Skip to main content

Strange Invader

Extension takes on hydrilla, the ‘King Kong of aquatic weeds.’

With Lake Gaston losing a battle against what one weed scientist calls one of the worst of the worst aquatic weeds, NC State University joined with Virginia Tech to create a cross-state Cooperative Extension aquatics associate position to help people and governments protect the hydroelectric reservoir.

Hydrilla is an invasive weed that has threatened property values on the lake for decades. Dr. Brett Hartis, who’d boated, fished, swam and even gotten married on the lake, was chosen in 2012 to fill the unique position aimed at helping manage the weed. Hartis recently left the position to join the Tennessee Valley Authority’s aquatic plant management program, but the university’s work on Lake Gaston coontinues.

The Extension aquatics associate position, funded largely by the Lake Gaston Weed Control Council, takes the knowledge that university researchers have gained about hydrilla and its management and apply that knowledge to Lake Gaston, which lies in both North Carolina and Virginia. The associate also makes what’s learned on the lake available to people throughout North Carolina and nation.

The work is varied: Hartis developed a long-term hydrilla management strategy for the lake, educated local officials and residents about the weed, and oversaw the work of herbicide applicators paid by the weed control council. He also trained and managed the 20 to 30 volunteers who map hydrilla’s presence or absence across the lake’s entire 350-mile shoreline to provide basic information needed for weed management planning.

The position is part of the College of Agriculture and Life Sciences’ Department of Crop Science and its weed science faculty. Aquatic weed management fits the faculty focus, Hartis says, because just as weeds threaten the economic value that farmers derive from their fields, hydrilla affects income from tourism and real estate associated with lakes and rivers.

Calling hydrilla “one of the worst of the worst” invasive plant species – “the King Kong of aquatic weeds” – he notes that it spreads rapidly and can grow as deep as 20 feet in clear water.

The first type of hydrilla to cause problems in the United States was introduced in the 1960s in Florida by someone growing plants for aquariums. No one knows precisely how the type of hydrilla that plagues Lake Gaston got there, but some contend it, too, was introduced via the aquarium trade, first to the Potomac River, then spread by wildlife and boats.

Hydrilla was first found in North Carolina at Umstead State Park in 1980. “Since then it spread to reservoirs, where you would expect this type of plant to go,” Hartis says. “There are no other native plants there when reservoirs are built, so it’s kind of an open pasture for this weed to take hold.”

Today hydrilla is “popping up all over the state, in places we’ve never seen it before,” Hartis adds. It’s shown up in the state’s natural bay lakes, such as Lake Waccamaw near Whiteville, and its streams and rivers, such as the Chowan River in eastern North Carolina.

There, it poses a significant environmental threat.

“When you throw it into a natural bay lake or in a coastal system that thrives on native submerged vegetation that we don’t have in reservoirs, you’ve got a No. 1 competitor that can out-compete all those plants and completely change the ecology of those areas, all the way up the food chain,” he says. “Hydrilla likes to form a monoculture, forcing everything else out, and only the things that benefit from hydrilla will survive. Well, nothing has evolved here to benefit from its presence, so it’s just overall bad news.”

Not only does hydrilla spread in thick mats that make areas unsuitable for recreational pursuits such as swimming, boating and fishing, it clogs drinking water and irrigation pipes; hurts plant, mussel, snail and fish populations; and can harbor bacteria harmful to birds.

Once established, hydrilla is hard to get rid of, Hartis says.

“It persists because it’s not like a traditional plant which reproduces via seed. It reproduces through fragmentation, so every little piece you chop up becomes a new plant,” he says.

If someone pulls the plant out of the water or kills the plant above the sediment, it can survive because of tubers that secure it to the lake bottom. And a piece of the plant that catches on a boat motor can dry out completely and yet regrow if the boat carries it back to a water body, he says.

Right now, hydrilla covers about 600 of Lake Gaston’s 20,000 acres, and another 2,400 acres have had evidence of hydrilla recently enough to continue to need treatment, Hartis says. Funding from state and local governments to control hydrilla allows for chemical treatment of just 1,000 to 1,500 acres a year.

That forces the weed control council, made up of volunteers appointed by governments of the five counties surrounding the lake, to make hard decisions about where and when to use herbicides. Hartis worked closely with the council, with a goal of ensuring “our management programs are based on the newest and most sound research … and helping people understand why we do what we do.”

And getting to such an understanding isn’t a simple and straightforward matter, Hartis adds. It was hard for homeowners who didn’t see hydrilla in an area that had been treated to understand why treatments continued in those areas while other areas with visible hydrilla weren’t being treated at all.

“The reason my job was even formed was that even 20 years after hydrilla was found in the lake, we weren’t getting anywhere long-term. What we had been doing is bouncing around every other year, treating different areas on and off, on and off, to keep homeowners happy,” he says.

“But that was keeping hydrilla in my lake. To get rid of it you have to treat hydrilla for six to eight years, even when you can’t see that it’s present. We found that out because of research conducted at NC State.”

J. Rives “Judge” Manning Jr., weed control council treasurer, says the council has spent “upwards of $1 million a year” to manage hydrilla on Lake Gaston, but funding has decreased in recent years because of the economic downturn. And because funds are tighter, it’s even more important to ensure that they are well spent, he adds.

“In the early years, without an expert weed control person who’s familiar with chemicals, our efforts were a hit-or-miss proposition. Some years the acres of hydrilla were increasing rather than decreasing,” Manning says.

Because of that, the council held several meetings over the past 10 to 15 years with NC State and Cooperative Extension officials “to try to create a position for someone with (the) knowledge, credentials and expertise to work on Lake Gaston,” Manning says. “It was only after Dr. Joe Zublena came on board (as director of the state Cooperative Extension Service) that it became a reality.”

For each of the two years Extension has had an associate working on the lake, hydrilla acreage decreased, Manning notes. “That’s a plus.”

While the weather had some to do with the decrease, Hartis believes that taking a more strategic approach will ultimately lead to solid, lasting results that have economic impact.

Brett Hartis looks at hydrilla
NC State’s outreach and research efforts have helped make Lake Gaston a model for those working to manage hydrilla.

A lake choked with weeds could affect property values and tourism, depriving people and local governments of a significant source of income in counties that are among North Carolina’s poorest.

Because hydrilla can also become an important economic and environmental problem in other areas of the state, Hartis was frequently called on to provide educational programs beyond Lake Gaston. For example, with North Carolina Sea Grant, he helped develop a video about the threat posed by hydrilla in Chowan River to the state’s estuaries. NC State University field trials have shown the weed can survive in water as saline as the sounds, where it can threaten the important seafood industry.

Extension’s outreach efforts – along with the research of NC State’s Dr. Rob Richardson, an aquatic weeds scientist, and agricultural technician Steven Hoyle – helped make Lake Gaston a model for those working to manage hydrilla.

And because the NC State aquatic weed science team is creating what council vice president Pete Deschenes calls a “repeatable and scientific process,” it is one that can have widespread impact.

The outreach program “is helping us within the communities on the lake understand the problem,” Deschenes adds. “And that’s important because county and state governments need to understand how potentially devastating a hydrilla infestation can be.”