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Grader grass (Themeda quadrivalvis)

Grader grass reduces the productivity of pastures and is an important weed in crops, particularly sugar cane. It can also replace native plants, reduce biodiversity and change fire regimes in grasslands, savanna woodlands and rangelands.

Key facts

Type: Weed, grass.

Native to: The Indian subcontinent, and possibly parts of south-eastern Asia..

Established in: QLD, NSW, WA, NT.

Other names: Habana Grass, Kangaroo Grass, Oatgrass.

Best time to act: In northern Australia, most seeds germinate with the wet season between October and December, flowering is mainly in summer and autumn, and infestations should be controlled preferably before seeding.

Identification

  • This short-lived, tufted grass usually grows 50 cm to 2 m tall.
  • It has several upright, hairless stems from each rootstock, which turn from green to reddish-brown or golden-brown as they mature.
  • Its long, narrow leaves are 7–60 cm long and 1–7 mm wide, and turn brown or reddish-brown with age.
  • Mature seed-heads are 15–60 cm long, brown or slightly reddish, and somewhat drooping.
  • Brown seeds have a cluster of reddish hairs at the base and a bent, twisted awn 10–45 mm long.
  • Look-alike: Kangaroo Grass (Themeda triandra) is longer-lived, usually grows to about 1 m, and has larger, less hairy flower spikelets.
  • Look-alike: Native Oatgrass (Themeda avenacea) is longer-lived with larger, hairy flower spikelets, while Lesser Tanglegrass (Themeda arguens) can grow to 3 m and has longer, softly hairy spikelets.

Where it grows

In Australia it occurs widely in coastal and sub-coastal Queensland and the Northern Territory, with scattered populations in northern Western Australia and coastal northern New South Wales, in places such as roadsides, disturbed sites, woodlands, grasslands, pastures and crops.

Why it matters

  • It can out-compete more useful grasses and seriously reduce pasture productivity, particularly in tropical and semi-arid northern Australia.
  • Flowering plants are unpalatable and rarely grazed, and the grass is a troublesome crop weed, especially in sugar cane.
  • It can form tall thickets that replace native plants and reduce biodiversity in grasslands, savanna woodlands and rangelands.
  • Its greater biomass creates higher fuel loads, helping carry more intense wildfires that can thin native woodlands and contribute to their conversion to exotic grasslands.

How it spreads

  • Seeds spread on animals and vehicles, in clothing and mud, and as contaminants of agricultural produce.
  • They are also dispersed during soil-moving activities, including road grading.
  • Contaminated pasture grass seed is a common means of introducing the species to new areas.

Control options

  • Prevent it from entering uninfested properties, and ensure pasture seed is free of Grader Grass seed.
  • Hand-pull or dig out small infestations, preferably before seeding, and burn the removed plants on site; spot-spray with registered herbicides where appropriate.
  • Larger infestations may need improved pasture management and registered herbicides, including application through a pressure rope-wick applicator where the weed grows above the pasture.
  • Dense infestations can be slashed before seed set, but plants may produce new seed-heads; avoid overgrazing, short slashing or burning of pastures, which can give the grass an advantage.

Hygiene and washdown

  • Avoid spreading seeds from infested areas on vehicles, machinery or livestock, and take care not to move contaminated mud or clothing into clean areas.
  • Check pasture seed for Grader Grass seeds before sowing.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Regional priority in 1 of 11 regions. Regional priority weed in North Coast. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Declared pest (no control category). Declared pest in WA without a control category, so there is no state-wide control requirement, but movement and keeping rules can still apply.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed, Class B. Class B: growth and spread must be controlled. All declared weeds are also Class C, so they must not be brought into the NT.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources