Wheat yields improved by timely powdery mildew control
They have also advised growers to be aware of the disease susceptibility of their chosen wheat varieties, and warned that significant levels of wheat powdery mildew inoculum has been carried over on infested stubble, which could be multiplied by the presence of a green bridge.
While historically powdery mildew has not caused significant wheat yield losses in WA, in 2015 it was widespread and damaging on crops in the northern and central grainbelt and in the Esperance region.
In 2015, field trials led by the Department of Agriculture and Food (DAFWA) with funding from the Grains Research and Development Corporation (GRDC), investigated foliar fungicide strategies for managing the disease in wheat from stem extension onwards.
DAFWA plant pathologist Ciara Beard told the GRDC Grains Research Update, Perth, that a single foliar fungicide spray applied at a registered rate to a susceptible variety significantly improved yields in four out of six trials across the grainbelt.
“The average yield response across all trials to a single fungicide spray was 8 per cent,” she said.
“However, yield responses and positive economic benefits from fungicide application are never guaranteed.”
Ms Beard said the best timing was before the disease became severe and before flag leaves and particularly heads were infected.
“Timing of fungicide application – as soon as possible after the disease was observed moving up the canopy – was more important than product choice,” she said.
“In cases where the onset of the disease occurred later in the season, the best timing was once all leaves had emerged, which provided maximum protection for the plant canopy.
“Fungicide sprays applied following head emergence were too late to provide effective head protection and were not economic.
“Researchers believe that a second, follow-up fungicide application could be warranted in some seasons if the weather outlook is conducive to disease persistence, but this was not the case in 2015 due to the hot dry spring.”
Ms Beard said that selection of wheat varieties with resistance levels better than ‘moderately susceptible’ would significantly reduce the risk of severe wheat powdery mildew infection.
She said there was an increased risk of powdery mildew for early sown or short season varieties where the upper canopy and heads were exposed to disease in favourable environments.
“Early sown, susceptible varieties should be monitored closely this season to avoid significant damage occurring before management is instigated,” Ms Beard said.
Researchers from the Centre for Crop and Disease Management (CCDM), which is co-funded by Curtin University and the GRDC, have so far been able to rule out fungicide resistance in wheat powdery mildew in WA, at least with respect to currently known resistance mechanisms.
But they have recently observed the first signs of mutations – in wheat powdery mildew samples from New South Wales and Tasmania – which could lead to fungicide resistance issues in the disease in Australia.
To reduce the risk of the development of fungicide resistance growers should:
- Where possible, use registered fungicide mixtures that contain different modes of action; rotate fungicide active ingredients; use recommended fungicide label rates; and avoid using more than two sprays of any product per season
- Control the disease as early as practicable and before it becomes severe; and spray fungicides when disease becomes evident in a crop, particularly if weather conditions are conducive to disease development
There are no in-furrow or seed dressing fungicides registered for powdery mildew control in wheat, but a list of registered foliar fungicides is available on the DAFWA website by following this link and searching ‘cereal foliar fungicides’.
Information about wheat powdery mildew is also available on the CCDM website by following this link. GRDC Grains Research Update papers about wheat powdery mildew are available by following this link.
Ciara Beard, DAFWA
08 9956 8504
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code DAW00229, CUR00016