What is Californian thistle?(Cirsium arvense)
- Californian thistle is a weed of pastures and crops.
- Californian thistle is a declared weed under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of Californian thistle are prohibited in Tasmania.
How to identify Californian thistle
thistle is a perennial (long-lived) plant. Over winter the top growth
dies off leaving only the root system. The roots remain alive from year
to year and actively spread through the soil.
- In spring the
roots produce rosettes (whorls of leaves close to the ground), which
send up a branched stem to about 1 metre in height. The stems are
usually hairless and there are no wings or other outgrowths from the
stem as occur in slender, cotton and nodding thistle.
- The bracts
which surround the flower heads are green with purple tips and although
tapering to a point are not spined. Each flower head contains a large
number of rose-purple to lavender florets smelling strongly of honey.
and female flowers are borne on separate plants. Infestations that have
either all male or all female plants spread by vegetative growth only.
If male and female plants are found within the same infestation, viable
seed is produced and the infestation spreads both vegetatively and by
- For help in identifying thistles in Tasmania, see Identifying Thistles in Tasmania and search the Dennis Morris Weeds and Endemic Flora database
for Californian thistle illustrations. If you are still in doubt about
the thistle you are dealing with, contact your Regional Weed Management
Officer on 1300 368 550 for help.
Image top right: Californian thistle.
Images above, left to right: Californian thistle flower (photo: Kiowa Fenner); Californian thistle.
Californian thistle in Tasmania
- Californian thistle occurs in most parts of Tasmania (see map).
thistle competes with pasture species and a heavy infestation can
significantly reduce production. Stock avoid grazing around the rosettes
and shoots, further reducing productivity of infested areas. Dense
infestations of flowering stems may totally exclude stock.
- Californian thistle also competes with crop species and can interfere with harvesting.
What is the legal status of Californian thistle in your area?
Detailed management and control guidelines for Californian thistle can be found in the Californian Thistle Control Guide. Refer also to Herbicides for Californian Thistle Control. For more information see DPIPWE's Weed Links and Resources.
See also:Californian Thistle Control Guide
Herbicides for Californian Thistle
Statutory Management Plan for Californian Thistle
Weed Links and Resources
Other useful links:Pest Genie
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