South American burr (Xanthium cavanillesii)

South American burr is an annual plant that produces a woody burr. It is found around Sydney and upper Hunter areas. It is very similar to other Xanthium burr species.

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How does this weed affect you?

South American burr competes with summer crops and pastures. In crops such as cotton, corn and soybeans, these weeds can out-compete crops for moisture and nutrients. Left untreated, infestations result in reduced yields and downgrading of grain due to contamination. These weeds also cause problems in livestock production. Large plants can create barriers for livestock and people around watercourses and in irrigation areas. The burrs can cling to livestock, making handling difficult and causing physical injury to people and the livestock. 

Where is it found?

South American burr is native to Argentina, Chile and Uruguay. It is found around Sydney, Windsor and upper Hunter areas.

How does it spread?

South American burr is an annual plant that reproduces by seed contained in a burr. The burrs are usually dispersed from the plant in autumn and winter but they may remain attached on undisturbed plants until the following spring.

Seeds germinate when the soil is moist in late winter to summer. Flushes of germination can occur after summer storms or irrigation events. On flood prone areas large germination events are common after floods.

What does it look like?

South American burr is similar in appearance to Noogoora burr, California burr and Italian cockleburr. They are stout, erect, single stem or many branched annual plants with large leaves similar to those on grapes. 

These burr plants are very similar and often confused. However, there is extensive variation between these species, especially in the number and length of the burrs and the spines on the burrs. Plant height can vary, as can leaf size and shape.

South American burr commonly grows to 1 m in height. 

Stems 

Plants tend to be single stemmed when growing in dense patches. Isolated plants have branched and spreading stems. Stems are green with a rough surface. 

Leaves 

Leaves are large grapevine-like that grow alternatively on the stems. Both upper and under surfaces are green and rough. Leaves are lightly lobed. 

Fruit (burrs)

The fruit or burr is hard and woody, more or less egg-shaped, densely covered with hooked spines and ending in longer terminal spines (or beaks). The burr is green when immature and brown when mature. The main way of distinguishing between burr species is by the burr shape and size. The burr of the South American burr is the largest (heaviest) of these species, 15-30 mm long. Terminal spines are straight and diverging, 6-8 mm long, not hooked at tips.

Acknowledgements

Contributing authors: Annie Johnson, Bob Trounce.

Technical reviewers: Graham Charles, Stephen Johnson and Bruce Auld.

References

Cotton CRC (2002) WEEDpak a guide for integrated management of weeds in cotton. Eds Stephen Johnson, Graham Charles, Ian Taylor and Grant Roberts. Cotton CRC, Narrabri.

Hocking PJ. and Liddle MJ 1995, Xanthium occidentale Bertol. complex and X. spinosum L. In Groves RH, Shepherd RC H and Richardson RG (eds), Biology of Australian Weeds, vol 1. RG and FJ Richardson Publishers. Melbourne, pp. 241-289.

National Herbarium of NSW. PlantNET – FloraOnline. www.plantnet.rbgsyd.nsw.gov.au. Accessed 27 March 2008.

Parsons, WT and Cuthbertson, E G (1992) Noxious Weeds of Australia, 2nd ed. CSIRO publishing.

More information

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Control

Prevention of seed set is the most important part of managing South American burr plants and eliminating infestations. Trials have shown that six years prevention of seed set leads to a decline in populations to 1% of previous populations. Repeated control is often needed as many germination events can occur from late winter to summer. Early control can prevent competition with crops and pastures, and later control can prevent seed set of plants that may have been missed by earlier control efforts. Large populations can be treated with herbicides, cultivation or slashing; follow-up control of smaller populations may include spot spraying, chipping (or hand-hoeing) or inter-row cultivation in crops.

Cultivation

Cultivation is an effective method of controlling the seedlings of these weeds. Successive flushes of seedlings during the summer may require follow up control. Inter-row cultivation is commonly used in row cropping such as sorghum, corn and cotton to control seedlings that have germinated after irrigation events.

Slashing

Slashing or mowing are useful in clean-up operations after spraying with herbicide or if infestations are small and scattered. Any burrs from the plant should be removed from the equipment to prevent spread.

Chipping

Chipping or hand hoeing is only economical for small areas, individual plants or isolated populations. It is an effective follow up control method for plants not controlled by other methods to prevent seed set.

Surveillance

After controlling burr plants it is important to monitor these sites for further germination events. High risk areas for new infestations include flood prone areas or areas where stock from burr infested areas have been.

Pasture management

Maintaining ground cover in pastures is vital. Pasture gaps result in an increase in burr germination and seedling survival. It is important to ensure that pastures are not overgrazed in spring and summer to reduce the potential for the establishment of burrs and other weeds.

Grazing

Adult plants are not easily eaten by livestock, due to the roughness of the leaves and stems. Care needs to be taken when grazing to ensure there are no seedling plants, which are toxic to animals and could result in death.

Herbicides

These plants are susceptible to a range of foliar and residual herbicides. Foliar herbicides are most effective if the plants are young and actively growing. Plants suffering from moisture stress are difficult to kill. Older plants may require repeat applications. Late control with some herbicides, when the burrs are green, can result in seed sterility – however this is not recommended as the primary form of control.

In crops, residual pre-emergent herbicides are useful, although there are sometimes problems as the burr can germinate and emerge from relatively deep in the soil, below the residual herbicide band. Follow-up control in the form of chipping or inter-row cultivation may be required. Spot spraying is an important tool for areas that are difficult to access and for scattered plants.

Herbicide options

See Using herbicides for more information.

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Glyphosate 360 g/L (Various products)
Rate: 10 mL per 1 L water
Comments: Spot spray. Spot spray. For general weed control in Domestic areas (Home gardens), Commercial, Industrial and Public Service areas, Agricultural buildings and other farm situations.
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.

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Reviewed 2021