Farm Table says:
What is the problem?
A three-year trial in South Australia shows early sowing has merit in medium and low-rainfall areas as a tactic to suppress late-germinating grass weeds.
What did the research involve?
In 2014 at Hart, the researchers sowed LongReach Scout wheat on 4 May and 2 June. The pre-emergent herbicide treatments used at each time of sowing were nil, Sakura® and Sakura® mixed with Avadex® Xtra (Table 1). There was an additional knockdown herbicide application between the two sowing times.
The trial was repeated in 2015 using nil pre-emergent herbicides, Boxer Gold®, Sakura® and Sakura® mixed with Avadex® Xtra incorporated by sowing wheat on 30 April and 27 May (Table 2). Again, there was an additional knockdown application of herbicide between the two sowing times.
In 2016, the trial was moved to Roseworthy where the ryegrass population was higher. The early sowing treatment was established on 6 May, while the delayed sowing treatment was sown on 1 June.
What were the key findings?
- the behaviour of annual ryegrass is changing, with greater levels of dormancy and later germination occurring under selection pressure from continuous cropping
- delayed sowing has become a less useful option for control of grass weeds in continuously cropped paddocks
- crop competition is an excellent partner with pre-emergent herbicides for the control of grass weeds
- trials showed sowing on time to maximise wheat competition with annual ryegrass helps reduce weed seed-set and increases crop yield
Dr Chris Preston, from the University of Adelaide, says early sowing, when soil temperatures are warmer, results in more rapid wheat growth and faster canopy closure. He says this provides an opportunity to increase the amount of competition against weeds without having to significantly change other aspects of the farming system.