European water chestnut grows in slow-moving, nutrient-rich rivers and lakes and can grow in shallow waters to depths of 16 ft. In Vermont, water chestnut has been found in southern Lake Champlain and its tributaries, Mississquoi Bay, Lake Bomoseen, and several other lakes and ponds throughout the state.
Water chestnut is a rooted aquatic plant. It has feathery submersed leaves that form whorls around the stem and glossy, green, triangular surface leaves with toothed edges that form floating rosettes at the end of the stem. Flowers are white and have four petals that bloom in June. The fruit is a hard nut with four sharp spines that are tipped with barbed hooks.
Water chestnut is extremely prolific. Each plant may have 10 to 15 rosettes that each produce up to 20 fruits, or nuts. Water chestnut forms dense mats that have little nutritional or habitat value to fish and waterfowl.
These mats limit light penetration and shade and crowd out native plants. When the plants decompose in the fall, they reduce the amount of dissolved oxygen in the water often resulting in fish and other plant die offs.
The dense mats also inhibit boating, fishing, and swimming. The sharp spines of the fruit can result in injuries to people walking or swimming in infested areas as well.
Control and Prevention
Water chestnut can be managed by hand pulling or mechanical removal and aquatic herbicides as a last resort. Treatment should be done before the plants go to seed. Successful management is much more likely for small infestations so early detection is critical.
Large infestations can be controlled using mechanical harvesters or herbicide and a professional should be contacted for those treatment options. Treatment is typically needed for five to twelve years and can be very costly, which is why spread prevention is the best management practice.
Water chestnut is usually spread unintentionally by people on fishing gear and boating equipment but can also spread by water currents and less commonly by waterfowl. To prevent its spread, make sure to remove all parts of the plant when pulling or harvesting plants. Water chestnut is on the Vermont Noxious Weed Quarantine list, and it is illegal to buy, plant, or transport it in the state.
Practice Clean, Drain, Dry spread prevention methods to stop the spread of water chestnut. Drain all water from your boat, canoe, kayak, and other vessels and any equipment used in the water. Clean vessels and gear and remove all plant fragments and dispose of properly. Dry all damp areas of boats and vessels, such as livewells and bilges, with a towel and let air dry in the sun for at least five days before using in another waterbody. If this is not possible, rinse equipment with hot, high-pressure water.
VT Department of Environmental Conservation
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