Giant salvinia, Salvinia molesta, is a fast-growing aquatic weed that came to the United States from South America via the imported plant trade. First appearing in 1995, severe infestations of the weed have taken over parts of the southeast.
Giant salvinia is a fern, therefore it does not flower. Its spores are mostly sterile, making its primary growth form asexual. Plants shoots grow from buds and are connected by an underwater rhizome. When the rhizome breaks, new shoots can grow from the fragments.
In 16 years giant salvinia has spread to cover much of Louisiana’s waterways. Major routes of dispersal include floodwater and boat movement between waterbodies.
A threat to industry
Thick plant mats clog boat motors and disrupt natural ecosystems. This impacts water activities from recreational boating to industrial fishing, farming, and waterfowl hunting.
Introducing a weevil
The salvinia weevil, Cyrtobagous salviniae, is a tiny black beetle from Brazil that specializes on salvinia species. The weevil has been used successfully to combat giant salvinia infestations since as early as 1980 in Queensland, Australia. The first weevils were brought to the United States 2001.
Weevils are mass-reared in outdoor giant salvinia ponds. Ponds are managed year-round to provide a nutrient-rich food source.
Ponds are harvested in spring or fall of each year and weevil-infested salvinia is distributed to landowners who need it. The Louisiana Department of Wildlife and Fisheries coordinates with the LSU AgCenter to oversee distribution in public waters.
Weevil-infested plants are packed into totes and transported to salvinia infestations. The plants contain eggs, larvae, pupae, and adults. Infested salvinia is incorporated into the plant mat to allow weevils to begin feeding and laying eggs on fresh material.
Salvinia weevil adults feed on nitrogen-rich buds and lay eggs into crevices of the plant. Larvae burrow into the underwater rhizome and complete their development among the “roots”.
Signs of control
Weevil feeding slows new bud growth and disrupts nutrient flow from salvinia’s “roots” to the leaves. Starving plants turn brown, begin to decompose, and eventually sink. This process can take months to a year or more.
Sinking of salvinia mats restores access to sunlight and oxygen beneath the water surface, allowing submersed aquatic plant life to return. Submersed vegetation is a key component of waterfowl habitat and provides habitat for native fauna to recolonize wetlands.
The LSU AgCenter and the LSU College of Agriculture