Quick Facts

Quick facts

• The Giant Rat's Tail grasses (Sporobolus natalensis and S. pyramidalis) are long-lived grasses usually growing 60–200 cm tall. They form large tussocks that can live for up to 10 years.
• These persistent and invasive grasses are well adapted to a wide range of climatic conditions and are quite drought and fire tolerant.
• The Giant Rat's Tail grasses are serious weeds of pastures in the coastal areas of Queensland and northern New South Wales, and have the potential to invade much of eastern Australia.
• They are of low palatability and significantly reduce the productivity and carrying capacity of pastures. It is estimated that losses to beef production in northern Australia could be in the vicinity of $60 million/year if they reach their potential distribution.
• The Giant Rat's Tail grasses also invade native grasslands, open woodlands, conservation reserves and wetlands. They replace native plants in these habitats, reducing the biodiversity of native ground cover species and impacting on native herbivores.

What Does It Look Like?

What is it?

The Giant Rat's Tail grasses (Sporobolus natalensis and S. pyramidalis) are upright and long-lived grasses that form large tussocks.

Sporobolus natalensis has slender, but somewhat wiry, flowering stems up 60–170 cm tall. The leaves are very narrow with a leaf sheath, which partially encloses the stem and is retained at the base of the plant, and a spreading leaf blade that may droop towards the ground. Leaves are mostly hairless and the leaf blades (25–50 cm long and 2–4 mm wide) may be flat or somewhat rolled inwards. Where the leaf sheath meets the leaf blade there is a tiny membrane topped with a fringe of hairs (i.e., ligule). The seed-heads are initially thin and spike-like in appearance, but become more open and droop slightly as they mature. These seed-heads (20–30 cm long and about 3 cm wide) have numerous relatively long lax branches. Each of these branches (3–7 cm long) bears numerous tiny, densely packed, flower spikelets. These dark green or greyish-green flower spikelets (1.6–2.3 mm long) contain a single tiny flower inside two bracts (known as glumes). The lower glume is 0.5–0.8 mm long and the upper glume is 0.8–1.3 mm long (at least half the length of the flower spikelet). The tiny seeds turn yellowish-brown or reddish-brown in colour as they mature. These seeds (0.7–0.8 mm long and up to 0.6 mm wide) separate from the remainder of the flower spikelet at maturity (Simon and Jacobs 1999; Navie 2007). Sporobolus natalensis is currently not a declared weed in New South Wales.

Sporobolus pyramidalis has slender, but somewhat wiry, flowering stems usually grow 90–200 cm tall. The leaves are very narrow with a leaf sheath, which partially encloses the stem, and a spreading leaf blade that may droop towards the ground. The leaves are hairless, or have some tiny hairs along their margins, and the leaf blades (20–70 cm long and 3–10 mm wide) may be flat or somewhat rolled inwards. Where the leaf sheath meets the leaf blade there is a fringe of tiny hairs or a very short membrane (0.2–0.3 mm long) topped with tiny hairs (a ligule). The seed-heads are initially thin and spike-like in appearance, but become more open and narrowly pyramid-shaped as they mature. These seed-heads (20–45 cm long) have numerous stiffly spreading branches. Each of these branches (5–10 cm long) bears numerous tiny, densely packed, flower spikelets. These dark green or greyish-green flower spikelets (1.7–2.2 mm long) contain a single tiny flower inside two bracts (glumes). The lower glume is 0.3–0.5 mm long and the upper glume is 0.5–0.8 mm long (less than half the length of the flower spikelet). The tiny seeds turn yellowish-brown or reddish-brown in colour as they mature. These seeds (0.8–1 mm long and up to 0.5 mm wide) separate from the remainder of the flower spikelet at maturity (Simon & Jacobs 1999; Navie 2007).

For further information and assistance with identification of Giant Rat's Tail grasses contact the herbarium in your state or territory.

Flower colour

Green

Growth form (weed type/habit)

Grass

Where it currently grows? Preferred habitat

The Giant Rat's Tail grasses are weeds of pastures, roadsides, disturbed sites, open woodlands, grasslands, parks, footpaths and lawns. They are found in the sub-tropical, tropical and warmer temperate regions of Australia (Navie 2007).

Are there similar species?

Sporobolus pyramidalis can usually be distinguished from S. natalensis by its more open mature seed-heads, with stiffly spreading branches. Its flower spikelets also have smaller upper glumes.

The Giant Rat's Tail grasses are very similar to other introduced grasses including giant Parramatta grass (S. fertilis), Parramatta Grass (S. africanus) and American Rat's Tail Grass (S. jacquemontii). They are also very similar to some of the native rat's tail grasses, particularly the widespread and common Slender Rat's Tail Grasses (S. creber and S. elongatus). Distinguishing between these species is often very difficult and a specialist may need to be consulted.

Giant Parramatta Grass (usually 80–160 cm tall) and Parramatta Grass (usually less than 50 cm tall) have spike-like seed-heads with numerous branches that are held close to the main stem. Giant Parramatta Grass seed-heads have relatively long branches (20–80 mm long), while Parramatta Grass much shorter branches (only 10–20 mm long). American Rat's Tail grass has more open seed-heads like the Giant Rat's Tail grasses, but it is smaller in stature (usually 50–75 cm tall) (Simon & Jacobs 1999; Navie 2004).

The Slender Rat's Tail grasses are moderately-sized plants (usually 50–100 cm tall) and are distinguished by their very narrow spike-like seed-heads. The seed-head branches are always held closely to the main stem, and are often widely spaced near the base of the seed-head (Simon & Jacobs 1999; Navie 2004).

Why Is It A Weed?

What are its impacts?

The Giant Rat's Tail grasses were included in the list of 71 species that were nominated by state and territory governments for assessment as Weeds of National Significance (WONS). Following an assessment process, the Giant Rat's Tail grasses were not included as one of the 20 WONS. However, they remain weeds of potential national significance.

Agriculture: The Giant Rat's Tail grasses are serious weeds of pastures in the coastal districts of Queensland and northern New South Wales. They are of low palatability and can greatly reduce the productivity of agricultural land by completely displacing desirable pasture species. This reduction in productivity can be exhibited in reduced stocking capacities, longer periods of time to record adequate weight gains in beef cattle, and higher costs in milk production on dairy farms. For example, the cost of producing milk on two dairy properties in the Rosedale/Miriam Vale area in Queensland was increased by 15 to 25% by Giant Rat's Tail grass infestations. The economic costs incurred in managing these species with herbicides are also quite high, and heavily infested areas have reduced land values (Walton 2001). Mature leaf blades and stems are tough for animals to graze, and have been known to loosen the teeth of cattle and horses (Land Protection 2006).

Native ecosystems: The Giant Rat's Tail grasses are also significant environmental weeds in eastern Australia. They invade native grasslands, open woodlands, conservation reserves and wetland areas. When fully established in an area they can form a grass monoculture, excluding native plants and reducing biodiversity of native ground cover species. This can also have an impact on native herbivores, which find the plants unpalatable (Walton 2001).

The Giant Rat's Tail grasses are among the exotic perennial grass species invading native plant communities in New South Wales that have been listed as a "key threatening process". Together, they are also ranked among the top 25 environmental weeds in south-eastern Queensland (Batianoff & Butler 2002) and are also thought to pose a significant threat to rangeland biodiversity in central and northern Queensland. The Giant Rat's Tail grasses are already of concern in several conservation areas in Queensland and heavy infestations may also increase fire intensity in sensitive environmental areas (Walton 2001).

How does it spread?

The Giant Rat's Tail grasses produce large quantities of tiny seeds that become somewhat sticky when wet. They may be spread about after becoming attached to animals, clothing and vehicles. They may also be dispersed by water, in mud, and in contaminated agricultural produce (e.g., fodder and pasture seed lots) (Navie 2007). In pasture areas the potential for spread is particularly high, due to the large number of potential vectors. These include incoming and outgoing agricultural produce such as pasture seed and fodder, the movement of livestock (both within and between properties), irrigation channels, the movement of milk tankers to and from nearby properties and fertiliser trucks, slashers and other farm machinery (Walton 2001).

What is its history in Australia?

Initial outbreaks of Giant Rat's Tail grass were reported in Queensland in the early 1960s and probably resulted from the importation of contaminated pasture seed from Africa. Many infestations can be traced back to pasture improvement plots. Giant Rat's Tail grass was first recognised as a problem in 1986 in the Burnett region in central Queensland. The Giant Rat's Tail grasses have since spread to cover over 2,00,000 hectares of coastal and sub-coastal land, from Mareeba in northern Queensland to Gloucester in New South Wales (Walton 2001).

How To Manage It?

Best practice management

Non-chemical control: Maintaining pastures in good condition reduces the chance of invasion and increases competition against Giant Rat's Tail grasses. Heavy grazing will not control Giant Rat's Tail grasses, and may actually favour their spread, so an appropriate grazing regime is important in any management strategy. Good hygiene and quarantine are also important to prevent the spread of seeds to uninfested areas. Moving stock from infested areas into clean areas is not recommended, unless they are spelled for at least five days in holding yards (Land Protection 2006).

Small infestations or isolated plants can be dug out or spot-sprayed with herbicide. Cut any seed-heads off and put them in a bag for destruction before digging out or spraying the plants, in order to prevent spreading the seed (Schulke & Elphinstone 2006).

In moderately to heavily infested areas you need to decide whether to keep the existing pasture and manage the Giant Rat's Tail grass population to reduce its effects, or to remove the existing pasture and replace it with more competitive and productive species. Replacing the existing pasture, by cultivating the soil and planting an appropriate sown pasture or crop, is a more intensive approach and is usually only practical in arable country (Schulke & Elphinstone 2006).

Where the existing pasture is to be kept, it should be managed is such a way to encourage a strong, competitive pasture understorey to replace the Giant Rat's Tail grass. This management strategy should involve appropriate levels of grazing, the selective application of herbicides, and possibly also burning to precondition the stand.

Chemical control: The use of a pressurised wick wiper to selectively apply herbicide to Giant Rat's Tail grass is probably the most useful tool in managing this species. It can be used to apply herbicides at a low rate to reduce seeding and improve grazing quality, and is relatively cost-effective. In certain large-scale situations, herbicides which are less active on native grasses can also be applied with a boom spray or by air, though this can be an expensive option (Schulke & Elphinstone 2006).

To get the most effective results with a pressurised wick wiper, a package of three treatments should be applied over an 18 month period. The first treatment should be applied in mid summer, when the Giant Rat's Tail grass is actively growing. Make sure there is a significant height difference between the Giant Rat's Tail grass and other pasture plants by allowing livestock to selectively graze down the good pasture plants. A second treatment should be applied in late summer or early autumn to prevent seeding, and a follow-up treatment should be applied the next summer (Land Protection 2006).

Check with your local council or state/territory government agency about its requirements for the control of Giant Rat's Tail grass.

Also see 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)

Giant Rat's Tail grass seedlings mainly emerge during spring or early summer, depending on rainfall. However, some may emerge throughout the year and can even emerge when soil moisture levels are near wilting point. Young plants are resistant to desiccation and fire, have significant drought tolerance and are able to respond quickly to rainfall. Giant Rat's Tail grass tussocks can live up to 10 years or more and can lie dormant in cold seasons (Walton 2001). Flowering can occur throughout the year, but is mainly apparent during spring, summer and autumn (from October through to June) (Navie 2007).

Where Is It Found?

Which states and territories is it found?

NSW, NT, QLD

What areas within states and territories is it found?

The Giant Rat's Tail grasses are widely naturalised in eastern Australia.

Sporobolus natalensis is most commonly found in the coastal districts of south-eastern Queensland and northern New South Wales. Scattered infestations also occur in the coastal districts of central and northern Queensland, near Sydney on the New South Wales central coast, and near Darwin in the Northern Territory (Navie 2007).

Sporobolus pyramidalis has a very similar distribution, but is probably slightly more widespread. It is most common in the coastal districts of south-eastern Queensland and northern New South Wales. It is also relatively common in the coastal districts of central and northern Queensland and recorded from a few locations in the northern and southern parts of the Northern Territory (Navie 2007).

Recent predictions based on climatic data indicate that the Giant Rat's Tail grasses could potentially cover an area of 223 million hectares in Australia (about 29% of the continent), with 108 million hectares of this area located in Queensland (about 60% of the state) (Walton 2001).

Where does it originate?

The Giant Rat's Tail grasses originated in Africa. Sporobolus natalensis is native to central and southern Africa (Ethiopia, Kenya, Tanzania, Uganda, Cameroon, Zambia, Botswana, Namibia and South Africa). Sporobolus pyramidalis has a somewhat wider natural distribution and is native to sub-Saharan Africa, Madagascar, Mauritius and parts of the Arabian Peninsula (e.g., Yemen) (GRIN 2007a, 2007b).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, 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

Sporobolus spp.

Other scientific names (synonyms)?

For Sporobolus natalensis:

• Sporobolus capensis var. laxus Nees
• Sporobolus indicus var. laxus (Nees) Stapf
• Vilfa natalensis Steud.

For Sporobolus pyramidalis:

• Sporobolus indicus var. pyramidalis (P. Beauv.) Veldkamp

Does it have other known common name(s)?

Giant Rats-tail Grass, Giant Ratstail Grass, GRT, GRT Grass