Many populations of common sowthistle across the northern region can be effectively controlled with glyphosate when treated early and at robust label rates.
Photo: Annie van der Meulen, DAF
A Grains Research and Development Corporation (GRDC) funded survey into glyphosate resistance in common sowthistle has found that 20 per cent of the sampled paddocks contain common sowthistle that is not susceptible to glyphosate at label rates.
However, Annie van der Meulen, a weeds scientist with Queensland’s Department of Agriculture and Fisheries has indicated that many populations of common sowthistle across the region can be effectively controlled with glyphosate when treated early and at robust label rates.
Speaking at a GRDC Grains Research Update in Goondiwindi earlier this year, Dr van der Meulen urged northern region growers to adopt an integrated approach to ensure the key herbicide, glyphosate, remains effective for common sowthistle control.
The Toowoomba-based researcher is part of a team, led by Michael Widderick, which has been benchmarking the level of glyphosate resistant sowthistle across the northern region and identifying ‘hot spots’.
The work started after Australia’s first cases of glyphosate-resistant sowthistle populations were found in north-west New South Wales in February 2014, confirmed by Tony Cook and the team at NSW Department of Primary Industries, Tamworth Agricultural Institute.
To date, 170 sowthistle seed samples have been received as part of the survey with approximately 20 per cent of tested samples showing resistance. In one seed sample, from a fallow paddock near Gunnedah, 93 per cent of plants survived a glyphosate application at the recommended rate.
Dr van der Meulen urges growers to incorporate a range of methods for weed control, including use of non-chemical and agronomic approaches, from rotations to crop competition to herbicides with different modes of action and potentially strategic tillage.
“Anyone with sowthistle should use integrated weed management to make sure glyphosate remains a viable choice for them in the future,” she said.
Dr van der Meulen also recommends growers test for herbicide resistance.
“Early detection is useful because if there is glyphosate-resistant sowthistle on a property, growers can target and hopefully eliminate the resistant populations, before the problem gets out of control.”
Tips for sowthistle management include:
- Know what herbicides will work. Glyphosate resistance is present in the northern region and Group B resistance is reportedly widespread.
- Aim for 100 per cent elimination of seed set, including roadsides and fencelines.
- Maximise crop competition. In paddocks where common sowthistle is a particular and persistent issue, competitive crop species such as barley at narrow row spacings (e.g. 25cm) can help to suppress the weed. Avoid growing chickpeas in these paddocks, as this crop is poorly competitive with common sowthistle and has high potential for sowthistle ‘blow outs’.
- If relying on knockdowns in fallow, treat sowthistle when plants are small and double knock with another mode of action to control survivors.
- Apply residuals early in fallow. When using Flame® to control summer grasses, remember to partner it with a herbicide that is effective for control of common sowthistle (i.e. check the label).
- Test weeds for herbicide resistance, rather than relying on spray failure as an indicator. Commercial resistance testing centres will screen weed samples for herbicide resistance, to help pin down which options will (and won’t) work. Tests range from $125–$175 for a single herbicide and $75–$95 for each additional chemical tested. For details on resistance testing options, contact the following herbicide resistance testing centres - Charles Sturt University, contact: John Broster, 0427 296 641, email or Plant Science Consulting, contact: Peter Boutsalis, 0400 664 460, email.
Annie van der Meulen, DAF research scientist
07 4639 8847
Sarah Jeffrey, Senior Consultant Cox Inall Communications
0418 152 859
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