Using glyphosate on fencelines is a major cause of glyphosate resistance in weeds, and growers can reduce the risks by adjusting their practices.
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This is the message in a new Grains Research and Development Corporation (GRDC) Glyphosate Resistance Fact Sheet about managing resistance on fencelines and crop margins.
GRDC crop protection manager Rohan Rainbow said the latest information from the Australian Glyphosate Sustainability Working Group (AGSWG) showed fencelines and paddock margins represented a large number of situations where glyphosate-resistant annual ryegrass occurred.
“There are currently 119 sites with documented glyphosate-resistant annual ryegrass in Australia, and of these, 33 are located along fencelines or crop margins,” he said.
“Many growers prefer to use glyphosate alone for weed control on fencelines due to its ease of use and low cost.
“However, using glyphosate as the only weed control practice along fencelines will result in glyphosate-resistant weeds occurring, which can easily spread to cropped areas.”
Dr Rainbow said strategies growers could use to reduce the risk of glyphosate-resistant weeds occurring along fencelines or paddock margins included:
- Removing fences which were no longer useful and cropping the area;
- Mowing or slashing weeds along the fenceline, with herbicide used only in the area immediately under the wire;
Dr Rainbow said GRDC-supported research conducted by the University of Adelaide in collaboration with the Hart Fieldsite Group was helping to identify effective herbicides strategies for paddock boundaries and fencelines.
“Trials showed that while glyphosate applied even at high rates provided little control, some mixtures with glyphosate were more effective,” he said.
“Mixtures with Spray.Seed (Group L) or Alliance (Groups L and Q) were effective as were two applications of Spray.Seed® 14 days apart.”
Dr Rainbow said growers needed to ensure residual herbicides were not used where they might damage desirable plants such as trees.
The GRDC Glyphosate Resistance Fact Sheet is available at www.grdc.com.au/GRDC_GlyphosateResistance or www.grdc.com.au/weedlinks.
It is also included with the November/December edition of the GRDC magazine Ground Cover.
