What is variegated thistle?(Silybum marianum)
Variegated thistle is a pasture and crop weed.
How to identify variegated thistle
thistle is a large biennial plant (living for two years) forming
rosettes of a metre or more in diameter and a flowering stem up to 2
metres in height.
- Rosette leaves are lobed and with
spiny margins, and the upper surface is a bright, shining green with
distinct white variegations. The flower heads are large and showy,
bright purple in colour, and surrounded by long, stiff, spiny bracts.
seed germination takes place in early autumn but can also occur in
spring and summer in irrigated areas. Variegated thistle normally
over-winters as a rosette but in spring-sown crops it can establish as a
seedling then flower and produce seed within the life of the crop.
Image top: Variegated thistle flower, photo: M. Baker.
Images above, left to right: Variegated thistle infestation, photo: M. Baker; Variegated thistle leaves, photo: M. Baker.
Variegated thistle in Tasmania
thistle occurs in most agricultural areas of Tasmania. Infestations are
most common in the Midlands and in the south, lighter in the north-east
and north-west, and very light in the far north-west.
thistle is found on roadsides and in waste areas, in pastures and
occasionally in crops. Variegated thistle grows best in areas of high
fertility such as sheep camps and stock-yards.
rosettes are strongly competitive in pastures and crops causing severe
yield losses. Dense infestations kill other vegetation, leaving large
bare patches when the thistles die off, which are then vulnerable for
re-infestation by weeds.
- Some livestock (especially
cattle) can suffer from nitrate poisoning from grazing variegated
thistle. Grazing of variegated thistle can lead to the rapid onset of
toxicity symptoms and death, or to chronic symptoms of ill-thrift
depending on nitrate concentrations in the plant and the amount of
material consumed. Variegated Thistles may be consumed in large
quantities where little alternative feed is available or palatability is
increased by cutting or by herbicide application.
Detailed management and control guidelines for variegated thistle can be found in the Variegated thistle Control Guide. Refer also to Herbicides for Variegated thistle Control. For further information see DPIPWE Weed Links and Resources.
See also:Variegated Thistle Control Guide
Herbicides for Variegated Thistle Control
DPIPWE Weed Links and Resources
Other useful links:Pest Genie
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