For years, resource managers have struggled to find a cost-effective and efficient way to control hydrilla. Mass application of herbicide can be cost prohibitive, as well as unpopular with anglers, environmentalists, and lakefront property owners. Grass carp, meanwhile, need years to bring the fast-growing exotic plant under control, unless they are stocked at exceptionally high rates, which also can be unpopular and expensive.
But Duke Energy Corporation has developed an effective management strategy for five of its Piedmont reservoirs that incorporates moderate use of both herbicides and carp. This reduces cost, as well as minimizes the likelihood of the adverse effects on fisheries that often accompany heavy stocking of grass carp.
This one-two punch, however, is not the sole reason for success, according to Ken Manuel, Duke’s reservoir aquatic plant manager.
“Early detection and rapid response is critical,” he said. “The plants grow so fast that you’re quickly past just a small infestation.
“Hydrilla grows faster than you think,” Manuel added. “It’s not just an inch a day. A plan can grow multiple feet per day from all of its growth tips.”
And too often, it’s spreading undetected. “Especially in the East, the states, which manage the fisheries and the water quality, rely on interested individuals to tell them about invasive plants,” the scientist said.
By contrast, Duke Energy’s mosquito control teams aren’t just controlling blood-sucking insects while they are on the water full-time for six months annually. “They are constantly looking for hydrilla and other invasive plants so that we can act quickly,” Manuel said.
Once hydrilla is confirmed, it is treated with herbicide. Sometimes, that is enough. More often it is not. That being the case, stocking of triploid grass carp follows, at a rate of 20 per acre of surface infestation.
The herbicide reduces the plant’s biomass, while carp graze on what sprouts from the surviving tubers. “If you have 1,000 acres of hydrilla, you have 1,000 acres until the tuber bank is exhausted,” said the scientist.
Additional “maintenance” stockings at a rate of 1 per 8 acres of the reservoir might follow for 8 to 10 years.
(This article appeared orginally in B.A.S.S. Times.)