Researchers continue quest to rid Louisiana waterways of salvinia

Bruce Schultz, Diaz, Rodrigo  |  8/24/2015 8:30:29 PM

A crew with the LSU AgCenter, the U.S. Fish and Wildlife Service and the Louisiana Department of Wildlife and Fisheries loads weevil-infested giant salvinia onto a conveyor belt near Houma, Louisiana, in October 2012. Photo by Tobie Blanchard

News Release Distributed 08/24/15

BATON ROUGE, La. – The LSU AgCenter is moving its facility for growing weevils to eradicate the aquatic weed called salvinia. A location in Terrebonne Parish on the property of Michael St. Martin had been used for the past four years.

“We appreciate the St. Martin family for allowing us to establish a weevil population on their land,” said Rodrigo Diaz, LSU AgCenter entomologist. “It provided an excellent location to maintain a healthy population of the insects.”

Diaz said three new locations will be used, all on LSU AgCenter property.

Salvinia is an invasive species that came to the U.S. in the 1990s from South America. It grows rapidly and forms dense mats on the water surface. Herbicides can be used to control salvinia, he said. But spraying is not completely effective, and enough plants survive to maintain a regrowth of the invasive species.

The weevils are originally from South America, too. “They are not good fliers, and they won’t move to crops,” Diaz said. “These weevils only attack salvinia.”

Dearl Sanders, who ran the LSU AgCenter weevil program before retiring last year, said the weevil project for large-scale releases began at Gheens in 2008, and the weevils were harvested and released from that site through 2011.

“Most of the success was achieved in Lafourche, St. John, St. Charles and Jefferson parishes,” Sanders said. “On monitored sites in Lafourche Parish, infestation levels of giant salvinia were reduced by 90 percent within three years.”

Sanders said the weevil nursery was moved to Houma in 2011, and salvinia populations had been reduced by 90 percent in that area.

Diaz said salvinia remains a problem in Cameron and Vermilion parishes. In addition, the weed is a big problem in lakes and streams in central and north Louisiana, such as Cross Lake near Shreveport and Lake Bistineau near Doyline.

But the weevils have difficulty surviving cold winters, so new strategies are being used to help maintain the insect’s population in north Louisiana.

Research by another team member, Steve Micinski, at the AgCenter Red River Research Station in Bossier City, is using pine straw and fabric to cover infested salvinia to help insulate weevils from the cold.

“Over time, maybe some of these weevils may survive these cold conditions. If this works, citizens may be able to participate in the process of modifying habitat to enhance weevil survival in north Louisiana,” Diaz said.

Seth Johnson, LSU AgCenter entomologist, said controlling salvinia with weevils on Cross Lake and Lake Bistineau has been inconsistent because of cold winters. “Control on those two lakes has been seasonal and intermittent with elimination or near elimination of the weevil population in three of the last five years due to winter temperatures below survival levels,” he said.

Johnson said another research project is in progress to find weevils in southern South America or Australia that can tolerate the harsh winter temperatures that occur in north Louisiana.

To find those winter-hardy weevils, Diaz plans to travel to Uruguay and Argentina in November and February to collect weevil populations in areas that have similar climate to north Louisiana.

“The weevils we have here in Louisiana are originally from Brazil where the weather is more tropical,” he said.

Diaz said the weevils grown by the LSU AgCenter are for research and demonstration projects conducted by the Louisiana Department of Wildlife and Fisheries on public lakes and waterways.

Diaz said it is feasible to harvest salvinia infested with the weevil in public waterways and relocate a starter population on private land.

Ponds for the new locations to raise weevils were prepared two months ago, Diaz said, and salvinia was placed in the ponds last month. “We hope the plant will grow and cover the entire ponds in the next few months.”

After the plant is established, the weevils will be released on these plants to increase their population.

“We hope they will go through three or four generations by next fall, which is when we expect to harvest these ponds,” Diaz said.

Bruce Schultz

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