Giant salvinia reduced in Lake Bistineau, still a problem in south Louisiana

Mary Ann Van Osdell, Sanders, Dearl E., Johnson, Seth J., Lorio, Wendell J.  |  5/5/2011 6:18:19 PM

News Release Distributed 05/05/11

Two consecutive cold winters along with biological control using weevils have helped ease the giant salvinia problem on Lake Bistineau near Bossier City. And more weevils are ready for distribution in a few months to areas in south Louisiana where this invasive, aquatic weed is continuing to be a problem, according to LSU AgCenter experts.

Almost 90 percent of the giant salvinia is gone at Lake Bistineau, which is back to its 2004-2005 level, said Dearl Sanders, an invasive species specialist at the LSU AgCenter. But waterways are infested from suburban New Orleans to Morgan City. “It’s just as bad as it ever was south of Alexandria,” he said.

The U.S. Army Corps of Engineers ran Mississippi River water in large volumes into the Gulf to keep out oil from the BP spill, but that the water pushed giant salvinia further into the marsh and over a wider area, Sanders said.

The invasive, resilient plant clogs waterways and threatens the water supply and its quality, said LSU AgCenter entomologist Seth Johnson. Giant salvinia grows in thick mats and clings to boat motors and trailers. It covers the water surface and doubles every day and a half, Johnson said. And it’s costly to control.

In recent years, the LSU AgCenter and Louisiana Department of Wildlife and Fisheries introduced a weevil to combat the noxious plant. Native to Brazil, Bolivia and Paraguay, the weevil is a specialist whose larvae burrow into the rhizomes of giant salvinia, Johnson said.

Adults consume leaves and buds, which inhibited plant growth, he said. Larval feeding causes the leaves to first darken and then drop off. The combined feeding of larvae and adults kills the plant.

South Louisiana infestations are mostly in marshes on private lands, Sanders said. The Lake Bistineau problem was an issue because it was in a residential area.

The Louisiana Department of Wildlife and Fisheries and the LSU AgCenter worked together to collect and and transport more than 30 tons of weevil-infested giant salvinia with approximately 2.3 million weevils to Lake Bistineau and four other north Louisiana lakes in 2009.

The weevil-infested plants came from weevil nurseries the LSU AgCenter helped establish in Lafourche, Terrebonne and St. Charles parishes. An initial weevil nursery in Gheens was used to develop the protocol for producing weevils in giant salvinia, the timeline for weevil population growth and the optimum times for weevil harvest and distribution.

A new nursery in Luling is being developed more quickly than anticipated, said LSU AgCenter fishery biologist Wendell Lorio. The weevils will be available in a couple of months for St. Charles and neighboring parishes, he said.

Lorio said duck-hunting areas in those regions are filled with giant salvinia, which destroy waterfowl habitat in particular and wildlife and fisheries habitat in general.

“You can work decades and don’t always see what you’ve accomplished,” Lorio said. “Seeing weevils help control salvinia is pretty exciting and encouraging. It works.”

Billy Montgomery, chairman of the Lake Bistineau Task Force which has members in Bossier, Bienville and Webster parishes, said he welcomes help from the LSU AgCenter. At its meeting March 31, the task force passed a resolution requesting the LSU AgCenter conduct further research on ways to control giant salvinia.

Sanders said the LSU AgCenter is still making recommendations and has added one new chemical in recommendations for spraying. “We still encourage them to attack salvinia aggressively,” he said.

Mary Ann Van Osdell



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