Black knapweed looks like a thistle, especially the flower, but it has no spines. It invades pastures, crops and natural areas.
Black knapweed invades pastures, crops and natural areas. It:
Black knapweed is a slender, upright, branched perennial herb that grows to 1 m tall. It looks like a thistle but doesn’t have spines on the leaves or flowers.
There are two types of leaves.
Leaves in a clump (rosette) at the base of the plant are:
Leaves along the flower stem are:
Black knapweed (and other knapweeds) look like thistles. Unlike thistles, knapweeds don’t have sharp spines on the leaves. Call the biosecurity hotline if you see any spineless thistles with pink-purple flowers in NSW.
Similar looking plants include:
Black knapweed has been found in Tenterfield, in the NSW Northern Tablelands.
There are over 500 species of knapweeds, most originating in Europe. Many Centaurea species are prohibited imports into Australia. Black knapweed is grown in gardens in the UK and North America.
Black knapweed grows in most soil types. It grows best in:
It has occasionally been sold as an ornamental species in NSW.
Plants can produce from 1,000 to 18,000 seeds each year. Seeds germinate in autumn and overwinter as rosettes. Seeds stick to animals and clothing. They are also spread by water, wind, vehicles and in contaminated soil. Grazing animals may also spread seed in manure.
Black knapweed can grow from root fragments which are spread by machinery or in soil or water.
PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 6 February 2023 from https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Centaurea
Richardson, F. J., Richardson, R. G., & Shepherd, R. C. H. (2011). Weeds of the south-east: an identification guide for Australia (No. Ed. 3). CSIRO.
Roche, C. T., & Ben Jr, F. (1991). Meadow knapweed invasion in the Pacific Northwest, USA, and British Columbia, Canada. Northwest science., 65(1).
Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the helpline listed at the top of this page immediately.
NSW DPI will lead an initial response for the treatment and disposal of the plant to stop it from spreading.
Check roadsides, paddocks, crops and areas close to waterways. Check feedout areas if you’ve brought hay or feed onto your property. Check regularly especially after rain.
See Using herbicides for more information.
Glyphosate 360 g/L
Rate: 10 mL per 1 L of water
Comments: Apply to actively growing plants from September to May. Spray to ensure full coverage of plants. A follow up treatment may be necessary for complete control and to restrict seedling re-establishment.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate
The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.
|All of NSW||General Biosecurity Duty
All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
|All of NSW||
A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries