Giant salvinia (Salvinia molesta) is an extremely invasive free-floating fern indigenous to South America. The USDA listed this plant as a noxious weed in 1983. The first discovery of salvinia in the U.S. occurred in a small pond in South Carolina in 1995. The infestation was identified quickly and the pond was treated successfully with herbicides. Infestations currently exist in Texas, Louisiana, Mississippi, Alabama, Georgia, Florida, Arizona, California, and since 2000, North Carolina has been added to this list.
Salvinia varies in color from green to gold. The leaves of this plant are about the size and shape of fingernails. Leaves of young plants tend to lie flat upon the water. The largest leaves may grow to about two inches. Giant salvinia can grow very rapidly. Under favorable conditions, infestations will double biomass in 4-10 days. Imagine if the tree in your yard doubled it's size every week!
Salvinia molesta can greatly alter aquatic ecosystems. Mature plants create a dense floating mat. In places where salvinia has not been controlled, mats have grown to be two feet deep. Vegetation beneath these thick mats suffers from lack of light. The level of dissolved oxygen (DO) will drop, forcing fish to move to other areas. Reptiles, amphibians, and other aquatic animals will be burdened by the change of habitat. Wading birds and other waterfowl will have difficulty finding food and will likely relocate. Swimming, boating, and other recreation will be inhibited. Drinking water and agricultural water intakes, hydroelectric and other industrial water intakes will all be faced with fouling problems.
Boats and other recreational watercraft transport salvinia from one water body to another. Some plants will get pushed by wind or carried by water flow to new areas. Unintentional introductions from flooded aquatic plant nurseries, ornamental ponds, and water gardens are a threat. Small salvinia plants will often "hitchhike" on other ornamental aquatics. Always inspect for hitchhikers when purchasing aquatic plants. Sometimes it is even for sale under disguising common names. Remember, salvinia is a controlled organism and is illegal to sell or transport.
Salvinia in Brazil is naturally controlled by an indigenous weevil (Cyrtobagous salviniae). This weevil is host-specific and doesn't feed on other vegetation. This particular characteristic makes C. salviniae an excellent candidate as a biological control agent for use outside of its native environment. USDA-APHIS scientists have experimented with the use of this bug and observed exciting results. Trial releases in North Carolina began in 2004.
The creation of the multi-agency Giant Salvinia Task Force has played a major role in monitoring and controlling the infestations in NC. The Task Force is praised as a model example of the Early Detection Rapid Response (EDRR) concept.