PLANT scientists are warning farmers resistance to herbicides, such as glyphosate, is growing “very quickly”.

New herbicide resistant weed populations are regularly being discovered, including “thousands of new populations” of glyphosate-resistant ryregrass.

And a previously low-key weed, winter grass, has also been shown to be challenging the “herbicide resistance crown” held by annual ryegrass, with glyphosate-resistant populations being confirmed in Victoria.

There are now at least 20 populations of winter grass exhibiting resistance to simazine (group C), propyzamide (group D), group B and group Z herbicides.

Another population is resistant to five herbicide modes of action.

“While winter grass might look like a soft plant, it has shown it is a force to be reckoned with,” according to Dr Peter Boutsalis, from Plant Science Consulting and the University of Adelaide.

He said this weed was a warning that any plant could develop herbicide resistance.

While winter grass is not a problem in Australian agriculture, only on turf and sports fields, it was “a problem in northern Europe”, he said.

“Grain growers should remember that present day problem weeds fleabane and sow thistle were not on the radar 20 years ago,” he said.

New problem weeds like milk thistle and feathertop grass were also showing herbicide resistance and moving south from Queensland and NSW.

Dr Boutsalis said 20 per cent of plants he tested for farmers, through his private company Plant Science Consulting, showed resistance.

“Farmers are terrified of glyphosate resistance as it is such a useful product,” he said.

He advised farmers to only use “high quality glyphosate products” because these enabled the chemical to dissolve and be absorbed properly by the plant, increasing effectiveness.

“Farmers should then monitor plants that survive (the herbicide application) and test to see if they are resistant or not and; ensure they do not let the survivors set seed.”

There are now about 300 products containing this chemical on the market.