State planning to deal with 605 acres of hydrilla in Lake Waccamaw

First herbicide treatment is scheduled for summer 2013

State officials are putting together a plan to deal with the discovery of hydrilla at Lake Waccamaw, a 9,000-acre natural lake in Columbus County.

Toby Hall, superintendent of Lake Waccamaw State Park, said that residents discovered the plant last year and reported the aquatic vegetation.

“Concerned residents saw what appeared to be a non-native aquatic weed,” Hall said. “This past fall, we had more concerns and Rob Emens investigated them.”

Emens, aquatic weed control program manager for the N.C. Department of Environmental and Natural Resources, is concerned that the state has never dealt with the aquatic vegetation in a natural lake and doesn’t want it to spread to any of the other ones in Southeastern North Carolina.

“It’s the first time we’ve had to deal with hydrilla in a natural lake,” Emens said. “I found hydrilla fragments floating around the (boat) ramp and colonies rooted within 1,000 feet of the ramp. From the extent, hydrilla has been there at least five years. Models with maps showed that by three years, it would be in the greater part of the lake.”

What makes hydrilla control difficult is a tuber bank. Some areas of Lake Waccamaw have dense tubers, but there has been no survey to pin those areas down.

“I think the introduction took place at the boat ramp,” Emens said. “If treated with herbicide, tuber-bank density is of no consequence. A certain amount of herbicide maintained in the water will affect many plants. We are hesitant to use grass carp, because it’s an all-or-nothing approach. They control all aquatic plants in a system.”

New technology was used to map infested areas of Lake Waccamaw, which total 605 acres; treating those areas is next. It will cost approximately $450,000 annually to treat the areas with Sonar, a herbicide.

“There’s a good chance to prevent hydrilla from spreading downstream, and we could eventually reduce the acreage,” Emens said. “We’ve seen a couple places where it established in flowing waters, and it doesn’t need a lot of light to grow, so it could establish in the Waccamaw River.”

Hydrilla originated in Asia and spreads primarily by fragmentation. In winter, the plant’s bud-like turions can generate new plants, and tubers growing in the bottom are actually subterranean turions. However, in cold weather, the grown plants become dormant.

Keith Ashley, a fisheries biologist with the N.C. Wildlife Resources Commission, said the first herbicide treatment will be applied early this summer. A technical advisory committee will determine the dispersal method and assess the amount of collateral damage to native vegetation.