European frogbit (Hydrocharis morsus-ranae) prefers calcium-rich, quiet waters such as marshes, swamps, ponds, slow-moving rivers and lakes, sheltered inlets and bays, and ditches. In Vermont, frogbit has been documented in southern Lake Champlain, Shelburne Pond, the Winooski River delta, the islands region of Lake Champlain, and Mississquoi Bay.
European frogbit is a free floating plant that has green, heart-shaped, leathery leaves with dark purplish-red, spongy undersides. The plants also have complex root systems but rarely anchor to the bottom. The roots tangle with other vegetation, which along with the rosettes that the leaves form, create dense mats. Plants have a single, 3-petalled white flower with a yellow center that blooms in summer.
Dense growths of European frogbit impact native plants and animals as well as human activity. Frogbit populations can quickly increase in size through vegetative reproduction forming thick mats that prevent light and nutrients from reaching submerged plants. In shallower waters, frogbit can even crowd out native vegetation.
These dense mats of interlocking plants also inhibit movement of large fish and diving ducks and impede recreational activities like swimming, fishing, and boating. In the fall when the plants die off, oxygen levels in the water decrease, which can result in the deaths of fish and native vegetation.
Control and Prevention
Individual plants or small infestations of frogbit can be controlled by hand pulling, though this removal method is usually only a temporary solution. The best management option is to prevent its spread to new waters.
European frogbit was originally introduced as an ornamental for water gardens. Now on the Vermont Noxious Weed Quarantine list, frogbit is illegal to buy, plant, or transport in the state. To avoid the spread of invasive plants, only use native vegetation when landscaping and dispose of all water garden vegetation properly in the trash or on high, dry ground where there is no risk of it washing into a waterbody.
Frogbit is usually spread unintentionally on fishing gear and boating equipment but can also spread by water currents. To prevent the spread of frogbit, practice Clean, Drain, Dry spread prevention methods. 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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