Group B herbicide resistance is an emerging issue for barley and brome grass across the WA grainbelt.
The first survey to assess the frequency of herbicide resistance in these weed species in WA’s grain producing areas was conducted by the GRDC-supported Australian Herbicide Resistance Initiative (AHRI) in 2010, with samples screened during 2012.
Of 466 randomly selected paddocks across WA, 91 had brome grass and 47 had barley grass.
Analysis of these samples has confirmed a small percentage of populations showing resistance to Group B herbicides, including both SUs and IMIs.
Barley grass sampling by AHRI senior researcher Mechelle Owen found that three of the 47 populations sampled had resistance to SU herbicides and two of these resistant populations also had cross resistance to the IMI herbicides.
For brome grass, 12 of the 91 samples showed resistance to SU herbicides. Only one population of brome grass showed resistance to the Group A herbicides, including both FOPs and DIMs.
Previous work conducted by AHRI found low level resistance to a range of Group B herbicides in brome grass in the northern WA Wheatbelt.
Currently, Group B resistance in barley grass appears to be more prevalent in central and southern areas.
For brome grass, northern areas are more likely to see resistance problems emerge.
Fortunately, no resistance was found to glyphosate or paraquat herbicides in both species and these knockdown herbicides provide good control options for brome and barley grass.
Group A and IMI herbicides generally provide good control for most populations of these weed species, although there are documented cases of resistance for these herbicides in WA and other areas of Australia.
This finding indicates that both brome and barley grass are becoming an increasing problem for grain producers in both low and high rainfall areas.
Emerging cases of herbicide resistance highlight the importance of adopting integrated weed management strategies, including crop competition, crop rotation, herbicide rotation and seed bank management - and to not solely rely on herbicides for weed control.
Full AHRI herbicide resistance survey results are now available on the AHRI website at: www.ahri.uwa.edu.au/surveys
Mechelle Owen, AHRI senior researcher
08 6488 1512
Melissa Williams, Senior Consultant, Cox Inall Communications
042 888 4414
AHRI Herbicide Resistance survey: www.ahri.uwa.edu.au/surveys
For more information about managing herbicide resistance:
Australian Herbicide Resistance Initiative: www.ahri.uwa.edu.au
Australian Glyphosate Sustainability Working Group: www.glyphosateresistance.org.au.
WeedSmart information hub: www.weedsmart.org.au
Ground Cover May/June supplement, Making Herbicides Last: www.grdc.com.au/GC104
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