Stemless thistle (Onopordum acaulon)
Stemless thistles have large spiny leaves that grow in a rosette on the ground. They can form dense stands that compete with pastures.
Profile
How does this weed affect you?
Stemless thistles:
- compete with pastures and reduce productivity
- can form dense stands that restrict movement for livestock and people
- can damage and devalue wool
- injure livestock and people handling the livestock or fleece.
What does it look like?
Stemless thistle is a biennial herb that has a rosette of leaves on the ground.
Leaves are large, up to 50 cm long and 12 cm wide. They are deeply lobed with triangular lobes. The leaves are hairy on both sides and have yellow spines up to 1 cm long.
Flowers grow in the centre of the rosette. They are white and 4- 6 cm in diameter. The flowers maybe stalkless or on stalks up to 3 cm long. Flowers are present from October to December.
The seeds are 4-5 mm long with barbed bristles 2-3 cm long.
Where is it found?
In NSW, most plants have been found in the Murray and Western region. A few infestations have also been found in the North West, Northern Tablelands, Central Tablelands and Riverina regions.
Stemless thistle is native to Europe.
Stemless thistles grow well in warm temperate climates They are typically found in cultivated areas, on disturbed ground such as roadsides, rocky slopes and wasteland. They are often a problem on non arable pastures.
How does it spread?
By seed
Thistle seeds can remain viable in the soil for more than 8 years.
Seeds are spread by:
- wind
- water
- attaching to animal wool or fur
- attaching to clothing
- machinery or vehicles and in hay.
References
PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 23 March 2026 from https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Onopordum~acaulon
Weed Management Unit DPI). (2008). Scotch, illyrian and stemless thistle. Primefact 711 New South Wasles Department of Primary Industries.
More information
Control
Herbicide options
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au
See Using herbicides for more information.
2,4-D LV ester 680g/L
(Estercide® Xtra)
Rate: 2.5 to 3.3 L per hectare
Comments: Boom spray application rosette stage to flowering
Withholding period: Do not graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate
Dicamba 750 g/L
(Kamba® 750)
Rate: 53 mL per 100 L of water. Add a surfactant.
Comments: Spray prior to flowering. For non crop situations.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate
Dicamba 750 g/L
(Kamba® 750)
Rate: 800 mL/ha Use a minimum of 1500 L of water per ha. Add a surfactant.
Comments: Boom spray for non-crop situations. Spray prior to flowering.
Withholding period: Do not harvest, graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate
Fluroxypyr 140 g/L + Aminopyralid 10 g/L
(Various products)
Rate: 500 mL in 100 L of water
Comments: Hand gun application
Withholding period: Not required for pastures when used as directed. Do not graze or cut crops for stock food for 7 days after application. See label for export restrictions.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate
Biosecurity duty
The content provided here is for information purposes only and is taken from the NSW 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. |
Reviewed 2021
