Saffron thistle (Carthamus lanatus)

Photo: (c) Harry Rose CC BY 2.0

Family: Asteraceae

Growth Habit: An erect, spiny plant which can grow up to 150 cm in height but averages 100 cm. Seedlings grow into a rosette which rarely exceeds 20 cm in diameter. In spring a single, stiff, wiry stem grows from the centre of the rosette and the rosette leaves die off. The stem leaves are very stiff with stout sharp spines at the tip and along the edges. The stem divides in to branches, each of which carries flower buds. Most of the plant is covered with minute hairs and it is often branched on the upper part of the plant.

Identifying Thistles in Tasmania

Type of Plant: Saffron Thistle is an annual.

Photo: (c) Harry Rose CC BY 2.0

Flowers: Saffron Thistle has solitary flowerheads at the top of each stem. The flower heads comprise many long, thin, bright yellow flowers. Flowering occurs throughout November and December.

Fruit/Seed: Large brown wedge shaped seeds are released in late summer. They generally germinate in autumn.

Dispersal: Saffron Thistle has a tendency to grow in dense clumps, rather than spread throughout a paddock, as the heavy seeds drop and germinate near the mother plant. Unlike many thistles, Saffron Thistle seeds are too heavy to be disbursed by wind.

Distribution: Saffron Thistle is a major weed of grazing areas in NSW. It occurs in several small patches in Tasmania. It usually occurs in low rainfall grazing areas.

Status: Saffron Thistle is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of saffron thistle are prohibited in Tasmania.

Weed Impact:

  • Land infested by Saffron Thistle is seldom grazed properly as the plants very spiny nature deters livestock. This allows plants to grow unhindered, and thus take over large areas of grazing land if left unchecked.
  • Seed may remain viable in the soil for many years, requiring landholders to reinspect and treat infested areas annually for many years to achieve successful eradication.

Control Methods:

  • Practice hygiene control when moving machinery and equipment around.
  • Pasture management (all year). Maintaining a vigorous pasture and avoiding overgrazing will help reduce Saffron Thistle incidence.
  • Grubbing can be used to remove saffron thistle where the number of plants involved is small.
  • Plants should be collected and burnt.
  • Slashing or cutting can be used to reduce maturing Saffron Thistle, but must be undertaken at the correct time. If plants are cut before the stem is fully developed, plants may regrow; if plants are cut after flowering has begun, viable seed may still be produced on the cut stem. The optimum time for slashing or cutting usually occurs around October to November.
  • Most saffron thistle infestations in Tasmania are relatively small and occur in low rainfall, stony areas, making control by cultivation difficult.
  • Herbicides. MCPA and 2,4-D amine can be used at a lower rate for seedlings and a higher rate for rosettes. 2,4-D ester can be used at a lower rate for seedlings and a higher rate for shooting plants. Clopyralid is also effective. If used during flowering it can reduce seed formation. DPIPWE’s Herbicides for Saffron Thistle Control.

N.B. Always check the herbicide label before use.