Foreign Fern Threaten Texas Lakes & Rivers

By: TP&W Email
By: TP&W Email

(CADDO LAKE)—The Texas Parks and Wildlife Department, the Cypress Valley Navigation District and the Caddo Lake Institute have gone to war with a floating fern from South America that threatens the state’s only naturally formed lake.

Caddo Lake, which has been designated as a wetland of international importance, is threatened by a fern called giant salvinia, which first appeared on the lake in 2006 and in two years spread from two acres of coverage to a thousand acres.

“We’re here at Caddo Lake to spray giant salvinia with herbicide to try to knock it back to a more manageable level,” said Craig Bonds, TPWD’s regional director for inland fisheries.

“We are at a tipping point with giant salvinia coverage. If we don’t get on it heavily, we could lose this battle and experience increased levels of giant salvinia, to the point where we won’t be able to control it. We will never eradicate it. This is going to be an on-going fight.”

Crews will apply EPA-approved herbicides for the next week using five spray boats, each of which can cover about 40 acres of lake surface a day.

“Hairs on the leaves of giant salvinia make it very resistant to herbicide application,” said Howard Elder, TPWD’s aquatic vegetation biologist.

“We have to use very aggressive herbicides and surfactants approved by the EPA to be able to control the plant. We have found herbicide applications to be about 90 percent effective; it takes a week to 10 days to see results.”

Crews are also using a mechanical harvester to remove the fern.

“We’re conducting trials to see how the harvester will handle the shallow, stumpy water of Caddo Lake,” said Jack Canson with the Caddo Lake Institute.

A private landowner bought the harvester and the City of Marshall appropriated $25,000 to test the machine.

“We don’t think that harvesting can cure the problems at Caddo Lake; we don’t think that herbicides alone can, either,” Canson said.

“We do think there are places on the lake where a harvester can provide relief—clearing boat roads and areas where there is a lot of public use. We’re very encouraged by the results so far.”

Giant salvinia can attach to boat trailers and can inadvertently be transferred to other lakes in the state, so the Parks and Wildlife Department is encouraging boaters and fishermen to be aware of the potential problem.

“We need every angler, recreational boater and waterfowler to implement a vital behavior: Clean your boat trailer when you exit a water body that has giant salvinia,” Bonds said.

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