Giant salvinia, an extremely invasive floating aquatic fern from southeastern Brazil, was found on Caddo Lake by a Louisiana research biologist on May 29, 2006. An initial survey, conducted by Texas Parks & Wildlife Department (TPWD) personnel, revealed a well-established population of giant salvinia in Jeem's Bayou on the Louisiana portion of the lake. The infestation was estimated to cover more than 150 acres.
The presence of giant salvinia in one of the most sensitive regions of the state prompted an immediate, aggressive response from both Texas and Louisiana officials to contain the infestation and prevent further expansion. Chemical treatment of the infestation on Caddo Lake began within days of its discovery. An estimated 190 acres of giant salvinia were treated by vegetation control crews from TPWD and the Louisiana Department of Wildlife and Fisheries. Repeated treatments and surveys are planned throughout the summer to eliminate any remaining colonies.
Giant salvinia management has been a priority for the Aquatic Habitat Enhancement office of TPWD for years on Toledo Bend Reservoir. Using an integrated pest management approach, focused chemical treatments are supplemented with large-scale introductions of giant salvinia weevils as a bio-control agent to help reduce giant salvinia populations on the 185,000 acre reservoir. Giant salvinia weevils may be introduced on Caddo Lake if surveys indicate chemical treatments alone are unable to establish control.
Giant salvinia was first found in Texas in 1998. It has since become established in several major reservoirs and numerous private ponds. Often called "the world's worst weed," giant salvinia has been responsible for substantial economic and environmental hardship in Asia, South Africa, Australia and the South Pacific.
Giant salvinia can negatively impact aquatic habitat wherever it occurs. Under ideal conditions, populations can double every 5-8 days, are resistant to cold weather and can survive for weeks out of water if kept moist. Once established, the fern forms dense mats that eliminate all other aquatic vegetation in the area, eliminating even phytoplankton and zooplankton, which are vital to healthy fish populations.
Giant salvinia typically has oblong floating leaves from ½ to 1 ½ inches long. Leaves have a velvety surface and are usually a shade of green. The leaves of younger plants lie flat on the water surface. In more mature plants the leaves are much larger, folded, and compressed into upright chains. When viewed with a magnifying glass, the tips of leaf hairs on giant salvinia can be seen to form a cage-like structure shaped like an eggbeater.
Giant salvinia is easily spread overland to new locations by boat trailers, propellers or even the intakes of jet-skis. Concerned anglers and other resource users can help by inspecting and cleaning their boats, trailers, jet-ski intakes and other equipment of all aquatic vegetation before leaving an infected area. Most new infestations of invasive species occur at or near boat ramps. Anglers fishing Caddo Lake should be aware of any suspicious floating aquatic vegetation, particularly around boat ramps and the backs of nearby creeks.