Biologists Battle Giant Salvinia Blocking Lake Access for Duck Hunters, Waterfowl

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AUSTIN – At North Toledo Bend Wildlife Management Area, giant salvinia covers about half of the WMA’s 500-acre wetland impoundment, blocking boat access for duck hunters and keeping migrating waterfowl from food and habitat. The problem would be worse without steady work to fight back the invasive floating fern, efforts that got a boost this year by recording funding from the Texas Legislature.

Hundreds of duck hunters will come to North Toledo Bend this winter, and they’ll still be able to hunt birds, but the giant salvinia problem does limit their options. According to WMA staff, it can literally depend on “which way the wind is blowing,” as floating mats of salvinia blow across the lake.

“In recent weeks the wind has been blowing from the east causing the western part of the WMA to be solid salvinia, with other smaller patches throughout the impoundment ranging in size from 10-15 square feet to several acres, and most of the sloughs or creeks have had some extent of salvinia in them,” said Bob Baker, a Texas Parks and Wildlife Department wildlife biologist at North Toledo Bend.

“We try to keep it at bay using herbicide through a collaborative effort with our Inland Fisheries team,” Baker said, adding that this is complemented by $50,000 in gamebird stamp funds (paid by hunters) to help treat giant salvinia at North Toledo Bend this year and next. “The hope is that more duck habitat becomes available when salvinia is slower to grow in late fall and winter and begins to die and sink as a result of the herbicide work. Another issue is parts of Toledo Bend reservoir used by hunters to boat to the WMA may be packed with giant salvinia as well.”

Giant salvinia may be better known as a problem for fishers and boaters, but it affects hunters, lakeside landowners and many others too. And the hunting access problem is not limited to Toledo Bend.

“Giant salvinia is bad on Caddo Lake Wildlife Management Area this year and has been consistently bad for the last four years at least,” said Vanessa Neace, Caddo Lake WMA wildlife biologist. “The closer to the big open water you go, the less salvinia there is. This still allows for some good duck hunting here, but the salvinia is another significant reason duck hunting is not what it once was at Caddo Lake.”

Neace points to an April 2016 photo of a duck blind placed in what hunters would have called a great duck hunting hole on Caddo Lake.

“This picture was taken after the 50-year Caddo Lake flood of March 2016,” Neace said. “The blind is draped in dead salvinia that was present during that March flood and simply clung to the blind as the water receded. I can show you photo after photo of this scene repeating at location after location, year after year, since about 2007. Getting to these locations requires a powerful air cooled boat engine and then it’s still not guaranteed you will get to that hole.”

Herbicide is also sprayed at Caddo Lake—EPA-approved herbicide that’s safe for use in water, doesn’t hurt wildlife and is sprayed directly on the problem plant by trained contractors. It’s part of a multi-faceted, statewide effort to slow the spread of aquatic invasive species. The success of this effort also relies on hunters, fishers and boaters to help take action to avoid spreading invasive species. And biologists have another tool in their arsenal—weevils that eat giant salvinia.

“Here on Caddo Lake, as at North Toledo Bend, the Inland Fisheries Aquatic Vegetation Management Program hires contractors to treat our salvinia,” said Neace. “They use herbicide and they grow giant salvinia weevils. Fortunately for Caddo Lake, we also have the Caddo Biocontrol Alliance and the Morley Hudson Weevil Greenhouse.”

Bio-controls will likely never completely replace management tools like herbicide, but the weevils are showing progress. Some key boat lanes are more open now because of herbicide treatment, and there is evidence of giant salvinia damage caused by weevils. But once a plant like this becomes established, eradication becomes almost impossible, and that makes steady management a necessity.

That kind of management, plus research to understand problems and explore practical solutions, is being greatly expanded because of a record funding increase in state dollars to fight aquatic invaders in waterways. In 2015, the Texas Legislative appropriated $6.3 million to Texas Parks and Wildlife Department for the 2016-2017 biennium to manage aquatic invasive species, an increase from $1.1 million in the previous two-year funding cycle.

Most of the funding is going for management actions to control multiple aquatic invasive species. But thanks to the increase, TPWD has also been able to fund a giant salvinia awareness campaign, which is also supported by contributions from the Sabine River Authority and Brazos River Authority. The campaign reminds people to “Clean, Drain and Dry” their boats, trailers, and gear before traveling from one water body to another.

More information about how to identify and help control giant salvinia and other invasive species is at Anyone can find more information about Texas public hunting and hunting at state wildlife management areas on the TPWD website.