Chrlotte Observer

Posted on Sun, Dec. 17, 2006

EXTENSION Q&A | DAVID FOGARTY

In battle against weeds, hydrilla is tough to beat

I don't know who coined the name "hydrilla" for the invasive exotic weed that has now been found in Lake Wylie.

Maybe they were thinking about "Hydra," the nine-headed monster from Greek mythology. Hercules fought the Hydra with his club, but each time he knocked off a head, two more grew back.

Or maybe "hydrilla" is short for "Godzilla of the Water"

In any case, hydrilla is a fast-growing aquatic weed that has been spreading through North Carolina lakes over the past decade. Despite numerous eradication efforts, the weed continues to spread.

Q. What is hydrilla?

Hydrilla verticillata is an underwater plant that is native to Africa, Asia and Australia. This plant was introduced into Florida in the 1950s when it was imported as a tropical plant for aquariums. Some of the hydrilla was discarded into a local canal, where it spread rapidly. It now occurs throughout the Gulf and Atlantic coast states and in parts of the West Coast.

Hydrilla can be identified by its stems, which contain three to six leaves arranged in whorls. The leaves have saw-like serrations on their edges and often have spines on the underside of the leaf's mid-vein. Hydrilla is dormant in the winter and sprouts again in the summer.

Q. Why is hydrilla a problem?

Hydrilla is a problem for several reasons. Hydrilla can develop dense mats on the surface of the lake, choking out native aquatic vegetation. Hydrilla also harms recreation. In coves, it can become so dense that boaters have trouble getting in and out of the docks.

Dense hydrilla growth can create areas of stagnant water that increase mosquito breeding habitat. Additionally, large mats of hydrilla can clog water intakes at power plants and other facilities.

Q. Why does hydrilla spread so fast?

Hydrilla can spread quickly because it has several methods of reproducing. Reproduction can occur when stem fragments break off and root. Hydrilla can also reproduce from root-like structures called stolons, and can form thousands of tubers that remain dormant in the soil for up to 10 years before sprouting. Once hydrilla infests a lake, it is next to impossible to eliminate.

In addition, hydrilla is adaptable. It is capable of growing in shallow water and in water that is up to 20 feet deep.

Q. How much hydrilla is in the Catawba River?

Hydrilla infests around 1,000 acres from Lake James to Lake Wateree. According to a 2002 study, if left unchecked, hydrilla has the potential to infest up to 21,000 acres in the basin. The weed has been most prevalent in Lake James, Lake Norman and Mountain Island Lake. It has recently been identified in Lake Wylie.

Q. How can we control hydrilla?

While it may be impossible to eradicate hydrilla from the Catawba River, it is possible to manage it. States, municipalities, utilities and industries have spent millions of dollars throughout the South on herbicide and mechanical removal of hydrilla. Herbicide applications may cost around $500 per acre, while mechanical cutting can cost more than $1,000 per acre. Both methods require repeated use.

Sterile grass carp provide the most cost-effective, long-term control of hydrilla. Stocking rates of 15 to 20 fish per acre of hydrilla usually provide reasonable control within two years. After control is achieved, maintenance stockings of grass carp are needed to maintain control.

Everyone can help prevent the spread of hydrilla by not introducing aquatic plants into the Catawba River and by removing all plant fragments from boats, trailers and bait tanks before leaving the lake.

For more details, visit www.weedscience.ncsu.edu/aquaticweeds/catawba.pdf or call the Gaston County Cooperative Extension Office at 704-922-2112.

Extension Q&A | David Fogarty