Background
What is the weed problem?
Common sowthistle is a widespread weed in Australia. It is a particular problem in the Western and Northern grain producing regions of Australia and in tillage systems in Northern Australia where it can be found growing throughout the year. It can dominate in fallows, where it uses stored soil moisture, and in the crop where it can reduce the crop yield and contaminate the harvested grain with green matter. Worryingly, there are now populations of common sowthistle that have been identified as resistant to routinely used herbicides, including Group B herbicides.
General morphological characteristics of common sowthistle. (A) Terminal yellow flower head, (B) Involucral scales exposing the maturing achenes, (C) Basal caudical leaves with large terminal lobes, (D) Erect sparsely branched stems.
How is the weed currently managed?
Unfortunately no single measure is capable of complete control of common sowthistle. It is recommended therefore to use several different control approaches in an integrated weed management framework to control the weed. These include the use of herbicides, strategies to reduce seed set and deplete the seed bank, growing competitive crops, strategic crop rotation and tillage, follow up/double-knock herbicide applications, and rotation of herbicide groups As the weed can germinate all year round, monitoring is required for its effective management.
For more details on the management of common sowthistle see:
Queensland Government Factsheet
Infestation of common sowthistle in fallow (photo courtesy of M. Widderick QDAF)
What can biocontrol offer to the weed’s management?
Biological control would offer an additional tool for the management of common sowthistle across the broader landscape, not just in agricultural situations. A successful classical biological control program for common sowthistle would reduce the need and/or frequency of other weed management tactics, especially during fallow. In a crop situation, it could potentially reduce yield losses by suppressing the competitive effects of the weed. By reducing the capability of the weed to reproduce, biological control agents could slow the spread of common sowthistle both within and outside of cropping areas and hence reduce the frequency of re-infestation.