Simple tools slash weeds in eastern wheatbelt
Before the trial commenced at the Western Australian No-Tillage Farmers Association (WANTFA) Cunderdin research site in 2012, the number of Group-A-resistant annual ryegrass (Lolium rigidum) at the site averaged 1200 plants per square metre.
Using rotations, row spacing, nitrogen (N) tactics and weed control, researchers were able to eliminate 99.5 per cent of this population to average five to nine plants/m2 at the end of the trial in 2014.
Led by Department of Agriculture and Food, WA (DAFWA) weed scientist Dr Abul Hashem, the GRDC-funded trial was a collaboration between the Australian Centre for International Agricultural Research and Murdoch University.
It showed that practical management techniques can be used to effectively control resistant annual ryegrass in the eastern wheatbelt.
Dr Hashem says a rotation of wheat/lupins or lupins/wheat followed by Roundup Ready® (RR) canola and use of alternative herbicides with diverse modes of action were the keys to success.
In 2012 and 2013 (lupin plots following wheat), about 60 per cent of annual ryegrass was controlled with simazine at two litres per hectare and 80 per cent control was achieved with the use of dimethenamid (such as Outlook®) at 1L/ha.
Weed control in 2012 wheat plots was very poor. However, in the 2013 wheat plots (following lupins), there was about 60 per cent control of annual ryegrass using trifluralin at 2L/ha.
Use of pyroxasulfone (such as Sakura®) at 118 grams/ha achieved 68 per cent control in wheat in 2013, which equated to about 1t/ha of extra yield benefit.
Despite application of these alternative effective herbicides in 2012 and 2013, there was still an average annual ryegrass density of 70 to 140 plants/m2 in lupins and 115 to 126 plants/m2 in wheat in the 2013 plots.
It was the addition of RR canola in 2014, following wheat and lupins, that cleaned up 99 to 100 per cent of annual ryegrass using glyphosate – with only five to nine plants/m2 persisting by the flowering stage of that year’s crop.
Dr Hashem says the trial compared row spacings of 22 and 44 centimetres and found that any moisture conservation benefit from using wider rows at the Cunderdin site was offset by reduced crop establishment (by 20 to 25 per cent on average for all crop types) and weed-control failure.
“Wide rows also reduced wheat yields by almost 30 per cent, but lupin and RR canola yields were unaffected by going to wider rows,” he says.
The trial compared N treatments of 25kg N/ha and 50kg N/ha drilled in front of tynes as urea and 50kg N/ha of ammonium nitrate (Flexi N®) deep-banded below the crop at seeding.
Dr Hashem says that the use of Flexi N® reduced canola establishment in both 22 and 44cm row spacing plots compared with urea, but increased canola crop vigour by 15 per cent and grain yield by 12 per cent.
He says Flexi N® also increased annual ryegrass emergence (more in the 44cm plot than the 22cm plots) compared with urea.
DAFWA research scientist Mohammad Amjad presented the results from the Cunderdin trial at this year’s WANTFA, GRDC and DAFWA Regional Crop Update meeting.
He says it highlighted that there are definite rotation, nutrition and herbicide tactics that can be used to significantly reduce weed burdens in the eastern wheatbelt.
“Once weed numbers are cut to low levels, it is then vital that weeds are maintained at these low levels using a range of integrated weed management strategies,” he says.
Dr Abul Hashem, DAFWA
08 9690 2136
End of Ground Cover issue 117 western edition
Read the accompanying Ground Cover Supplement:
GRDC Project Code UWA00146, UA00149