Cabomba (Cabomba caroliniana)

Cabomba is a submerged water weed with small white to yellow flowers above the water surface. It chokes water bodies and degrades water quality.

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How does this weed affect you?

Dense underwater stands of cabomba can:

• taint drinking water, increasing treatment and storage costs
• become dangerous for swimmers who become entangled in it
• block pumps
• prevent boating and water sports
• make the water foul-smelling and stagnant
• outcompete native water plants
• make water unsuitable for fish and other water animals.

What does it look like?

Cabomba is completely submerged except for its flowers and occasional floating leaves. 

Leaves:

There are two types of leaves, submerged and floating.

Submerged leaves are:

• emerald green
• divided into many strands giving them a ‘feathery’ look
• fan-shaped
• covered in a sticky mucous
• opposite along the stem.

There are usually only a few, if any, leaves that float on the surface. They are:

• up to 2 cm long
• not divided into strands
• narrow to diamond shaped
• alternate on the flower branches.

Flowers are:

• usually white with yellow centres, but can be pale yellow or purplish
• 2 cm in diameter
• with 6 petals
• raised 1–4 cm above the water surface on stalks
• above water during the day and underwater at night.

Stems are:

• usually up to 5 m long, but can grow up to 10 m long
• with white or reddish hairs
• with roots at the nodes of creeping runners.

Roots are:

• attached to the bottom of the water body.

Similar looking plants

• Pink cabomba (Cabomba furcata) looks similar. It has pink leaves and stems and purple flowers with yellow centres. It is legally sold in some states as an aquarium plant. It has not yet been seen growing naturally and is not considered a weed risk.

Where is it found?

Severe infestations are on the NSW far north coast in the upper catchments of the Richmond River and the Burringbar Creek system. There are other infestations in:

• the Tweed River near Murwillumbah
• the Orara River near Grafton
• Glenbrook Lagoon in the Blue Mountains
• water bodies at Coffs Harbour, Port Macquarie, Taree, Forster, and the Greater Sydney region.

Cabomba could invade most waterways in eastern, central and southern NSW.

Cabomba is native to South America. 

What type of environment does it grow in?

Cabomba grows in warm-temperate, humid climates with temperatures 13° to 27°C. Though it can survive in water underneath ice. It grows well in:

• slow-moving or still freshwater less than 4 m deep
• nutrient-rich water 
• acidic water with pH 4–6
• fine, soft silty sediments
• areas with year-round rainfall
• lots of light.

It can grow on the edges of deeper water bodies or faster moving waterways. 

Cabomba does not grow as well:

• on stony, clay or sandy sediments
• when water pH is above 7
• in very low light.

Maps and records

• Recorded presence of Cabomba during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By plant parts

Any stem fragment with a node can grow into a new plant. Stems break easily. Fragments can be as small as 1 cm. Water moves floating fragments into new areas. Fishing equipment, watercraft and animals can also move fragments. 

In autumn and winter the stems sink. They either:

• break down into fragments that regrow the following spring, or 
• take root along the stem to produce daughter plants.

By Seed

So far the only cabomba to produce viable seed in Australia is in the Darwin River in the Northern Territory. Reasons for this are unclear.

References

CRC for Australian Weed Management (2003) Weed Management Guide: Cabomba (Cabomba caroliniana).

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.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 24 January 2020 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Cabomba~caroliniana

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.

More information

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Control

Successful weed control relies on follow up after the initial efforts. This means regularly looking for any new plants or plant fragments and controlling them. Using a combination of control methods is usually more successful.

To tackle cabomba:

• Act quickly to control new infestations.
• Check for regrowth after treatments and follow up as soon as more plants are seen.
• Be very careful not to transport plant parts to new locations.

Prevention:

• Don’t run boat/watercraft motors through weed beds.
• Check and remove all plant material from boats, canoes, trailers, vehicles, machinery and fishing gear before leaving waterways.
• Stop nutrient-rich runoff entering infested waterways.
• Never dump unwanted water plants.

Early detection is important in managing cabomba. Once established cabomba is extremely difficult to control. 

Drawdown

Draining or lowering water levels works in smaller dams or retention ponds. Expose stems and leaves until they, and the substrate beneath, are completely dry. Ensure cabomba is not spread to other areas in the drained water. 

Shading

Use builder’s black plastic to cover cabomba. Maintain in place for 3–4 months. 

Physical Removal

By hand

Hand weed small infestations or regrowth. Wade into shallow water and pull up plants by the roots. In deeper water SCUBA divers can use hand-held suction hoses to remove plants. Collect fragments that break off the plants.

By machine

Aquatic weed harvesters can suppress an infestation, and keep the upper part of the water free of weed. The harvesters cut cabomba back from the surface, but the roots and stems remain. Treatments need to be frequent, as cabomba can regrow to uncut levels in as little as a few weeks.   

Biological Control

An aquatic weevil (Hydrotimetes natans) has been identified as a potential biological control agent for cabomba. It’s host range is currently being tested in quarantine for introduction to Australia. 

Chemical Control

Carfentrazone-ethyl can control cabomba with 1–3 treatments in a 12 month period. It may take 9 months for the plants to die. Carfentrazone-ethyl is a contact herbicide. It works by attacking the fats and proteins of plant cell membranes. It does not translocate through a plant. The herbicide needs to reach a concentration of 2 parts per million in the treated area.

Do not treat more than 50% of a waterbody at one time. 

Apply:

• when cabomba is actively growing in late spring to summer
• in the morning - the herbicide needs light to work
• in clean water - you should be able to see your fingertips when your hand is 45 cm below the water surface
• via subsurface spray, injecting the herbicide into the water at high pressure (15-20 bar with a 3 mm nozzle) to break the surface tension and spread it through the water. 

Do not apply:

• in the afternoon
• in murky water
• before rainfall which could dilute the herbicide or wash it into non-infested areas
• sprayed onto the water surface as herbicide might remain there and have little impact.

Herbicide options

See Using herbicides for more information.

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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: Not required when used as directed.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: 1 tablet for every 37.5 cubic metres of water to achieve 400 parts per billion.
Comments: For use on dense or established weed populations in enclosed water bodies, deeper than 0.5 m and larger than 37.5 cubic metres, or margins of larger, still water bodies. Throw tablets directly into the water to achieve uniform distribution of the herbicide. Alternatively, if weeds grow in clusters, concentrate the tablet application on the densest areas. See label for restrictions.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: 1 tablet for every 75 cubic metres of water to achieve 200 parts per billion.
Comments: For use on low density, establishing or re-establishing weeds in enclosed water bodies, deeper than 0.5 m and larger than 37.5 cubic metres, or margins of larger, still water bodies. Throw tablets directly into the water to achieve uniform distribution of the herbicide. Alternatively, if weeds grow in clusters, concentrate the tablet application on the densest areas. See label for restrictions.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: Inject solution into water body. 1 tablet per 37.5 cubic metres. Each tablet dissolved in at least 20L of water + 0.5 - 1.0% adjuvant/surfactant
Comments: For use on dense or established weeds in water bodies less than 0.5 m deep or with a volume less than 37.5 cubic metres. Dissolve tablets in water (at least 20L per tablet) mix thoroughly and then inject the solution directly into the water body.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: Inject solution into water body. 1 tablet per 75 cubic metres. Each tablet dissolved in at least 20L of water + 0.5 - 1.0% adjuvant/surfactant
Comments: For use on on low density, establishing or re-establishing weeds in water bodies less than 0.5 m deep or with a volume less than 37.5 cubic metres. Dissolve tablets in water (at least 20L per tablet) and additives in a spray tank, mix thoroughly and then inject the solution directly into the water body. See label for restrictions.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW	Prohibition on certain dealings Must not be imported into the state, sold, bartered, exchanged or offered for sale.
Greater Sydney	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Notify local control authority if found.
Hunter	Regional Recommended Measure* (for Regional Priority - Eradication) Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant.
Murray	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
North West	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found. This applies to all species of Cabomba except for the native Cabomba furcata
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2023