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.
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.
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.
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.
The distinguishing feature of corn sowthistle is its network of long creeping roots.
- 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
- 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
- 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
- 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
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.
Written by Rachele Osmond.
Reviewed by Rod Ensbey.
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
Small infestations and individual plants can be removed manually by hand or hoe. Care must be taken 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.
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The requirements in the Noxious Weeds Act 1993 for a notifiable weed must be complied with