Cabomba is regarded as a major threat to freshwater systems due to its range of environmental, social and economic impacts.
Dense stands of cabomba cause many problems including;
Cabomba occurs in several locations in NSW. The most severe infestations are on the NSW far north coast in the upper catchments of the Richmond River and the Burringbar Creek system. These infestations have existed for about 10 years.
Other infestations include sites in the Tweed River near Murwillumbah, the Orara River near Grafton, Glenbrook Lagoon in the Blue Mountains, and waterbodies at Coffs Harbour, Port Macquarie, Taree, Forster, and Botany Bay.
Cabomba has a much broader potential distribution, and most waterways throughout eastern, central and southern NSW could be at risk of invasion by cabomba.
Cabomba is a highly invasive species that can rapidly colonise an entire waterbody. In Australia, reproduction is mostly by stem fragments and through the production of daughter plants.
Any stem fragment that includes a node (a piece as small as 1 cm long) can grow into a new plant. Stems break easily when disturbed, creating thousands of fragments, all capable of spread and reproduction. Stem fragments float on the water surface and can spread throughout a catchment by normal flows or flooding. Fragments are also moved between catchments and waterbodies by fishing activities and equipment, watercraft and trailers, and animals.
In autumn and winter plants lose buoyancy and stems sink to the bottom, where they either break down into fragments that may regrow the following spring, or take root in the substrate, producing new daughter plants.
The only cabomba to produce viable seed in Australia is currently in the Darwin River in the Northern Territory, and reasons for this are unclear.
Cabomba is strictly aquatic and completely submerged except for its flowers and occasional floating leaves. The roots attach to the bottom of the water body and stems can be up to 10 m long, but usually range up to 5 m.
The submerged leaves and stems have a thin gelatinous coating. Leaves are arranged in opposite pairs along the stems and are finely dissected giving the characteristic feathery, fan-shaped appearance.
Single flowers approximately 2 cm in diameter are raised 1–4 cm above the water surface on stalks. They can be milk-white, pale yellow or purplish (usually white petals with yellow centres), and appear to have 6 petals (3 of these are sepals). Flowers emerge from the water during the day and recede into the water overnight. The raised flowers are often the first visible sign of an infestation.
Pink cabomba (C. furcata) is legally sold in some states as an aquarium plant. It is not currently known to occur naturally and is not considered to pose a significant weed risk. It has distinctive pink leaves and stems and purple flowers with yellow centres.
Cabomba will invade freshwater systems, particularly if they are nutrient rich, slow-moving, or permanently standing water less than 4 m deep. Dams, ponds, lakes and freshwater streams all provide habitat for cabomba, as well as the margins of deeper water bodies or faster moving waterways. It prefers fine, soft silty sediments and is less vigorous on stony, clay or sand substrates.
Cabomba prefers warm-temperate, humid climates with rainfall throughout the year. Optimal temperatures range from 13° to 27°C; however, it has been known to survive under ice in Canada. Cabomba can tolerate both acid and alkaline water, but optimal pH is 4–6 with growth inhibited above 7–8. Light availability is the main environmental variable affecting cabomba growth, although it can tolerate very low light intensities.
Authors: Rod Ensbey, Elissa van Oosterhout
Technical reviewer: Birgitte Verbeek
Inkson, T., Petroeschevsky, A., Officer, D. and Schmitzer, T. (2013) Cabomba Control Case Study 2011-2013, Mid North Coast Weeds Coordinating Committee, Great Lakes Council, Forster.
Mackey, A. P. and Swarbrick, J. T. (1998) Cabomba caroliniana, Gray. In Biology of Australian weeds, Volume 2, RG and FJ Richardson, Melbourne.
Schooler. S., Cabrere-Walsh, W. and Julien, M. (2009) Cabomba caroliniana, Gray (Cabombaceae). In R. Muniappan et al. (eds) Biological control of tropical weeds using arthropods, Cambridge University Press, Cambridge, pp. 88–107.
Early detection is critical as once established cabomba is extremely difficult to control. Control methods focus on drawdown, shading, manual removal and mechanical removal. All of these methods are costly and labour intensive and only effective over small areas. In larger infestations it is only viable or practical to reduce cabomba in strategic locations such as swimming areas or to prevent spread by containment.
Management practices to prevent nutrient-enriched run-off entering infested waterways should also be considered.
Draining or ‘drawdown’ of a water body can be effective, particularly in smaller dams or retention ponds. Stems and leaves must be exposed until they and the substrate are completely dry. Care must be taken to ensure that cabomba is not spread to other water bodies in the drained water.
Shading can be created by floating blankets made from builders’ black plastic. This must be maintained over a period of 3 or 4 months to kill the cabomba.
Manual removal can be useful for small infestations or as a follow-up method to remove regrowth. It requires plants to be pulled up by the roots, either while wading through shallow water or by diving with SCUBA. Contract divers have developed this method to include hand-held suction hoses to dredge the plants out.
Mechanical aquatic weed harvesters can cut and remove large amounts of cabomba from a waterway. This can suppress an infestation and keep the upper section of the water column free of weed. This will be an ongoing operation as regrowth occurs quickly (over just weeks) to uncut levels. For further detail and information about control and management of cabomba, consult the Cabomba control manual.
An aquatic weevil (Hydrotimetes natans) is known to have a significant impact on cabomba, and is currently being tested in quarantine for introduction to Australia. Other potential biological control agents have been identified for testing.
Control trials have shown that carfentrazone-ethyl can afford a 100% reduction of cabomba, based on 1-3 treatments over a 12 month period, with an absence of cabomba maintained for three years to date (but requiring monitoring for five years before eradication is deemed to have occurred. In some sites the treated cabomba took up to 9 months to die completely. In most sites the cabomba was still present for 3-6 months after initial treatment.
Carfentrazone-ethyl is a contact herbicide with no systemic properties. It works by attacking the fats and proteins of plant cell membranes. It does not translocate through a plant, and requires a high level of contact to afford control. For effective control, cabomba must be actively growing. Late spring to summer generally provides the optimum treatment window. Carfentrazone-ethyl is light dependant, and treatment should be carried out early in the day (to afford more daylight hours), and in relatively clean, clear water (as a rough guide, avoid treatments in water where fingertips are not visible when held 45 cm below the surface). Avoid treatments prior to rainfall, where water levels could increase dramatically (either diluting the concentration of herbicide in the water, or moving the herbicide treated water away from the cabomba infestation and into non-target areas).
The herbicide is applied to the water body, either through surface or subsurface spraying or injection. Injecting the herbicide into the water at high pressure (15-20 bar with a 3 mm nozzle) helps break the surface tension of the water and distributes the herbicide through the water column. Surface spraying may not allow the herbicide to reach the cabomba due to thermal stratification layers in the water column.
Effective control of cabomba is possible when the carfentrazone-ethyl concentration reaches 2 parts per million (ppm) in the water column where cabomba is present. Only 50% of any waterbody can be treated at one time.
See Using herbicides for more information.
Carfentrazone-ethyl 240 g/L
(Shark™ Aquatic Herbicide)
Rate: 830 mL per 100,000 L water [2 ppm (2 mg/L) carfentrazone-ethyl]
Comments: Non-flowing water bodies. Apply onto the surface or below the surface where cabomba is growing. The intention is to achieve a concentration of 2 ppm (2 mg/L) carfentrazone-ethyl in the water where cabomba is growing. Refer to the label for nozzle requirements. Do not apply to more than 50% of the volume of the water body in a single application. Do not apply subsequent application to the waterbody within 3 months. Retreatments of heavy infestations may be required.
Withholding period: Nil.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate
All species in the Cabomba genus are declared, except Cabomba furcata.
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The requirements in the Noxious Weeds Act 1993 for a notifiable weed must be complied with