WHILE glyphosate remains the most important herbicide in broadacre cropping operations, researchers have worrying news regarding rates of resistance.
Peter Boutsalis, Plant Science Consulting, said that while it had taken 20 years from the registration of glyphosate for the first case of confirmed resistance, in the past 10 years this number had increased exponentially.
"More effective use of glyphosate combined with effective weed management (IWM) strategies will be required to reduce further instances of resistance," Dr Boutsalis said at a recent Grains Research and Development Corporation (GRDC) update in Bendigo.
He said the tried and true 'double knock' strategy of hitting problem weeds with two separate modes of action to ensure any weed populations resistant to glyphosate were cleaned up by the other product, usually paraquat, was a sound option but pointed out other techniques could help retain glyphosate efficacy.
Particularly pertinently for summer and early autumn spraying, when weather can remain hot, Dr Boutsalis said farmers needed to be aware that efficacy could drop off markedly when spray went out in hot conditions.
In contrast, glyphosate applied in cool conditions immediately after a hot spell had much better control, indicating plans can rapidly recover from temperature stress.
Water quality is another big factor in spray efficacy.
Dr Boutsalis said ammonium sulfate was a useful tool to help soften water to ensure maximum solubility of the herbicide and to get better leaf penetration.
Targeting the optimum plant size was another trick Dr Boutsalis said could have a big impact on overall efficacy.
He said in pot trials good control was achieved in older ryegrass plants but at the one leaf or younger stage the plants rely on seed reserves for growth meaning little glyphosate moves towards the roots and effectiveness is impacted.
There may be more options on the cards to help keep glyphosate use down.
Chris Preston, a herbicide specialist with the University of Adelaide, said there had been a number of registration of new products made with Group G modes of action.
"These new registrations are expanding the way these type of herbicides can be used," Dr Preston said.
He said while care needs to be taken with pre-emergent applications of the products, especially in areas with lighter soils and where crop tolerance is not high there was good efficacy in a number of applications.
At present there is no resistance in any species in Australia to Group G products, however Dr Preston said there have been 13 reports globally.
Gregor Heard
Gregor Heard is ACM's national grains industry reporter, based in Horsham, Victoria. He has a wealth of knowledge surrounding the cropping sector through his 15 years in the role. Prior to that he was with the Fairfax network as a reporter with Stock & Land. Some of the major issues he has reported on during his time with the company include the deregulation of the export wheat market, the introduction of genetically modified crops and the fight to protect growers better from grain trader insolvencies. Still involved with the family farm he is passionate about rural Australia and its people and hopes to use his role to act as an advocate for those involved in the grain sector.
Gregor Heard is ACM's national grains industry reporter, based in Horsham, Victoria. He has a wealth of knowledge surrounding the cropping sector through his 15 years in the role. Prior to that he was with the Fairfax network as a reporter with Stock & Land. Some of the major issues he has reported on during his time with the company include the deregulation of the export wheat market, the introduction of genetically modified crops and the fight to protect growers better from grain trader insolvencies. Still involved with the family farm he is passionate about rural Australia and its people and hopes to use his role to act as an advocate for those involved in the grain sector.
