Corn sowthistle (Sonchus arvensis)

Also known as: perennial sowthistle

Corn sowthistle is a long-lived, vigorous, perennial herb that is a potentially serious weed of temperate Australia’s cropping systems and environmental areas.

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How does this weed affect you?

Corn sowthistle is a long-lived, vigorous, perennial herb. It is closely related to other sowthistle species that are common and persistent weeds of crops, pastures, roadsides and environmental areas. It is potentially a serious weed of temperate Australia’s cropping systems and environmental areas.

The perennial nature of corn sowthistle, together with its ability to spread both by seed and spreading roots, makes it a difficult weed to control. Closely related species are already major weeds of cropping systems and environmental areas in Queensland, New South Wales and Victoria.

If corn thistle becomes established, it has the potential to rapidly become a serious agricultural and environmental weed. 

What does it look like?

The distinguishing feature of corn sowthistle is its network of long creeping roots.

Stems

• upright with 2 or more stems per plant
• 50–150 cm high and 3–10 mm in diameter
• flowering stems are branched with many flower heads
• hollow and filled with a milky substance
• finely ribbed.

Leaves

• occur alternately along the stem
• dark green on upper surface and paler underneath
• lobed with coarsely toothed edges
• variable in size and shape
• lower leaves are deeply lobed, 15–35 cm long and 3–10 cm wide
• upper leaves clasp the stem and are narrower

Flowers

• dandelion-like
• occur on stalks 1–5 cm long
• yellow petal-like florets
• 4–5 cm across
• many green bracts (leaf–like structures) surround the base of the flower
• open 2-3 hours after sunrise and close around midday
• many fruits are produced per flower-head

Fruit and seed

• fruit contains only one seed that is encased within a thin wall
• entire fruit is dispersed when ripe
• oval, flattened and ribbed
• 2.5–3.8 mm long and 1–1.5 mm wide
• has a tuft of fine, silky, white, fluffy hairs

Roots

• fine spreading roots occur in top 5–­15 cm of soil and can reach over 1 m in length
• vertical roots are thickened and can reach depths of up to 2 m
• vegetative buds form along both spreading and vertical roots

Where is it found?

Native to Europe, northern Africa and Asia. It is widely distributed throughout temperate parts of the world and is reported as a weed in 59 countries. Considered a serious weed of cereal and oilseed crops in Canada, the northern United States and Russia. It is also a weed in South America, New Zealand and the United Kingdom.

To date, corn sowthistle has only been recorded in the Clare region of South Australia. This population is now thought to have been eradicated. Currently it is not known to be present anywhere else in Australia.

How does it spread?

New plants are produced by seed and vegetatively from buds that form along its spreading roots. Vegetative spread allows the plants to quickly invade new areas and continue to persist, particularly in cultivated and disturbed areas. Root pieces as small as 2.5 cm, that contain reproductive buds, can start a new infestation. Root fragments can be transported to new sites by machinery and soil movement.

The seed is dispersed by wind and water. Fluffy hairs at the tip are well adapted to wind dispersal, the main method of seed spread. The hairs contain small hooks that can attach to animals, clothing, vehicles and equipment. Spread also occurs through contaminated produce, such as seed and hay.

Lifecycle

Shoots and new roots of established infestations begin to develop when the soil starts to warm, usually around mid-spring. Seeds will also germinate in spring. Flowering stems emerge during summer and set seed from late summer to early autumn.

Plants generated by seed do not often flower in their first year.

What type of environment does it grow in?

Corn sowthistle prefers warm temperate climates and fine textured loam and clay soils. It favours slightly alkaline to neutral soil conditions that are rich in organic matter. It tends to thrive in areas that have been cultivated and the soil is not compacted.  It does not tolerate frost.

Corn sowthistle prefers to grow in disturbed areas, but can also invade intact habitats. Areas most at risk of invasion include cultivation, pastures, roadsides, bushlands and the shorelines of lakes and rivers. 

Acknowledgements

Written by Rachele Osmond. Reviewed by Rod Ensbey.

References

CABI (2014) Sonchus arvensis In: Invasive Species Compendium. Wallingford, UK: CAB International. Available at: www.cabi.org/isc.

Department of the Environment (2011) Weeds in Australia: Sonchus arvensis. Australian Government. Available at: http://www.environment.gov.au/biodiversity/invasive/weeds/identification/index.html 

Lemna WK and Messersmith CG (1990) The biology of Canadian weeds. 94. Sonchus arvensis L. Canadian Journal of Plant Science, 70: 509–532

More information

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Control

Small infestations and individual plants can be removed manually by hand or hoe. Take care to remove the whole root network. Continue to monitor the site for any re-growth.

Property hygiene practices should be in place to restrict movement of roots, fruits and seed into clean areas.

If you suspect you have corn sowthistle, contact your state herbarium or local government weeds officer for correct identification.

Herbicide options

See Using herbicides for more information.

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2,4-D 300 g/L + Picloram 75 g/L (Tordon® 75-D)
Rate: 300 mL per hectare
Comments: Commercial and industrial areas, rights of way, pastures and non-crop areas
Withholding period: Do not graze or cut crops (except sugar cane 8 weeks) or pastures for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Glyphosate 540 g/L (Various products)
Rate: 1.35 to 2 L per ha
Comments: Boom spray. Use higher rate on weeds over 15 cm or where dense weed cover limits spray coverage.
Withholding period: Not required when used as directed.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 540 g/L (Various products)
Rate: 330 - 480 mL per 100 L of Water
Comments: Handgun. Use higher rate on weeds over 15 cm
Withholding period: Not required when used as directed.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 540 g/L (Various products)
Rate: 50 - 70 mL per 15 L of water
Comments: Knapsack spray: use higher rate on weeds over 15 cm and when applying less than 5 L spray per 100 sqm.
Withholding period: Not required when used as directed.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
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.

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Reviewed 2024