Grader grass (Themeda quadrivalvis)

Also known as: Habana oat grass

Grader grass is a tussock grass up to 2 m tall. It outcompetes native plants and reduces productivity in grazing lands.

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How does this weed affect you?

Grader grass can form dense infestations that:

• outcompete native plants, especially in grasslands and woodlands
• reduce habitat for native animals
• are not grazed once the plants start to flower
• compete with native and improved pastures, reducing productivity
• invade cropping land
• reduces yields in sugarcane 
• increase biomass and therefore increase fire risks. 

What does it look like?

Grader grass is a robust annual (sometimes biennial) tussock grass up to 2 m tall that turns brown, orange-red or golden when it matures.

Leaves are:

• green, turning brown with age
• up to 60 cm long and 1.3 cm wide 
• flat sometimes with rolled margins
• folded when emerging.

Seedheads:

• usually 15 – 60 cm long but may be up to 1.3 m long
• are branched, open and drooping
• are made up of fan-shaped clusters of spikelets, each 4-7 mm long 
• have short leaflike spathes
• mostly flower summer to autumn, sometimes in winter.

Seeds are:

• brown with reddish hairs on the base
• 6-7 mm long
• topped with an awn up to 4 cm long that is bent and twisted
• enclosed by a glume that has distinct bristles with swollen bases.

Stems are:

• green, then changing to golden- or reddish-brown
• cane-like 4- 6 mm thick 
• upright
• hairless
• sometimes single stems or up to 10 per plant.

Roots are

• fibrous 

Similar looking plants:

Grader grass looks similar to some native Australian grasses including:

• kangaroo grass (Themeda triandra), which is a shorter perennial grass, usually less than 1.2 m tall. Its individual flower spikelets are larger (6-14 mm long) and the seeds have longer awns (25-70 mm long).
• Oat kangaroo grass (Themeda avenacea), which is a perennial grass with much larger flower spikelets (13-30 mm long), densely hairy leaves and the awns on the seeds are much longer (4-10 cm).

Where is it found?

In NSW plants have naturalised in the North Coast and South East regions. It is also present along much of coastal Queensland, the Northern Territory and northern parts of Western Australia.

Grader grass is native to India and was first found in Australia in 1935. It is likely to have been accidentally introduced in contaminated straw packing.

What type of environment does it grow in?

Grader grass can grow in a wide range of conditions including tropical, subtropical and semi-arid climates. In Australia it has been found in areas with 450 to over 2000 mm of annual rainfall. It prefers well drained soils.

Grader grass grows:

• in moist disturbed sites such as roadsides and overgrazed pastures
• in native grasslands and open eucalyptus forests
• amongst crops, including sugar cane, lucerne and other legumes.

Maps and records

• Recorded presence of Grader grass during property inspections (Map: Biosecurity Information System - Weeds, 2017-2024)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

Plants can start producing seed when they are only 10 weeks old. Dense infestations of grader grass may have over 20,000 seeds per square metre. Most seeds fall close to the parent plant and seed germinate in moist conditions with adequate light, usually spring and summer but they may germinate year round. Most seed is viable for about 15 months.

The seeds can spread:

• by attaching to wool, fur and clothing
• by vehicles
• in contaminated soil and mud on vehicles and machinery including roadside graders (which is why it is called grader grass)
• in agricultural produce, especially pasture seed.

References

Abom, R., Vogler, W., & Schwarzkopf, L. (2015). Mechanisms of the impact of a weed (grader grass, Themeda quadrivalvis) on reptile assemblage structure in a tropical savannah. Biological Conservation, 191, 75-82.

Identic Pty Ltd. & Lucid central (2016). Environmental Weeds of Australia Fact sheet: Themeda quadrivalvis (L.) Kuntze . Retrieved 23 August 2023 from https://keyserver.lucidcentral.org/weeds/data/media/Html/themeda_quadrivalvis.htm

Keir, A. F., & Vogler, W. (2006). A review of current knowledge of the weedy species Themeda quadrivalvis (grader grass). Tropical Grasslands, 40(4), 193-201.

Parsons, W.T., & Cuthbertson, E. G. (2001). Noxious weeds of Australia. CSIRO publishing.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 23 August 2023 from https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Themeda~quadrivalvis

Vogler, W.D. and Owen, N.A. (2008). Grader grass (Themeda quadrivalvis): changing savannah ecosystems. In: van Klinken, R.D., Osten, V.A, Panetta, F.D. and Scanlan J.C. (eds). Proceedings of the 16th Australian Weeds Conference. Queensland Weeds Society, Brisbane. p 213.

More information

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Control

Prevention

To prevent grader grass from spreading:

• Clean vehicles and machinery after being on infested sites.
• Clean boots and clothing before leaving an infested site.
• Purchase clean seed and feed. You can request a vendor declaration.
• Where possible maintain vigorous pastures as grader grass will not germinate in low light conditions.
• Hold new livestock in a paddock for four days before moving them to weed free paddocks.
• Do not overgraze pastures, as this can facilitate germination of grader grass seeds. 

Physical removal

If there are only a few plants they can be dug out. If the plants have seeds they can be destroyed by burning.

Slashing

Slash plants below the flowering head in the early flowering stage before they set seed. Timely slashing will limit seeding but not kill the plants.

Disposal

For small infestations, plants that have been dug up plants can be burnt with a hot fire in a contained area to destroy seed. Check burn sites regularly for seedlings.  Contact your local council for further disposal advice.

Chemical control

Spraying 

Spray actively growing plants at the early flowering stage. Cover all of the plant with the herbicide mix.

Wick wiping

On pastures, graze the site first so that all desirable plants are at least 15 cm shorter than the grader grass. The wiper must be at least 10 cm higher than the desirable plants. Apply twice in opposite directions and at a low speed (less than 8 km/hr) for best results.

Herbicide options

See Using herbicides for more information.

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Glyphosate 360 g/L (Various products)
Rate: 10 mL per 1 L of water
Comments: Handgun/ knapsack spot spray. Follow directions on label as per Kangaroo grass (Themeda australis/ Themeda triandra).
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 6 L /ha
Comments: Boom spray. Follow directions on label as per Kangaroo grass (Themeda australis/ Themeda triandra).
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 1 L per 2 L water (Wiper only)
Comments: Apply using wiper equipment (e.g. ropewick, canvas, felt or carpet applicators). Apply to actively growing plants at the early head stage. Operate wiper equipment a minimum of 10 cm above the crop or pasture.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
North Coast Exclusion zone: Bellingen Shire LGA, Clarence Valley LGA, Kempsey Shire LGA, Lord Howe Island, Nambucca Valley LGA, Port Macquarie-Hastings LGA. Core infestation (containment) zone: Ballina Shire LGA, Byron Shire LGA, Coffs Harbour City LGA, Kyogle Shire LGA, Lismore City LGA, Richmond Valley LGA, Tweed Shire LGA.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. A person should not buy, sell, move, carry or release the plant into the environment. Exclusion zone: Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. Core infestation: Land managers should mitigate spread of the plant from their land. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2024