Spotted knapweed (Centaurea stoebe subsp. micranthos)

Spotted knapweed is a thistle-like plant without the sharp spines and has pink-purple flowers. It competes with native plants and pasture.

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How does this weed affect you?

Spotted knapweed:

• outcompetes pasture plants and native plants 
• produces chemicals that suppress the growth of other plants
• is not usually eaten by livestock. 

What does it look like?

Spotted knapweed grows to 1.2 m tall. It is a slender, upright, branched herb that looks like a thistle but without sharp spines on the leaves. It is a biennial or short lived perennial plant. 

Leaves

All leaves are grey-green and finely hairy to velvety. There are two types of leaves.

Leaves that grow in a clump (rosette) at the base of the plant that are:

• up to 20 cm long and 5 cm wide
• deeply lobed.

Leaves that grow along the flower stem that are:

• 2.5–7.5 cm long
• oval or lobed
• alternate along the stem.

Flowers are:

• 2–3 cm wide
• purple to pink
• on the ends of stems
• surrounded by rows of scales (bracts) below the petals. The scales:
  • are mostly green
  • have pointed, dark-brown to black tips
  • sometimes have a stripy appearance.

Seeds are:

• 2-3 mm long
• brown when mature.

Seeds sometimes have a tuft of hairs (pappus), which is usually less than 3 mm long. 

Stems are:

• 0.3–1.2 m tall
• branched.

Similar looking plants

Spotted knapweed looks like some thistles. Unlike thistles, knapweeds don’t have sharp spines on the leaves or bracts. 

Compared to other knapweeds:

• spotted knapweed usually has deeply lobed leaves and bracts with a dark-brown or black tip
• black knapweed (Centaurea x moncktonii) usually has oval-shaped leaves and golden-brown bracts
• creeping knapweed (Rhaponticum repens) can have deeply lobed leaves but does not have a dark-brown or black tip on the bracts.  

Larkdaisy (Centratherum punctatum) also looks like knapweeds, but its leaves have serrated edges.

Where is it found?

In Australia, spotted knapweed has only been found in the Australian Capital Territory. These plants have been controlled.

Spotted knapweed is native to eastern Europe. It was accidently introduced to North America where it has become a wide spread weed. 

What type of environment does it grow in?

Spotted knapweed mostly grows in cool temperate areas with over 250 mm of rain per year. It grows in a wide range of soil types, though it prefers well drained soil to water logged soils. Overseas it is a weed of disturbed sites (e.g. overgrazed or cultivated paddocks, roadsides, creek lines), although it can invade non-disturbed areas.

Maps and records

• Recorded presence of Spotted knapweed during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

Spotted knapweed seeds are spread by water, wind, soil, contaminated hay, vehicles or on clothing. Spotted knapweed seed can also be spread via wildlife and livestock, either on their fur or after being eaten. 

By roots

Spotted knapweed grows and spreads from root fragments.

References

CABI (2019). Invasive Species Compendium, Data sheet, Centaurea stoebe subsp. micranthos(spotted knapweed) https://www.cabi.org/isc/datasheet/12040#todescription 

Invasive Org (2018). spotted knapweed Centaurea stoebe ssp. micranthos (Gugler) Hayek. https://www.invasive.org/browse/subinfo.cfm?sub=3013 

Mangin, A. R., & Hall, L. M. (2016). First report: spotted knapweed (Centaurea stoebe) resistance to auxinic herbicides. Canadian Journal of Plant Science, 96(6), 928-931.

More information

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Control

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.

Herbicide options

See Using herbicides for more information.

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Glyphosate 360 g/L (Various products)
Rate: 10 mL per 1 L water
Comments: Spot spray. For general weed control in domestic areas (home gardens), commercial, industrial and public service areas, agricultural buildings and other farm situations.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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Biosecurity duty

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.

Area	Duty
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	Prohibited Matter 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

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Reviewed 2021