Gamba grass (Andropogon gayanus)

Also known as: Rhodesian andropogon, Rhodesian bluegrass, tambuki grass

Gamba grass is a clumping tropical grass up to 4 m tall. It forms dense patches that outcompete native species.

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How does this weed affect you?

Gamba grass grows quickly and forms dense stands. It:

• outcompetes native plants in grasslands, woodlands and along watercourses
• uses much more water than native grasses which can reduce water levels in downstream wetlands and streams
• reduces available soil nitrogen levels 
• reduces food and habitat for native wildlife
• fuels intense bushfires that can cause permanent loss of trees and other native plants
• may impede movement of livestock and vehicles.

What does it look like?

Gamba grass is a perennial grass that grows in clumps up to 1 m wide and 4 m high. The clumps grow close together to form dense stands. There is variation within this species as plants can have many or few shoots, stems that are thick with wide leaves or stems that are fine with thinner leaves. Most seed production is in May and June.

Leaves are:

• elongated with a pointed tip and a prominant white midrib
• up to 1 m long and 1.5–5 cm wide
• attached to the stalk by a hairy sheath
• often covered with soft hairs.

Seedheads:

• are triangular shaped and loosely branched
• have up to 6 groups of primary branches and 2–18 branches per group
• have hairy flower spikelets in pairs of one stalked and one stalkless spikelet, the stalkless spikelet has a spiral shaped awn (bristle).

Seeds are:

• light brown to brownish black
• 2–3 mm long and 1 mm wide.

Stems are:

• hairy
• may be robust and thick or slender.

Roots:

Gamba grass has three types of roots:

• fibrous roots, close to the soil surface that grow up to 1 m away from the tussock
• rhizomes, stems that grow just under the surface
• deeper vertical roots.

Similar looking species:

• Elephant grass (Cenchrus purpureus), which can grow even taller up to 7.5 m and has dense cylindrical seedheads.

Where is it found?

Gamba grass is not currently found in NSW. 

It was originally introduced as a pasture grass in northern parts of Western Australia, the Northern Territory and Queensland. It has since spread along roadsides and into native grasslands and woodlands. 

It is native to tropical and subtropical Africa.

What type of environment does it grow in?

Gamba grass grows in dry tropical climates. It can grow in areas with between 400–3000 mm of rainfall per year if there is a dry season of up to 9 months. It grows best in areas that have at least 750 mm per annum with 3–7 months of dry season.  It usually grows in full sun and can only tolerate light shade. It has adapted to a wide range of soils and is drought and fire tolerant.

Maps and records

• Recorded presence of Gamba grass during property inspections (Map: Biosecurity Information System - Weeds, 2017-2024)
  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?

Gamba grass was intentionally introduced as a pasture grass in northern Australia. 

By seed

Gamba grass produces up to 244 000 seeds per plant per year if it is not grazed. The seeds are not viable for very long. After 6 months the viability is less than 1%. 

Gamba grass seeds are spread by:

• wind (though most seed falls within 10 m of the plant)
• water
• movement of contaminated hay
• sticking to mud attached to vehicles, slashers and other machinery.

References

Cook, G. D. (1991) Gamba grass: Impending doom for Top End savannas, CSIRO Tropical Ecosystems Research Centre Newsletter, 91.

Csurhes, S. and Hannan-Jones, M. (2016) Pest plant risk assessment: Gamba grass Andropogon gayanus. Queensland Department of Primary Industries and Fisheries, Brisbane, Queensland. Retrieved 31/07/2020 from: https://www.daf.qld.gov.au/__data/assets/pdf_file/0017/58004/IPA-Gamba-Grass-Risk-Assessment.pdf

Department of Agriculture, Water and the Environment. (2013). Weeds in Australia. Andropogon gayanus. Australian Government. https://www.environment.gov.au/cgi-bin/biodiversity/invasive/weeds/weeddetails.pl?taxon_id=66895 Retrieved  25/2/2020.

Jones, C (1978) Potential of Andropogon gayanus in the oxisol and ultisol savannas of tropical America. Retrieved 25/8/20 from http://ciat-library.ciat.cgiar.org/ciat_digital/ciat%20(colombia)%20000038.pdf

Kean, L., & Price, O. (2002). The extent of Mission grasses and Gamba grass in the Darwin region of Australia's Northern Territory. Pacific Conservation Biology, 8(4), 281-290.

Rossiter et. al. (2009) Invasive Andropogon gayanus (gamba grass) is an ecosystem transformer of nitrogen relations in Australian savanna, Ecological Applications, 19(6), 2009, pp. 1546–1560.

Timothy Neale (2019) A Sea of Gamba: Making Environmental Harm Illegible in Northern Australia, Science as Culture, 28:4, 403-426.

More information

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Control

Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the helpline listed at the top of this page immediately.

NSW DPI will lead an initial response for the treatment and disposal of the plant to stop it from spreading

Herbicide options

See Using herbicides for more information.

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: One part product to 50 parts water
Comments: Spot spray
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: One part product to 9 parts water
Comments: Splatter gun
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
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	Prohibited Matter A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries

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Reviewed 2020