Spiny burrgrass - spinifex (Cenchrus spinifex)

Spiny burrgrass is a summer-growing grass. It can spread rapidly to develop large infestations.

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How does this weed affect you?

Spiny burrgrass is a weed because of its sharp and clingy burr, ability to spread rapidly and tendency to develop into dense infestations in favourable conditions. It is also difficult and expensive to manage, especially in marginal rainfall areas.

Mature burrs cause a range of problems such as:

• injury to stock causing swellings and ulcers in the mouth
• injury to people and dogs
• clinging to wool and penetrating the skin of stock, reducing the value of both
• shearing difficulties, which often attracts penalty rates as working with contaminated wool requires leather gloves and/or aprons
• inconvenience and discomfort to workers in irrigated crops such as vegetables, vines and citrus, and
• contamination of dried fruit and hay.

Where is it found?

Spiny burrgrass is commonly found in drier regions with rainfall of 250 to 600 mm. It prefers sandy to light soils and is generally not found on heavy clay soils. It readily establishes on disturbed sites such as roadsides, creeks and riverbanks.

Spiny burrgrass has spread extensively throughout NSW because of:

• large numbers of travelling stock, foxes and kangaroo
• movement of fodder
• an increase in areas of stubble from cereal crops that provide little competition and an ideal situation for the rapid build-up of the weed
• lack of pasture competition in low rainfall areas due to variable seasons
• road graders, slashers and vehicle tyres
• the use of contaminated sand for building roads, amenity and construction purposes
• irrigation water.

Maps and records

• Recorded presence of Spiny burrgrass - spinifex 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?

The major spread of this weed is by seed. The seed is well equipped for spread because of the barbed spines on the burr, which detach easily from the mature plant.

Seeds are normally produced from late spring to late autumn depending on available soil moisture. There are up to three seeds produced by each “burr” resulting in each plant producing up to 1000 seeds. The first-formed, or primary seed, is the largest and is capable of germinating within a few months of maturity. The other seeds, or secondary seeds, are usually dormant for up to three years.

Spiny burrgrass has several germination regulating mechanisms to ensure its survival during hot, dry summers. The germination process is slow. It is reliant on extended periods of moist soil and is suppressed by light and high temperatures. The seed needs to be buried a few centimetres to maximise germination. Germination generally occurs in spring allowing seedlings to establish during a period favourable for growth but it can occur at any time of the year provided soil temperature and moisture are suitable.

Dormancy of secondary seeds is prolonged by exposure to light on the soil surface or by burial under dense vegetation. Exposure of seed to high or low temperatures will also induce dormancy with the optimum temperature range for germination being 10°C to 20°C. Both primary and secondary seeds have the ability to establish from depths of up to 20 cm below the soil surface.

What does it look like?

Spiny burrgrass is a summer-growing grass that forms large clumps and generally grows to 30 cm but can reach 60 cm or more.

The species C. spinifex can be either annual or perennial depending on the environment. The other Cenchrus weed species are annuals. In many areas of NSW, C. spinifex is usually killed by frosts and therefore acts as an annual.

For each plant, several stems grow from the base and can be either erect or spreading.

The leaves can be up to 20 cm long and are smooth but sometimes twisted and finely serrated.

The roots are fibrous and usually shallow but can be more than 30 cm deep in some soils.

The flowers are a spike-like panicle, 3–8 mm long and consisting of up to 40 ‘burrs’. The burrs are straw-coloured, sharply pointed, rigid, with finely barbed spines up to 7 mm long and a purplish colour in C. longispinus and up to 5 mm long in C. spinifex.

What type of environment does it grow in?

Spiny burrgrass prefers sandy to light soils and is generally not found on heavy clay soils. It readily establishes on disturbed sites such as roadsides, creeks and riverbanks.

Acknowledgements

Contributing authors: C. Mullen, J. Dellow, A. McCaffery.

This Primefact is an updated edition of Agfact P7.6.21 Spiny burrgrass.

Technical reviewers: A. Storrie, K. Pengilley, Birgitte Verbeek.

References

Parsons, W.T. and Cuthbertson, E.G. 2001, Noxious Weeds of Australia, second edition, CSIRO Publishing, Collingwood, Vic.

Johnston, W.H. 1989, ‘Consol lovegrass (Eragrostis curvula complex) controls spiny burrgrass (Cenchrus spp.) in south-western NSW,’ Australian Journal of Experimental Agriculture, 29, 37–42.

Twentyman, J.D. 1974, ‘Control of vegetative and reproductive growth in sand burr (Cenchrus longispinus),’ Australian Journal of Experimental Agriculture and Animal Husbandry, 14, 764–770.

Spiny burrgrass, Integrated Weed Management fact sheet, Cooperative Research Centre for Australian Weed Management.

More information

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Control

Integrated weed management

The key to the effective control of spiny burrgrass is to prevent seeding and exhaust any reserves of seed in the soil. This can be achieved through integrating cultivation, herbicide application, increasing competition through good pasture establishment and management and cropping.

A management strategy should consider any physical and climatic limitations and cover a three to five-year period.

Preventing spread

Prevent spiny burrgrass from spreading by: excluding livestock from infested areas especially when burrs are likely to adhere to livestock and thoroughly cleaning any vehicles or machinery used on site before leaving. It is important to restrict vehicle access and/or notify anyone who may be accessing the infested site to ensure that they also practice good hygiene.

Control of infestations on roadsides

Infestations can occur as a result of moving livestock, contaminated road graders or road building material. The integration of several control options is necessary in these situations. The application of non-selective herbicides can be followed by cultivation to remove established seedlings or burning the dead plants, in suitable conditions, to destroy the remaining seed heads. It is also useful to put up signs where infestations occur to alert others of the presence of spiny burrgrass and of restrictions on moving machinery or livestock through the area.

Once the seed reserves have been depleted, summer-growing perennial grasses such as Consol lovegrass, Rhodes grass or kikuyu should be established along roadsides to provide competition to germinating weed seedlings.

Pasture management

Maintaining vigorous perennial pastures is critical to prevent spiny burrgrass from becoming dominant. Spiny burrgrass does not establish readily in situations where there is competition from other vegetation. Good ground cover in spring and summer will limit germination and seedling establishment. Management of existing and native naturalised pastures should aim to maintain perennial grass content and ground cover. Identify the species present, their growth cycles and their response to grazing and fertiliser to formulate a management regime that will maximise their competitive behaviour.

Establishing a new pasture

Establishing perennial pastures is expensive so thorough preparation and research into suitable species and varieties is required. The establishment of adequate plant numbers is the first step to a successful pasture. Seek advice from your agronomist on the best pasture establishment steps for your situation.

Competitive summer grasses such as Rhodes grass, Premier digit and Consol lovegrass have proven successful in controlling spiny burrgrass on sandy soils. These grasses are summer-growing perennials and are excellent competitors where the weed is a problem. They establish readily, are drought-tolerant and are reasonably palatable to stock (depending on grazing management).

Ideally, these summer grasses should be sown with an annual legume suitable to your area such as a subterranean clover, medic or serradella. Lucerne may also be included if the soils are not too acidic.

Grazing management

In the vegetative stage, spiny burrgrass is readily eaten by livestock. In paddocks dominated by spiny burrgrass heavy grazing may be used to suppress growth and production of burrs as a short term management strategy. However, it has limited value if the spiny burrgrass infestation is sparsely scattered throughout a paddock. Stock have the potential to spread infestations so it is important to remove stock before seeding commences.

In paddocks that have sparse infestation overgrazing must be avoided. Every effort must be made to keep pastures competitive to prevent dominance by spiny burrgrass.

Cultivation

Timely cultivation to bury the burr or remove surface cover will increase germination and lead to the rapid exhaustion of dormant seeds in the soil.

Follow-up cultivation or the application of an appropriate knockdown herbicide is required to remove the resultant seedlings before they set seed. Under warm, dry conditions this might only be four weeks after germination.

If using only cultivation, repeated workings over a prolonged period will be required to control subsequent seedlings. Intermittent cultivation will create conditions which are ideal for the germination, growth and reproduction of spiny burrgrass, potentially leading to dense infestations becoming established. Avoid over-cultivation as this can increase the risk of soil erosion and soil structural problems such as compaction or surface crusting.

In arable situations a management strategy may involve one or two cultivations during spring and summer combined with fallow spraying. Alternatively, the cultivations may be followed by the application of a pre-emergent herbicide and sowing with a winter crop such as wheat, barley, triticale or lupins.

Some landholders have eradicated spiny burrgrass by using a combination of cultivation and knockdown herbicides for three to five years to prevent any plants present from seeding.

Cropping prior to pasture establishment

It is preferable that the seed reserves of spiny burrgrass be reduced as much as possible before sowing a competitive pasture. This can be achieved by either a period of winter cropping, incorporating the use of a pre-emergent herbicide followed by sowing an appropriate winter crop, or a period of summer cropping, incorporating the use of a pre-emergent herbicide followed by sowing an appropriate broadleaf crop (e.g. cowpeas).

A post emergent application of a selective grass herbicide might be required to control any burrgrass that has escaped the pre-emergent herbicide.

Control in permanent horticulture

Spiny burrgrass can be a problem in permanent horticulture, particularly as a contaminant of dried fruit. Management can be difficult, particularly in irrigation situations, but will generally involve the integration of control options such as close mowing of cover crops, inter-row cultivation, physical removal of isolated plants, the application of non-selective herbicides and good farm hygiene practices to prevent the spread of burrs.

For advice on the management of spiny burrgrass in horticulture consult your local horticulturist or refer to the DPI publications Grapevine Management Guide or Orchard Plant Protection Guide.

Dried fruit producers can refer to the ADFA Dried Fruit Manual produced by the Australian Dried Fruit Association, Mildura, Victoria.

Chemical control

Herbicides can play an integral role in the control of this weed but are best used in a strategy incorporating cultivation, crop rotation and pasture improvement.

Pre-emergent herbicides with soil residual properties have been successful in the control of spiny burrgrass in broadacre crops such as cotton, sunflowers, soybeans, pulses, lucerne and vegetables. However, because seeds can germinate from depths of up to 20 cm, pre-emergent herbicides are not always completely effective. In the event of germination, post-emergent grass herbicides can be considered in broadleaf summer crops and lucerne. Obtain advice from your local agronomist before undertaking this option.

Non-selective knockdown herbicides will kill existing plants but repeated applications are necessary to control subsequent germinations. These herbicides are best used in situations such as fallows, along fencelines and along roadsides. They are best applied when the weed is actively growing (late spring/early summer) before the burrs are produced.

Herbicide options

See Using herbicides for more information.

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Glyphosate 360 g/L (Various products)
Rate: 500–700 mL in 100 L of water
Comments: Spray with a handgun on actively growing. Use the lower rate on weeds up to 15 cm tall and the higher rate for weeds over 15 cm tall.
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: 2.0–3.0 L/ha. Use 75 - 200 litres of water/ha
Comments: Boom spray actively growing plants. Use the lower rate on weeds up to 15 cm tall and use the higher rate for weeds over 15 cm tall.
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.
Central Tablelands Contain recorded populations across the Central Tablelands region. Goal will be to contain spiny burr grass spread across the whole region with focus on spread or potential spread into production areas.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
Western	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land A person should not buy, sell, move, carry, or release the plant into the environment. 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