Crop protection - Growing concern over resistance


By Bernie Reppel

Herbicide resistance is an increasing challenge across Australia’s northern grain belt. It is not just resistance to the essential glyphosate, but resistances to herbicide groups A, B and C have also either been identified or are expected.

In central Queensland, summer weeds are mostly at risk, while a mix of summer and winter weeds are the worry in southern Queensland and northern NSW. Winter weeds are mostly at risk in central NSW.

Seven weeds are confirmed resistant in southern Queensland and seven in northern and central NSW. Central Queensland has no confirmed resistance but a number of weeds have been identified as having “moderate to high risk” of developing resistance.

The only constant across the region is the rating of common sowthistle and summer grasses as “at high risk” of developing resistance to group M herbicides.

In all parts of the northern region, the risk of resistance developing is greatest for the cropping systems using zero tillage and/or limited rotation between summer and winter crops.

According to Queensland Department of Primary Industries Toowoomba specialist, Dr Steve Walker, glyphosate resistance is the main concern. “Growers and advisers know what they can do about resistances to the other groups, but glyphosate underpins the continuing viability of conservation cropping in the north. So our aim is to ensure the maximum effective life of important herbicides.

“When growers have zero till systems with little rotation between summer and winter crops and they use more and more glyphosate, they are hitting the same weed spectrum all the time.”

Dr Walker leads the GRDC-supported project ‘risk assessment and preventive IWM (integrated weed management) strategies for herbicide resistance in the diverse farming systems in the northern region’.

The team has established 10 long-term, on-farm, field experiments across the region to test strategies to prevent at-risk weeds developing herbicide resistance under the main crop rotations.

“We are evaluating more cost-effective options for managing weeds in the long term, with the focus on running down the seed bank so paddocks face fewer weed problems in the future,” says Dr Walker.

Common weeds of the three cropping zones of thenorthern grainr egion that have developed herbicide resistance ( ), or are considered to have a moderate to high risk of developing resistance (  ) for the four main mode of action groups.

For more information:
Dr Steve Walker, 07 4639 8888,


Region North, South, West