Hawkweeds - Pilosellas (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 in alpine regions and outcompete pastures, reducing productivity.

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How does this weed affect you?

Hawkweeds are highly invasive weeds that threaten Australian biodiversity and agriculture. They form dense infestations that: 

• outcompete native plants, especially native grasses in alpine regions 
• reduce food and habitat for native animals 
• compete with pastures, reducing productivity 
• invade gardens and roadsides.

What does it look like?

Hawkweeds are perennial herbs of variable height. They have a milky sap which can be seen when the stems or leaves are broken. 

Key identification features 

• A rosette of leaves that are stalkless, hairy on both surfaces, with smooth or slightly toothed margins. They are sometimes ‘sticky’ to touch. Some species may also have 2–4 alternate leaves on the lower part of the flower stem. 
• Flowers are yellow, orange or red and daisy-like. They grow at the top of the stems and may be solitary or in a cluster of 5 to 30 flower heads. The flowers are 10–20 mm in diameter with square-ended petals. 
• Flower stems are up to 40 cm tall and are covered in short, stiff hairs. 
• Seeds are purplish-black and ribbed with a bristly tuft up to 6 mm long. 

Three species of Pilosella occur in Australia: 

• Orange hawkweed, (P. aurantiaca) previously named Hieracium aurantiacum), which has many orange flowers per stem. 
• Mouse-ear hawkweed (P. officinarum previously named Hieracium pilosella), which has lemon yellow flowers and only one flower per stem. 
• King devil hawkweed (P. piloselloides previously named Hieracium praealtum), which has many bright yellow flowers per stem. 

Where are they found?

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

• Orange hawkweed is present in NSW in Kosciuszko National Park and on farmland near the National Park. It is also present in Victoria and Tasmania. 
• Mouse-ear hawkweed is present in NSW in Kosciuszko National Park NSW and in Victoria and Tasmania.
• King devil hawkweed has been found in Victoria but not NSW. 

How does it spread?

Hawkweeds 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 by human activity e.g., on skiing and hiking equipment. The seeds can survive in the soil for many years. 

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

References

CRC for Weed Management (2003). Orange Hawkweed Weed Management Guide. Cooperative Research Centre for Weed Management 

Williams, N.S.G. and Holland, K.D. (2007). The ecology and invasion history of hawkweeds (Hieracium species) in Australia, Plant Protection Quarterly, 22(2): 76-80 

Wilson, L. M. (2006). Key to Identification of Invasive and Native Hawkweeds (Hieracium Supp.) in the Pacific Northwest. British Columbia, Ministry of Forests and Range, Forest Practices Branch, Invasive Alien Plant Program. 

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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PERMIT 14558 Expires 30/06/2024
Clopyralid 300 g/L (Lontrel®)
Rate: 5 mL in 1 L of water
Comments: Spot spray application only for National Parks and non-agricultural adjoining lands. Only for use by NPWS employees and contractors, See permit for further critical comments.
Withholding period: 1-12 weeks (see label).
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
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: Spray actively growing plants before flowering. Do not apply more than once per season. See permit for critical comments.
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: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
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: Spray actively growing plants before flowering. Do not apply more than once per season. See permit for critical comments.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
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 only in Kosciuszko National Park and lands in the Snowy Monaro Regional Council area. See permit for further critical comments.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
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 genus Pilosella are Prohibited Matter

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Reviewed 2024