Bana grass (Cenchrus purpureum x americanus)

Assessment ID: 1006
Jurisdiction: North Territory
Methodology: Northern Territory Weed Risk Management System - terrestrial
Management area: Darwin Region

Notes:

Status: PUBLISHED
Last updated: 27/3/2026 5:15:38 pm AEST

Questions answered: 39 / 47

Weed Risk: 34.57 (Low)
   Invasiveness (raw/adjusted): 2.00 / 1.666
   Impacts (raw/adjusted): 15.00 / 7.890
   Potential distribution (raw/adjusted): 5.00 / 2.630

Feasibility of Control: 562.71 (Very high)
   Control costs (raw/adjusted): 7.00 / 6.363
   Current distribution (raw/adjusted): 10.00 / 10.000
   Persistence (raw/adjusted): 11.50 / 8.844

Result: Monitor

Invasiveness

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

Comments: It is densely tufted with short underground runners. In ideal conditions it can grow at a rate of up to 70cm per week and can be very invasive [referring to C. purpureum x typhoides] (Bellinger Landcare Inc. 2022). Bana grass does not produce viable seed. It is deep rooted (Cameron, A. pers. comm. 19 May 2022). The bana grass growing at coastal plains is in several rows, about 13m long growing as wind breaks and insect refuge. It is cut and watered regularly and it seeds occasionally but it never spreads. The only way to propagate it is from cuttings (Finney, M. pers. comm. 19 May 2022). Forms bamboo-like, densely tufted clumps which become invasive in bushland vegetation. Is an opportunistic weed with the ability to persist in disturbed areas, out-competing other native vegetation. In north Queensland, populations have become naturalised [referring to C. purpureum] (QDAF 2000).

A2. What is the reproductive ability of the plant?

(a) Time to seeding
Answer: >3 yrs/never

Comments: Bana grass does not produce viable seed (Cameron, A. pers. comm. 19 May 2022).

(b) Annual production of viable seed /m2 or /plant
Answer: None

Comments: Mainly vegetative propagation, though sexual reproduction has been reported in some species. Unpredictable seed producer, and in some environments, it seldom develops seeds, probably due to low pollen viability. Seeds are dispersed by wind but viability via this method is often very low. Matures rapidly (Matore 2019). Although elephant grass can produce viable seed, seed set is usually very poor and seed is rarely harvested [referring to C. purpureum cv. Capricorn] (Qld DPIF 2007).

(c) Vegetative reproduction
Answer: Infrequent

Comments: Bana grass is mainly vegetative propagation, though sexual reproduction has been reported in some species of bana grass (Matore 2019).

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: No

Comments: Bana grass does not produce viable seed (Cameron, A. pers. comm. 19 May 2022). The bana grass growing at coastal plains seeds occasionally but never spreads. The only way to propagate it is from cuttings (Finney, M. pers. comm. 19 May 2022).

(b) Other wild animals
Answer: No

Comments: Bana grass does not produce viable seed (Cameron, A. pers. comm. 19 May 2022). The bana grass growing at coastal plains seeds occasionally but never spreads. The only way to propagate it is from cuttings (Finney, M. pers. comm. 19 May 2022). Elephant grass can spread by wind, moving water and seeds attached to fur, clothing and vehicles. Also spread by humans moving plants or plant parts [referring to C. purpureum] (QDAF 2000).

(c) Water
Answer: No

Comments: Bana grass does not produce viable seed (Cameron, A. pers. comm. 19 May 2022). The bana grass growing at coastal plains seeds occasionally but never spreads. The only way to propagate it is from cuttings (Finney, M. pers. comm. 19 May 2022). Elephant grass can spread by wind, moving water and seeds attached to fur, clothing and vehicles. Also spread by humans moving plants or plant parts [referring to C. purpureum] (QDAF 2000).

(d) Wind
Answer: No

Comments: Bana grass does not produce viable seed (Cameron, A. pers. comm. 19 May 2022). The bana grass growing at coastal plains seeds occasionally but never spreads. The only way to propagate it is from cuttings (Finney, M. pers. comm. 19 May 2022). Elephant grass can spread by wind, moving water and seeds attached to fur, clothing and vehicles. Also spread by humans moving plants or plant parts [referring to C. purpureum] (QDAF 2000).

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

(a) Deliberate spread by people
Answer: Occasional

Comments: The grass has a purpose and people might deliberately spread it because of that (Opden, R. pers. comm. 19 May 2022). Elephant grass can spread by wind, moving water and seeds attached to fur, clothing and vehicles. Also spread by humans moving plants or plant parts [referring to C. purpureum] (QDAF 2000).

(b) Accidentally by people and vehicles
Answer: Unlikely

Comments: Elephant grass can spread by wind, moving water and seeds attached to fur, clothing and vehicles. Also spread by humans moving plants or plant parts [referring to C. purpureum] (QDAF 2000).

(c) Contaminated produce
Answer: Unlikely

Comments: Elephant grass can spread by wind, moving water and seeds attached to fur, clothing and vehicles. Also spread by humans moving plants or plant parts [referring to C. purpureum] (QDAF 2000).

(d) Domestic/farm animals
Answer: Unlikely

Comments: Elephant grass can spread by wind, moving water and seeds attached to fur, clothing and vehicles. Also spread by humans moving plants or plant parts [referring to C. purpureum] (QDAF 2000).

Impacts

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

Comments: P. purpureum is a fast-growing perennial grass that flowers at different times of the year depending on climatic condition, for example, in Florida, the grass flowers between July and February. In Mexico and Central America, flowering occurs all year long with peaks from December to May. In South Africa, this species flowers from January to June. As many other C4 grasses, P. purpureum is well adapted to environments with high daytime temperatures, intense sunlight, drought, and nitrogen and/or CO2 limitation. Though the grass grows best during the rainy season, its deep root system allows it to survive long drought periods (Matore 2019).

B2. What is the plant’s potential to modify the existing fire behaviour and alter the fire regime?
Answer: Significant potential

Comments: P. purpureum is a fast-growing perennial grass that flowers at different times of the year depending on climatic condition, for example, in Florida, the grass flowers between July and February. In Mexico and Central America, flowering occurs all year long with peaks from December to May. In South Africa, this species flowers from January to June. As many other C4 grasses, P. purpureum is well adapted to environments with high daytime temperatures, intense sunlight, drought, and nitrogen and/or CO2 limitation. Though the grass grows best during the rainy season, its deep root system allows it to survive long drought periods (Matore 2019).

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

Comments: When bana leaves reach maturity stage, its leaves will be razor sharp and can occasionally hurt foraging animals. This is common in instances where cutting back rate will be low (Matore 2019).

B4. What is the plant’s potential to negatively affect the health of animals and/or people?
Answer: Low

Comments: When bana leaves reach maturity stage, its leaves will be razor sharp and can occasionally hurt foraging animals. This is common in instances where cutting back rate will be low (Matore 2019).

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

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

Comments: It is likely to grow on river banks and threaten any native species that depend on them (Cameron, A. pers. comm. 19 May 2022).

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

Comments: Species that depend on river banks include: 1. Purple crown fairywren – Malurus coronatus 2. Mertens’ water monitor – Varanus mertensi 3. Mitchell’s water monitor – Varanus mitchelli (Nano, C. pers. comm. 19 May 2022).

(c) Sites of natural or cultural significance
Answer: One

Comments: Sites likely to be affected by bana grass include the Daly River middle reaches due to its proximity to areas of likely infestation, but not the Mary River region, because its structure is not suitable for infestation (Cameron, A. pers. comm. 19 May 2022).

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

(a) Soil chemistry/stability
Answer: No

Comments: No specific information was found regarding soil chemistry or stability (WRTC 2022).

(b) Water quality
Answer: No

Comments: No specific information was found regarding impacts on water quality (WRTC 2022).

(c) Hydrology
Answer: Yes

Comments: No specific information was found regarding impacts on hydrology (WRTC 2022).

Potential distribution

C1b. What is the Climatch suitability score (which indicates the proportion of the NT environment that is suitable for the plant)?
Answer: 2

Comments: Bana grass is grown in both the tropical and subtropical regions with rainfall from 750 to 2500 mm per year and a temperature range of 25–40°C. Generally it grows very well in regions that receive high rainfall, but its deep rooted system adapts it to drought risk areas that receive less rainfall. It can grow on a wide variety of soils with a range of nutrient levels, if they have good drainage (Matore 2019). The original climatch model produced a compatibility score of 10. This score was rejected by the Weed Risk Technical Committee due to the grass’s dependency on rainfall and it was agreed that the data used to feed the model likely came from irrigated plantings rather than wild-growing weeds. Based on evidence for bana grass requiring at least 1000mm of annual rainfall or riverine habitat the climatch model was re-run with any data points that occurred in areas with less than 1000mm of rainfall removed. This produced a lower score of 7 out of 10, however; the image was not a reasonable fit, as the points that are at or above 7 (orange) fall well south of the 1000mm rainfall cutoff line. Due to the poor fit of this model, the default threshold Climatch suitability score of 7 (see page 27 of the NTWRMS User Guide) was adjusted to 8 for this assessment, which returned a score of 2.2 , with the cut-off line being brought north to around the Katherine region, and just south. It does include some regions in the south of the NT, which are in error, but it seems to be the best fit (WRTC 2022).

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

Comments: Two – tropical riparian and rainforest (WRTC 2022).

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

Comments: Incidental (WRTC 2022).

Control costs

A1. How detectable is the weed?

(a) Distinguishing features
Answer: Sometimes distinct

Comments: Bana grass resembles sugarcane in appearance (Saccharum officinarum), but it is easily distinguished by its narrow leaves and stem height of 4m (Matore 2019). Elephant grass is a tufted perennial that can grow up to 4m high. It has pale green leaves up to 4cm in width, with a strong midrib tapering to a fine point. The large flower heads range in colour from yellow to purple, and can be up to 30 cm in length. It is similar in appearance to sugar cane, but with narrower leaves and does a shorter height [referring to C. purpureum] (QDAF 2000). Tufted perennial grasses growing to 4m, resembling sugar cane in appearance. Pale green leaves up to 4cm in width, strong mid-rib tapering to a fine point. Flower heads up to 30cm in length, colour from yellow to purple. Forms bamboo-like, densely tufted clumps on creek banks and roadsides [referring to C. purpureum and C. purpureum x typhoides] (RIC 2015).

(b) Active growth period
Answer: 4-8 months

Comments: Bana grass is a hybrid derived from the annual Babala (Pennisetum americanus) and the perennial Napier grass (Pennisetum purpureum) (Matore 2019). P. purpureum is a fast-growing perennial grass that flowers at different times of the year depending on climatic condition, for example, in Florida, the grass flowers between July and February. In Mexico and Central America, flowering occurs all year long with peaks from December to May. In South Africa, this species flowers from January to June. As many other C4 grasses, P. purpureum is well adapted to environments with high daytime temperatures, intense sunlight, drought, and nitrogen and/or CO2 limitation. Though the grass grows best during the rainy season, its deep root system allows it to survive long drought periods (Matore 2019).

(c) Height at maturity
Answer: >2 m

Comments: Tufted perennial grasses growing to 4m, resembling sugar cane in appearance. Pale green leaves up to 4cm in width, strong mid-rib tapering to a fine point. Flower heads up to 30cm in length, colour from yellow to purple. Forms bamboo-like, densely tufted clumps on creek banks and roadsides. [referring to C. purpureum and C. purpureum x typhoides] (RIC 2015).

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

Comments: Forms bamboo-like, densely tufted clumps on creek banks and roadsides [referring to C. purpureum and C. purpureum x typhoides] (RIC 2015).

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: Control may be improved by first slashing bana grass. After slashing, actively growing stems can be effectively controlled with a foliar application of glyphosate at a rate of 10ml/L. Followup spraying at the same rate may be needed after this initial knockdown [referring to C. purpureum x typhoides] (Bellinger Landcare Inc. 2022). There is no herbicide currently registered for control of elephant grass in Queensland; however, an off-label use permit (PER82307) allows the use of glyphosate at up to 2 L (360 g/L formulation)/100L water for the control of environmental weeds in non-agricultural areas, bushland and forests as listed in Table 1. Permit PER11463 allows for the use of imazapyr and imazapyr + glyphosate at the rates listed in Table 1. Control will be more effective if applied to regrowth after slashing. Follow-up treatment may be required [referring to C. purpureum] (QDAF 2000).

(b) Labour cost
Answer: Very low

Comments: Labour costs associated with control would be low due to the restricted distribution (Elliott, L. pers. comm. 19 May 2022).

(c) Equipment cost
Answer: Very low

Comments: Control may be improved by first slashing bana grass. After slashing, actively growing stems can be effectively controlled with a foliar application of glyphosate at a rate of 10ml/L. Followup spraying at the same rate may be needed after this initial knockdown [referring to C. purpureum x typhoides] (Bellinger Landcare Inc. 2022).

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

Comments: Community perception is non-existent for bana grass and most people are unaware of it (Cameron, A. pers. comm. 19 May 2022).

Current distribution

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

Comments: It is used as a wind break on horticultural properties and research farms and is highly restricted to these uses only (Cameron, A. pers. comm. 19 May 2022).

Persistence

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

Comments: Time to maintenance period would be extremely short due to it not producing viable seeds, and its vegetative production being very slow (Cameron, A. pers. comm. 19 May 2022).

C2. What is the minimum time period for reproduction of sexual or vegetative propagules?
Answer: Do not know

Comments: The minimum time to for reproduction of vegetative propagules is unknown (Cameron, A. pers. comm. 19 May 2022).

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

Comments: The maximum longevity of vegetative propagules is unknown, but they would likely rot in the ground at some point (Cameron, A. and Elliott, L. pers. comm. 19 May 2022).

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

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

Comments: If long distance dispersal were to occur by natural means, it would be vegetative spread via floodwater, and it would be rare (Cameron, A. pers. comm. 19 May 2022).

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

Comments: Long distance dispersal by humans is unlikely (Cameron, A. pers. comm. 19 May 2022).

References

Bellinger Landcare Inc. (2022) ‘Bana Grass – Cow Cane Pennisetum purpureum x Pennisetum typhoides’, in Grasses, https://www.bellingerlandcare.org.au/wp-content/uploads/Grasses.pdf, accessed 16 May 2022. Cameron, A. 2022. Senior Agronomist, Plant Industries, NT Department of Agriculture and Fisheries. Personal communication during Weed Risk Technical Committee meeting, 19 May 2022. Elliott, L. 2022. Senior Botanist, NT Herbarium, NT Department of Lands, Planning and Environment. Personal communication during Weed Risk Technical Committee meeting, 19 May 2022. Finney, M. 2022. Extension Officer, Plant Industries, NT Department of Agriculture and Fisheries. Personal communication during Weed Risk Technical Committee meeting, 19 May 2022. Matore, Z. (2019). 'Bana Grass Growing in Sub Saharan Africa', in R. L. Edvan, E. M. Santos (eds.), Forage Groups, IntechOpen, London. 10.5772/intechopen.82367. Nano, C. 2022. Flora and Fauna, NT Department of Lands, Planning and Environment. Personal communication during Weed Risk Technical Committee meeting, 19 May 2022. Opden, R. 2022. Weed Management Branch, NT Department of Lands, Planning and Environment. Personal communication during Weed Risk Technical Committee meeting, 19 May 2022. QDAF (Queensland Department of Agriculture and Fisheries). (2000). Elephant grass Pennisetum purpureum. Queensland Department of Agriculture and Fisheries, https://www.daf.qld.gov.au/__data/assets/pdf_file/0003/52581/elephant-grass.pdf, accessed 16 May 2022. Qld DPIF (Queensland Department of Primary Industries and Fisheries), (2007). PASTURES: Mackay Whitsunday region. A guide for developing productive and sustainable pasture-fed grazing systems, Queensland Government. RIC (Redlands Indigiscape Centre), (2015). Environmental Weeds of the Redlands. Redland City Council, Capalaba. WRTC, (2025). Meeting Minutes, NT Weed Risk Technical Committee, NT Government, 19 May 2022.