RESISTANCE to succinate dehydrogenase inhibitor (SDHI, Group 7) in spot form of net blotch (SFNB) has been discovered in barley crops in the Western Australia grainbelt.
The fungicide resistance was found by the Centre for Crop and Disease Management (CCDM) in barley samples collected in the Cunderdin region, with the discovery being the first case of SDHI resistance in barley SFNB confirmed in Australia.
Researchers from CCDM confirmed the presence of SDHI resistance in a sample sent to them by local agronomist Dan Taylor after he became concerned about disease levels in a barley paddock.
A total of 124 samples from five paddocks within a 10 kilometre radius of Cunderdin were collected, in partnership with Mr Taylor and then analysed by CCDM researchers in the laboratory.
CCDM researcher Wesley Mair said genetic analysis of the SFNB pathogen isolated from the initial sample also showed multiple mutations in the target of the SDHI fungicides.
"That suggests resistance may have been developing over a significant period of time," Mr Mair said.
"Initial testing identified the presence of SFNB resistant to SDHIs, so we followed up with a more comprehensive ground survey from areas around the Cunderdin region.
"While the results confirmed the presence of low frequencies of SDHI resistance in three of the surveyed paddocks, more than 40 per cent of disease lesions tested positive for reduced sensitivity."
The barley samples were from a barley-on-barley rotation with fluxapyroxad (Group 7) used over consecutive years.
CCDM fungicide resistance expert Fran Lopez-Ruiz said researchers have run a monitoring program for SDHI resistance in WA since 2014, but this is the first time it has been detected in SFNB of barley.
"SFNB is a prevalent foliar fungal disease in Australian barley and the most widespread in WA, so being able to detect early signs of SDHI resistance is very important for the industry," Dr Lopez-Ruiz said.
"Knowledge is the greatest defence we have against fungicide resistance, and growers, agronomists and the wider grains industry are among our key informants.
"Finding where the problem exists, detecting it early so growers can respond and knowing which strategies are most effective and economical for managing fungicide resistance are crucial and form a major part of our research at CCDM."
CCDM director Mark Gibberd said the discovery was indicative of changing patterns in the significance of the net blotches to barley production in the Australian grains industry.
"Net blotches are a major limitation to the yield of barley in Australia and, while closely related, there are two main types - spot form net blotch (SFNB) and net form net blotch (NFNB)," professor Gibberd said.
"In WA we have seen a changing pattern in the distribution of impact of the two types due to an increasing area sown to barley, reliance on SFNB susceptible varieties and a considerable reduction in the rotation time for this crop in all rainfall areas.
"Importantly, efforts to enable the development of new crop varieties with high levels of disease resistance to the net blotches are advancing at the CCDM, however, fungicide control currently remains the primary crop protection mechanism to counteract disease impacts."
The latest SDHI resistance discovery is a timely reminder that growers need to be vigilant in monitoring for disease and implement a resistance management strategy that has an integrated approach.
Growers should avoid growing consecutive barley crops and instead look for suitable alternative break crops, while also choosing fungicide mixtures with different modes of action.
In the Cunderdin region, growers and agronomists should avoid using Group 7 fungicides and consider stubble management heading into next season, while in general Group 7 fungicides (seed dressing and foliar) should not be used more than once per season in any crop rotation.
The same Group 3 fungicide should not be applied twice in a row and to prevent indirect fungicide resistance selection, growers should avoid using Group 3 fungicides as a standalone product in barley for any disease.
Lastly it is critical that fungicides be used as early as possible after symptoms develop if conditions are highly conducive for disease development and never spray below label rates.
The discovery in Cunderdin follows the detection last year of cases of resistance to SDHIs in NFNB in Australia's southern growing region.
"We have already seen examples in South Australia of how selection pressure, due to limited crop and chemical rotation, has sped up the evolution of net blotch fungicide resistance and it appears to be the same drivers here," Dr Lopez-Ruiz said.
"Good integrated disease management plans for next season should now be a priority for growers in the Cunderdin region by limiting resistance spread through stubble management and protecting their seed with a formulation that does not contain a SDHI."
Growers and agronomists in WA who suspect SDHI resistance should contact the CCDM's fungicide resistance team at email@example.com or firstname.lastname@example.org