Cabomba (Cabomba caroliniana)

Assessment ID: 1057
Jurisdiction: North Territory
Methodology: Northern Territory Weed Risk Management System - aquatic
Management area: Darwin Region

Notes:

Status: PUBLISHED
Last updated: 30/3/2026 10:59:16 am AEST

Questions answered: 38 / 46

Weed Risk: 353.41 (Very high)
   Invasiveness (raw/adjusted): 11.00 / 9.163
   Impacts (raw/adjusted): 11.00 / 5.786
   Potential distribution (raw/adjusted): 6.00 / 6.666

Feasibility of Control: 293.59 (High)
   Control costs (raw/adjusted): 6.00 / 5.454
   Current distribution (raw/adjusted): 10.00 / 10.000
   Persistence (raw/adjusted): 7.00 / 5.383

Result: Prevent entry, contain regional spread, protect priority sites

Invasiveness

A1. What is the ability of the plant to establish amongst intact native environments?
Answer: Very High

Comments: It is extremely persistent and can establish a monoculture by excluding native plant species (ARMCANZ 2000). Under suitable environmental conditions Cabomba is extremely persistent and competitive and can exclude well established native species (Riemer & Llnicki 1968). Cabomba grows quickly and produces a large amount of plant material... It is extremely persistent and can take over a water body, excluding native plant species (Cooperative Research Centre for Australian Weed Management 2003). Cabomba has established in Darwin River, which is a natural river system, with slightly altered flow due to environmental flow from Darwin River Dam. However Cabomba has also established in the bottom section of the river, where the river is mainly fed by natural springs (P. Clifton [NT Weed Management Branch] 2006, pers.comm.).

A2. What is the reproductive ability of the plant?

(a) Time to seeding
Answer: 1 year or less

Comments: Cabomba in Australia is not known to produce viable seed, with the exception of the infestation in the Darwin River in the Northern Territory. Although flowering occurs throughout Australia, viable seed production has not yet been observed outside this infestation. Seeds have been produced in some other infestations but have not yet been observed to germinate. It is thought that most of the cabomba in Australia is a hybrid between an American and an Argentinean variety and is therefore infertile (van Oosterhout 2009). Seed has been discovered in the Northern Territory. They are viable and germinable, but do not germinate due to dormancy. A low rate of germination has been reported from shade house trials and we are still unsure what the triggers are. Do not know field germination rates at present (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Depending on the depth of water, once it reaches the surface it can begin to produce flowers and probably seed if pollinators are present. Therefore time to seeding equals the time to reach the surface. I would say it seed in the first year, if not in the first 6 months (P. Clifton [NT Weed Management Branch] 2006, pers.comm.).

(b) Annual production of viable seed /m2 or /plant
Answer: High

Comments: Cabomba can flower any time of year in the Northern Territory (C. Collins [NT Weed Management Branch] 2012, pers. comm., 17 September.). Cabomba in Australia is not known to produce viable seed, with the exception of the infestation in the Darwin River in the Northern Territory. Although flowering occurs throughout Australia, viable seed production has not yet been observed outside this infestation. Seeds have been produced in some other infestations but have not yet been observed to germinate. It is thought that most of the cabomba in Australia is a hybrid between an American and an Argentinean variety and is therefore infertile (van Oosterhout 2009). Seed viability has not been studied, but germination seems very low (Parsons & Cuthbertson 2001). This assessment notes “In Louisiana viable seed is produced but viability is low and only about 25% of seeds germinate naturally” (Mackey 1996). Seed has been discovered in the Northern Territory. They are viable and germinable, but do not germinate due to dormancy. A low rate of germination has been reported from shade house trials and we are still unsure what the triggers are. We do not know field germination rates at present (P. Clifton [NT Weed Management Branch] 2006, pers.comm.). If left alone, dense infestations of Cabomba can produce 50 flowers per m2 per day for close to 10 months of the year (depending on flooding and drowning of the flowers). I don’t know how many seeds are produced but it could be as many as 9 seeds per flower, therefore we are looking at up to 135 000 seeds/m2/year in dense areas flooded for 2 months. However, the number of seeds is a big factor. If only 1 seed is produced per flower it could be 15 000 seeds. Probably between. Studies are currently being carried out to examine whether all seeds are viable (i.e. 100% viability) (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

(c) Vegetative reproduction
Answer: Frequent

Comments: Cabomba reproduces and spreads by the movement of small plant pieces . . . plant fragments may survive in water for six to eight weeks, and a detached shoot with at least one pair of leaves can grow into a mature plant. Pieces as short as 10mm may be viable (Cooperative Research Centre for Australian Weed Management 2003). Stem fragments readily take root, which accounts for most dispersal (Parsons & Cuthbertson 2001). Cabomba grows and disperses mainly from fragmentation... any detached shoot with at least one paid of expanded leaves is capable of growing into a mature plant (Mackey & Swarbrick 1997). This pest assessment notes “it can rapidly infest water bodies through vegetative growth of stem fragments as small as 1cm" (Mackey 1996).

A3. Do propagules of the plant have properties that allow them to be dispersed long-distance by natural means?

(a) Flying animals (birds, bats)
Answer: Yes

Comments: Like most water plants seed dispersal [of Cabomba] is due to water birds, and this could be important in ensuring dispersal between lakes or rivers (Orgaard 1991). This paper notes that its foliage and seed are eaten by wood, mallard and ruddy ducks …although transport of seeds or fragments by waterfowl cannot be ruled out, the low level and irregularity of flowering, together with its limited use by waterfowl, indicate more effective means of dispersal (Les & Mehrhoff 1999). Propagules do not have any specific properties such as bristles to attach to birds, but stems and vegetative fragments could be dispersed by birds (P. Clifton [NT Weed Management Branch] 2006, pers.comm.)

(b) Other wild animals
Answer: Yes

Comments: Feral pigs may disperse vegetative fragments and/or seeds of Cabomba (P. Clifton [NT Weed Management Branch] 2006, pers.comm.).

(c) Water
Answer: Yes

Comments: Cabomba reproduces and spreads by the movement of small plant pieces . . . plant fragments may survive in water for six to eight weeks, and a detached shoot with at least one pair of leaves can grow into a mature plant. Pieces as short as 10mm may be viable (Cooperative Research Centre for Australian Weed Management 2003). Dispersal by water is a major dispersal mechanism for Cabomba (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

(d) Wind
Answer: No

Comments: It is possible that seeds or vegetative fragments can be blown upstream in open waters with low or stagnant flow (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

A4. How likely is long-distance dispersal by human-assisted means?

(a) Deliberate spread by people
Answer: Common

Comments: Cabomba has been dispersed throughout the world by the aquarium trade. It is still sold as an aquarium plant in many states of Australia, supplied by both growers and wild harvest operations (Cooperative Research Centre for Australian Weed Management 2003). Humans surely are the major agents of introduction and dispersal for Cabomba... within 60 years of discovery, Cabomba was recommended for use in aquaria and water gardens (Les & Mehrhoff 1999).

(b) Accidentally by people and vehicles
Answer: Common

Comments: Recreational equipment (eel traps, boat trailers and propellers) may transport and spread Cabomba fragments (ARMCANZ 2000). The spread of Cabomba in New Hampshire was facilitated by stem fragments cut by motor boats (Les & Mehrhoff 1999). Seed or vegetative fragments can be transported accidentally in mud or soil (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Seed or vegetative fragments can be transported accidentally by cars driving through crossings (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

(c) Contaminated produce
Answer: Unlikely

Comments: This is unlikely, as it is illegal to sell Cabomba anywhere in Australia (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

(d) Domestic/farm animals
Answer: Unlikely

Comments: No evidence to suggest this (NT Weed Risk Management Committee 2006).

Impacts

B1. What is the plant's competitive potential?
Answer: High

Comments: Cabomba grows quickly and produces a large amount of plant material (Cooperative Research Centre for Australian Weed Management 2003). It is extremely persistent and can establish a monoculture (ARMCANZ 2000). Under suitable environmental conditions Cabomba is extremely persistent and competitive and can exclude well established native species (Riemer & Llnicki 1968). Cabomba can grow at 5cm per day (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Plant extracts have allelopathic properties, inhibiting seed germination in wheat and lettuce, and vegetative growth in some aquatic species (Parsons & Cuthbertson 2001). Extracts of Cabomba have allelopathic effects at medium and high concentrations and since allelopathy plays a role in determining the distribution of high plants in the case of Cabomba it would seem to be a mechanism for invading new habitats and ousting native species (Elakovich & Wooten 1989). Cabomba is sensitive to drying out and requires permanent shallow water, usually less than 3 m deep, although it can grow in water up to 10m deep producing stems that reach the surface. With the ability to grow quickly, Cabomba can respond to wide fluctuations in water depths (ARMCANZ 2000). Water quality affects the growth of Cabomba. It grows well in eutrophic conditions with low pH but conditions above pH 8 tend to defoliate the stems. High calcium levels also inhibit growth (ARMCANZ 2000).

B2. What is the plant’s potential to modify the existing fire behaviour and alter the fire regime?
Answer: No potential

Comments: No potential (NT Weed Risk Management Committee 2006).

B3. What is the plant’s potential to restrict the physical movement of people, animals, vehicles, machinery and/or water?
Answer: High

Comments: Cabomba’s dense mass of underwater stems and leaves provide a hazard for recreational water users (Cooperative Research Centre for Australian Weed Management 2003). Dense stands of Cabomba make it unsafe for swimming activities of any kind and have direct implications for associated water sports. It also creates a work place health and safety issue for local government, water engineers, weed managers, field staff and park managers (ARMCANZ 2000). In North America it clogs channels and drains, seriously restricting water flow and recreational activities, and give indication of causing similar problems in Queensland, particularly in nutrient-rich waters (Parsons & Cuthbertson 2001).

B4. What is the plant’s potential to negatively affect the health of animals and/or people?
Answer: None

Comments: Cabomba grows quickly and produces a large amount of plant material. It can significantly reduce water storage capacity and taint drinking water supplies (Cooperative Research Centre for Australian Weed Management 2003). No evidence to suggest any adverse effects resulting from toxicity to native animals or humans.

B5. Does the plant potentially have negative effects on natural and cultural values?

(a) Reducing habitat quality for native animals?
Answer: High

Comments: Cabomba 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 (Cooperative Research Centre for Australian Weed Management 2003). Monocultures also affect resident native fauna, the infestations in the Kenny-Leslie creek system in far north Queensland has resulted in reduced numbers of platypus and water rats (ARMCANZ 2000). Its [Cabomba] ability to replace native aquatic plants with the likely result that native fish and invertebrate populations are displaced together with the ability to effectively infest large areas of water suggests that if allowed to establish throughout the state native aquatic life would be considerably endangered (Mackey 1996).

(b) Threatened species or communities
Answer: More than one

Comments:

(c) Sites of natural or cultural significance
Answer: More than one

Comments:

B6. Is the plant presumed to have negative effects on environmental health?

(a) Soil chemistry/stability
Answer: No

Comments: Not likely to affect soil quality (NT Weed Risk Management Committee 2006).

(b) Water quality
Answer: Yes

Comments: 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 $50a megalitre. Heavy infestations can also raise water levels to a point where overflows and heavy seepage losses occur (Cooperative Research Centre for Australian Weed Management 2003). This study has shown that Cabomba has a negative impact on native aquatic plants and water quality in Lake MacDonald, Queensland. In summer, the mean standing crop of Cabomba was 1.02 kg/sq m, a 7 fold increase from early spring levels. Other species were only found at very low standing crops in infested areas and water clarity decreased, but it is not clear whether this was due to an increase in suspended solids or due to the physical presence of the weed (Anderson & Garraty 1994). Cabomba dies back at certain times of the year (depending on temperature) and the massive amount of decomposing vegetation causes dramatic oxygen reductions. This results in foul-smelling, oxygen deficient water that reduces water quality in the impoundment and further downstream. These anoxic conditions may have an adverse impact on the biological community and also increase the rate of release of some nutrients from the sediments, making them more available for plant growth. It has also been speculated that the decomposition process could release large amounts of iron, manganese and other metals, further reducing water quality (ARMCANZ 2000). Cabomba can increase siltation (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

(c) Hydrology
Answer: Yes

Comments: A heavy infestation can also raise water levels to a point where overflows and heavy seepage losses occur (ARMCANZ 2000). In North America it clogs channels and drains, seriously restricting water flow and recreational activities, and give indication of causing similar problems in Queensland, particularly in nutrient-rich waters (Parsons & Cuthbertson 2001). A heavy infestation of Cabomba can increase flooding (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

Potential distribution

C2. How many broad habitat types in the NT will the plant potentially naturalise in (up to 5)?
Answer: Two

Comments: Now that Cabomba is producing seed, and we have found that this seed can tolerate some desiccation, we are concerned that it may be able to survive in ephemeral water bodies, although there is no evidence to support this yet (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). The broad vegetation types that Cabomba caroliniana will potentially naturalise in are: - Permanent water bodies - Tropical wetlands; floodplains The favoured vegetation type is permanent water bodies (NT Weed Risk Management Committee 2006) (Rachor-Rossiter et al. 2012).

C3. What is the potential of the plant to occur throughout its favoured habitat in the NT (as identified in question 2)?
Answer: Most

Comments: Cabomba caroliniana has the potential to spread throughout most of its favoured habitat (NT Weed Risk Management Committee 2006).

Control costs

A1. How detectable is the weed?

(a) Distinguishing features
Answer: Non-descript

Comments: Cabomba is non-descript (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.). Cabomba caroliniana (Cabomba) is a mostly submerged perennial plant, 2-10 m long with slender stems; usually rooting in bottom mud but can survive unattached. Stems have a thing gelatinous coating. Two types of leaves; submerged leaves on a 3 cm stalk, also coated, are opposite or whorled, finely divided to form a fan shape 3-6 cm across; floating leaves are few, narrow-elliptical, not divided to 2 cm long, stalk attached to the lower surface. Flower emergent , solitary 2 cm in diameter, white and cream, often with a pink tinge at the tip and yellow bases (Smith 2011). Native species with a similar appearance included Myriohylluam aquaticum (Parrots feather) and Ceratophyllum demersum (Hornwart) (Smith 2011).

(b) Active growth period
Answer: >8 months

Comments: Cabomba grows for >8 months in the Darwin region (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.).

(c) Height at maturity
Answer: >2 m

Comments: Cabomba caroliniana (Cabomba) is a mostly submerged perennial plant, 2-10m long (Smith 2011).

A2. What is the general accessibility of infestations at the optimum treatment time?
Answer: Low

Comments: The general accessibility of cabomba infestations is low (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.).

A3. How expensive is control of the weed in the first year of targeted control, for an infestation that has reached maximum weed density?

(a) Chemical costs
Answer: Very low

Comments: Chemical costs for cabomba in the Darwin region would be very low due to its restricted distribution (T. Price [NT Weed Management Branch] 2010, pers. comm.). To treat a cabomba infestation you would need 12/L of 24D per megalitre, as well as a chemical to pull the chemical down the water column [Note: This would place Cabomba control in the High ($200-500/ha) chemical costs category] (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.).

(b) Labour cost
Answer: High

Comments: Cabomba control would require at least 2 people and is slow [Note: This would place Cabomba control in the High (at least $200/ha) labour costs category] (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.).

(c) Equipment cost
Answer: High

Comments: To control Cabomba you would need boats and other equipment to work in an aquatic environment. [Note: This equipment would place Cabomba control in the High equipment costs category] (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.).

A4. What is the general community perception of this weed within the region?
Answer: High

Comments: Medium as Cabomba is a conflict species (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.). Cabomba is a WONS (ARMCANZ 2000).

Current distribution

B1. What is the current pattern of the species’ distribution across the weed management region?
Answer: Restricted

Comments: Cabomba is currently restricted in the Darwin region (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.).

Persistence

C1. How long will it take to reach the maintenance period?
Answer: Low

Comments: Low, as it is likely to take more than 5 years to reach the maintence period (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.). In barramundi ponds on the Atherton tablelands it took 4 years to reach the maintence period and that was a controlled environment, so in an uncontrolled environment it would take longer (P. Jeffery [NT weed control contractor] 2007, pers. comm.). Cabomba is difficult to eradicate as it tends to be herbicide resistant; also physical removal is not recommended because of fragmentation (Smith 2011).

C2. What is the minimum time period for reproduction of sexual or vegetative propagules?
Answer: <1 growing season

Comments: The minimum period for reproduction is <1 growing season (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.). Depending on the depth of water, once it reaches the surface it can begin to produce flowers and probably seed if pollinators are present. Therefore time to seeding equals the time to reach the surface. I would say it seeds in the first year, if not in the first 6 months (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

C3. What is the maximum longevity of sexual or vegetative propagules?
Answer: 2-5 years

Comments: We don’t know, as it is unclear how long the vegetative propogules would remain viable (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.). In Louisiana seed is produced but viability is low and only about 25% of seeds germinate naturally. Seeds can remain viable for more than two years (Mackey & Swarbrick 1997).

C4. What is the threat of reinfestation from outside the management region?

(a) Long-distance (>100m) dispersal by natural means
Answer: Rare

Comments: Long distance spread by natural means is likely to be rare (P. Jeffery, M. Fuller & G. McSkimming [NT weed control contractors] 2007 pers. comm.). Like most water plants seed dispersal [of Cabomba] is due to water birds, and this could be important in ensuring dispersal between lakes or rivers (Orgaard 1991). This paper notes that its foliage and seed are eaten by wood, mallard and ruddy ducks …although transport of seeds or fragments by waterfowl cannot be ruled out, the low level and irregularity of flowering, together with its limited use by waterfowl, indicate more effective means of dispersal (Les & Mehrhoff 1999). Since flowering is regular, occurring for at least 10 months of the year, potential distribution by water birds is more likely (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Propagules do not have any specific properties such as bristles to attach to birds, but stems and vegetative fragments could be dispersed by birds (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Feral pigs may disperse vegetative fragments and/or seeds of Cabomba (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Cabomba reproduces and spreads by the movement of small plant pieces . . . plant fragments may survive in water for six to eight weeks, and a detached shoot with at least one pair of leaves can grow into a mature plant. Pieces as short as 10mm may be viable (Cooperative Research Centre for Australian Weed Management 2003). Dispersal by water is a major dispersal mechanism for Cabomba (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). It is possible that seeds or vegetative fragments can be blown upstream in open waters with low or stagnant flow (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

(b) Long-distance (>100m) dispersal by human means
Answer: Rare

Comments: Long distance spread by human means is likely to be occasional (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Cabomba has been dispersed throughout the world by the aquarium trade. It is still sold as an aquarium plant in many states of Australia, supplied by both growers and wild harvest operations (Cooperative Research Centre for Australian Weed Management 2003). Humans surely are the major agents of introduction and dispersal for Cabomba …within 60 years of discovery, Cabomba was recommended for use in aquaria and water gardens (Les & Mehrhoff 1999). Recreational equipment (eel traps, boat trailers and propellers) may transport and spread Cabomba fragments (ARMCANZ 2000). The spread of Cabomba in New Hampshire was facilitated by stem fragments cut by motor boats (Les & Mehrhoff 1999). Seed or vegetative fragments can be transported accidentally in mud or soil (P. Clifton [NT Weed Management Branch] 2006, pers. comm.). Seed or vegetative fragments can be transported accidentally by cars driving through crossings (P. Clifton [NT Weed Management Branch] 2006, pers. comm.).

References

Anderson T & Garraty K (1994). Cabomba caroliniana down under in Lake MacDonald: Additional Paper. In: 'Proceedings of the 3rd Queensland Weeds Symposium'. Weed Society of Queensland, Toowoomba. ARMCANZ (2000). Weeds of National Significance Cabomba (Cabomba caroliniana) Strategic Plan. National Weeds Strategy Executive Committee, Launceston. Cooperative Research Centre for Australian Weed Management (2003). Weed Management Guide: Cabomba -Cabomba caroliniana. Department of the Environment and Heritage, Canberra. Elakovich SD & Wooten JW (1989). Allelopathic potential of 16 aquatic and w etland plants. Journal of Aquatic Plant Management 27: 78-84. Les DH & Mehrhoff LJ (1999). Introduction of non-indigenous aquatic vascular plants in southern New England: a historical perspective. Biological Invasions 1: 281-300. Mackey AP & Sw arbrick JT (1997). The Biology of Australian Weeds. Plant Protection Quarterly 12 (4): 154-165. Mackey AP (1996). Cabomba in Queensland: Pest Status Review Series, Land Protection Branch. Queensland Government Natural Resources and Mines. Orgaard M (1991). The genus Cabomba (Cabombaceae) - a taxonomic study. Nordic Journal of Botany, 11, 179-203. Parsons WT & Cuthbertson EG (2001). Noxious Weeds of Australia, 2nd edn, CSIRO Publishing, Melbourne. Rachor-Rossiter N, Setterfield S, Ferdinands K & Elliott L (2012). Northern Territory Weed Risk Management User Guide. Northern Territory Government, Darwin. Riemer DN & Llnicki RD (1968). Reproduction and over w intering of Cabomba in New Jersey. Weed Science 16 101-102. Smith N (2011). Weeds of Northern Australia: A Field Guide. Northern Territory Environment Centre, Darwin. van Oosterhout E (2009). Cabomba control manual: current management and control options for cabomba (Cabomba caroliniana) in Australia. NSW Department of Primary Industries, Orange, NSW.