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Stubble samples urgently wanted to map fungicide resistance

Researchers are calling on growers and advisors to urgently send them samples of stubble infected with wheat powdery mildew (WPM), so they can grasp the extent of fungicide resistance across Australia.

The call comes after the Fungicide Resistance Group at the Centre for Crop and Disease Management (CCDM), a national research centre co-supported by Curtin University and the Grains Research and Development Corporation (GRDC), recently discovered resistance to strobilurin fungicides in WPM from 2016 crop samples from Victoria and Tasmania.

Dr Fran Lopez-Ruiz, leader of the Fungicide Resistance Group at CCDM, said the situation was quite fragile at the moment, as there were only two modes of action registered for WPM control – DMI (group 3) and strobilurins (group 11, QoI) fungicides which were already sold in mixtures with a DMI, such as azoxystrobin and epoxiconazole.

“And with one of those modes of action – QoI fungicides – compromised in some regions of Australia, growers will now look to the other mode of action – DMIs,” he said.

“This does raise concerns for an increased use of DMIs which in turn would put even more pressure on a group of fungicides that already have a considerable risk for resistance development. This is why integrated disease management strategies are essential.”

Dr Lopez-Ruiz said samples of infected wheat powdery mildew stubble will help his team put together a map of where resistance to strobilurin has occurred, and communicate targeted fungicide resistance management strategies to those areas.

“These samples will help us get an idea if it really is only in a few areas in Victoria and Tasmania, or a widespread issue for all grain growing regions – currently, we don’t know,” Dr Lopez-Ruiz said.

“We would also like to let growers know if fungicide resistance is near their properties, so they can be proactive and select the best fungicides to control wheat powdery mildew which will help save them time and money.”

For the coming season, Dr Lopez-Ruiz recommends only one QoI spray per year and if additional sprays are needed, use a DMI formulations that was not in the previous fungicide application, even if that DMI was in a DMI and QoI mixture. For a full list of registered fungicide formulations, visit www.apvma.gov.au.

“Levels of WPM can be reduced early on by avoiding sowing wheat into infected wheat stubble, selecting wheat varieties with disease resistance, and implementing good crop hygiene such as removing volunteer plants that may carry disease between seasons,” he said.

“Consider also discussing with your neighbours about controlling strategies, as WPM is what we call a social disease and it does not understand fences or paddock boundaries. It is an airborne disease and incorrect resistance management decisions will have an impact on everybody.”

Dr Lopez-Ruiz said the discovery was first identified in Tasmania thanks to agronomists reporting issues with fungicide control. Shortly after it was also identified in Victoria thanks to field samples from the Foundation for Arable Research (FAR) who also noticed fungicide control changes similar to those occurring in Tasmania.

The Fungicide Resistance Group is now urging growers and advisers to send in a sample of their infected stubble as soon as possible, to get fungicide resistance analysis underway.

For a sample kit, email frg@curtin.edu.au, or for more information, visit www.ccdm.com.au/FRG