Because it forms dense tussocks, is stimulated by fire and is resistant to grazing, Uruguayan rice grass may compete well against native plants in Australia. Uruguayan rice grass is related to the genus Nassella, which includes the Weeds of National Significance Chilean needle grass (Nassella neesiana) and serrated tussock (Nassella trichotoma), which costs south-eastern Australia’s grazing industries more than $40 million a year in lost production and control expenditure.
Uruguayan rice grass is native to Argentina, Bolivia, southern Brazil, Paraguay, Uruguay and Chile, and is also considered native in parts of North America. Its only known distribution in Australia, where it was first recorded as naturalised in 1988, is an infestation in disturbed grassland dominated by kangaroo grass (Themeda triandra) near Altona, Victoria.
In South America, Uruguayan rice grass produces many seeds. Although the exact volume of seed produced is unknown, the closely related species serrated tussock (N. trichotoma) can produce tens of thousands of seeds per plant per year. The seed is dispersed by wind and also by browsing animals ingesting the plant and excreting the viable seed elsewhere. Seeds can also be spread by movement of contaminated soil. Anecdotal evidence suggests that seeds are not carried or dispersed externally by stock.
Uruguayan rice grass is a perennial that forms dense tussocks to about 0.5 m high.
The leaf blades are about 0.5 mm in diameter and almost the same length as the stems, which are jointed. While the leaf sheath may have scattered hairs, the leaf blades are hairless but covered with minute rough projections. The ligule (a small flap located at the junction of the leaf blade and leaf sheath) is 1–2 mm in length and hairless. The ligule can be located by tracing a leaf down to where it joins the sheath and bending the leaf back at this point.
The plant has dense, branched flowering heads to about 100 x 15 mm. The seed is about 2 mm long, and the bristle-like tail of the seed (the ‘awn’) is about 10 mm long. The leaf-like structures (glumes) at the base of the flowering spikelet are up to 3.5 mm long and purplish in colour when young.
Uruguayan rice grass grows best in temperate and subhumid climates. Stipoid grasses (such as Uruguayan rice grass) generally invade sites with modified soils that are highly degraded and have a history of disturbance, especially land with higher fertility that has been used for grazing or farming. However, they can also invade relatively undisturbed vegetation.
CRC for Australian Weed Management: Val Stajsic (National Herbarium of Victoria), David McLaren (DPI Vic/Weeds CRC), David Cooke (APCC).
Because there has been only one Uruguayan rice grass infestation detected, it can potentially be eradicated before it becomes established. Any new outbreaks should be reported immediately to your local council weed officer and the state herbarium. Do not try to control Uruguayan rice grass without their expert assistance. Control effort that is poorly performed or not followed up can actually help spread the weed and worsen the problem.
Uruguayan rice grass (Piptochaetium montevidense) is not declared in NSW under the Noxious Weeds Act 1993.