GroundCover™ Supplement Issue: 137 November - December 2018 | Author: Dr Bhagirath Chauhan and Dr Sudheesh Manalil
Abundant seed production, seed dispersal through wind, small seed size and the ability to germinate under a range of conditions make common sowthistle a problem weed but it can be controlled using an integrated approach
Common sowthistle (Sonchus oleraceus) depletes precious stored soil water during summer fallows and can contaminate harvested grain with green material. The weed has become a dominant problem particularly in cotton and fallow systems of Queensland and New South Wales that rely on glyphosate as populations have become resistant to the herbicide.
Following reports of increased infestations of this weed in northern region cropping systems GRDC has invested in research at the University of Queensland since 2015 to better understand the biology of common sowthistle to help identify viable non-chemical options to integrate with herbicide-based weed management.
Common sowthistle has very low dormancy with fresh seeds of populations collected from Queensland readily germinating in the laboratory. Additionally, seeds can germinate at temperatures ranging from 5°C to 35°C. For both reasons, seeds can germinate straight away, provided that soil moisture is sufficient. Therefore, growers need a suite of management tactics that can be implemented throughout the year for effective control of common sowthistle.
Strategic tillage possible
Germination of common sowthistle seed has been shown to be greatest (80 to 90 per cent) when the seeds were placed on the soil surface in pot trials at Gatton, Queensland, but seedling emergence declined sharply with increasing soil depths. Less than 25 per cent emergence was observed from two-centimetre depth and no emergence from 6cm.
A field study at Gatton on common sowthistle seedbank persistence indicated substantial seed depletion within a six-month period and no viable seeds were found after 24 months (Table 1).
|TABLE 1 Seed burial studies showed no viable seeds of common sowthistle were found up to 10cm depth after 24 months of burial indicating a short-lived seedbank.|
| ||Seed survival (%)|
|Depth (cm)||6 months||18 months||24 months|
|SOURCE: Dr Bhagirath Chauhan|
The results of the burial depth and persistence studies indicate that strategic tillage could be used as a tool in integrated weed management to bury the seedbank of common sowthistle below the depth of emergence. Subsequent tillage operations would need to be kept shallow or avoided to ensure the seeds are not brought back to the soil surface.
In a wheat crop harvest weed seed control of common sowthistle may not be possible as it has been shown to flower within 85 days and a large proportion (greater than 95 per cent) of seeds can be dispersed by wind prior to wheat harvest. Therefore, there is a need to integrate herbicide use with crop competition, for example by using narrow row spacing, to reduce emergence of common sowthistle in the early crop phase.
A better understanding of the efficacy of herbicides in combination with other non-chemical methods will help us refine the management options to contain this weed.
Dr Bhagirath Chauhan, University of Queensland
07 5460 1541