Frequently Asked Questions about Weed Management
Why are some weeds a problem? Invasive aquatic weeds displace the biologically diverse plant and animal populations that are so important to a healthy, stable ecosystem. They also endanger the fish population by reducing dissolved oxygen and entangle swimmers and boaters with their dense growth. As the plants aggressively colonize and merge into a monoculture just below the water surface, they often make the area conducive to algae that is toxic to other pond life. Once an invasive weed like milfoil is established, it is unlikely to be fully eliminated. A lake in the late stages of milfoil infestation looks more like a marsh or swamp than a lake. For more details and resources on the impact of invasive weeds, visit Weed Identification. Here’s a great video too.
What weeds are in Leverett Pond? In 1993, a pond resident noted a rapidly spreading aquatic plant and sent it to a state botanist. It was identified as Eurasian milfoil, an aggressively invasive plant. Since then, other invasive weeds have been identified, including variable watermilfoil, curly-leaf pondweed, swollen/purple (hybrid) bladderwort, European/brittle naiad, and waterweed. In addition, about 40% of Leverett Pond is covered by a large number of floating-leaf plants. The Commonwealth permits both invasive and other aggressive plants to be managed under a permit from the Department of Environmental Protection (DEP).
How did invasive weeds get into the pond? Waterfowl, especially Canada geese, and boats act as carriers of plant fragments. Unfortunately, it only takes a tiny amount of even dried plant matter to establish a new infestation. Once a body of water has been infested with milfoil, ongoing active management of the pond is required.
How did FLP decide to use herbicides? A few years after its founding, FLP joined the Massachusetts Coalition of Lakes and Ponds (COLAP), an organization which has experience dealing with invasive and nuisance weeds in ponds across the state. We also worked with the WaterWatch Partnership at UMass, which conducted several tests on the Pond to determine the best weed management strategy. Their advice was based on the pond’s characteristics: spring-fed, a slow water-turnover rate, a general state of eutrophy (a high nutrient load and low oxygen levels), and the extent of the milfoil infestation. A state-approved herbicide was recommended as the best means to achieve effective weed management in the long term.
Are herbicides safe for the water and wildlife? FLP has always used carefully selected herbicides approved by the State and the Leverett Conservation Commission and applied by fully licensed specialists in small portions of the lake. Over time, these applications have become safer and more precise. In 2019, FLP used the herbicide ProcellaCOR, a selective chemical weed control that can target specific invasive plants and leave other plants unaffected. It is absorbed rapidly into the root system, can kill milfoil without fragmentation, and remains in free form in the water for only a few days. The treatment in 2019 was so effective in removing milfoil that we have gone two years without needing additional treatment. This herbicide may be effective for up to three years. For more info on ProcellaCOR, see Minnesota Department of Agriculture Technical Bulletin for Florpyrauxifen-benzyl.
Are the large island-like masses of dead plants that float in the summer caused by weed management? No. Floating islands (also known as tussocks) occur naturally in many ponds with shallow depths, lily pads and slow water turnover. They provide resting areas for many species. Early records confirm they have been a presence on the pond for many years prior to herbicide application.
What are the alternatives to chemical treatment? Ideally, FLP would prefer to avoid the use of herbicides and hopes, with the recently restored dam, that an occasional drawdown of the pond water level could eventually replace a chemical method of weed management. Weeds in the pond were controlled by the dam before it lost its drawdown function decades ago (and it’s how Lake Wyola currently manages its weeds). The drawdown would occur in late fall by opening the dam gate, gradually allowing shoreline fauna to temporarily migrate with the receding water. This would expose the invasive roots that tend to grow near the shoreline to freezing in the winter. The dam gate would then be closed, allowing the pond to refill by spring. No habitats would be permanently affected. Securing the permits for this process is a lengthy and complex process that must be undertaken with care. In the meantime, here are other management options we’ve explored:
- Hand picking. This requires removing the entire plant, including the roots, and preventing fragmentation that would allow milfoil to float to other areas and colonize them. This method is impractical on a large scale. The foot-deep mucky bottom on most of the Pond’s edges makes wading in difficult, and once plant removal begins, the silt obscures visibility, making it hard to find the weeds and remove them carefully.
- Scuba divers. We tried this once, but the availability and cost of using divers — as well as the silty water obscurity — made this option unfeasible.
- Bottom barriers. These impermeable, expensive sheets are spread across the bottom to block growth but are not practical for large areas. They are expensive and have to be turned over regularly.
- Biological control. FLP has explored the use of insects and fish that eat invasive plants, both reported to be effective under certain circumstances. Unfortunately the recommended milfoil-consuming weevils do not consume the species of variable milfoil present in the pond. And while grass carp has been used in many countries to control aquatic plant growth, it can consume native species prior to attacking invasive plants. Introducing these fish and other similar species to a water body is illegal in Massachusetts.
- Mechanical harvesters. These underwater lawnmowers cannot be used in very shallow waters near shorelines, where much of the milfoil exists. Their use inevitably causes fragmentation and spread of milfoil and does not remove the root of the plants, allowing them to regrow.
- Hydro-raking. FLP uses this method as a way to clear the decaying matter of plants after an herbicide treatment. Dead matter in a pond can use up oxygen as it decays, leading to low oxygen levels and high nutrient levels (called eutrophication). Thus, the raking improves water circulation and fish habitat while making conditions better for boating. Hydro-raking also minimizes the regrowth and spread of milfoil by removing roots and fragments after herbicide applications. This management approach is expensive and not a large-scale solution as it involves the equipment going back and forth from water to shore, one scoop at a time, and can only be used for clearing small areas. In addition, hydro-raking does not replace the use of herbicides; rather, it needs to be used in conjunction with chemical treatment.
- Channel cutting. At the suggestion of the Massachusetts Division of Fisheries and Wildlife, the FLP has proposed cutting channels through dense areas of water lilies using a mechanical harvester. These new channels would increase water circulation and thereby improve oxygen levels and boater access but would not reduce the weed level as the plants will grow back from their roots
Why not just accept the weed invasion as a natural process? If we opt to do nothing, within a span of five to ten years, the spread of invasive weeds will considerably reduce open water areas, be detrimental to fish and other wildlife, reduce the pond’s recreational value, and make access from the shores—including the boat launch—considerably more difficult. In essence, the FLP is applying for a permit that attempts to keep the pond as we know it now.
Is there something I can do? Yes! If you use your boat in other waters, please spray down your boat after every use, both at Leverett Pond and elsewhere. Be careful removing any invasive weeds. If they fragment, they can colonize other water bodies and other sections of the Pond (See Pond Use Guidelines).
