UNCERTAIN — A large number of plant-munching weevils have survived the winter and are making strides in the fight against invasive giant salvinia at Caddo Lake.

"It's a marathon, for sure," Daren Horton recently told the Harrison County Commissioners Court. Horton is a member of the Bio-Control Alliance, which operates the bio-control-based giant salvinia management program.

"We've got some challenges ahead, but we're doing well," he said.

Giant salvinia, an invasive aquatic fern that's native to Brazil, first was found on Caddo Lake in 2006. Since then, the state has spent millions of dollars spraying aquatic herbicides in an effort to control the plant.

Horton said the Morley Hudson Weevil Greenhouse in Uncertain opened in August 2014 as the first high-production weevil rearing facility in the world.

"We've released over 300,000 weevils onto Caddo Lake," Horton said.

The insect helps control the aggressive plant by feeding on the leaves and buds while its larvae attack the rest.

Horton said while Lee Eisenberg, the scientist who managed the greenhouse, no longer is at the facility, they are excited about the partnership that the Bio-Control Alliance has formed with the Texas Parks and Wildlife Department.

Horton said volunteers now are running the facility, which is more cost efficient for the program.

Through the partnership with Texas Parks and Wildlife, a two-pronged approach — herbicide application and weevil releases — are used to combat the salvinia.

"The most exciting thing right now is the fact that we have very high numbers of weevils on the lake going into this year that have (survived the cold climate)," Horton said. "One of the main things that we hope to do is develop (a) more cold-tolerant weevil that has lived through the winters and passes that June launch beyond (so) we don't have to rely as much on greenhouse raising weevils and releasing them."

Tim Bister, district fisheries biologist for the Texas Parks and Wildlife Department, said the Bio-Control Alliance is paid 10 cents per weevil.

Horton noted the weevil release at Pine Island Pond on Caddo Lake has been successful.

"They actually have open water from the weevils killing the salvinia," he said.

Horton said he anticipates the same success at Willowson's Woodyard Slough, where the Bio-Control Alliance recently released weevils.

"We are turning the tanks around, getting the chemical balances adjusted and getting on our feet, learning with the help of Parks and Wildlife, right now," he said. "But we're in a real good place going into this year, and we're cautiously optimistic about the future of the program and weevils involved and in control of the salvinia here and in other places."

Bister noted the weevils in the Park and Wildlife's greenhouses at the Caddo Lake National Wildlife Refuge in Karnack are growing. He said the number of adult weevils, however, is lower than what was desired, but officials still are hopeful about the season.

"It's just that kind of year, but we're hoping for a good release this summer with a turnaround for another release in the fall," he said.

Weevils received from other sources also have helped.

"The two releases that we've done so far at Caddo Lake have been from weevils we got from the Lower Neches River Authority," Bister said.

While progress has been made, Horton said there's still a long fight ahead.

"There's a lot of salvinia out there," he said. "It's going to be a tough year.

"This is just a tool in a toolbox," Horton said. "But make no mistake. This is going to be a management program that will be in place from now on at Caddo Lake."

He said because of the structure of the lake, there are many giant salvinia-infested areas that aren't accessible to spray boats or mechanical harvesters.

"You can't aerial spray, so giant salvinia is always going to be there," Horton said.

But controlling the infestation is necessary, because the invasive plants can harm the ecosystem and hurt recreational activities.

"The biggest problem with giant salvinia is because it has no natural predator, it really grows out of control, and it forms a mat on the surface of the water and with that mat on the surface, it doesn't allow sunlight to penetrate down into water," Bister said. "With no sunlight, you can't have any natural plant growth. If you don't have plants growing under the water, you don't have photosynthesis occurring and that's the process where plants give off oxygen.

"If there's no oxygen, (it results in) poor condition for fish," he said. "So in addition to having that negative impact on fish and fish habitat, it also prevents native plants from growing."

Bister said public awareness is important to help stop the spread of the plant.

"We instituted our public awareness campaign for giant salvinia and other invasive species," he said. "We painted a stencil on the ramp that says: 'Clean your equipment; clean your boat before you go someplace else.'

"We're trying to keep that awareness up there as much as possible to keep people from transporting the plant" from one body of water to another, he said.