Saline Water Controls Salvinia molesta in Louisiana Coastal Bayou
 

Excellent control of giant salvinia (Salvinia molesta) has been achieved by pumping high salinity water to flood an infested canal and adjacent marshes in Cameron, Louisiana. Dearl Sanders, Louisiana State University (LSU), working alongside the Cameron Parish Police Jury, the Cameron Parish Drainage Districts, Louisiana Department of Wildlife and Fisheries (LDWF) and the LSU AgCenter reports the following exciting summertime effort.  Before: / After:

In mid-May when salinity in the nearby ship channel had risen to about 25 ppt, freshwater in the infested habitat was pumped down as low as possible. The area was then reflooded with high salinity water, resulting in an average salinity level of 20 ppt. This hammered the giant salvinia.  Four weeks later, barely a single live plant could be found.  Salinity had returned to normal (0-2 ppt) and native plants experienced little impact.  The high salinity water had extended as far back as the infested marsh ponds, about 1.5 miles on either side of the canal.  Ponds that had a connection to the canal, both through a culvert or an open ditch, were first pumped as low as possible and then refilled with saline water. Floating booms were placed across each opening to trap floating salvinia that might otherwise have drifted out.  The only plants that survived were in isolated potholes that did not have an open connection to the canal. The potholes were sprayed twice with herbicide from a marsh buggy or airboat. Charlie Dugas, LDWF, provided most of the herbicide. The entire drainage area affected was roughly 7 miles long and 3 miles wide.

Biologists along the coastal region of southeastern Texas also employ the practice of raising salinity to control the smaller species, Salvinia minima. Floating weeds are controlled and waterfowl habitat is improved by regularly opening gates to allow saline water from the Gulf of Mexico into freshwater coastal bayous.

Giant salvinia has little tolerance for brackish or marine environments. In experimental trials (Divakaran et al., 1980) salinity above 7 ppt retarded growth and damaged plant tissue. Higher concentrations of salt were lethal.  Plants maintained at 11 ppt were killed after 20 hours exposure, mortality resulted in less than 1.5 hours at 20 ppt, and full strength seawater, 34 ppt, destroyed plants in 30 minutes.