Australia
August 14, 2013
Research aimed at slowing the evolution of herbicide resistance in weeds has delivered farmers some useful guidelines on effective herbicide combinations for spraying fencelines.
The results were generated from 2012 trials in Western Australia in areas with glyphosate and phenoxy resistance problems.
As part of a Grains Research and Development Corporation (GRDC) funded project coordinated by the University of Adelaide, two adviser ‘learning groups’ in Esperance and the northern agricultural region investigated 13 herbicide treatment alternatives to glyphosate for weed control in crop margin areas along fencelines, firebreaks and boundaries.
Department of Agriculture and Food WA (DAFWA) senior researcher Sally Peltzer, who coordinates the groups, said the trials were driven by information showing that many of the documented sites in Australia with glyphosate resistant annual ryegrass were along fencelines or in crop margin areas.
“Sole reliance on chemicals such as glyphosate for the control of weeds in these areas can fast track the evolution of herbicide resistance,” she said.
“If resistance develops in crop margin areas, it is likely to spread to paddocks.
“Directing adviser and farmer attention on the state of herbicide resistance along crop margin areas will prompt higher adoption of strategies to monitor and prevent its onset across whole properties.”
Dr Peltzer, who presented the trial results to this year’s GRDC and DAFWA-supported Agribusiness Crop Updates, said knockdown herbicides alone performed poorly in the trials due to the big size of weeds at the start of the trials, and led to later weed germinations.
“At both 2012 trial sites, in Esperance and Dalwallinu, the best control of annual ryegrass, wild radish, other grasses and broadleaf weeds was achieved with tank mixes of residual herbicides coupled with paraquat, or paraquat plus amitrole (Alliance®),” she said.
“The stand-out residual herbicides were simazine, hexazinone, bromacil and Trimac® (terbacil plus sulfometuron).
“Other successful residual herbicides that were tested need careful management as they are either highly soluble, presenting a high risk of leaching down the profile and moving away from the area of application, or can kill trees where their roots extend.”
Dr Peltzer said she would recommend a less soluble option for crop margin areas, such as simazine, which - when added with Alliance® - was highly effective and took into account a lower risk of resistance developing.
The northern group had good success with Arsenal® Xpress, but she said this was a glyphosate plus imazapry (a MOA Group B) product which was not a sustainable option for the longer term.
She recommended, although more expensive, a combination of a knockdown and a residual for fencelines.
Dr Peltzer said further fenceline trials in 2013 were investigating herbicide timing and application rates.
“Most WA farmers tend to spray their fencelines in August or September, but this year’s trials are investigating controlling weeds earlier at seeding time in April and May, possibly followed up by a spray in July,” she said.
“It is expected that better control of weeds will be achieved if they are controlled earlier in the season when they are smaller, particularly if herbicide resistance is developing in these areas.”
Dr Peltzer encouraged growers to use full label rates of herbicides, to reduce the risk of weeds developing resistance to them, and to adopt an integrated weed management strategy for fenceline, firebreak and crop margin areas.
“One strategy could include mowing or slashing, or cropping as close as possible to the area and then cutting a firebreak later in the season,” she said.
Information on managing resistance along fencelines and in crop margins is available from the GRDC Glyphosate Resistance Fact Sheet at www.grdc.com.au/GRDC_GlyphosateResistance
The GRDC Ground Cover supplement Making Herbicides Last aims to help growers make limited herbicides last as long as possible and can be downloaded at www.grdc.com.au/GCS104
The GRDC, with government, university and commercial partners, has also launched a website www.weedsmart.org.au – where growers can access the latest information on sustainable herbicide use in Australian agriculture.
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