Resistant plants in the background and susceptible in the foreground. All pots were treated with the same rate of glyphosate.

Since the discovery of the world’s first case of glyphosate resistance in barnyard grass, the need to find effective and alternative control options has increased and the search has delivered hope.

The glyphosate-resistant plants were found last summer in a paddock with a long history of winter cropping and summer fallow weed control based solely on glyphosate, with 15 to 20 applications over a five year period.

Yet, despite repeated warnings of the threat of glyphosate resistance developing in several important species, most farmers continue to rely on this method to control weeds in fallow.

NSW Department of Primary Industries (DPI) is investigating alternative treatments for barnyard grass as part of a Grains Research and Development Corporation (GRDC)-funded herbicide resistance management project for the northern grains region.

Technical officer with the DPI’s weeds research and demonstration unit at Tamworth, Tony Cook, said the results from six experiments were encouraging.

"Some of these alternative options are highly effective and can be used to prevent or control glyphosate resistant populations," he said.

"Useful options include the preemergence application of atrazine or Dual, the post-emergence use of Sprayseed or paraquat (as a part of the double-knock technique) and selective grass herbicides Verdict and Fusilade."

Barnyard grass is a highly competitive weed of summer crops and fallows in NSW and Queensland, with each plant producing up to 42,000 seeds.

Overseas growers with resistant barnyard grass are left with few options, as there is already resistance to herbicide mode-of-action groups A, B and C.

Glyphosate resistance is obvious here.

Back left, glyphosate has failed, front right shows the results from the use of an alternative herbicide.

One population in northern NSW is resistant to atrazine - group C - already, which means early action is required by Australian farmers to prevent a major resistance problem.

"This season, due to frequent rainfall, many flushes of barnyard grass are occurring which require multiple control applications," Mr Cook said.

"No doubt there will be many applications of glyphosate this season and this will result in more cases of glyphosate resistance.

"Herbicide-resistant weeds cannot persist or increase in number if they do not set seed, so growers must stop seed set.

"Paddock inspections are essential a week or two after spraying to see if there are any suspect resistant patches.

"If you suspect that you have any glyphosate resistance plants, call your local district agronomist for advice."

NSW DPI plans to conduct a longterm field trial to determine how best to reduce barnyard grass populations over time.

Combinations of crop rotation, best herbicide practice and cultural control will be used to form an optimal integrated program.

The GRDC-funded herbicide resistance management project for the northern grains region is a joint initiative of NSW DPI and Queensland DPI and Fisheries.

Contact Andrew Storrie or Tony Cook, Tamworth, (02) 6763 1100.