeted herbicide treatment using diquat dibromide as the most effective solution. Before implementation, they studied various herbicides over several years, including how chemicals would move through the river system. Using dye tests, they identified the most effective treatment zones and minimized the amount of herbicide needed. The Corps also held three public meetings in riverfront towns to share findings and gather feedback prior to project implementation.

After just a month, the project has shown promising results: Hydrilla levels have decreased, and native aquatic plants are rebounding.

Diquat isn’t without its drawbacks, and must be managed appropriately. If too much is sprayed in a body of water, it can lead to lower oxygen levels due to the decomposing vegetation, a risk to fish and aquatic organisms. However, the Army Corps is applying the herbicide in tightly controlled amounts to avoid this outcome. Diquat doesn’t break down easily in sediment, but it also doesn’t leach into groundwater, so there’s little risk to drinking water. A trace contaminant, ethylene dibromide or EBD, is a known carcinogen, which can sound alarming. But it exists only in extremely small quantities and naturally breaks down over time. While these risks may seem concerning at first, experts have determined that when used responsibly, the impact on human health is minimal and the benefits to restoring the river’s ecosystem are substantial.

You may have seen news headlines recently in regards to this project after misinformation was circulated by a CT based rapper on social media. After seeing a video of a lake in the aftermath of spraying diquat on social media, Chris Webby took an interest in the chemical and did some research of his own. While acknowledging that he is not an expert on Hydrilla or the methods of its removal, he used his large fanbase to get a petition signed by 14,868 people and urged his followers to call legislators and the project leaders demanding they stop spraying the chemical.

Meanwhile, experts have spoken out against Webby’s misinformation campaign, citing there are no viable alternatives to ridding Connecticut of Hydrilla. Alicea Charamut, Executive Director of the Rivers Alliance of Connecticut and a public advocate who worked with the Army Corps of Engineers on how best to combat Hydrilla, says they considered using benthic mats to prevent the plant from growing upward but it proved to be impractical as the whole river would have to be covered with these mats. Additionally, the mats would also smother native plants, defeating the purpose of the treatment.

In closing, it’s completely fair to ask questions and feel uneasy about chemical treatments in natural spaces. A few weeks ago, our staff attended a press conference organized by Connecticut Senator Blumenthal, and we listened closely to the experts, advocates, and officials working on this issue. We’ve done our best to dig into the facts and understand why experts landed on this approach, even with its trade-offs. There’s no perfect solution, but right now, diquat seems to be the most effective way to stop Hydrilla’s decimation of our river ecosystems. If you’d like to learn more or hear directly from those involved, we recommend reading this CT Mirror article.