Hawkweeds (Pilosella species)

Hawkweeds are highly invasive plants forming dense stands of up to 3800 plants per square metre. They are a major threat to biodiversity and a problem in pastures, on roadsides and in gardens.

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How does this weed affect you?

Hawkweeds are highly invasive plants forming dense stands of up to 3800 plants per square metre. This is a major threat to biodiversity in conservation areas and native grasslands. Hawkweeds can also be a problem in pastures, on roadsides and in gardens.

Worldwide there are several hundred species known as hawkweeds. Hawkweeds belong to the Asteraceae or daisy family and were promoted as cottage garden plants. Hawkweed plants were previously sold by nurseries and these are likely to be sources of further infestations.

What does it look like?

The general appearance of a hawkweed plant is similar to a dandelion (Taraxacum officinale) or a flatweed (Hypochaeris species). Hawkweeds are perennial herbs of variable height (15–40 cm), and have a milky sap which is seen when their stems or leaves are broken.

Key identification features

• Leaves are stalkless, hairy on both surfaces, with smooth or slightly toothed margins and are sometimes ‘sticky’ to touch. They occur in rosettes. Occasionally 2–4 alternate leaves appear near the base of the upright flower stem.
• Flowers are yellow, orange or red and ‘daisy-like’. They may be solitary or formed in a cluster of 5 to 30 flower heads. The flowers are 10–20 mm in diameter with square-ended petals, and grow on stems up to 40 cm. The flower stems are covered in short, stiff hairs.
• Seeds are purplish-black and ribbed with a bristly tuft up to 6 mm long.

Where is it found?

Hawkweeds are native to the northern hemisphere, South Africa and South America. Several European species have become major weeds of pastures, gardens and natural areas in eastern North America, Japan, Patagonia and New Zealand.

Four Hawkweed species are known to occur in Australia. These are in either the Hieracium or Pilosella genera and include:

• orange hawkweed (Pilosella aurantiaca*) in Victoria and New South Wales (NSW)
• mouse-ear hawkweed (Pilosella officinarum*) which was first reported in Kosciuszko National Park NSW in early January 2015.
• king devil hawkweed (Hieracium  praealtum) in Victoria
• wall hawkweed (Hieracium murorum) in NSW.

Small infestations have been found around ski fields where seed was introduced on equipment from New Zealand.  Prompt treatment of known populations of hawkweeds has limited their spread so far.

*Orange and mouse-ear hawkweeds were previously grouped in the Hieracium genus as Hieracium aurantiacum and Hieracium pilosella respectively.

Maps and records

• Recorded presence of Hawkweeds 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?

Hawkweed can reproduce and spread both by seed and vegetatively. Vegetative spread of plants by rhizomes (underground stems) and stolons (above ground rooting stems) is common. Stolons arise from buds at the base of the leaves.

Up to 40 000 seeds per square metre are produced in summer. Seeds have tufts that enable them to attach to hair, fur and vehicles. Seed can also be spread by wind, water, in contaminated fodder and garden waste, and even on ski or hiking equipment. The seeds can survive in the soil for many years.

Hawkweed seeds usually germinates in spring after rain. Seedlings establish readily on bare soil and disturbed areas.

What type of environment does it grow in?

Hawkweeds have the potential to be serious weeds in the temperate areas of south-eastern Australia, including the Australian Alps and Tasmanian grasslands. They are frost-tolerant and competitive across a wide range of soil types, preferring cool climates with an annual rainfall above 500 mm.

Acknowledgements

2008 edition prepared by Annie Johnson; 2012 edition prepared by Elissa van Oosterhout; Reviewed by Scott Charlton, Andrew Storrie and Birgitte Verbeek.

References

Hawkweeds Agfact (2005) NSW DPI

Orange Hawkweed Weed Management Guide (2003) CRC for Weed Management

Williams NSG and Holland KD (2007) The ecology and invasion history of hawkweeds (Hieracium species) in Australia, Plant Protection Quarterly, 22(2): 76-80

More information

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Control

Herbicide options

See Using herbicides for more information.

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PERMIT 14558 Expires 30/06/2024
Clopyralid 300 g/L (Lontrel®)
Rate: 5 mL in 1 L of water
Comments: Spot spray application
Withholding period: 1-12 weeks (see label).
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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PERMIT 14928 Expires 30/09/2024
Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon Extra®)
Rate: 250-500 mL per 100 L plus BS 1000 or equivalent at 100 mL per 100 L
Comments: Foliar application
Withholding period: Where product is used to control woody weeds in pastures there is a restriction of 12 weeks for use of treated pastures for making hay and silage; using hay or other plant material for compost, mulch or mushroom substrate; or using animal waste from animals grazing on treated pastures for compost, mulching, or spreading on pasture/crops.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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PERMIT 14928 Expires 30/09/2024
Triclopyr 300 g/L + Picloram 100 g/L (Various products)
Rate: 250-500 mL per 100 L plus BS 1000 or equivalent at 100 mL per 100 L
Comments: Foliar application
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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PERMIT 14301 Expires 31/07/2026
Picloram 20 g/kg (Tordon® Granules)
Rate: 45 g/m2
Comments: Granular application.
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
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 All species in the genera Pilosella and Hieracium are Prohibited Matter except for Hieracium murorum.

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Reviewed 2020