GRDC-sponsored PhD student Mike Ashworth, at the Australian Herbicide Resistance Initiative, has uncovered glyphosate resistance in wild radish.
Australian Herbicide Resistance Initiative (AHRI) researchers in Western Australia have detected the nation’s first glyphosate-resistant wild radish (Raphanus raphanistrum
L.), further highlighting the importance of diverse control strategies and eliminating weed seed-set.
Three glyphosate-resistant populations were recently identified by GRDC-sponsored PhD scholar Michael Ashworth, who is based at AHRI in Perth.
Two field populations of wild radish were sampled following ineffective control in glyphosate-treated fallow. They were screened at AHRI and were confirmed to have moderate levels of glyphosate resistance.
The two populations exhibited high rates of survival (63 and 86 per cent respectively) following glyphosate application onto two-leaf plants at the label rate to control wild radish in Australia (540 grams per hectare).
At a higher rate, of 810g/ha, applied to two-leaf wild radish, more than half of both populations still survived and flowered.
Mr Ashworth says that both populations also exhibited a multiple resistance profile to label rates of the Group B acetolactate synthase-inhibiting herbicides Glean® (chlorsulfuron), Oust® (sulfometuron-methyl), Eclipse® (metosulam) and Raptor® (imazamox); the Group F phytoene desaturase step-inhibitor diflufenican; and the Group I synthetic auxin 2,4-D amine.
- Over-reliance on glyphosate for weed control has increased globally in recent years
- Resistance to glyphosate has now evolved in 25 weed species around the world
- Australia has 411 documented glyphosate-resistant populations of annual ryegrass, 95 of awnless barnyard grass, 57 of fleabane, 11 of windmill grass, three of liverseed grass and three of great brome grass
- Wild radish now joins the list in Western Australia
“The presence of such a diverse multi-resistance profile highlights the continual difficulties of controlling wild radish solely with herbicides,” he says.
“Although the evolution of glyphosate resistance in wild radish will come as no surprise to growers and agronomists, the good news is that the resistance is currently rare,” Mr Ashworth says.
Populations of wild radish screened at the Australian Herbicide Resistance Initiative in WA showing three known susceptible (left) and one glyphosate-resistant population (right) when exposed to 750 grams per hectare of glyphosate (which is above the recommended rate for wild radish control in Australia).
“Finding these populations early means growers have the opportunity to adopt proactive control strategies.”
Mr Ashworth says knowledge is power and growers and agronomists should not over-rely on glyphosate.
He says the aim should be to control weed survivors, eliminate weed seed-set and maximise diversity of control strategies.
“We have non-herbicide tools of crop competition and harvest weed-seed control to greatly reduce weed numbers,” he says.
“By maximising diversity and eliminating seed-set, Australia can aim to avoid the rapid rise of glyphosate-resistant weeds that has occurred in the US through over-reliance on glyphosate.”
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Australian Herbicide Resistance Initiative,
Australian Glyphosate Sustainability Working Group,
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