Cabomba (DSE Vic)

August 1999 Cabomba LC0259 Keith Turnbull Research Institute, Frankston ISSN 1329-833X

This Landcare Note describes the weed cabomba, floating plant for 6-8 weeks. The stems die off in winter Cabomba caroliniana, and outlines options for its and break up and the fragments can take root and give rise control. to new plants. The plant is coated with gelatinous mucus giving it a slimy texture. Common name Stems - 1 to 2 mm diameter, up to 10 m long, rhizomatous, Cabomba, common cabomba, fanwort with a thin gelatinous coating and short, scattered, white or reddish-brown hairs. Stems can grow up to 50 mm per day. Botanical name Cabomba caroliniana A. Gray Family Cabombaceae Status Cabomba is not a declared noxious weed in Victoria, but is widely sold for use in aquariums and poses a significant threat to waterways. It is a declared weed in Queensland, New South Wales, Tasmania, Western Australia and the Northern Territory. Trade and sale of cabomba is prohibited in much of Australia. Origin and distribution Cabomba is native to the south-eastern United States of America and South America. It was introduced into Australia from the USA as an aquarium plant and was first recognized as naturalized in 1981. Cabomba has since become widely established in Queensland, New South Wales, the Northern Territory and Victoria due to dumping of unwanted plants into local waterways, and, more commonly, as a result of deliberate ‘seeding’ of areas to allow wild cultivation for the aquarium trade. Bioclimatic modeling indicates cabomba can successfully establish and survive in Victoria. It is currently being sold through the aquarium trade in this State and has the potential to be a very damaging environmental weed. A number of large infestations have been recorded including a farm dam near Dollar in South Gippsland (1989), a channel running beside “Jaycee” Island in Lake Benalla (1990) and a heavy infestation in Lake Nagambie (1996). Description Cabomba is a submerged perennial aquatic herb which Figure 1. Cabomba. reproduces vegetatively from stem fragments. All parts of the plant grow under water except for a few floating leaves and emergent flowers in season. Cabomba generally grows Leaves - of two types, submerged and emergent. Leaf in water 1 to 3 m deep with the roots in mud or silt, but can colour may change in response to environmental live in waters to 10 m deep and continue to grow as a free- conditions.

Submerged leaves - usually green, shortly stalked, opposite, repeatedly divided (3 to 7 times) to form feathery, fan-shaped structures up to 70 mm across when evenly spread and ultimately with from 3 to 20 terminal divisions if on the lower stem and 150 or 200 terminal divisions on the upper parts of stems; segments cylindrical with outermost segments slightly spoon-shaped; covered with a thin gelatinous coating. Emergent leaves - occasional or absent, arranged alternately on the stem, undivided, ovate or narrowly elliptical in shape with the stalk attached to the undersurface. Shoots are grass green to olive green or sometimes reddish brown, and more or less hairy. Flowers - solitary, 6 to 15 mm diameter, with 3 petals and Figure 2. Cabomba growing in an aquarium. 3 similar sepals 4 to 12 mm long and 2 to 7 mm wide, white, cream, yellow, dark reddish-black or purplish in colour depending on variety; usually 6 stamens about 4 Properties mm long; produced on 10 to 40 mm long stalks above the Cabomba is an aggressive invader of freshwater systems, water surface in summer or autumn. Flowers open during especially if they are nutrient rich. Its rapid, prolific growth the day and close during the afternoon. On closing the allows it to dominate native vegetation and obstruct creeks, flowers submerge. lakes and dams and foul irrigation and aquaculture Fruit - green when fresh, leathery, consisting of 2 to 4 systems. It outcompetes native freshwater plants to quickly segments shaped like rounded bottles with long necks; form a dense monoculture and has a negative impact on carried below the water surface. biodiversity, affecting native plants, fish, birds and aquatic Seeds - green when fresh with scattered dark pigmentation, invertebrates. Thick stands block out sunlight and turning brown; 1 to 3 per fruit; oval, 1.5 to 3 mm long and accelerate the aging of lakes by increasing siltation. Water 1 to 1.5 mm wide, covered in gelatinous slime, pitted, with quality is degraded due to discolouration and tainting. 4 longitudinal rows of tubercles on each side. Seeds have Dense infestations impede aquatic recreational activites. not been found on cabomba growing in Australia. Drowning as a result of entanglement in the stems is a Roots - fine, white, unbranched adventititious roots grow danger to swimmers. from the nodes of stems whether they are free-floating or Cabomba is able to live in a wide variety of climates but its attached to the substrate. Roots embedded in the substrate preferred temperature range is 13 to 27ºC. It grows best in are long, thin, branched and purplish in colour or dark acidic (pH 4 to 6) and turbid waters. brown to black when dried out. Erect stems can become prostrate and partially buried and become like rhizomes. Dispersal These are fragile and break readily. Fibrous roots grow Vegetatively from stem fragments. Regeneration from seed from their nodes. has not been observed in Australia. New infestations are usually the result of deliberate human activities. Similar species Control C. caroliniana is the only Cabomba species known to have become naturalised in Australia, however the four other Control of cabomba, like that of other submerged aquatic species have the potential to invade. C. furcata Schultes & plants, is difficult. The best form of control is prevention - Schultes f., pink cabomba, is regularly sold by aquarists cabomba should not be allowed to establish in the first and is the most likely to appear as a weed. The other three place. Early detection and treatment of new infestations species, Cabomba aquatica Aublet, C. haynesii Wiersma should be a priority because eradication of larger and C. palaeformis Fassett are also traded. infestations may be impossible. Regular monitoring for weeds should be integrated into the routine management of Aquatic plants that might be confused with cabomba all water bodies. Containment plans need to be include parrots feather, Myriophyllum aquaticum (Vell.) implemented immediately when infestations are detected in Verdc., and hornwort, Ceratophyllum demersum L. running waters. New infestations of cabomba should be Parrots feather is native to South America and has bright reported to the nearest Department of Natural Resources green leaves that grow in groups of four to six, are widely and Environment office. separated at the base of the stem and become densely packed towards the stem apex. Hornwort is native to Limiting Dispersal Australia and can be distinguished from cabomba by the The major concern is to prevent introduction into natural direct attachment of the leaves to the stem (cabomba leaves water bodies, dams and irrigation systems. Aquariums have 20 mm long stalks). should never be emptied into drains or waterways. Cabomba from aquariums should be dried and burnt, or

© State of Victoria Department of Natural Resources and Environment 2002 Page 2 Cabomba LC0259 buried. Plants which pose no risk to Victorian waterways can be used in aquariums instead of cabomba. Indigenous References plants such as curly pondweed (Potamogeton crispus), Queensland Department of Natural Resources (1998) blunt pondweed (P. ochreatus) and water thyme (Hydrilla Cabomba. Pest Facts PP30. Brisbane, Department of verticillata) may be suitable. Natural Resources. Manual Control Entwisle, T.J. (1996) Cabombaceae. Pp. 32-33 in Walsh, N.G. and Entwisle, T.J. (Eds.), Flora of Victoria Small infestations can be removed by handpulling. All Volume 3 Dicotyledons, Winteraceae to Myrtaceae. parts of the plant must be removed. Scuba gear may be Melbourne, Inkata Press. required. Follow-up inspections are essential and retreatment will probably be necessary. Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious Weeds of Australia. Melbourne, Inkata Press. Mechanical Control Mackey, A.P. and Swarbrick, J.T. (1998) Cabomba Mechanical harvesting of cabomba using suction dredges caroliniana A.Gray. Pp. 19-36 in Panetta, F.D., or other equipment has been undertaken in Queensland but Groves, R.H. and Shepherd, R.C.H. (Eds), The Biology is unsuitable for small infestations. of Australian Weeds Volume 2. Melbourne, R.G. and Dehydration F.J. Richardson. Cabomba is a true aquatic plant and is susceptible to Acknowledgements dehydration. Draining of the water body to expose the stems and leaves for several weeks and dry out the Compiled by Ian Faithfull and Lalith Gunasekera. Robin hydrosoil is an effective method of control. High Adair and David McLaren provided information and temperatures associated with exposure will hasten the comment. Figure 1 courtesy of Queensland Department of destruction. Supplementary herbicide treatment of the soil Natural Resources. Figure 2 by L. Gunasekera. may be desirable. Chemical Information No herbicides are registered for the control of cabomba in Victoria.

The Department of Natural Resources and Environment is a participating contributor to the Cooperative Research Centre for Weed Management Systems.

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