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Sites where Salvinia molesta (giant salvinia) occurs in cultivation
may serve as sources for introduction to natural systems.
Surveys conducted by various agencies found Salvinia molesta in cultivation in sixteen U.S. states (mapped above). "In cultivation" refers to cultivation in tanks at commercial nurseries, botanical gardens and homeowner's backyard water-gardens. For example, the species has endured many years in university greenhouses at St. Paul, Minnesota (W. Crowell, pers. comm.) and was present during the autumn of 2000 at Kenilworth Park and Aquatic Gardens, Washington D.C. [B.W. Steury 000905.2 (US)].
Florida hosts an early record of Salvinia molesta in the aquatic plant and water-garden market, during 1983 (Nelson 1994). By the early 1990s it was observed at nurseries in other southern states. Infestations at some Texas ponds have been linked directly to purchases from water-garden nurseries. How plants entered Toledo Bend Reservoir and other natural waters is likely related to the prevalence of Salvinia molesta in the horticultural trade and its escape from cultivation.
Nursery surveys have recently been conducted in many states, an action encouraged by the Southern Plant Board. Nursery sales have been documented in twelve states: Texas, Louisiana, California, Hawaii, Arizona, New Mexico, Alabama (Haynes and Jacono 2000), Oklahoma, Oregon, Washington, Virginia, and Pennsylvania. A business in Lafayette, Louisiana recorded an excess of 400 individual sales before their stock was destroyed (C. Dugas, pers. comm.). A California survey of commercial nurseries between May and August 1999, found Salvinia auriculata-type plants (here presumed S. molesta) for sale in 48 cities in 15 counties (CDFA 1999). California sales centered around distributors in Sonoma and Los Angeles county (F. Hrusa pers. comm.). Nine counties in North Carolina reported nursery sales of Salvinia molesta (D. Patterson, pers. comm.). An Oklahoma survey stated that Salvinia molesta often arrived as an unwanted contaminant in other plant shipments and was difficult, if not impossible, to remove from their stock (Edwards 1999). This sentiment has been repeated by nurserymen across the country.
Federal regulatory efforts apparently postponed the advent of giant salvinia into the country.
As a Federal Noxious Weed , the importation of Salvinia molesta into the United States and transport across state lines has been prohibited for decades. Yet, the species must be listed by each individual state as a State Noxious Weed in order to be prohibited for sale, possession or transport within a particular state. Salvinia molesta is prohibited in Arizona, California, Florida, Georgia, Louisiana, North Carolina, South Carolina and Texas. It can be freely cultivated and sold within the other 42 states, as long as it is not transported across the state line. Transport of plants across state lines is not uncommon, the Mississippi infestation resulted from a gift of plants brought from Louisiana.
The four closely related species in the Salvinia auriculata complex (S. auriculata, S. biloba, S. herzogii, and S. molesta) are all prohibited as Federal Noxious Weeds. These species all share the feature of "egg beater-like hairs". Of these four plant species, only Salvinia molesta has been recognized in the recent U.S. nursery industry surveys. It is also the only species that documented as a serious weed in other countries.
Modes of transport and spread.
Human transport will spread giant salvinia locally. Copious hairs on leaf surfaces and deeply embedded lateral buds are two features that provide protection against desiccation. Plants easily adhere to and can be carried overland on anything entering infested waters. Boats, trailers, vehicular wheels, engine intakes, fishing and recreational gear, even boots can host and carry hitchhiking plants. Trails of plants are common along boat ramps and roads leading from Toledo Bend Reservoir. Toledo Bend is a famous fishing spot within a days drive from many favorite fishing lakes. Lakes Sam Rayburn, Steinhagen and Livingston are at considerable risk as they host thousands of boats that are commonly trailered back and forth. These large Texas reservoirs have thousands of acres of quite backwaters and drain into sensitive natural areas downstream (R. Jones pers. comm.).
Spread will continue through natural drainage and flow in river and stream systems. In lakes and large water-bodies upright well buoyed leaves are effectively dispersed by wind and currents to infest new coves.
Contributor Acknowledgements
References
Author: C.C. Jacono
Updated: 06 July 2005
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