Hydrilla infestation at Lake James

At a recent meeting of the Catawba River Study group, Duke Power Company's Ken Manuel noted the presence of a 350-acre hydrilla bed in Lake James. The nonnative aquatic weed was first observed in 1999 and Duke responded by lowering the lake level that winter to freeze the then exposed weed bed followed by spraying with an aquatic herbicide. Both efforts failed and the infestation now threatens to grow and cover more than 1,400 acres.

Hydrilla is called the perfect aquatic weed because it grows robustly like kudzu and shades or crowds out other plants including algae. It thrives in low light levels and needs only about one percent of direct sunlight to take root and grow. As the rooted plant stem grows near the surface it aggressively branches out to form a dense mat that shades out and kills plant life below it, inhibits swimmers and effectively bars passage by jet or propeller driven boats. Recently a Duke mosquito control boat had to be rescued from a hydrilla bed near Burnettes' Landing.

In Florida's experience dealing with hydrilla, they found it grows in extremely clear water to a depth of 45 feet. For small areas, they typically use mechanical harvesters to remove the weed from swimming areas and to cut out boating lanes. For larger areas they rely on genetically sterilized hydrilla eating carp at a rate of 5 to 20 carp for each acre to be controlled.

Hydrilla propagates from tubers, hidden buds called turions, stem fragments, and seeds. A stem fragment with a single leaf whorl is often enough to infect a new area. Left alone, hydrilla will eventually take root and establish itself throughout Lake James and then go on to infect the entire Catawba River chain of reservoirs. In very cloudy water it can grow and effectively deny access to areas where the water is 10 to 15 feet deep or less. In very clear water, hydrilla can take root in waters up to 45 feet deep. Without aggressive control measures and over time, shallow water hydrilla beds can deny open water access to most if not all marinas, boat ramps and docks on the lake. Lake James would then cease to exist as a viable recreation lake. The annual lake Clean Sweep would become a thing of the past as cleanup crews are denied access to the shoreline and litter is left to accumulate.

Mountain Island Reservoir is currently infested with 625 acres of hydrilla. State and local governments have introduced 12,000 grass carp in an effort to control the weed and estimate another 16,000 will be needed at about five dollars per fish. While Mountain Island is a drinking water reservoir that is absolutely essential to Charlotte-Mecklenburg as a community, Lake James is no less essential to Burke and McDowell Counties and is equally deserving of help in controlling this introduced aquatic weed.

Our elected representatives need to do the right thing and require effective hydrilla control measures on Lake James. Our citizens need to encourage those officials to act sooner rather than later.

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-Citations of note-

Hydrilla is adapted to use low light levels for photosynthesis (Van et al. 1976, Bowes et al. 1977). This means that hydrilla can begin to photosynthesize earlier in the morning and thus successfully compete with other aquatic plants for limited dissolved carbon in the water . The low light requirement (1% of full sunlight or less) also allows hydrilla to colonize in deeper water than other aquatic plants. Hydrilla has been found growing at a depth of 15 m in Crystal River and commonly occurs in water 3 m deep in Florida lakes. (Center for Aquatic Plants, University of Florida)

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Hydrilla has many effective means of propagation. It can sprout new plants from stem fragments containing as few as two nodes or whorls of leaves. Fragments from rhizomes and root crowns can also form new plants. ... It has been shown that one tuber can lead to the production of over 5,000 new tubers per square meter. The tubers and turions can withstand ice cover, drying, ingestion and regurgitation by waterfowl, and herbicides. (Hydrilla verticillata)

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Hydrilla also has several physiological and morphological adaptations which allow it to outcompete native aquatic vegetation. (Washington State Department of Ecology)

• It can grow at lower light intensities than many other plants. This makes it difficult to shade out, and allows it to grow for longer periods during the day.
• It can absorb carbon from the water more efficiently than other plants, so can continue to thrive during the summer when carbon can become limiting.
• It can also store extra phosphorus, so when lack of this nutrient limits the growth of other plants, hydrilla can use what it has stored.
• It is tolerant of a wide range of water conditions, though water quality and sediment density can influence tuber production and growth.
• It will thrive in flowing water as well as still water. Studies have shown that it actually grows faster in flowing water.
• It will tolerate salinity of up to 9 -10 parts per thousand, so could encroach upon the outer limits of estuaries.

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Grows at 10 to 35 º C. (California Department of Food and Agriculture)

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