Strategy shift as wild oats resistance becomes a reality - Elders Rural Services
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Strategy shift as wild oats resistance becomes a reality

The increased incidence of wild oats resistance to Group 1 (Group A) resistance means farmers and agronomists are looking at alternative options for control.

Group 1 chemistries have been widely used in broadacre cropping over many years. In more recent times their use has increased as generic options became available.

Corteva Agriscience ANZ Marketing Director Dan Dixon, said there was a lot of evidence that overuse of Group 1 herbicides had caused a marked increase in resistance.

“It is important for growers to identify resistance issues on their property and look at other alternatives for wild oats control,” he said.

“Corteva sponsored wild oat tests from New South Wales and Queensland in 2021 to help identify the extent of the problem.”

Group 1 herbicides fall into three sub-families. They are identified as the “Fops” (such as diclofop, clodinofop), the “Dims” (such as tralkoxydim, clethodim) and the “Dens” (pinoxaden (such as Axial)).

Mr Dixon said from2019 to 2021 Charles Sturt University tested 179 wild oat samples to a “fop” herbicide and 128 (71 per cent) were classed as either resistant or developing resistance to that herbicide.

“Unfortunately, we can assume that the “fop” herbicide sub-family is just not working to control significant weeds such as wild oats,” he said.

“In the “dim” sub-group, 7 per cent of wild oat samples were resistant. with Select, Factor and Achieve all of concern.

Mr Dixon said the results build on findings from previous years that Group 1 herbicides should not be relied upon to control weeds in broadacre crops in all phases of the rotation. The use of Select or Factor (Dims) in the pulse phase of the rotation remain a valuable strategy in a lot of areas.

“Last season there were many incidences of wild oats poking up through chickpea and wheat crops at harvest. This causes issues with an increased seed bank and a likely spread of herbicide resistance across paddocks and farms.”

He said growers with Group 1 herbicide issues do have some limited post-emergent options in the Group 2 sector including Sulfonyl Urea (SU), Imidazolinone (imi) and Triazolopyrimidine sufonamides (TPS) herbicides. These products vary in their performance on wild oats, crop selectivity and rotational flexibility.

“Fortunately, in the populations tested by Charles Sturt University TPS herbicides, and in particular Rexade® Arylex® active, remains a viable option for growers going forward. Out of the 160 samples tested over the three years only 1 per cent were found to be resistant.”

Rexade® Arylex® active is registered in wheat and triticale as a selective herbicide for post-emergent control of grass and broadleaf weeds.

It provides control of key grass weeds such as wild oats and brome grass and suppression of annual ryegrass, barley grass and silver grass.

In the broadleaf space, Rexade® Arylex® active has very good activity on a wide range of key weeds including bedstraw, climbing buckwheat, deadnettle, doublegee, fleabane, fumitory, Indian hedge mustard, prickly lettuce, sowthistle, wild radish and wireweed.

It will also control volunteer crops from the previous cropping phase such as canola, chickpea, faba bean, field pea, lentil, lupins, sub clover and vetch.

Mr Dixon said the excellent control over a wide spectrum of weed species meant Rexade® Arylex® active was the obvious choice when rotating away from the issues with Group 1 herbicides in wheat.

“This is a product which also works best in a tank mix with herbicides such as LVE MCPA to further enhance weed control. Unlike other grass herbicides, mixing Rexade with LVE does not cause any reduction in wild oat control.”

“It offers excellent flexibility with relatively low rainfall and time required for breakdown to rotate into the following winter crop or summer crops like sorghum, maize, sunflower or mungbeans,” he added.

“Most importantly, Rexade® Arylex® active is an alternative mode of action to the failing Group 1 chemistry and an excellent option for growers to control wild oats, along with their broadleaf weeds increasing yields and profitability from their crops.”

Article written by Corteva for Seasons magazine. 

Header image shows the excellent wild oats control from a tank mix of Rexade® Arylex® active, LVE and NIS (left) compared to a typical Group 1 based mix (right).

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