Introduction:
Fanwort (Cabomba caroliniana) Water Weed.
Cabomba caroliniana is a submerged perennial aquarium plant that grows in stagnant to slow flowing freshwater. It spreads primarily by stem fragments and forms dense stands that crowd out well-established plants. C. caroliniana may clog ecologically, recreationally or economically important water bodies and drainage canals. Depending on its location (ie: drinking water supply or small closed water body) it may be managed by a number of control techniques including mechanical removal (being careful not to spread fragments to new locations) and habitat modification to increase shading (via planting trees) or decrease hydration (via draining).
Description:
C. caroliniana is fully submerged except for occasional floating leaves and emergent flowers. The roots grow on the bottom of water bodies and the stems can reach the surface. Parts of the plant can survive free-floating for six to eight weeks. It is a perennial, growing from short rhizomes with fibrous roots. The branched stems can grow up to 10m long and are scattered with white or reddish-brown hairs. The underwater leaves are divided into fine branches, resulting in a feathery fan-like appearance. These leaves are about 5cm across and secrete a gelatinous mucous which covers the submerged parts of the plant. The floating leaves, however, are small, diamond-shaped, entire, and borne on the flowering branches. The solitary flowers are less than 2cm across and range in colour from white to pale yellow and may also include a pink or purplish tinge. The flowers emerge on stalks from the tips of the stems.
General impacts:
C. caroliniana is an extremely persistent and competitive plant. Under suitable environmental conditions it forms dense stands and crowds out previously well-established plants. Once established, this plant can clog drainage canals and freshwater streams interfering with recreational, agricultural, and aesthetic uses.
Fanwort (Cabomba caroliniana) Distribution in North America shown in green.
In Austrailia Cabomba is regarded as a “Weed of National Significance”. It is one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts. It is choking waterways along Australia’s east coast. It is extremely persistent and can take over a water body, excluding native plant species. It can also have an impact on native animals - in northern Queensland platypus and water rat numbers are lower in infested creeks.
Cabomba grows quickly and produces a large amount of plant material. It can significantly reduce water storage capacity and taint drinking water supplies. Water treatment costs can be increased by up to $50 a megalitre. Heavy infestations can also raise water levels to a point where overflows and heavy seepage losses occur.
Cabomba’s dense mass of underwater stems and leaves provide a hazard for recreational water users. When this vegetation dies off, decomposition causes dramatic oxygen reductions and foul smelling water.
Management Measures:
Preventative measures:Preventing new outbreaks is critical and can be achieved by sterilising boats and boating equipment, disposing plants using burning or drying-out methods and discouraging the deliberate seeding of waterways with cabomba (which is done to supply the aquarium
Close up of the Fanwort (Cabomba caroliniana) Water Weed.
trade). As the plant is submerged and not easily visible education and public awareness is needed to prevent the spread of cabomba. Community awareness about the weed and identification skills need to be increased. People also need to be educated to buy other species of aquarium plants to stop the demand for cabomba.
Physical: Cabomba is sensitive to drying out and requires permanent shallow water; where possible, draining a water body can provide temporary control. If the base of the water storage dries out completely there is little chance of cabomba surviving but if it remains damp there is a more than 50% chance it will return. In the case of drinking water supplies lowering water levels is particularly effective; in the southern USA water level draw-downs have been used to reduce C. caroliniana growth. Extreme drying is required to prevent regrowth from seed. Cabomba easily fragments from disturbance, so control activities can actually contribute to spread of the weed if great care is not taken. Using a venturi dredge, which is like a giant vacuum cleaner, can overcome this problem. It minimises fragmentation and also extracts the root ball.
Chemical: A herbicide is registered for cabomba control in non-drinking water in Queensland and the Northern Territory but there is community opposition to its use. There is no herbicide registered for cabomba control in drinking water. In the north American region herbicide treatments have been used for cabomba control. Endothall provides excellent control but it is a contact herbicide only. Fluridone provides good control.
Biological: A new project being funded under the Natural Heritage Trust to identify potential biological control agents in the native range of the weed.
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