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The distribution and spread of Salvinia molesta (giant salvinia) has progressed from independent introductions across the southern United States.

A 1995 outbreak in South Carolina was the earliest U.S. record outside of cultivation. Salvinia molesta has not reappeared at this site since control measures were completed that year.  However, its prevalence in the horticultural market during the early 1990s provided a source from which the fern began escaping in other southern states.

Salvinia molesta resurfaced in Texas, May 1998, at a Houston schoolyard demonstration pond. Within a few months infestations were found at farm ponds scattered across southeast Texas.  By September it appeared on the massive Toledo Bend Reservoir, bordering Texas and Louisiana.

Within the next year, a large number of reports resulted in confirmation of 50 new localities. All the southern tier states (except New Mexico) and Hawaii had discovered Salvinia molesta outside of cultivation. The word on Salvinia molesta had been well publicized and many were engaging survey and educational campaigns to actively seek out populations.  Important western infestations were discovered.  Plants originating in California’s Palo Verde Irrigation District were found downstream at Imperial National Wildlife Refuge, on the lower Colorado River, in Arizona.  Salvinia molesta has since entered Mexico, through the Colorado River.

North Carolina recorded significant appearances of Salvinia molesta in 2000.  Since then new reports have slowed. While herbicide treatments have abated some of the more isolated outbreaks, as in Mississippi and Alabama, the severity of many infestations has not diminished.

Texas and Louisiana still bear the brunt of Salvinia molesta.  Four public reservoirs, seven rivers/streams, two large marshlands and over 20 ponds have been recorded within the two states. Swinney Marsh, a vast swampy complex on the Lower Trinity River remains the most extensive infestation in Texas.  In 2001, marshlands in southwestern Louisiana were similarly affected.  Inaccessible by boat and full of obstructions, (including ranging cattle!) natural marshes are difficult to treat with chemicals.  Biological control research poses good promise in these two regions.

C.C. Jacono, M.M. Richerson
Updated: 22 July 2004