FOLLOWING the lifting of the state's moratorium on genetically-modified crops last year, SA croppers can grow glyphosate-resistant canola this season, but there are factors to consider, according to respected WA farm consultant Geoff Fosbery.
Mr Fosbery was a guest speaker at the recent GRDC Grains Research Update in Adelaide, where he talked about the lessons learned in WA since adoption in 2010.
"Prior to then, we had a lot of resistance to Group Bs, plus growing resistance clethodim and trifluralin - we were light on for tools to manage annual ryegrass," he said.
Mr Fosbery said GM canola had largely been adopted in WA's central and northern 325-millimetre rainfall regions, where there was a long history of intensive pulse or lupin-cereal rotations, with some canola "thrown in".
"In SA, this is like the South East. But that's also where clethodim resistance is starting to take off, trifluralin is growing and there is about 27 per cent resistance to glyphosate," he said.
Mr Fosbery stressed growers needed to "protect" GM varieties by introducing another chemistry in the rotation.
"Initially WA growers didn't want to use another chemistry at $20 a hectare to $25/ha to support glyphosate - but that thinking has changed," he said.
"Today at least 90pc of RoundUp Ready canola crops utilise another chemistry to minimise the selection pressure on glyphosate."
Mr Fosbery said before GM canola arrived, clethodim resistance rates were climbing in WA, but had since "plateaued".
"Trifluralin and glyphosate have also stayed relatively flat, with less than 30pc and 10pc, respectively, of the populations showing signs of resistance," he said.
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He said GM canola would also be suitable in the higher rainfall areas of the Mid North, Yorke Peninsula and lower Eyre Peninsula, while in lower rainfall areas, the technology may be used more "opportunistically".
"Interestingly, in WA around Merredin - 300mm annual rainfall country - canola (a combination of TT and RR depending on problem weeds) has been the most profitable crop the past five years," he said.
"But they only grow it when conditions are right to get the canola out of the ground in late March/April.
"If there's no summer rain, no establishment until May, they'll avoid it - so they keep some paddocks flexible.
Mr Fosbery also went into the economics of growing GM canola compared with open pollinated TT varieties.
"The price spread has ranged from about $120 a tonne difference in 2019 because of China to about zero difference a month ago," he said.
"There can be large differences, but on average GM canola is more like $38/t less."
Mr Fosbery said when it came to profitability, there needed to be a 200 kilogram to 300kg yield differential to warrant growing GM canola relative to OP TT canola.
"In above 1.5t/ha yield areas, that's often easily achieved, but in areas below 1.5t/ha yield, it's not as easy - one of the reasons why the adoption of RR is relatively little in lower rainfall regions of WA," he said.
"But when the technology is needed for weed control, that's different.
"Hybrid TT and Clearfield canolas, as long as you are getting decent weed control between those two, the yield differential needs to be 50-100kg to warrant the cost differential."
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