Scientists with the LSU AgCenter and the Louisiana Department of Wildlife and Fisheries are combining their efforts in an attempt to control giant salvinia — a noxious aquatic weed that is spreading across Lake Bisteneau in northwest Louisiana near Doyline, La.
On June 23, Dearl Sanders, an LSU AgCenter weed scientist, and Seth Johnson, an LSU AgCenter entomologist, brought the salvinia weevil to the lake control weed there.
“We have a nursery in Lafourche Parish where we grow the weevils, and when we’re ready to transfer the weevils, we harvest the giant salvinia along with the weevils,” Sanders said. “We load them onto trucks and bring them here to be released into the lake.”
Sanders said during two weeks in June, more than 50,000 pounds of the weed with more than 1 million weevils made the trip from south Louisiana.
He said the weevils have been released in 17 Louisiana water bodies, but none this large so far.
The LSU AgCenter has been involved in the giant salvinia eradication program since the weed was found at Toledo Bend in 1999.
Sanders said he got involved in the project initially from a chemical standpoint, but the problem is so big now that there simply are not enough resources available to buy the herbicides to spray the weeds.
“There are some effective herbicides, but they are very expensive,” he said. “They would be OK for 2 acres, but what about 10,000 acres?”
For this reason, Sanders and his team decided to look at biological control. He said the weevils do all of the work, and his only expense is the cost of transporting the weevils.
According to Sanders, giant salvinia is native to Brazil and spread to many areas of the world in the 1950s and 1960s.
“They appeared here by the water garden trade in the 1990s,” Sanders said. “When people saw that the weed was taking over their ponds, they pulled it out. Some people threw it in ditches, and it ended up in the waterways.”
He said the plant almost doubles in size every day. “It grows so fast that you just can’t keep up with it by spraying,” Sanders said.
Johnson said he is interested in the reproductive development of the Brazilian weevil and identifying characteristics related to development.
“We are dissecting weevils and developing a way to age the female weevils based on the condition of the reproductive system,” Johnson said. “We will then be able to estimate age and reproductive potential of populations in the field.”
Johnson said this will enable him to predict the condition of field populations of weevils and the potential for biological control of giant salvinia at that site.
Sanders said not only is the weed a problem for boaters and fishermen who want to use the lake, but it also is causing economic problems for property owners in the area.
“There are some very expensive properties on this lake that are losing value because of the damage being done by this weed,” Sanders said. “Many areas on the lake are totally covered with it.”
James Seals, District One fisheries biologist manager with the Department of Wildlife and Fisheries, said the weed was first discovered in scattered areas of Lake Bisteneau in 2006.
“We immediately brought in spray crews and began our eradication program,” Seals said. “Thus far, herbicides have proven ineffective.”
Seal said the most effective control measure has been the drawdown of the water level in the lake.
He said 4,500 acres of the 17,000-acre lake were covered before the drawdown on July 15, 2008, and only 850 acres were covered coming out of the drawdown.
“We will continue the control and research program on giant and common salvinia as long as we have funding,” Johnson said.
Sanders said boaters should try to remove as much of the weed from their boats as possible when they leave the water because the weed has been shown to live up to two weeks on boats out of the water.