Aquatic vegetation is the proper name for the "moss" seen in ponds and other bodies of water. Unfortunately, many people do not view aquatic vegetation in a favorable light, with coontail (Ceratophyllum demersum) being a species that is often viewed negatively. In truth, coontail has both positive and negative attributes, and methods are available to control its growth.
Coontail is classified as a submerged aquatic species, meaning it grows below the surface of the water. It is a free-floating, rootless, perennial native aquatic plant that is capable of forming dense colonies covering large areas of water. The green, forked, serrated leaves are relatively stiff and are arranged in whorls on the stem. These leaves have a strong resemblance to a raccoon's tail which is probably how coontail got its name. The plant is found in ponds, lakes and streams across the United States, Mexico, Canada and much of the world. It reproduces through very small seeds and fragmentation. Fragmentation occurs when a portion of the plant breaks off and becomes a new plant. Coontail and other aquatic plants spread to new areas when impoundments containing the plants overflow into other water bodies or when seeds or fragments are introduced by birds, boats, livestock, etc.
Coontail can be either desirable or undesirable depending on the management goals for a particular body of water. Desirable attributes may include increasing species diversity, limiting unwanted fishing, creating fish habitat, providing food for waterfowl and improving water clarity. When coontail is excessive, undesirable effects can include a reduction of open water, creation of a "scummy" appearance, limiting of desirable fishing access, interfering with boating and swimming, stunting fish by hiding too many from predators and becoming invasive.
Water clarity typically improves with abundant underwater aquatic vegetation such as coontail. Coontail can be considered desirable when managing for waterfowl and fisheries. The leaves and seeds of coontail are eaten by waterfowl, and it provides a home for a variety of aquatic insects. These insects then serve as food for many species of fish and waterfowl. Coontail also provides cover for small fish, which is probably more important in relatively clear ponds. As a rule of thumb, aquatic vegetation may become counterproductive in an impoundment managed for sport fishing when it covers more than 25 percent of the surface area. With this in mind, it is not typically recommended to plant coontail in a sport fishing impoundment due to its aggressive growth.
Due to coontail's potentially rapid growth, many managers assume control is needed. Before attempting to control this or any other aquatic vegetation, determine the pros and cons of the plant relative to the goals for an impoundment. It may not need controlling, but there are several options if it does.
Herbicides with active ingredients such as 2,4-D, diquat, endothall and fluridone have been shown to be successful in treating coontail, but results are often short-term and expensive. Use caution when using herbicides to avoid decreasing dissolved oxygen levels, which can cause a fish kill. When using herbicides, always read and follow directions on the label. Grass carp have been proven effective for long-term control when stocked at the proper rate. Studies have shown grass carp will eat coontail, but only after eating other more preferred aquatic plants. Fish barriers should be installed in pond spillways before stocking grass carp. These structures reduce the likelihood of grass carp escaping the impoundment, entering public waters and making future management decisions difficult due to the unknown population. Check with your state wildlife and fisheries agency for grass carp stocking regulations.