Glaucous starthistle (Carthamus leucocaulos)

Glaucous star thistle is an annual weed. It is usually found growing along roadsides, in cultivation and degraded pastures.

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How does this weed affect you?

Glaucous starthistle is capable of growing in dense thick patches and eliminating all other vegetation. Glaucous star thistle has the potential to become a serious weed of pastures, native grasslands and crops. In pasture situations, it can reduce carrying capacity and the spiny leaves contaminate wool. In cropping situations, it can reduce crop yields by directly competing with crops for nutrients. It can also cause harvesting problems by clogging machinery.

Where is it found?

Native to Turkey, Greece and Crete in the Mediterranean, glaucous star thistle is not widely distributed around the world. It is recorded as a crop weed in Israel and the USA.

Isolated infestations have been recorded in the East Tambellup region of Western Australia. Scattered infestations are also present in western Victoria, Kangaroo Island and the Bordertown region of South Australia.

Glaucous starthistle is not currently recorded as present in New South Wales. 

How does it spread?

Glaucous star thistle reproduces by seed. Most mature seed will fall close to the parent plant. Seed may be spread further distances by becoming entangled in the wool and fur of animals. It may also be spread by contaminated hay and mud attached to vehicles and machinery.

Lifecycle

Seeds germinate in autumn or early winter. Young plants develop into a rosette during winter. Flowering begins late spring and early summer. Seeds ripen early summer and plants die back leaving a stiff, upright stem.

What does it look like?

Glaucous starthistle is an annual herb growing 50–100 cm high.

Stem

  • upright
  • white to greyish in colour
  • a single stem, branching in the upper half
  • ribbed

Leaves

  • greenish white in colour
  • divided into deep lobes that end in a yellow-brown spine
  • stem leaves stiff and shiny

Flower

  • pale violet to pinkish-purple in colour
  • an individual flower head occurs at the end of branches
  • 10–13 mm across
  • outer bracts —leaf-like structures surrounding flower—shiny and bent back

Seed

  • grey-brown in colour
  • four-angled
  • topped with stiff, scale-like protrusions 5–7 mm long.

What type of environment does it grow in?

Glaucous starthistle prefers a warm temperate climate with a predominantly winter rainfall. It can grow on a range of soil types with an annual rainfall of 400–600 mm. Commonly found growing along roadsides, in cultivated paddocks, degraded pastures and wastelands.

References

Australia’s Virtual Herbarium (2007) Council Heads of Australian Herbaria (CHAH) Available at: http://avh.chah.org.au. Accessed August 2014.

Department of Agriculture and Food (2014) Glaucous star thistle control, Government of Western Australia. Available at https://www.agric.wa.gov.au/grains/glaucous-star-thistle-control. Accessed August 2014.

Department of the Environment (2011) Weeds in Australia: Carthamus leucocaulos. Australian Government. www.environment.gov.au/biodiversity/invasive/weeds/identification/index.html. Accessed August 2014. 

Hosking JR, Sainty GR, Jacobs SWL & Dellow JJ (in prep) The Australian WeedBOOK.

Parsons, WT and Cuthbertson, EG (2001) Noxious weeds of Australia, CSIRO Publishing, Collingwood.

Victorian Resources Online (2011) Invasive assessment – Glaucous star thistle (Carthamus glaucus) in Victoria, State Government of Vicrtoria. Available at http://vro.depi.vic.gov.au/dpi/vro/vrosite.nsf/pages/ weeds_glaucous_star_thistle. Accessed August 2014. 

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Control

In cropping situations, cultivation stimulates the germination of glaucous starthistle seeds. Using cultivation combined with herbicides can give positive results as long as plants are treated at the seedling or rosette stage of growth. This is usually during winter and early spring. Using crop and pasture rotations can help to manage glaucous star thistle. In the pasture phase, it is important to maintain a competitive pasture. Treat any new emergence of thistles with either physical measures or herbicide.

Physical control

Individual plants and small infestations can be removed with a hoe and dug from the ground. Remove the entire plant and at least 50 mm of the tap root. Treat plants at the rosette stage and before flowering.

Herbicide treatment

Infestations can be treated using a foliar application of a registered herbicide.  Best results are obtained when treated at the seedling or rosette stage of growth.

Always monitor control efforts and treat regrowth as required.

Herbicide options

WARNING - ALWAYS READ THE LABEL
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.


Dicamba 500 g/L (Kamba® 500)
Rate: 1.6 L per ha
Comments: Non-crop situation: Spray prior to flowering
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 100 mL in 100 L of water
Comments: Non-crop situation: Spray prior to flowering
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 24 mL in 15 L of water
Comments: Non-crop situation: Spray prior to flowering
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 280 mL to 1.1 L per ha
Comments: Grass pastures and perennial grasses
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 40 mL and 76 mL per 100 L of water
Comments: Grass pastures and perennial grasses: Low rate for seedlings
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 10 mL and 18 mL per 10 L of water
Comments: Grass pastures and perennial grasses: Low rate for seedlings
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


MCPA 340 g/L + Dicamba 80 g/L (Kamba® M)
Rate: 2.8 to 4.0 L per ha
Comments: Grass pastures
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


MCPA 340 g/L + Dicamba 80 g/L (Kamba® M)
Rate: 190 to 270 mL per 100 L of water
Comments: Grass pastures
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


MCPA 340 g/L + Dicamba 80 g/L (Kamba® M)
Rate: 60 mL per 15 L of water
Comments: Grass pastures
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
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 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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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2018