Macquarie Valley Weeds Committee & Lachlan Valley Weeds Advisory Committee


Star Thistle

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Botanical Name: Centaurea calcitrapa
Other Common Names:


Class Regions
Class 4Cootamundra Shire Council,Forbes Shire Council,Lachlan Shire Council,Parkes Shire Council,Upper Macquarie County Council,Weddin Shire Council
Landholder Responsibilities: The growth and spread of the plant must be controlled according to the measures specified in a management plan published by the local control authority
Why Is It Bad?: Star thistle has become a serious weed of cereal crops and pastures in NSW, VIC and SA. It is now mostly confined to roadsides, channel banks and neglected areas. In NSW it is more widespread than elsewhere and is important in pastures on the Central and Southern Tablelands. It is also a problem in seed crops in lower SA. Star thistle competes with crops and pastures and once heads are formed, their spines injure grazing animals, particularly in eyes and mouth. It also denies animals access to pasture species. It is beleived that star thistle may be toxic to animals, but it is rarely grazed.


Habit: Herb
Leaves: Darkish green, shortly haired, deeply lobed and sometimes toothed but wothout spines.Leaves are 25cm long with stalks.
Flowers: Flowers are purple, they occur singly at the ends of branches or the axils of upper leaves.the are surrounded by numerous bracts each ending in a rigid, sharp, white or yellowish spine 1.5 to 3 cm long.
Fruit: Seeds are whitish with brown streaks or blothches, 3 to 4mm ling, 2mm wide, ovoid, smooth.
Roots: Fleshy taproot, 2 to 3 cm in diameter.

Control Methods

Manual Removal:
Chemical Use: Star thistle is susceptible to a range of herbicides in the seedling and rosette stages, please contact your local weeds officer or agronomist to receive a list of suitable herbicides.
Slashing & Cutting: Slashing is effective is carried out just before flowering. Mowing is equally effective but if left until early flowering, there may be enough food material in the cut stems to allow the seeds to mature. If either slashing or mowing is carried out too early the plants may regrow from buds at the base and produce new flowering stems.
Biological Control:
Cultivation & Scalping: Isolated plants should be grubbed, ensuring that the bulk of the taproot is removed. If near the seedling stage then plants should be heaped and burnt to destroy the seeds. Cultivation is effective in the early growth stages. Cultivation must be at least 10cm deep to sever the taproot at a depth from which regrowth does not occur.

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