Giant salvinia returns in Texas

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Kevin Storey with TPWD

AUSTIN, Texas – Once thought eradicated, giant salvinia has again been confirmed in Texas' Lake Fork. And this time, it's probably there to stay. That's bad news for both fish and fishermen at one of the nation's premiere bass waters.

"It can turn a lake into what looks like a pasture," said Dave Terre, chief of Fisheries Management & Research for Texas Parks and Wildlife Department (TPWD). "Terrestrial plants can grow on top of it.

"The water underneath is anoxic. There are no fish, and nothing can grow under it."

That's also bad news for TPWD, which now must devote more resources to monitoring and managing what often has been labeled "the world's worst weed." Texas now has 20 lakes infested with the exotic from South America, according to John Findeisen, aquatic invasive species biologist, "and with giant salvinia, it's important to go back regularly for treatments."

And there's bad news next door as well. At about the same time as the discovery in Lake Fork, giant salvinia (Salvinia molesta) was found in Arkansas, at Smith Park Lake in Miller County. Jason Olive, assistant fisheries chief for the Arkansas Game and Fish Commission, knows well the importance of containing and/or eradicating it as quickly as possible.

"Louisiana spends nearly $9 million a year spraying aquatic nuisance vegetation, and nearly three-quarters of that is to fight giant salvinia," he said. "That's money that could go to fisheries habitat management and other important work. We want to knock this out as quickly as possible to prevent it from getting a foothold in Arkansas."

Randy Westbrooks, an invasive species specialist with the U.S. Geological Survey (USGS) added, "This is the most sinister aquatic plant I've ever dealt with. It takes no prisoners.

"You have to take it seriously, just like a disease, and get rid of it as fast as you can."

According to the USGS the invasive floating fern was first discovered in 1995 in a small pond in South Carolina. Some think that it might have hitched a ride in a shipment of Brazilian lilies. However it arrived, it since has spread to more than a dozen states, mostly from Texas to the Carolinas, as well as the Colorado River area of southern California and Arizona. In some waters, resource managers were able to quickly eradicate the invader. In others, it is there to stay and must be controlled with regular applications of herbicide. That's because one plant can turn into 60 million in less than two months, and a handful can spread across more than 40 acres in just a few weeks.

"It can double in size in seven to 10 days," said Texas' Findeisen. "With water hyacinth, it's 30 to 45 days. And if left untreated, giant salvinia can completely take over a backwater."

Findeisen and his five-man invasive species control crew are more familiar with giant salvinia than they would like to be. That's because east Texas and west Louisiana fisheries are Ground Zero for the battle against exotic, with some of worst infestations in the border lakes of Caddo and Toledo Bend. Texas alone has 35,000 acres of giant salvinia in its waters.

How did this area become the hot spot? Along with favorable climate, anglers likely were the primary culprits. They did not "clean, drain, and dry" to eliminate hitchhikers.

"It likely came to Texas by boat," Terre said.

"Giant salvinia was at Lake Fork two years ago, and we contained and eradicated it," Findeisen added. "It was the same thing at Lake O' the Pines and Palestine. It was gone and now it's back."Once the floating plant is established in a fishery, wind and currents hasten its spread. Additionally, the invasive is a disguise artist and hides well as it becomes established. In its early stages, it looks like innocuous duck weed.

If the infestation is confined to dense floating mats, the invader often can be contained with booms and eradicated with herbicides. But when it starts growing among beneficial plants, it likely is there to stay.

“When with other vegetation, giant salvinia can be tricky to treat with herbicides.” Findeisen said. “Our experience with treating salvinia in mixed plant colonies has been the salvinia rebounds faster after the treatment and is no longer being held in place by the other plant species. This gives the giant salvinia free rein to float all over the lake, creating a bigger problem. Additionally, we don’t want to disrupt the habitat those native plants provide to fish and wildlife.”

As part of its arsenal, Texas also is using weevils, a natural control for the plant in its native South America. Unfortunately, the insects are not cold tolerant, which limits their use.

Of course, giant salvinia isn't the only invasive plant that threatens Texas fisheries. Water hyacinth is another. Findeisen estimates that his crew works on more than 50 vegetation control projects at any one time. For Louisiana, Florida, and other states, the situation is much the same.

To help deal with aquatic invasives, including zebra mussels, in the Lone Star State, the Texas Legislature appropriated $6.3 million for fiscal years 2016 and 2017.

"We mostly use state dollars, not angler dollars," Terre said.

"We work closely with river management authorities and other agencies," he added. "There's no way that Parks and Wildlife can deal with this alone."

Boaters can help by pulling off plants from their boats and trailers before they leave a lake. "A big component of controlling giant salvinia is to prevent its spread," Findeisen said.

A public awareness campaign has done a good job of alerting fishermen and others to the problem and reminding them to clean, drain and dry their boats when they leave a fishery, Terre added. But that's not enough.

"A lot of folks are not taking an active role," he said.

"For one thing, anglers could be doing more (to identify and report invasives), especially tournament anglers," he said. "Tournaments are at ramps all the time. Organizers need to look around at weigh-in sites.

"If we had been notified early at Lake Fork, we could have stopped it. We find most of the infestations during routine surveys.        

"Anglers could save us a lot of time and effort," Terre continued. "What we want is to convert from general public awareness to action on the ground. If you see it (giant salvinia), call somebody. Take a photo and send it to us. Don't worry about being wrong. Anglers need to make that leap."