Water spangles, water fern
Native to: Central and South America
Common salvinia was first reported in the US in 1928 along the St. John’s River in Florida. The source of this first introduction was likely an unintentional release from a grower whose cultivation ponds had flooded. Since then, populations have been recorded in more than 80 freshwater drainage areas across the US. This plant remains widely available in the water garden trade but is prohibited in Florida. It can thrive in any slow moving aquatic system including lakes, ponds, swamps, ditches, and marshes. It is easily unintentionally spread via both human and animal activities when plant fragments hitchhike on boats, gear, fur, or feathers.
Habit: free-floating aquatic fern with a horizontal stem or rhizome that floats at or just below the water surface.
Leaves: almost round to elliptic, from 1-1.5 cm long. Obtuse or notched at the apex and round to heart-shaped at the base. The upward surfaces of the fronds are covered with stiff hairs, with four separated branches. The under surface are brown and pubescent with slender and unbranched hairs.
Reproduction: vegetative means through fragmentation or the production of new plants from lateral and terminal buds. Stems may have as many as 5 buds per node and each bud can develop new fronds.
Distribution in Florida: throughout the peninsula and into the panhandle
With an extremely high reproduction rate, it can rapidly colonize a water body displacing native species, altering water chemistry, clogging irrigation channels, impairing flood control infrastructure, and impeding recreational activities. These impacts can decrease waterfront property values. It can also cause problems in rice, catfish, and crawfish cultivation. A public health consideration is that it enhances habitat for mosquitos which vector diseases such as West Nile Virus.
Thoroughly clean boats, motors, and gear when moving from one water body to another. Do not purchase for use in water gardens or aquariums.
When populations are small, manual removal can be effective. Where possible, water level manipulation may be employed as well.
Mechanical harvesting is most effective on early stage, localized populations or as a part of a larger integrated pest management strategy as it is often cost prohibitive.
The salvinia weevil (Cyrtobagous salviniae), native to South America, is widespread in Florida. It feeds and reproduces only on plants in the Salviniaceae family.
Herbicides can provide effective short and/or long-term control depending on the choice of product and the method and frequency of application. Of the herbicides currently registered by the US Environmental Protection Agency for use in aquatic sites, ten provide good (> 75%) to excellent (> 90%) control of common salvinia. The most widely used herbicides include diquat, glyphosate, flumioxazin and carfentrazone-ethyl. It is important to consult an expert for assistance in developing the most effective and integrated approach to management.