Common sowthistle field infestation (photo courtesy of Michael Widderick QDAF).

Common sowthistle (Sonchus oleraceus) is an increasingly important weed in Australia, especially in cropping systems. Predominant in the fallow period, it uses vital stored soil moisture during this period, acts as an alternate host for insects and is difficult to control. Development of resistance to herbicides is making populations increasingly difficult to manage in agricultural environments. Given the success of previous biological control programs against other weeds in the Asteraceae family (e.g. Onopordum and Cirsium thistles), there were promising prospects of establishing an effective program for the management of common sowthistle.

This research on common sowthistle was part of the projects ‘Biocontrol solutions for sustainable management of weed impacts to agricultural profitability’ (2016-2020) and ‘Underpinning agricultural productivity and biosecurity by weed biological control‘ (2019-2022), led by AgriFutures Australia (the trading name of the Rural Industries Research and Development Corporation (RIRDC)). These projects have been supported by funding from the Australian Government Department of Agriculture, Water and the Environment as part of its Rural R&D for Profit programme rounds 2 and 4, respectively. The Grains Research and Development Corporation (GRDC) and US Department of Agriculture are also acknowledged for their financial support.

Despite extensive surveying of the native range of sowthistle and preliminary testing from 2016 to 2020, no promising candidate agents for the biological control of sowthistle were identified and research has been discontinued.