Grain growers in Central Western NSW will be forced to reconsider their approach to wild radish control following the discovery of resistance among the Group I herbicide chemicals.
The resistance was confirmed late last week in wild radish populations near Nyngan by Trangie Agricultural Research Station research and development agronomist Greg Brooke.
Testing of survivor plants in the affected paddocks showed that 50 percent were resistant to the Group I chemical 2,4-D.
This is the first time wild radish resistance to Group I herbicides has been identified in in NSW and Mr Brooke is urging growers and agronomists to be vigilant over spray efficacy and if suspicious, submit samples for resistance testing.
“The resistant species were found on a farm where successive sprays of 2,4-D had failed to control wild radish over two seasons,” Mr Brooke said.
“Wild radish arrived on this particular property 27 years ago in floodwater and phenoxy herbicides have been used for a long time to control it.
“We know from the Western Australian experience that once you reach about 20 years of use of Group I chemicals in wild radish, resistance will begin to develop.
“Our message to growers and agronomists is if they have spray failures, they need to access seed testing.
“Samples of the survivor plants along with the grower or agronomist’s contact details can be sent to Trangie Agricultural Research Station and we will arrange to have them tested through the national crop protection program. All information will remain confidential.”
Representatives from the NSW Department of Primary Industries (NSW DPI) have been scouting crops across the state for the past two years for broadleaf weed survivors in species such as wild radish, sow thistle, fleabane and the mustard weed species.
Testing has been carried out under the Grains Research and Development (GRDC) funded crop protection program, Understanding and Management of Resistance to Group M,L and I herbicides.
The GRDC has also been encouraging growers to adopt advice from the WeedSmart program, an industry-led initiative to enhance on-farm practices and promote the long-term sustainability of herbicide use.
To date, NSW has only had limited cases of herbicide resistance in wild radish and in all cases the resistance has been in Group B chemicals.
Most herbicide resistance issues in NSW have occurred in grass weeds species, mainly within the Group A, B and M chemicals.
Wild radish is a notoriously difficult weed to control due to its extremely long seed bank life, preventing adequate control through herbicide application or tillage alone.
The discovery of Group I resistance heralds the need for changes in on-farm weed management practices and Mr Brooke said growers needed to rethink their approach to control or risk further resistance problems in phenoxy modes of action.
An effective weed management strategy should also include methods to target any survivors from weed treatment to ensure they do not reach seed set.
For technical information on a range of different tactics and details required to manage weeds effectively visit www.weedsmart.org.au.
Caption: Wild radish resistance to the Group I herbicide 2,4D.
Trangie Agricultural Research Station
0437 140 577
Senior Consultant, Cox Inall Communications
07 4927 0805
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