Salvinia, Water Fern, Water Spangles (Salvinia minima) Baker.
Salvinia, Water Fern, Water Spangles (Salvinia minima) Baker.
A complete review and evaluation of the biological control of this species was conducted (Coulson 1977). Searches for potential biological controls were begun in South America during 1960. Research revealed the identification and release of three host-specific insects (Zeiger 1967; see the insect section of this report for more details). In 1964, several host-specific biological control agents were released in the United States to manage alligatorweed and have generally been effective in the reduction of this weed's aggressiveness. These host-specific insects and plant pathogens increased leaf mortality, decreased plant size, and reduced overall population expansion. This biological weed control remains the most successful to date in Florida because alligatorweed only occasionally requires emergency control. Insects, usually the alligatorweed flea beetle (Agasicles hygrophila), are transported from existing colonies elsewhere to create new infestations. Control is usually achieved within a few months (Schardt and Schmitz 1990).
Salvinia is native to the region from southern Mexico through Central and into South America (Weatherby 1937). In Florida, it was first collected in the St. Johns River during 1928 (Long and Lakela 1976). The exact nature of its entry into the state is unknown but may have been through the discharge of spore-contaminated ship ballast at the Port of Jacksonville (Schmitz et al. 1991) or from discarded aquaria. Rataj and Horeman (1977) among others list this species as the most convenient and acceptable salvinia species for aquaria. This species has long been used as an ornamental and as a shade and habitat provider for pools and aquatic gardens. It is one of the more widely dispersed plants in Florida waters and present in 208 of the surveyed public lakes and rivers in 1990. With more than 506 reported hectares, it ranks 47th in abundance of observed aquatic plants (Schardt and Schmitz 1990).
Salvinia can be a nuisance floating plant that grows best in warm, quiet, often nutrient-enriched waters. Its buoyant, horizontal stems spread out on the surface of the water. Reproduction is sexual and asexual, and the fragmentation of stems prevails in spreading the plant (Cook and Gut 1971). This plant grows extremely fast and is capable of doubling its size in approximately 3.5 days (Gaudet 1973). This is even faster growth than the closely related S. molesta, which is one of the world's worst weeds (Nelson 1984). Problems with salvinia in Florida are usually confined to drainage systems and are few in lakes and rivers. This species is controlled most often with the herbicide diquat. Mechanical controls are ineffective (Schardt and Schmitz 1990). Thomas and Room (1986) discussed the taxonomy and control of Salvinia molesta.
