Coontail (Ceratophyllum demersum) is a common, submersed aquatic plant that often becomes a nuisance in ponds. It is a rootless perennial, meaning it floats freely or is loosely anchored to the sediment, allowing it to move and spread easily. While it provides habitat and oxygenation, its rapid growth can lead to dense, underwater mats that interfere with swimming, fishing, and boating activities. Unchecked growth contributes to oxygen depletion when large masses of the plant die and decompose, potentially leading to fish kills. Controlling coontail requires a multi-faceted approach, combining physical removal with long-term environmental management and, in some cases, targeted chemical application.
Confirming the Presence of Coontail
Correctly identifying the plant is the first step to ensure control methods are effective against Ceratophyllum demersum. Coontail is characterized by stiff, dark green leaves arranged in dense whorls along the stem, giving it a brush-like or “raccoon’s tail” appearance near the growing tips. The leaves are typically forked once or twice and possess small, spiny teeth along the edges, making the plant feel rough when handled. It does not possess true roots, instead anchoring itself loosely to the sediment or floating freely in the water column. Unlike some other submerged weeds, coontail often maintains its color and continues to grow throughout the cooler months.
Manual and Physical Removal Strategies
Direct physical removal is a viable option for small, localized infestations or for clearing specific areas like docks and swimming zones. This method involves using specialized aquatic weed cutters, rakes, or nets to pull the plant mass from the water. Mechanical harvesting, using specialized equipment, can be employed for larger areas, though this is often more expensive and requires specialized contractors.
It is necessary to collect and remove every piece of plant material from the water after cutting or raking. Coontail reproduces easily from fragments, so any small segment left floating can drift to a new location and start a new infestation. Failure to remove all fragments can worsen the problem by dispersing the plant throughout the pond. The removed plant material should be disposed of on dry land, away from the pond edge, to prevent it from washing back into the water or contributing to the pond’s nutrient load as it decomposes.
Managing the Pond Environment Biologically
Long-term management requires addressing the underlying conditions that allow coontail to thrive, primarily high nutrient levels. Coontail flourishes in water with excessive amounts of phosphorus and nitrogen, which often enter the pond through runoff from surrounding landscapes, such as fertilized lawns or agricultural fields. Diverting nutrient-rich runoff and establishing vegetative buffer strips along the shoreline can significantly reduce nutrient input. Applying nutrient binders, such as aluminum sulfate (alum), can help precipitate and lock up phosphorus in the bottom sediment, making it unavailable for plant growth.
Reducing Sunlight and Introducing Grass Carp
Reducing the amount of sunlight that reaches the submerged plants is an effective suppression technique. Non-toxic aquatic dyes can be added to the water to tint it blue or black, blocking the light necessary for photosynthesis in deeper areas. This method is most effective in ponds with minimal water flow that receive direct sunlight. Biological control involves introducing sterile triploid grass carp, which are herbivorous fish that feed on coontail. These fish are effective in reducing plant biomass, but they are non-selective feeders and may consume desirable vegetation; stocking requires a permit in many states and should only be done with verified sterile fish.
Selecting the Right Aquatic Herbicide
Chemical control offers a rapid solution for severe coontail infestations but must be approached with caution and precision. Effective aquatic herbicides include contact herbicides like Diquat and Endothall-based products, and systemic herbicides such as Fluridone. Contact herbicides kill the plant material quickly, while systemic herbicides are absorbed and move throughout the plant, offering slower, more thorough control.
Before application, accurately measure the pond’s surface area and average depth to calculate the total water volume, ensuring the herbicide is applied at the correct concentration. Treating a large, dense infestation all at once carries a high risk of causing a massive die-off, which consumes dissolved oxygen as the plant material decomposes. This rapid oxygen depletion can lead to a fish kill, so it is safer to treat the pond in sections, often no more than one-third to one-half of the total area at a time. Always follow the product label directions regarding application rates, required water-use restrictions (such as for irrigation or swimming), and the necessity of mixing in an aquatic surfactant to improve chemical contact with the waxy plant surface.