The cotyledons of common sowthistle (milk thistle) (Sonchus oleraceus) are spoon-shaped and often have a greyish powdery film on their surface. Leaves are bluish green and predominantly net-veined.
Adult leaves are characterised by their serrated appearance and are commonly deeply lobed with a major triangle-shaped lobe at the tip of the leaf. Adult leaves are characterised by auricles that clasp the stem, and the leaf margins are never spiny.
Stems are hollow and exude a milky sap when broken.
Seeds are flat and possess a wrinkled surface at maturity and a fine white pappus.
Factors that make common sowthistle a major weed:
Further detail about this weed including integrated weed management tactics that could be considered when developing a management plan can be found in the section on problem weeds in the Integrated Weed Management Manual.
In 2014, populations of Sonchus spp. have been found to be resistant to glyphosate on the Liverpool Plains in NSW.
Ecology and biology of common weeds are outlined in section 6 of the Integrated Weed Management Manual.
Sowthistle update on glyphosate resistance survey and overview of resistance testing and management options (2016)
Weed issues and action items (2015)
GRDC Youtube: Webinar on the ecology and management of common sowthistle (2016)
Management of sowthistle, DAFF Qld
Genetic diversity among ALS-inhibiting herbicide resistant and susceptible populations of Sonchus oleraceus L. (sowthistle) in Australia, Robin S. St John-Sweeting, Christopher Preston, Jeanine Baker, Steve Walker and Michael Widderick pp. 281-284, 17th Australasian Weeds Conference (2010)
Ecology and management of common sowthisle fact sheet, Queensland Alliance for Agriculture and Food Innovation.