St. Barnaby's thistle (Centaurea solstitialis)
St Barnaby’s thistle is a summer growing annual. It can outcompete crops and pastures.
Profile
How does this weed affect you?
It will outcompete crops and pastures and dense patches can restrict stock movement.
What does it look like?
St Barnaby’s thistle is an annual or biennial herb to 1 m high. The stems have many branches and are greyish with wings.
Flower heads are bright yellow surrounded by rows of yellow spines.
Leaves are grey and covered in cobweb-like hairs. The leaves in the rosette at the base of the plant are lobed and up to 20 cm long. The leaves on the branches are not lobed but sometimes toothed on the edges. They are 1–7 cm long and 2–8 mm wide.
Seeds are up to 3 mm long and have a tuft of hairs (5 mm long) or short bristles.
Where is it found?
It is well established through many parts of NSW.
References
Parsons, W.T., & Cuthbertson, E. G. (2001). Noxious weeds of Australia. 2nd edition. CSIRO publishing.
More information
Control
Pasture management
Legume-based pastures on fertile or fertilised soils can compete strongly with St. Barnaby's thistle.
By hand
Dig or chip out single plants or small populations. Wear personal protection clothing and equipment to prevent injuries from the spines.
Slashing and mulching
Mowing or slashing in the early stages of flowersing can limit seed production and prevent regroth. Flowers on cut stems can produce seeds if plants are slashed hen flowers are more mature.
Do not slash seeding plants as this will spread the seeds.
Cultivation
Shallow cultivation can control seedlings and rosette plants but must be repeated to control new seedlings.
Herbicide control
Spraying
Spray actively growing plants. Cover all of the foliage with the herbicide mixture. Herbicide rates vary for different stages of growth. Check the labels for more information.
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: 1.15 - 1.7 L per Hectare
Comments: Boom spray application
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
Clopyralid 750 g/L
with
MCPA 500 g/L (Lontrel 750 SG Herbicide)
Rate: 20 or 28g/ha plus 1-1.5 L/ha MCPA amine (500 g/L)/ha
Comments: Spray rosette stage prior to stem elongation. For pasture and fallow land.
Withholding period: Do not graze or cut for stock food for 7 days after application. For harvesting up to 12 weeks, see label for details.
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
Glufosinate-ammonium 200 g/L
(Basta® )
Rate: 1.5–5.0 L/ha
Comments: Boom spray. Actively growing rosettes.
Withholding period: Variable, up to 16 weeks, see label for more information.
Herbicide group: 10 (previously group N), Inhibition of glutamine synthetase
Resistance risk: Moderate
Glufosinate-ammonium 200 g/L
(Basta® )
Rate: 500 mL in 100 L of water
Comments: Hand gun application
Withholding period: Variable, up to 16 weeks, see label for more information.
Herbicide group: 10 (previously group N), Inhibition of glutamine synthetase
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 2025
