Fungicides no match for mildew

Almost 100 per cent of barley powdery mildew tested in WA during the past three years has been found to be resistant to common fungicides.

Richard Oliver, director of the Australian Research Centre for Necrotrophic Fungal Pathogens (ARCNFP), has warned growers, breeders and chemical companies to change their ways or face potential resistance issues.

Professor Oliver, who is also Grains Research and Development Corporation (GRDC) western panel deputy chairman, said growers planning their 2011 barley crop should take note and carefully consider which varieties to plant.

“Barley powdery mildew costs growers in WA around $39 million a year in lost yield, particularly in the medium to high rainfall zones, which experience high humidity, ” he said.

“The fungus has abundant wind-borne spores, so all you need is the right conditions to be affected.

“Unfortunately, most of the malt barley and many feed grade varieties available are susceptible, which has created a lot of pressure in disease-prone areas.

“Many growers have used fungicides with the same mode of action several times a year, including seed treatments — a perfect recipe for the situation we’re now facing.”

Using genetic testing, Professor Oliver’s ARCNFP team found that mutations in barley powdery mildew collected over the past three years had made them resistant to fungicides, including tebuconazole and propiconazole, the active ingredients in Folicur and Tilt, respectively.

Triadimefon has also been compromised, while there was suspicion over fluquinconazole (in Jockey) as well.

Professor Oliver said growers in mildew-prone areas should avoid susceptible varieties, using the varieties guide put out every year to review their options.

It was also critical to eliminate barley volunteers prior to sowing to reduce the early disease pressure.

Growers should also avoid using compromised fungicides in favour of newer triazole fungicides and fungicides with alternative modes of action. These include Amistar Xtra (a mixture of triazole and azoxystrobin), Prosaro (including prothioconazole) and Opus (epoxiconazole).

Professor Oliver said 2010 had been a tough year for barley and its diseases.

“Chances are only the toughest — and likely resistant — strains of the fungus have survived, ” he said.

“We can deal with the issue by changing fungicide resistance management practices and longer term looking for new disease resistant varieties, not just for barley and powdery mildew but right across the grains industry.”

Professor Oliver will present the results of the GRDC-supported work at next month’s Crop Updates.