Quick Facts

Quick facts

• Originally from Africa southern Europe and western Asia, Coolatai Grass (Hyparrhenia hirta) is a large tussock like plants to 1.2–1.5 m tall, with blue-green leaves, and flowers many V-shaped spikes about 5–6 cm long.
• It is a highly successful and invasive introduced species which germinates and grows in a wide range of temperatures, produces vast quantities of seed and persists under heavy grazing.
• It spreads by seeds which have hairy, awned husks that stick to clothing, animals and vehicles.
• It impacts on biodiversity by out competing and replacing native plants, preventing their regeneration and reducing available fauna habitat.
• Human activities such as slashing or traffic assist in spreading the weed, especially along roadsides.
• It cannot be controlled by herbicide alone.

What Does It Look Like?

What is it?

Coolatai Grass (Hyparrhenia hirta) is a tall densely tufted perennial grass reaching up to 1.2 –1.5 m in height. The leaves are rough to touch, grey-green to blue-green and have a waxy bloom that can be rubbed off. The leaf-blades are flat, folded or in-rolled, to 40 cm long and 4 mm wide, with the leaf sheath (part of the leaf rolled around the stem). The leaf ligule (between the base of the leaf blade where it joins the stem; and the leaf-sheath) is membranous and 2–3 mm long.

The flower-heads inflorescence are panicle elongated, loose, rather sparse, 15–40 cm. Each flowering stalk has paired branches of numerous flowers forming a ‘V” at the end of the flowering stalks on lateral stalks, each  3–5cm long, each with 5–8 spikelets. The spikelets (clusters of small flowers) are arranged along the main axis with the oldest at the base and the youngest at the top. Each spikelet is about 4–6 mm long with two flowers, one fertile lemma (flower) is on a short stalk and awnless and is shorter and narrower than the other, the sterile without a stalk and awned. The awn is 1.5–2.5 cm long, golden-brown with a hairy base. 

The fruit or seed is about 2 mm long and is dispersed inside the hairy awned husk (Walsh & Entwistle 1994; Wheeler et al. 2002; CRC 2007; Harden 2007; Plant NET 2021;  VicFlora 2016).

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

Flower colour

Green

Growth form (weed type/habit)

Grass

Where it currently grows? Preferred habitat

Coolatai Grass grows in a range of climatic conditions from a Mediterranean to humid sub-tropical climate . Although it was originally introduced for light soils, it has been recorded on a wide range of soil types including hard rocky soils and deep sands. It prefers to grow in pasture and in open habitats such as woodlands and grasslands and is not as common in closed forests or areas with a dense shrub understorey. Observations in Kwiambal National Park, New South Wales suggest that it is less abundant under dense tree cover (McArdle et al. 2004). Most large populations currently occur in areas with annual average rainfall of 400–800 mm, but the species also occurs in arid regions (CRC 2007).

Are there similar species?

In addition to Coolatai Grass, one native and one introduced species of Hyparrhenia occur in Australia. 

Tambookie Grass (H. filipendula) is the native species. It differs from Coolatai Grass by having 1–3 awns per spikelet and the awns are 4–5 cm long. 

Jaragua Grass (H. rufa) is a tropical pasture species introduced from Africa it has 9 or 10 awns per raceme which are 16–22 mm long. 

Coolatai Grass is the only one that currently occurs south of Sydney. it has 5–7 (rarely 8) flowers per raceme and awns 15–25 mm long.

 Other native species similar to Coolatai Grass are Kangaroo Grass (Themeda triandra) [as Themeda australis and T. triandra], Barbed Wire Grass (Cymbopogon species) and Red-leg Grass (Bothriochloa macra) (CRC 2007).

Why Is It A Weed?

What are its impacts?

Coolatai Grass is a highly successful and invasive introduced species. It germinates and grows in a wide range of temperatures, produces vast quantities of seed and persists under heavy grazing. Coolatai grass (Hyparrhenia hirta) is an invasive drought, fire and herbicide tolerant tussock forming perennial grass. It has become a major invasive species in northern New South Wales (NSW) and southern Queensland, dominating pastures over a range of soil types and conditions. It is also one of the few perennial grasses capable of invading undisturbed natural ecosystems and is a major threat to natural biodiversity in stock routes, nature reserves and National Parks. Pasture dominated by Coolatai Grass can be productive, although the management requirements are higher than that commonly employed (DPI NSW 2019).

Agriculture: It impacts on grazing by dominating paddocks which are not intensively grazed or managed and although stock will graze fresh leaf growth they avoid older growth. Selective grazing by stock of more palatable grasses assists Coolatai Grass to become dominant in pastures (McCormick & Lodge 1991; Lodge & McCormick 1995; Lodge et al. 2005). DPI NSW (2019) state the following: Coolatai Grass readily invades pastures and dominates them, particularly where ground cover is low (less than 70%) due to the grazing regime (set stocking) and low soil fertility. Failure to appropriately manage a Coolatai grass dominated pasture will see a monoculture of tall rank growth of low digestibility (<40%) and protein (<7%). Sheep production will be poor and cattle will need supplementary nitrogen or protein to be able to utilise the feed. Most graziers feel that if you don’t already have Coolatai grass you don’t want it as there are more easily managed perennial and annual pasture options available. On the other hand, studies have shown that with significant management inputs where Coolatai grass is kept short, it can be a highly productive pasture and meet the feed requirement of dry stock. Coolatai grass also has the benefit of not having damaging seeds like wiregrasses (Aristida spp.) and corkscrew grass (Austrostipa spp.), however there are other more easily managed tropical perennial pasture species available that also have benign seed. If large areas have been dominated by Coolatai Grass, management strategies of rotational grazing, spring burning and/or slashing will be essential. The maintenance of a legume component in a Coolatai Grass dominated pasture is difficult.

Native ecosystems: Coolatai grass poses a huge risk to the biodiversity of the fragmented areas of native ecosystems remaining  as it easily invades relatively undisturbed ecosystems being only one of few grasses to invade a wide range of intact native variegation. Coolatai Grass impacts on biodiversity by out competing and replacing native plants, preventing their regeneration and reducing available fauna habitat. It creates a fire hazard by producing large amounts of dry material resulting in a large fuel load (AMLR NRM undated). In a survey carried out in Kwiambal National Park, New South Wales the total number of species and number of native species was considerably lower in plots heavily infested with Coolatai Grass compared with plots relatively uninfested with the grass (McArdle et al. 2004). In regions where Coolatai Grass is widespread, sites of high biodiversity value should be a priority for control measures (CRC 2007). 

Areas of linear remnant vegetation such as road side reserves and railway lines are particularly prone to infestation due to their long edge to area ratio and their proximity the moving traffic (McArdle et al. 2004). Remnant grassy box woodlands in southern Australia are being threatened by the invasion of Coolatai Grass (CRC 2007). Indirectly, invasion of Coolatai Grass changes the nutrient and water cycle, and alters fire regimes (McArdle et al. 2004).

Urban areas: Also invades areas in and around towns, on urban fringes, roadsides and other transport corridors, colonising bare and degraded areas, lawns and disturbed sites. 

How does it spread?

Coolatai Grass spreads by seeds which have hairy, awned husks that stick to clothing, animals and vehicles. Human activities such as slashing or traffic assist in spreading the grass, especially along roadsides. It is often dispersed by mowing and water movement (CRC 2007). It is self pollinating and can produce many seeds from one original plant (CRC 2007). When heavily grazed the basal stems form a dense, hard tuft that successfully protects it from close grazing by sheep and makes it resistant to fire (McCormick et al. 2002).

What is its history in Australia?

Coolatai Grass is believed to have been introduced into northern New South Wales somewhere between 1890 and the 1930s near a town or property called Coolatai. It remained in relatively small populations for an extended period of time but has spread rapidly in recent years (Storrie 2003). It was originally sown as a pasture species and until recently was still being recommended for that purpose (McCormick & Lodge 1991; CRC 2007). It has also been used as a soil stabilizer (DECC 2004). It spreads along waterways, stock routes and roadways carried by stock and vehicles. It was first recorded in the Adelaide area about 12 years ago as a weed in the late 1970s to  early 1980s (eFlora 2021), although earlier collection records exist these are most likely from cultivated sources.

How To Manage It?

Best practice management

Coolatai Grass should be accurately identified before control measures are undertaken. The greatest problem with invasive species like Coolatai Grass is the lack of early detection and management. Grasses are particularly difficult because they look innocuous and rarely raise land managers’ attention until the species is well established. This is because most grasses look much the same to the untrained eye. Coolatai Grass is an invasive undesirable species and new occurrences must be correctly identified and controlled. In any management program, infestations should be mapped and early efforts directed at lightly infested areas, working back toward more heavily infested areas (DPI NSW 2019). As seed viability is only two years, when Coolati Grass is removed from a site, and germinating seedlings killed before seed set, with no further seeds transported to the area, an are can be become Coolatai free in two three years. 

Non-chemical control: Small infestations of the grass can be grubbed out. A single dose of herbicide may not kill mature Coolatai Grass tussocks, but combining physical and chemical treatment can be effective. Correct timing is essential when removing weedy grass species (CRC 2007). The spread of the grass along roadsides could be reduced by modifying maintenance activities. For example, grass trash and seed could be removed from slashers and graders before they move from infested to uninfested areas or slashing could occur before the grass flowers (McArdle et al. 2004). It appears unlikely that grazing could be used as a management strategy to completely remove the grass from pasture and heavily infested properties will need to learn to manage the grass to achieve adequate levels of production. Where it has not yet invaded intensive effort should be undertaken to prevent it from doing so (Lodge et al. 2005). Intensive grazing will reduce the biomass of the grass but will not control the infestation and may disadvantage native species (McArdle et al. 2004).

Fire: Anecdotal evidence suggests that fire may encourage the spread of the plant. Fire is known to reduce the bulk of grassy weeds but it can also increase their rate of invasion and density (Milberg & Lamont 1995) and fire can be used with other follow-up treatment. 

Chemical control: Herbicides are useful to spot remove infestations of grassy weeds before seed set but Coolatai Grass is resistant to many of them (Lodge et al. 1994). Herbicides are most effective for the control of Coolatai Grass when used in two carefully timed applications after a pre-application burning. Coolatai Grass is therefore perceived by landholders as difficult to control. Burning and mowing may spread an infestation or make it denser if used alone. However, heavy, constant grazing over a few years can provide control. A combination of chipping and spraying is used to control Coolatai Grass in native vegetation, allowing native regeneration to exclude the weed. Persistent Coolatai Grass forms tough long-lived perennial tussocks that resist grazing and resprout after burning. There is likely to be a seed bank formed with seedlings appearing for at least a few years after tussocks are sprayed out (Government of South Australia 2021). 

Please see Invasive Species Unit, Biosecurity SA (2018); DPI NSW (2019);  the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au 

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Coolatai Grass grows and flowers during late spring to autumn, depending on adequate moisture being available. It grows rapidly after summer rains and if the winter is relatively mild the plant may be green all year. With low temperatures the leaves may dry off, but the plant generally survives and will resprout from the base. Plants usually produce seed in their first growing season and production continues over an extended period shedding as it matures. Germinating quickly in relatively warm conditions the grass has a competitive advantage by rapidly capturing soil moisture from summer rainfall, especially in sandy soils (CRC 2007).

Where Is It Found?

Which states and territories is it found?

ACT, NSW, NT, QLD, SA, VIC, WA

What areas within states and territories is it found?

Coolatai Grass is in all mainland states and territories, found extensively in New South Wales in western regions as well as the central and north coast (Harden 2007). In Western Australia it occurs in south western areas (Western Australian Herbarium 1998- ). It is present in south eastern South Australia (eFlora2021), is found in central Northern Territory and is distributed widely in Queensland from the southeast to the northeast. In Victoria it occurs along the northern border of the state particularly in the Wodonga to Shepparton area (AVH 2021).

Where does it originate?

Coolatai Grass is native from South Africa to the Mediterranean region, and western Asia,  where it grows in warm Mediterranean-type climates to humid and dry tropical environments in open savannahs with other temperate grass species (McArdle et al. 2004). In South Africa it is known as Thatching Grass because of its use as a roofing material (CRC 2007).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, SA

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

Hyparrhenia hirta

Other scientific names (synonyms)?

• Andropogon hirtus L.
• Hyparrhenia quarrei Robyns

Does it have other known common name(s)?

Tambookie Grass, Thatching Grass