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Using bugs for weed control

LSU AgCenter researchers think the salvinia weevil may be what they’ve been looking for as a way to control giant salvinia — an invasive aquatic species in the state.

Dearl Sanders, an LSU AgCenter weed scientist, and Seth Johnson, an LSU AgCenter entomologist, have been cooperating with the Corps of Engineers and Louisiana Department Wildlife and Fisheries to look at ways to produce the weevil in large-enough numbers to push back the growth of the noxious water weed.

Sanders has an agreement with Benny Cenac, owner of Golden Ranch Plantation in lower Lafourche Parish, to produce the weevils on a large scale.

“We agreed to grow the weevils here on Mr. Cenac’s 50,000-acre plantation, then transfer them as needed to areas of the state where the infestation is worst,” Sanders said.

He said giant salvinia has begun to affect property values in some parts of the state, creating an urgency to find a way to slow the progression of the plant.

During the first week in October, LDWF’s Inland Fisheries Division transported initial batches of the weevils from Golden Ranch to Bayou Des Allemands, Lake Salvador, Turkey Creek Reservoir and the Atchafalaya River Basin.

Since then, they’ve made additional releases in Toledo Bend Reservoir, Clear/Smithport Lake, Loggy Bayou and Black Bayou Lake in Caddo Parish.

“Our aquatic plant control program utilizes a multiple management plan approach that includes weevils, herbicide applications and drawdowns in water bodies with significant weed growth,” said Rachel Walley, LDWF aquatic program biologist.

“If weevil colonies can be established in waterways with existing salvinia problems and weather conditions provide for continued weevil growth, they could become an effective tool for controlling the expansion of this prolific aquatic weed,” Sanders said.

The LSU AgCenter weed scientist said the invasive plant came into the United States through the water garden trade. He said people bought the plants, which are native to Brazil, to use in their koi ponds. But when the salvinia took over the ponds, people threw it in ditches and caused the problem we have today.

Sanders said the plant is prolific and can overtake a body of water in a short period of time.

“This thing almost doubles in size everyday,” he said. “It grows so fast that you just can’t keep up with it by spraying.”

Sanders and Johnson put 1,600 pounds of the weed in a 6-acre research test pond, and Sanders said it had covered the pond in 28 days.

In late 2007 and again in 2008 the researchers infested the salvinia with weevils.

Johnson is looking at reproductive issues and the life cycle of the weevils.

He said he’s interested in how many eggs the females lay and how low the temperature has to be before the weevils’ reproductive activity decreases.

Sanders said they also are interested in learning whether the weevils can fly as some other weevils that develop wing muscles when they are distressed.

He said the LSU AgCenter’s agreement with Cenac is to produce the weevils on his property with half going to LDWF and the remainder to be used on the ranch where the giant salvinia already covers more than 10,000 acres.

Sanders said the weevils have been effective in controlling salvinia in other parts of the world, and small research trials at Toledo Bend and other Louisiana locations have produced good results.

Sanders said more than 500,000 pounds of weevil-infested salvinia currently at the research pond in Lafourche Parish are earmarked for LDWF to transfer to other areas where salvinia infestation is heavy.

“If we were to take all of the salvinia out of this pond today, it would take about 20 tractor trailer loads, which would include roughly 2.5 million salvinia weevils,” Sanders said.

Success, according to Sanders, is not necessarily to eradicate the weed, but to get it to manageable levels would be a giant step in the right direction.

Giant salvinia’s relative, common salvinia, has been in the state for many years and does not cause nearly as much trouble.


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