Hydrilla has joined Eurasian milfoil as an invasive exotic plant that threatens northern fisheries. It now has been found in Kansas and Missouri, and the Nature Conservancy is reporting “a number of populations on the doorstep of the Great Lakes.”
Giant salvinia, meanwhile, has emerged as a significant danger to some southern waters, especially in eastern Texas and Louisiana.
Yet much of the news these days is good for anglers in regard to troublesome aquatic plants, particularly hydrilla. Resource managers assert that they have learned from past mistakes and now strive to control this fish-attracting invasive, rather than obliterate it.
“We’re not trying to wipe it (hydrilla) out anymore,” said Howard Elder, aquatic plant biologist with Texas Parks and Wildlife. “We’re trying to find a happy median.”
Bill Caton, leader of the Invasive Plant Management Section at Florida’s Fish and Wildlife Conservation Commission, echoed the sentiment, emphasizing that “spot treatment” is preferred.
“It’s like treating weeds in a flower bed,” he said. “It’s much better if you don’t let it get out of control. If you do, then it costs you more, you have to use more herbicides, and you have more dead vegetation to deal with.”
Caton acknowledged that sometimes the aftermath of a herbicide treatment for hydrilla and other invasives still “can look bad” to anglers.
“But the public is just looking at the immediate impact of the treatment and not thinking about the results,” he said. “Treatments are like prescribed fires. They can look bad, but they’re often the only alternative that we have for providing good fish and wildlife habitat and preserving places for people to fish.”
Mechanical harvesting, he added, “is too expensive and destroys everything,” including fish and invertebrates trapped in the plants.
Grass carp, meanwhile, are an option in some states, including Texas and South Carolina.
“We knock the hydrilla back with herbicides and then use grass carp for control,” Elder said.
For the massive Santee Cooper system, the exotic grass-eaters are the preferred primary tool, and Chris Page, manager for the aquatic plant program at the South Carolina Department of Natural Resources, believes balance has been achieved with this method as well.
“We do maintenance stocking of one fish per eight acres,” Page said. “That’s about 20,000 fish. And we’re going to put in another 10,000 to manage an additional 400 acres of (hydrilla) coverage.”
Such a formula is a far cry from the 700,000 fish stocked in the 160,000-acre system from 1989 to 1996, he explained.
“I understand the problem that the public had with that. There were too many carp for several years.”
But as they better manage hydrilla, state agencies also are challenged with new threats to fisheries, including crested floating heart (see below) and giant salvinia.
Unlike hydrilla, giant salvinia has no redeeming value as fish habitat, and it can double in area in 10 days or less. It destroys primary productivity in a fishery and acidifies water until only a desert remains under its canopy.
In Texas, giant salvinia is established in 12 lakes. It also has spread to Louisiana, California, Arizona, and New Mexico, as well as other states.
“Hydrilla is a greater threat overall because it is so popular and so widespread,” Elder said. “Giant salvinia is not as easily distributed and it prefers acidic waters, which is why it is a threat in east Texas.”
This latest invader also is more difficult to control with herbicides than hydrilla, and carp won’t eat it. That’s why both Texas and Louisiana are raising weevils that will feed on the exotic plant.
There’s a new bad kid on the block: crested floating heart. It’s been in Florida for awhile, and now is causing problems in South Carolina.
Chances are good that this native of Asia also is established in other states, but hasn’t yet been identified. With flat, floating leaves and white flowers, it resembles the native banana lily, according to the Center for Aquatic and Invasive Plants (CAIP) at the University of Florida.
“I think that this could be a bad one,” said Mike Netherland, an aquatic plants expert for the Army Corps of Engineers.
As with so many other exotic plants now degrading our waterways, it likely “escaped from a water garden somewhere,” according to Chris Page, program manager for aquatic plant management in the South Carolina Department of Natural Resources.
Within four to five years, crested floating heart spread from 10 to 15 acres to 2,000 in the 160,000-acre Santee Cooper system, he added.
“We’ve done some (herbicide) treatment in coves, where there’s no water movement,” said Page, adding that effective application is difficult in open water.
“It’s the most aggressive floating-leave plant that we’ve encountered on the lakes,” said Larry McCord, supervisor of analytical and biological services for the Santee Cooper power and water utility. “It is rooting in high-energy areas along the main shoreline and can grow quite successfully in 10 to 12 feet of water.”
In Santee Cooper’s lakes Moultrie and Marion, this invasive exotic has the potential to spread over 40 percent of the acreage, McCord explained. Plus, reports from Asia suggest that grass carp won’t eat the plant, not good news for a waterway where they are used to control hydrilla.
Once established, cresting floating heart blankets the surface, blocking light penetration to beneficial submersed plants.
In Florida, according to CAIP, the invader is considered a Category II ecological threat. That means it has increased in abundance, but has not yet altered Florida plant communities to the extent shown by Category I species (hydrilla).
(A variation of this article was published in B.A.S.S. Times a few years ago.)