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June 5, 2009
TPWD Battles Giant Salvinia On Caddo Lake
Fate of unique wetland hangs in the balance
UNCERTAIN, Texas — Caddo Lake, the only large, naturally formed lake in Texas, has been designated as a wetland of international importance. It supports an ecosystem found nowhere else in Texas.
And we may be losing it.
Not to development or global warming or neglect, but to a floating fern from South America first found in Texas little more than a decade ago: giant salvinia, or Salvinia molesta.
Giant salvinia first appeared on Caddo Lake in 2006, and it quickly progressed from invader to near-conqueror.
In just two years the plant expanded its coverage of the surface from two acres to more than 1,000.
Texas Parks and Wildlife Department (TPWD), in partnership with the Cypress Valley Navigation District and the Caddo Lake Institute, launched an offensive against giant salvinia on June 1. "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."
TPWD and Cypress Valley Navigation District crews will be on the lake applying Environmental Protection Agency (EPA)-approved herbicides until about June 12. Each of the five spray boats operating can cover about 40 acres per 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."
The battle against giant salvinia is being fought mainly by the herbicide boats and a mechanical harvester that gobbles up the plant from the surface of the water and carries it to shore for disposal. Salvinia-eating weevils are also in use on several lakes, but results are slow.
"We’re conducting trials to see how the harvester will handle the shallow, stumpy water of Caddo Lake," explained Jack Canson with the Caddo Lake Institute. "This came about because we have a private landowner at Caddo Lake, Mr. John Sanders, who has a long association with the lake and a background in heavy machinery. He purchased the machine and brought it here. The City of Marshall appropriated $25,000 so we could test to see how the harvester will actually operate. We don’t think that harvesting can cure the problems at Caddo Lake; we don’t think that herbicides alone can, either. 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."
While it may seem impossible for a simple plant to defeat all the efforts to get rid of it, such has already happened. "At Toledo Bend Reservoir south of here, the magnitude of the problem is so great that we are relegated to just keeping boat ramps free and clear and improving boat access and navigation where we can," said TPWD’s Bonds. "Actually controlling giant salvinia is no longer an option on that lake given current resources, and we are trying to keep Caddo from reaching a similar condition."
The stakes are nothing less than survival-for the lake and for the people around it. "Caddo Lake is a national treasure because of its ecosystem and the diversity of plants and animals it supports," Bonds said. "Giant salvinia has the capability of wreaking havoc here. It can double its coverage every five to seven days under optimal growing conditions. We have nature tourism here, we have anglers, recreational boaters, waterfowlers-and every single user of this lake is impacted by this plant. If we don’t ramp up our efforts to control this plant now, we may lose control of it. That’s our fear, that this wonderful, wonderful place is at risk."
The threat does not end with Caddo. Giant salvinia has the capability of riding on boat trailers to other lakes throughout Texas and causing similar problems. And that offers hope-if all boaters and anglers will help.
"The ultimate answer for combating this problem outside the Caddo Lake area is not herbicide control," Bonds explained. "It’s public awareness and public participation. 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. Signs at boat ramps at reservoirs where giant salvinia occurs warn anglers to watch out for this plant. It is critical to have 100 percent compliance from boaters to stop the spread of this plant. It only takes one person to spread this problem to other areas."
Bonds and Elder also urge people using any lake to report any plants they suspect might be invasive species. "Angler reports to us have been instrumental in eradicating giant salvinia on several other lakes," Bonds stated. Suspected infestations can be reported to Elder at (409) 384-9965. The TPWD web site has information that anglers and boaters can use to learn to identify this and other invasive species.
While the efforts to combat giant salvinia are expensive — $64,000 for herbicides alone for the current operation-the cost of doing nothing could be even greater. "We cannot even think of not doing what we can to control the giant salvinia on the lake," said Elder. "If not controlled, giant salvinia can and will take over the entire lake. It will block out all light from the water beneath, displacing native fish and plant species, negatively impacting the water quality and displacing waterfowl and other wildlife. Should giant salvinia progress to the point where access is affected, all recreation will cease. You won’t be able to launch a boat or move a boat through dense salvinia mats. It will cost local communities and reservoir-based businesses countless revenue."
Until now, life in Uncertain, Texas, has allowed many people to fulfill the dream of living in a special place where the pace is slow and the world’s problems seem far away.
Thanks to giant salvinia, the town’s name now seems prophecy, not promise.
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