Quick Facts

Quick facts

• Gamba Grass (Andropogon gayanus) is a large perennial tussock grass that can grow up to 4 m tall.
• It grows in pastures and along roads, but will actively invade other habitats such as savanna.
• Gamba Grass was introduced from tropical Africa and is a serious weed in northern Australia, from Western Australia to Queensland.
• It mainly spreads by seeds which are dispersed by wind or water, but also during hay transport or in mud attached to vehicles and machinery.
• It has profound impacts on the nutrient and water availability in the soil and leads to reduced tree cover.
• During bush fires it creates very intense fires that can kill trees and present a potential danger to properties and people.
• Gamba Grass can be controlled by herbicide treatment of young or regrowing plants before seed maturity.

What Does It Look Like?

What is it?

Gamba Grass (Andropogon gayanus) is a perennial grass that forms dense tussocks up to 70 cm in diameter and can grow up to 4 m tall. Leaves, stems and spikelets are covered with soft hairs. The leaf blades are up to 60 cm long and 1.5-5 cm wide, with a prominent, white midrib (Oram 1987; Csurhes & Hannan-Jones 2008).

The flowering stems are loosely branched with up to six groups of 2-18 primary branches. The flower spikelets are arranged in pairs of one sessile and one stalked spikelet. The sessile spikelets are 5-8 mm long, hairless and have a spirally twisted awn that is 15-30 mm long. Stalked spikelets are 5-7 mm long and hairy, with an awn of 5-10 mm in length. The seeds are 2-3 mm long, 1 mm wide and light brown to brownish black (Oram 1987; Csurhes & Hannan-Jones 2008).

For further information and assistance with identification of Gamba Grass contact the herbarium in your state or territory.

Flower colour

Green

Growth form (weed type/habit)

Grass

Where it currently grows? Preferred habitat

In its native range, Gamba Grass mostly grows below 980 m in altitude in areas with an annual rainfall between 400 and 1500 mm. In northern Australia, it often grows in pastures and along road verges (Hussey et al. 1997). However, it can invade a variety of habitats from wetland margins to savanna (Csurhes & Hannan-Jones 2008).

Are there similar species?

Mature Gamba Grass is easy to recognize, but immature plants may be confused with other introduced or native grass species (Northern Territory Department of Natural Resources, Environment, the Arts and Sport 2009).

Why Is It A Weed?

What are its impacts?

By replacing native grasses, Gamba Grass has a profound impact on savanna biodiversity. Firstly, Gamba Grass infestations lead to a loss in tree cover (Ferdinands et al. 2006) as a result of dramatically increased fire intensity produced by gamba grass fuelled fires. Furthermore, Gamba Grass alters nitrogen availability in the soil, leading to increased ammonium levels but decreased nitrate and total inorganic nitrogen levels (Rossiter-Rachor et al. 2009). Also water conditions were altered, with water use three times higher and deep drainage of water halved at Gamba Grass-infested sites (Rossiter et al. 2004). It can be assumed that if the areas invaded by Gamba Grass are very large, even the hydrology of a water catchment can be altered, with an impact on downstream wetlands and rivers (Csurhes & Hannan-Jones 2008).

Gamba Grass forms dense stands that produce high amounts of biomass. Consequently, savanna sites infested with Gamba Grass exhibit up to eight times higher fire intensities than native grass savannas (Rossiter et al. 2003). These high fire intensities can lead to a reduction of the tree layer and finally turn woodlands into grasslands (Csurhes & Hannan-Jones 2008). Furthermore, these intense fires are harder to control, leading to higher risks of property damage, loss of life and impacts to cultural sites (Csurhes & Hannan-Jones 2008).

How does it spread?

Gamba Grass reproduces from seeds. Up to 240,000 seeds can be produced per plant and year, with a seed viability of about 65%. However, the seeds lose their viability with time. Seeds that are a few years old are unlikely to germinate, so there is no long-lived soil seed bank (Flores et al. 2005).

The seeds mostly fall within 5 m of the mother plant, but can also be dispersed by wind or by water, as well as in mud attached to vehicles (Queensland Department of Agriculture, Fisheries and Forestry). It probably also spreads during hay transport or by roadside slashing machinery (Csurhes & Hannan-Jones 2008).

In the Northern Territory, rates of spread between 110 and 333 m per year have been reported (cited in Csurhes & Hannan-Jones 2008). Gamba Grass seems to spread more rapidly in disturbed vegetation than in undisturbed savanna woodlands (Csurhes & Hannan-Jones 2008).

What is its history in Australia?

Gamba Grass was first introduced to Australia in 1931 for trials to use it as a pasture grass. After the first trials with two varieties at the Katherine Research Station from 1946, residuals of these trials were grown at Berrimah Experiment Farm. The material from this cultivation formed the basis of a new cultivar that is now widely distributed in northern Australia. This new cultivar “Kent” probably originated by natural selection from a cross of the two initial varieties, var. squamulatus and an unknown variety (Oram 1987). In 1942, it was introduced to Queensland, but large-scale planting only occurred from around 1983 (Queensland Department of Agriculture, Fisheries and Forestry). Since it effectively improves pastures, it was widely sown (Csurhes & Hannan-Jones 2008).

How To Manage It?

Best practice management

Non-chemical control: If possible, Gamba Grass infestations should be removed when they are still small. Small plants can be pulled out or dug out, but care should be taken to shake soil from the roots to make sure that the plant dies (Queensland Government, Department of Agriculture, Fisheries and Forestry).

Gamba Grass is a fire tolerant plant, but burning can be applied, especially early in the wet season, to remove old growth and reduce the establishment of young plants. The new growth after burns is also more susceptible to herbicides. Plants with seeds should not be burned to avoid further seed dispersal (Queensland Department of Agriculture, Fisheries and Forestry).

Chemical control: Herbicide treatment is best on plants that are still small or regenerating after burning or slashing. Gamba Grass is most susceptible to herbicides during flowering (Northern Territory Department of Land Resource Management). For effective chemical control, at least two treatments should be applied within a growing season. First, active growth after the onset of the we saison rains. Two to four weeks later, newly emerging seedlings and plants that were potentially missed should be sprayed. A further inspection before April is advisable to treat newly germinated seedlings and surviving plants, if necessary (Australian Weeds Committee 2011).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au .

In order to avoid spread from Gamba Grass to other sites, hygienic procedures should be followed so that machinery etc. is not contaminated with seeds (Northern Territory Department of Land Resource Management).

To avoid regrowth from seeds, the site should undergo follow-up controls for two years after eradication (Flores 2005, Northern Territory Department of Land Resource Management).

In areas where the use of Gamba Grass is permitted, pastures should be well-grazed to keep plant height below 90 cm in order to minimize seed spread. Further spread of the species within or from the property should be avoided (Northern Territory Department of Land Resource Management 2010).

Biological control: There is currently no known biological control agent.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Gamba Grass flowers from April until about August, with most seeds produced in May and June (Csurhes & Hannan-Jones 2008). Germination occurs mostly in November and December (Northern Territory Department of Land Resource Management).

Where Is It Found?

Which states and territories is it found?

NT, QLD, WA

What areas within states and territories is it found?

Gamba Grass is naturalised in the east Kimberley region of Western Australia, in the northern parts of the Northern Territory and coastal and sub-coastal areas of North Queensland (Csurhes & Hannan-Jones 2008). In the Northern Territory, it covers up to 1.5 million hectares, primarily in the regions of Darwin and Katherine. In the Cape York Peninsula, Queensland, it affects at least 18,000 hectares (Australian Weeds Committee 2011). Gamba Grass has also been introduced to other parts of the world, especially tropical America, where it became naturalised in Brazil and Venezuela (Csurhes & Hannan-Jones 2008).

Where does it originate?

Gamba Grass is native to tropical Africa. Its native distribution range stretches from Senegal to Sudan, south to Mozambique, Botswana and South Africa (Csurhes & Hannan-Jones 2008).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

YES

Where is it a declared weed?

NT, QLD, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO
Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Andropogon gayanus

Other scientific names (synonyms)?

Does it have other known common name(s)?

Rhodesian Blue Grass, Rhodesian Andropogon, Bluestern, Sandabahar