Glaucous Star Thistle

Carthamus leucocaulos Sibth. & Sm.

Synonyms - Carthamus glaucus, Kentrophyllum glaucum.

Family: - Asteraceae.


Carthamus is from the Arabic words for the dyes that were extracted from the flowers.

Leucocaulos is from the Greek for white stem referring to the white waxy bloom on the stem.

Glaucous Star Thistle refers to the white waxy (glaucous) bloom on the stem and the star shape formed by the spiny bracts under the flowers.

Other Names:

Whitestem Distaff Thistle (California).


A spiny, erect, slightly hairy or cobwebby thistle with unwinged stems and single violet flowers at the ends of stems.





Form a rosette.

Stipules -

Petiole -

Blade - Greenish white with a waxy bloom. Deeply divided with lobes ending in a sharp spine. Sparsely glandular.

Stem leaves - Stiff, shiny, deeply divided into 2 or 3 pairs of lobes. Each lobe is 13-17 mm long and ends in a sharp spine.


Slightly hairy to cobwebby. 500-1000 mm high. White to purple with a waxy bloom. Rigid. Erect. Ribbed. Not winged. Usually a single stem branching in the top half only.

Flower head:

Single. At end of stem. 10-14 mm diameter.


Pale violet.

Bracts - Outer bracts shiny, usually less than 30 mm, bent backwards to form star shape under flower head. Inner bracts about 1/3 as long as the outer ones.

Stamens -

Anthers -


Achene, 3-4 mm long.


Grey-brown. Large. 4 angled. Pappus of flat topped scales, 5-7 mm long.


Simple taproot. Branching fibrous secondary roots.

Key Characters:

Purple flowers, spine on the ends of the lobed leaves, waxy bloom on stem and leaves, stems without wings.


Life cycle:

Annual. Seeds germinate in autumn and winter and produce a slow growing rosette of leaves. A single flowering stem emerges from the centre in spring and branches in the upper half and forms flowers in November to December. Plant dies in summer, leaving the rigid stems standing.



By seed

Flowering times:

November to December.

Seed Biology and Germination:

Vegetative Propagules:




Population Dynamics and Dispersal:

Most seed falls close to the plant and little is spread by wind. The spiny flower head and the long pappus scales on the seed help it entangle in wool and fur to assist spread. The main long distance spread is probably as a contaminant of cereal grain, pasture hay and other produce. Some may be spread in mud clinging to animals or machines.

Origin and History:

Mediterranean, South West Asia, Greece, Crete.

First recorded at Tambellup in WA in 1975.



C. glaucus has been recorded in SA and VIC.



Warm temperate regions with winter dominant rainfall.


Wide range.

Plant Associations:




Weed of roadsides, disturbed areas, pastures, fallows and crops.

Little feed value.

Restricts grazing and competes with pasture.

Contaminates wool, hay and grain.

Interferes with harvesting grain crops.


None recorded.


Noxious weed of WA.

Management and Control:

Spread mainly by animals and machinery or as a contaminant of grain or produce. Seed is not effectively spread by wind. Plough area to more than 100mm deep to bury seeds deeply. Kill seedlings with follow up shallow cultivation or herbicides. Plant a cereal crop and use selective herbicides at the 3-6 leaf stage. Crop the paddock for 3 years before returning to pasture. In pasture, paraquat or diquat at early flowering time of the thistle provides good control of seed production.


Eradication strategies:

Eradication will be difficult and may and take many years.

The following is a best bet set of options.

Plan on going into a continuous crop rotation for 5-8 years.

Apply 500 mL/ha glyphosate(450g/L) the bud stage (November). 2 weeks later apply 500 mL/ha paraquat(250g/L) plus 1% oil (i.e. 1 L spraying oil per 100 L of spray mix).

Graze with goats over summer to eat escaping flower heads.

Burn in summer to expose seed to high alternating temperatures which probably helps break dormancy. (Herbicide applications in spring will make the thistle more susceptible to fire).

Shallow cultivate (10 mm deep) 5 days after the first rains to kill germinating seed and bury others so they will germinate.

Apply 750 mL/ha glyphosate(450g/L) plus 500 mL/ha Tordon 75-D plus 1% wetting agent 7 days after the second rain. (the extra wetting agent gives greater germination of surface seed). 7 days after the third rain, plough to 100 mm or more deep to bury seed too deep to emerge. Plant a short season wheat with a minimum tillage seeder to avoid disturbing buried thistle seed. Increase the seeding rate by 30% to increase crop competition with the weeds.

Apply 500 mL/ha paraquat(250g/L) plus 1% oil just before the crop emerges.

If more than 20 thistles /m2 emerge, spray the crop at the 2 leaf stage with 300 mL/ha Lontrel. Otherwise, wait until the 6 leaf stage of the crop and spray with 200 mL/ha Lontrel plus 500 mL/ha of Tordon 75-D.

Check the crop at the elongation stage and if thistles are found respray with 250 mL/ha of Lontrel plus 1000 mL/ha 2,4-D amine(500g/L).

Use a seed catcher behind the harvester to collect weed seed. Treat with diesel, burn or dump it where it can't reinfest the paddock.

Graze with goats after harvest.

Burn stubble.

In the second season, shallow cultivate, 5 days after the first rain. Apply 750 mL/ha of glyphosate(450g/L) plus 250 mL/ha dicamba(200g/L) 7 days after the second rain and plant barley with a minimum tillage seeder. Use a higher seeding rate. If more than 20 Glaucous Star Thistle per square metre, apply 300 mL/ha Lontrel. If less, apply Lontrel at the 6 leaf stage of the crop (Don't use Tordon because this may carry through to next years crop). For the rest of the season treat as for wheat above.

In the third season, shallow cultivate after the first rain.

5 days after the second rain, apply 500mL/ha of glyphosate(450g/L) plus 250 mL/ha of Dicamba(200g/L) plus 1 kg/ha of Atrazine(900g/kg) granules plus 1% oil plus 1 kg of crystalline ammonium sulphate per 100 L of spray mix.

Plant triazine tolerant canola a day or two later. Extra nitrogenous fertiliser will be required to improve crop competition and make up for the run down over the previous two cereal crops. Avoid using insecticides detrimental to ants such as Talstar and endosulfan, because the ants are probably helping to reduce the dormant seed bank.

At the 3-4 leaf stage of the crop, apply 1 kg/ha of Atrazine(900g/kg) granules plus 300 mL/ha Lontrel plus 1% oil.

Check the crop at stem elongation and if thistles are found apply 300 mL/ha of Lontrel.

Swath the crop or desiccate with 2-3 L/ha of paraquat(250g/L) or Reglone. This will also control any late emerging thistles.

Graze with goats after harvest.

In the fourth season a legume is required to replenish soil nitrogen.

Shallow cultivate after the first rain

Apply 500 mL/ha glyphosate(450g/L) plus 100 mL/ha Goal CT.

Apply 1 L/ha Simazine(500g/L) plus 2 L/ha Diuron(500g/L) immediately before planting Lupins, Faba Beans or Chickpeas. Use 3L/ha Diuron(500g/L) if planting peas. Use short season varieties so that the crop has finished pod fill before the thistle flowers.

Apply 1 L/ha paraquat(250g/L) plus 1% oil when the crop seeds have reached full size and the Glaucous Star Thistle is budding to just starting to flower. Repeat after harvest if necessary.

Graze after harvest with goats.

Alternatively use a green manure crop for the fourth season, These have shown potential in the Glaucous Star Thistle areas. Plant the legume species that will provide the greatest bulk for your district, then shallow plough it in spring to kill it and conserve moisture for the following cereal.

Repeat the 4 year program above.

Talk to your local agronomist about the best crop rotations for your area and modify the above accordingly.

In paddocks that can't be cropped, a combination of;

1) planting and encouraging pasture legumes then fertilising with superphosphate,

2) goat grazing over spring and summer plus

3) 'spray grazing' (750-1000 mL/ha of 2,4-D amine(500g/L) applied in winter when the thistle is in the rosette stage followed 7 days later with 4-5 times the normal stocking rate of wethers) plus

4) 400 mL/ha glyphosate (450 g/L) plus 400 mL/ha 2,4-D amine at the budding to early flowering stage of the Glaucous Star Thistle and

5) using goats for grazing will reduce Glaucous Star Thistle to low levels over a number of years.

In higher rainfall areas, establishing perennial pasture species will reduce Glaucous Star Thistle to insignificant levels.

On fence lines, roadsides and other unused areas, use an annual application of 2 L/ha of Tordon 75-D at the beginning of stem elongation (late September) plus a follow up spray of 1 L/ha of paraquat(250g/L) if required in early summer. This will not kill most grasses which helps prevent reinfestation. Bromacil may also be used in industrial situations where there are no trees close by and no run off from the site.

Prevent reinfestation.

Shear all sheep that have been exposed to Glaucous Star seed before moving them into clean paddocks.

Don't buy feed or seed from infested farms. Your thistle problem most probably arose from contaminated seed or produce purchased many years ago.

Watch creek lines and flood ways. Glaucous Star Thistle seed will float and this is a potential source of external infestation.

Remove odd plants and spray the area and a 3 metre buffer strip, until it is just wet, with a mixture of 1 litre of Tordon 75-D in 100 litres of water.

Herbicide resistance:

None reported.

Biological Control:

Because Glaucous Star Thistle is closely related to the commercial Safflower, biological control is not likely to be implemented.

Related plants:

Safflower (Carthamus tinctorius)

Saffron Thistle (Carthamus lanatus)

Toothed Thistle (Carthamus dentatus).

Plants of similar appearance:

Spear Thistle (Cirsium vulgare) has much broader lobes on the leaf and shorter spines around the flower.

Sheep and Slender Thistles (Carduus species) have several flower heads clustered at the end of the stem and wings on the stems.

Cultivated Safflower (Carthamus tinctorius L.) has undivided leaves and dark yellow flowers.

St Barnaby's Thistle (Centaurea solstitialis) and Maltese Cockspur (Centaurea melitensis)have yellow flowers and they don't have lobed and spined leaves.

Golden Thistle (Scolymus hispanicus) has yellow flowers.

Spotted Thistle (Scolymus maculatus) also has yellow flowers and only occurs in NSW and QLD.

Toothed Thistle (Carthamus dentatus) has pink/purple flowers and only occurs in central NSW and Vic.


Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P937.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). (as C. glaucus) #260.1.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P197-199. Photos.


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