Molecular data collected by Curtin University fungal pathologist, Professor Richard Oliver, has backed recent reports that barley powdery mildew disease and fungicide resistance is rife throughout Western Australia.
Baudin barley, the most common WA barley cultivar is the most affected. A large portion of the WA Wheatbelt region is severely affected by powdery mildew disease.
Professor Oliver said he had received reports from the Esperance region, the Great Southern, Corrigin and as far north as Jurien Bay.
“We have molecular data that backs up these reports. It appears that the entire WA pathogen population has developed resistance to the old triazoles (fungicides) but retains sensitivity to the newer products,” Professor Oliver said.
“Growers are reporting that crops sprayed with foliar (leaf) fungicides, containing tebuconazole, flutriafol, propiconazole and triadimefon are giving unsatisfactory control of the disease, whereas products such as [Prosaro], [Opus], [Opera] and [Amistar Xtra] are performing reasonably well.”
Professor Oliver said it was early in the season and growers still had a chance to protect their crops from the disease.
“The advice has to balance the efficacy of fungicides as a protectant and as an eradicant, versus the risk of further development of resistance,” he said.
“All the evidence suggests that spraying an old triazole will have no impact on the disease and may even increase the chance of resistance development to newer fungicides.”
Professor Oliver said the four registered products; [Prosaro], [Opus], [Opera] and [Amistar Xtra] were useful as a protectant but had lower efficacy as an eradicant.
“Growers shouldn’t be looking to them to clean up infected crops, however all four products should give useful protectant activity,” he said.
“With very large pathogen populations already present, the risk of resistance development to these four products will be higher than before.
“The fungicide Epoxiconazole, found in [Opus], has been used for a long period in Europe without a major decline in efficacy, albeit in situations in which most pathogens are well under control.
“Mixtures are reported to delay the development of resistance so the other three products are also likely to maintain usefulness for this season at least. However, growers should be vigilant for cases of failure of these fungicides and report them to us.”
Professor Oliver said fungicides should be used at the label rates in these circumstances and growers should avoid excess nitrogen as mildew grows best on overfed crops.
“Several other types of fungicides with proven activity against mildew are available but not registered for use on cereals. Registration of these products would give growers more options,” he said.
“We also urge growers and breeders to replace susceptible cultivars with ones that have one of the many known disease resistance genes.”
Professor Oliver’s research is funded by the Grains Research & Development Corporation.
Professor Richard Oliver, Department of Agriculture and Environment, Curtin University
Tel: 08 9266 7872, Mob: 0414 305 999, Email: firstname.lastname@example.org
Andrea Barnard, Public Relations, Curtin University
Tel: 08 9266 4241, Email: email@example.com