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How to control weeds under dry seeding systems 13 May 2013

Herbicide selection and timing of application can dramatically influence the performance of crops grown under a dry-seeding system and the weed pressure they encounter. 

Research from the WA No Till Farmers Association (WANTFA) has revealed that crop competition with early seeding, in combination with a good pre-emergent, give the best weed control in dry seeding systems. 

According to a new fact sheet detailing results and recommendations from the research, most pre-emergent herbicides give adequate annual ryegrass control under dry seeding, except for Trifluralin which recorded variable results in the projects field trials. 

“Dry seeding is increasing in popularity in no-till farming systems as it maximises water use and offers a yield advantage when sowing early,” WANTFA lead researcher Dr David Minkey said. 

“However, dry seeding carries risks for weed control due to the inability to use a knockdown herbicide, as well as the risk of developing resistance due to the heavy reliance on a pre-emergent herbicides. 

“Overcoming these barriers of weed management to maximise the benefits of a good no tillage system could lead to large productivity gains in the crop growing areas of Western Australia.” 

Dr Minkey’s research project was conducted as part of the National Weeds Program, managed by the Rural Industries Research and Development Corporation (RIRDC). It provided $12.4 million of Commonwealth funds to support more than 50 weeds research projects, including 11 projects which dealt directly with herbicide resistance issues. 

Support was also provided by the National Adaptation and Mitigation Initiative (NAMI) through the Department of Agriculture and Food Western Australia (DAFWA), the Grains Research and Development Corporation (GRDC) and the Australian Government's Climate Change Research Program. 

The project objectives were to give growers confidence and best practice weed management options for the practice of ‘dry seeding’ and residue retention by: 

  • Demonstrating the benefits of weed management prior to dry seeding. 
  • Improving the efficacy of pre-emergent and glyphosate (in a glyphosate-tolerant crop) herbicides under dry seeding, high stubble retention systems. 
  • Demonstrating the effect of water rates and droplet sizes on the efficacy of pre-emergent herbicides and glyphosate (in a roundup ready crop) under varying stubble loads. 
  • Demonstrating, through the use of computer modelling, the long-term economic and weed seed bank benefits of various integrated weed management practices under a dry seeding stubble retention farming system. 

“Our aim was to identify weed management practices that would enable growers to dry seed and continue to retain stubble and the benefits of no-till farming,” Dr Minkey said. 

Following field trials set up in Esperance, Mingenew, Cunderdin, and Wickepin, the research team found that yield increases could be achieved under dry seeding regimes if weeds are adequately controlled. 

“Weed seed set control at the preceding harvest, through tools such as the Harrington Seed Destructor, was shown not to be a ‘silver bullet’ in all seasons and must be carefully managed to collect as much weed seed as possible,” Dr Minkey said. 

“Under dry seeding treatments Boxer Gold® was the best treatment for early germinations of annual ryegrass but it failed to control subsequent germinations. 

“Comparatively, Sakura® had an overall better control in these conditions for early and late germinations – even when compared to delayed seeding with a knockdown.” 

Dr Minkey noted that when seeding was delayed, all pre-emergent herbicides performed better than the untreated control. 

Results of the dry seeding research have now been incorporated into the Australian Herbicide Resistance Initiative (AHRI) weed management model “RIM”. 

A fact sheet on the dry seeding research project and recommendations for growers is available from WANTFA, www.wantfa.com.au.