European Frog-bit is an invasive aquatic plant native to Europe and parts of Asia and Africa. Imported from Europe in 1932 for possible commercial use as an ornamental plant, it was first observed in the Rideau Canal in 1939. It has since spread to the St. Lawrence River, Lake Ontario, Lake Erie and several rivers and inland lakes. A rapid growing plant, it prefers calcium-rich water and forms dense floating mats with free-floating roots up to 30 cm long in slow moving water bodies such as marshes, swamps, quiet bays and shorelines, sheltered coves and poorly drained ditches.
European Frog-bit is an annual plant that reproduces primarily by producing juvenile plants from stem-like extensions during the growing season and new plants from winter buds, called turions, that sink to the water bottom to lie dormant over the winter and float to the surface in spring. The plant can spread between water bodies via seeds, plant fragments and turions spread by boats and equipment. A single plant produces 100 to 150 turions each year.
Control methods include hand and mechanical harvesting, although care must be taken to prevent fragments from escaping the infestation site. Chemical herbicides are also effective, where permitted by law.
European Frog-bit is found in southern Ontario and along the St. Lawrence River in Quebec, with isolated populations in New York, Vermont, Michigan and Washington and the southern margin of the Canadian Shield.
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