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.
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.
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.
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.
Glaucous starthistle is an annual herb growing 50–100 cm high.
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.
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.
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.
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.
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.
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The requirements in the Noxious Weeds Act 1993 for a notifiable weed must be complied with