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Spotted Knapweed

Spotted knapweed

Black knapweed bracts

Black knapweed flowers

St Barnaby's thistle rosette

St Barnaby's thistle

Star thistle rosette

Star thistle

 


family

Asteraceae

status

Spotted knapweed (Centaurea maculosa) is listed as noxious in category 1 (Local Control Authorities must be notified of its presence and the plants must be eradicated and land kept free of the weed) throughout NSW.

Description

A non-spiny member of the thistle group. Erect, much-branched short-lived perennial herb to 1m high. Leaves are divided almost to the midrib, hairy, stalked at the base of the plant but becoming smaller and stalkless towards the top of the stems. Flowers are pink, in thistle-like heads at the tips of long branches, and the enclosing bracts are not spiny. Bracts are comb-like, with a black tip, giving a spotted appearance. The photo of this species is taken from www.jeantosti.com and those of black knapweed (Centaurea nigra) provided by RG and FJ Richardson.

A serious weed of crops and pastures in the Northern Hemisphere, it is not well established in Australia. One infestation has been recorded in the ACT.

Dispersal

Seed is spread in soil and attached to machinery, vehicles and livestock. Knapweeds have been occasionally found for sale as garden plants in NSW (this is illegal since they are class 1 noxious weeds).

Look-alikes

Black knapweed (Centaurea nigra) is very similar but has black comb-like bracts on the flower heads. Perennial thistle (Cirsium arvense) has similar flower heads, being pink without spiny bracts, but it has spiny leaves.  See the perennial thistle page for images of this weed. Other thistles in the genus Centaurea are common weeds of the tablelands, particularly star thistle (Centaurea calcitrapa) and St Barnaby's thistle (Centaurea solstitialis).  Their rosettes are similar to those of spotted knapweed, with deeply lobed, spineless grey-green leaves.  However, their flower heads are surrounded by bracts with very long slender spines.

Control

Notify your local control authority if you think you have seen this weed. Chip or spot spray prior to seeding. Selective herbicides can be used to remove knapweed from pasture.

View the fact sheet for this weed here:






knapweed knapweed 539.6 KB