Controlling giant salvinia takes patience, herbicides

Bruce Schultz, Sanders, Dearl E.  |  8/24/2013 1:58:03 AM

News Release Distributed 08/23/13

CROWLEY, La. – Giant salvinia in southwest Louisiana should be under control in a few years. In the meantime landowners can combat the invasive aquatic weed with herbicides, according to an LSU AgCenter weed specialist.

Dearl Sanders told landowners at a meeting on Aug. 22 at the Rice Research Station that salvinia came to Louisiana in 1999, imported by commercial water garden companies. He said the plant also is a problem in Australia, Indonesia and New Zealand.

“It is the poster child of invasive species,” he said.

The floating plant is closely related to Boston ferns, and it reproduces by spores instead of seeds. He said one plant can multiply until it covers 40 square miles of water in one year.

“It has the fastest growth rate of any plant on the planet,” he said.

Once waterways are covered with the weed, fish and other aquatic creatures either die or leave the area. Other vegetation, blocked from sunlight, inevitably dies, leaving an underwater desert, Sanders said.

He said controlling 90 percent of a weed is considered a success, but controlling 90 percent of a salvinia infestation is ineffective. “Within 30 days you are back to 100 percent coverage again.”

He said the best chemical is Diquat, but it is expensive. Glyphosate works well at high concentrations, he said, but it is more effective when mixed with a small amount of Diquat.

For a list of herbicides and the concentrations, visit the LSU AgCenter website (www.LSUAgCenter.com) and search for aquatic weed management guide or ask at the local LSU AgCenter parish extension office.

The herbicide combination should be used with a surfactant to get coverage on the plant’s hairy leaves. Dishwashing soap is not an acceptable surfactant because it interferes with the herbicides’ chemistry, so commercial surfactants should be used, he said.

He said spraying can be accomplished with a high-pressure sprayer or by aircraft. He said spraying three times will be required within a few weeks.

Plants that have turned brown but are still floating will be able to reproduce. “The only time you know it’s dead is when you can’t see it.”

Sanders said salvinia weevils, raised at the LSU AgCenter’s Bob R. Jones-Idlewild Research Station near Clinton, have been released across southwest Louisiana, and they should solve the salvinia problem within three years. He said the insect was used in the Terrebonne Basin, and the weed was eradicated in large areas.

The insect should work well in southwest Louisiana, too, he said, although it’s unknown if insecticides used in adjacent crop production may affect the salvinia weevil.

He said once the salvinia weevils have eaten salvinia, they no longer have food, and they crawl on land where they fall prey to fire ants.

Saltwater kills salvinia, he said, and that’s what killed an outbreak in the Prien Lake area at Lake Charles.

He said the weevils are being used in north Louisiana also, but the colder winters there tend to kill the insect population.

Bruce Schultz

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