THE WORRYING outbreak of loose smut in winter barley last year was not caused by resistance developing to the active ingredients in seed treatments, according to new research.

Studies by Bayer on barley seed stocks used in outbreak fields and confirmed by seed testing prior to the lab studies as infected, have shown no evidence of resistance.

Using 500 untreated and 500 seeds treated with Bayer’s fungicidal seed treatment Raxil Star (fluopyram + prothioconazole + tebuconazole) grown in the lab, it had leaves tested for the presence of ustilago nuda – the fungus that causes loose smut. The results showed a clear reduction of loose smut in the treated seeds, with efficacy of more than 90%, as expected in normal practice.

Ongoing field trials results should provide a conclusive assessment, but this it will provide reassurance to growers that last season’s outbreaks were probably not the result of resistance developing to single purpose seed treatments, pointed out Bayer’s Claire Matthewman.

The studies were commissioned after loose smut was detected in winter barley crops that had been treated with azole-based single purpose dressings (SPDs). Cases were identified across the UK and are independent of variety or SPD-choice and were not identified in any other crops.

The cause now appears likely to have been a perfect storm of weather during and following establishment, Mrs Matthewman suggested. “Higher temperatures accelerate growth of the loose smut fungus. In this case, it is thought that the fungus may have grown so rapidly that the seedling was unable to uptake the azole active quickly enough to control the disease.”

Her recommendation is to take a ‘back to basics’ approach, testing seed to make sure it is within the certified limits for loose smut and in good condition. This will help to ensure that the seed is viable for planting and suitable for a seed treatment.

“A specialist winter barley SPD, such as Raxil Star, is still the best approach to controlling seed- and soil-borne diseases in this crop, but if the warm autumns at establishment continue then testing the seed to ensure it is within certified limits will be vital to protect yields,” she argued.