(Carthamus Ianatus)
Saffron thistle flower.
What is saffron thistle?
Saffron thistle is a weed of pasture and crops.
Saffron thistle is a
declared weed in Tasmania under the Tasmanian Biosecurity Act 2019 and associated Regulations. The importation, sale and distribution of saffron thistle are prohibited in Tasmania.
How to identify saffron thistle
Saffron thistle is an annual plant (living for one year) which grows to 90 cm tall. Saffron thistle belongs to the daisy family and is closely related to slender and spear thistles.
Saffron thistle seeds usually germinate with the onset of autumn rains although some seeds may germinate in winter and spring. The seedling grows into a rosette (a whorl of leaves close to the ground) 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 wither and disappear. The stem leaves are very stiff with stout sharp spines at the tip and along the edges.
The stem divides into many branches with each branch carrying flower buds. The buds are enclosed in large spiny bracts very similar to the stem leaves. The flowers are slender, bright yellow florets which are partially hidden by the large bracts, making the flowers rather inconspicuous. Flowering occurs throughout November and December. The seed has a small fringe of stiff hairs which adheres to wool and clothing.
The plant generally dies during late autumn to early winter. Dead plants may remain standing for many months.
For help in identifying thistles in Tasmania, see
Identifying Thistles in Tasmania and search the
Dennis Morris Weeds and Endemic Flora database for saffron thistle illustrations. If you are still in doubt about the thistle you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.
Saffron thistle in Tasmania
Several small infestations of saffron thistle occur in Tasmania. These infestations can usually be traced back to feed-grain imported from mainland states.
Saffron thistle is most common in run down pastures, roadsides and waste areas, particularly in areas of low rainfall and low soil fertility.
Saffron thistle competes strongly with crops and the stiff, wiry stems impede harvesting operations. The seed also contaminates grains and other crop seeds.
In pastures, dense infestations of saffron thistle impede grazing. Wool from sheep grazing in infested areas may become contaminated with sharp leaf fragments. Animals grazing in dense saffron thistle infestations can also suffer injury to their mouths and eyes from the spines.
Legal status of saffron thistle in your area
Detailed management and control guidelines for saffron thistle can be found in the Saffron Thistle Control Guide. Refer also to
Herbicides for Saffron Thistle Control. For further information see
Weed Links and Resources.
See also
Saffron Thistle Control Guide
Spread of saffron thistle
Saffron thistle is spread by seed.
Saffron thistle seed is not readily moved by wind, and most seed falls directly below the parent plant. As a result infestations tend to persist in the same area and spread is not rapid.
Sheep may eat the seeds and pass them through the digestive system, assisting the weed's spread throughout a property.
Seeds may also spread in the fleece and coats of livestock, through soil movement on equipment and machinery, and through water movement along drainage lines.
Saffron thistle seed remains dormant in the soil for at least eight years. Seed buried more than 10 mm deep may remain dormant until cultivation or other soil disturbances bring it to the surface.
Avoid the introduction of saffron thistle
Avoid introducing seed into clean areas, or into areas from which the weed is being eradicated.
Implements which have been used on infested areas should be thoroughly cleaned on leaving.
All feed grain or hay should be free of saffron thistle seed.
Any livestock suspected of carrying seed on their bodies or in their digestive system should be held in a suitable area for approximately two weeks before being put on clean paddocks.
Special care should be exercised when buying sheep from other properties as seed is readily carried in wool.
See the
Washdown Guidelines for Weed and Disease Control for detailed information on how to wash-down equipment and personnel to reduce the chance of spreading.
Physical removal
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.
Cultivation
Most saffron thistle infestations in Tasmania are relatively small and occur in low rainfall, stony areas, making control by cultivation difficult.
Where cultivation is possible, a three years' program of establishing a competitive pasture or crop (wheat or barley) can induce germination and exhaust the reserve of thistle seed in the soil.
Any thistles which survive the cultivations should be sprayed with herbicide in the crop.
Chemical control
A number of herbicides are registered for use on saffron thistle in Tasmania. See
Herbicides for Saffron Thistle Control for more information.
Saffron thistle can germinate from autumn through to late spring, and it may be advisable to delay spraying until late in the season to ensure all plants are found and treated, particularly for scattered and sparse infestations.
Herbicides for Saffron Thistle Control
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