Winter grass: the cold, hard truth on herbicide resistance

A previously low-key weed, winter grass (Poa annua) is challenging the herbicide resistance crown held by annual ryegrass, with glyphosate-resistant populations being confirmed in Victoria.

Perhaps considered as being more like Clark Kent than Superman, herbicide resistance testing has shown otherwise with 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 the five herbicide modes of action B, C, D, M and Z.

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

“The levels and extent of resistance have surprised me, and while all the resistant populations have developed on golf courses, it is a warning that any weed can develop resistance,” Dr Boutsalis, who reports to the Australian Glyphosate Sustainability Working Group (AGSWG), said.

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