Sowthistles are a major weed of Australian cropping systems.
Management and control of sowthistles in Australia
Scientists are undertaking surveys to identify potential biocontrol agents to help manage sowthistles in Australia.
26 June 2007 | Updated 14 October 2011
About the weed
Sowthistles, Sonchus oleraceus and S. asper (Asteraceae), are common weeds throughout Australia.
S. oleraceus was identified as one of the major weeds of Australian cropping systems, especially in South-East Queensland and Northern New South Wales (NSW). Its incidence has increased over the past two decades (Walker et al. 2005, Widderick et al. 1999) and its importance as a weed in southern Australia is also increasing (Chauhan et al. 2006).
The evolving resistance to chemical controls such as chlorsulfuron and atrazine, and the push towards conservation tillage contributes to S. oleraceus' rise in importance (Adkins et al. 1997). These plants can also be alternative hosts, harbouring pests and diseases of crops.
A single S. oleraceus plant may produce up to 8 000 seeds which are capable of germinating all year round, particularly after rainfall.
Field tests in the subtropical grain region of south-east Queensland and Northern NSW showed few S. oleraceus seeds are capable of maintaining their viability past eight months if in the top two centimetres of soil. Seeds buried deeper are capable of germinating some 30 months later.
Weeds can act as alternative hosts, harbouring pests and diseases of crops.
In zero tillage systems, most seeds would remain in the top two centimetres of soil, therefore requiring control for at least eight months to avoid seed bank replenishment (Widderick et al. 2004).
CSIRO scientists are researching biological control as a possibility for managing sowthistles.
Specific aims of this project include:
a survey of pathogens associated with Sonchus species in Australia to identify potential biological control organisms
determining the impact in glasshouse and field trials of Miyagia pseudosphaeria and the eriophyid mite on the native species S. hydrophilus and Actites megalocarpa and compare this with the weedy S. oleraceus and S. asper
investigating the origins of M. pseudosphaeria by comparing the genetic diversity from Australia and overseas
identifying the biological control options that would be of use in Australia.
Sowthistle species S. arvensis, S. asper and S. oleraceus have been the target of biological control in Canada (Peschken 1984). Origins of S. oleraceus lie in Europe and preliminary surveys for biological control agents have been made in southern France (Scott & Jourdan 2005) to complement northern European surveys made for the Canadian study (Peschken 1984).
Before any biological control project can be implemented, it is advisable to determine what organisms are already present in Australia. Important for consideration in any biological control program, is whether sowthistle has any native relatives in Australia.
Sowthistles belong to the subtribe Sonchinae (Family: Asteraceae; Tribe: Lactuceae) and Australia has two native species within this subtribe. These include S. hydrophilus, and the closely related dune thistle, Actites megalocarpa.
A preliminary survey of pathogens and arthropods associated with Sonchus in Australia has found two widespread organisms with biological control potential:
The Cooperative Research Centres (CRC) for Australian Weed Management are collaborators on the sowthistle project.
Learn more about the Biological control of weeds.
Chauhan BS, Gill G, Preston C. 2006. Factors affecting seed germination of annual sowthistle (Sonchus oleraceus) in southern Australia. Weed Science. 54: 854-860.
Scott JK, Jourdan M. 2005. Biological control of Sonchus species (Sowthistles). Unpublished report.
Walker SR, Taylor IN, Milne G, Osten VA, Hoque Z, Farquharson RJ. 2005. A survey of management and economic impact of weeds in dryland cotton cropping systems of subtropical Australia. Australian Journal of Experimental Agriculture. 45: 79-91.
Widderick M, Walker S, Sindel B. 2004. Better management of Sonchus oleraceus L. (common sowthistle) based on the weed's ecology. In: Proceedings of the 14th Australian Weeds Conference. Weed Society of New South Wales. Pp. 535-537.
Widderick M, Sindel B, Walker S. 1999. Sonchus oleraceus (common sowthistle) in the northern cropping region of Australia. In: Bishop AC, Boersma M, Barnes CD. (eds). Proceedings of the 12th Australian Weeds Conference. Tasmanian Weed Society, Hobart. P.198.
Adkins SW, Wills D, Boersma M, Walker SR, Robinson G. 1997. Weeds resistant to chlorsulfuron and atrazine from the north-east grain region of Australia. Weed Research. 37: 343-349.
Peschken MP. 1984. Sonchus arvensis L., perennial sow-thistle, S. oleraceus L., annual sow-thistle, and S. asper (L.) Hill, spiny annual sow-thistle (Compositae). In: Kelleher JS, Hulme MA. (eds). Biological control programmes against insects and weeds in Canada 1969-80. Slough, UK. Commonwealth Agriculture Bureau. Pp. 205-209.