When it comes to dealing with weeds in fencelines researcher Chris Preston understands growers want to battle the issue when ‘they’re not busy’ with the pressing task of farming.
Speaking at the Grains Research Development Corporation (GRDC) Update in Goondiwindi recently the researcher, warned that relying solely on knockdown herbicides, like glyphosate, to control weeds in fencelines and crop margins, risked creating resistance issues for the whole farm.
Dr Preston, who chairs the Glyphosate Sustainability Working Group, said growers had commonly used the broad-spectrum herbicide along fencelines, because it controlled both seedlings and larger plants, did not leach through the soil, and was easy and cheap to use.
“But, glyphosate is also the most important herbicide we have for fallow management, pre-crop seeding and inter-row weed management and its use in all of these places has resulted in the evolution of glyphosate resistant weeds,” Dr Preston said.
“Once these weeds occur in one location on the farm they can easily move to other locations.
“Fencelines and crop margins are particularly problematic, because due to the lack of competition in these locations glyphosate resistance weed survivors can set a lot of seed.”
However, he said there were several management options for growers to use for weed control in these areas and changing tactics would reduce the looming glyphosate resistance issue.
“The area around crops can be cultivated, slashed, rolled for hay, or grazed by stock to control the weeds,” Dr Preston said.
“But, I understand all these options can result in other problems: cultivation can leave the area prone to erosion and reduce trafficability; slashing and hay making takes extra time and grazing can be a challenge unless you already have livestock on farm.
“Increasing competition will also limit the impact of glyphosate resistant weeds, but does mean limiting the area left bare,” he said.
Dr Preston said other effective strategies included planting crops closer to fences, or removing fences and cropping over the area, as well as ensuring crop margins changed from year to year.
Yet the University of Adelaide-based expert said he also recognised that for many on-farm situations, herbicides would remain the preferred option for weed control in fencelines.
“But clearly, relying on glyphosate alone will be a risky option for resistance and for the Group B options available resistance has already occurred,” he said.
As part of a GRDC-funded research project he has investigated a range of chemical alternatives for weed control along fencelines in Queensland and New South Wales farming operations. Among the chemicals trialled was bromacil (Uragan).
“Uragan is a Group C herbicide with grass and broadleaf activity, is not overly mobile and belongs to a sub-group to which we don’t have resistance.
