Understanding sowthistle biology aids management

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Photo of Dr Bhagirath Chauhan
Dr Bhagirath Chauhan inspecting a mungbean crop. PHOTO: University of Queensland

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

KEY POINTS

  • Management tactics need to be used throughout the year as common sowthistle can germinate all year round
  • Strategic tillage can be used to manage sowthistle as germination decreases with seed burial depth
  • Increased crop competition, together with herbicide use, may reduce infestations of common sowthistle

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.

Year-round 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 months18 months24 months
Soil surface1100
23560
1035130
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.

Competition

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.

More information

Dr Bhagirath Chauhan, University of Queensland
07 5460 1541
b.chauhan@uq.edu.au