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What the fluff? Wheat powdery mildew is fungicide resistant!

We’re not going to lie, this blog is not great news for wheat growers.

Wheat powdery mildew (WPM) has gone and got itself mutated and can now survive strobilurin fungicides (from group 11 the QoI fungicides).

Thanks a lot wheat powdery mildew, thanks a lot.

Okay, now before I hear you say “Far out CCDM, not another doom and gloom story from you guys!”

Let’s get positive again. Our Fungicide Resistance Group has detected it early. There is still time to act. Although too early to tell where else it may be, we have so far only detected it in Victoria and Tasmania. And we have integrated disease management (IDM) tools we can use. Phew.

Now let’s get down to the nitty gritty of it all, and see how we can delay fungicide resistant wheat powdery mildew developing in your paddocks.


The nitty gritty of the situation

Last year, agronomists in Tasmania phoned CCDM’s Fungicide Resistance Group, reporting strobilurins were not working as well as they should in controlling wheat powdery mildew. The Foundation for Arable Research (FAR) also noticed a similar pattern in Victoria.

Samples were sent to CCDM laboratories immediately, and using our quick, high throughput Digital PCR machine (developed for the rapid detection of cancer cells) we were able to screen multiple samples for the mutation in wheat powdery mildew that was causing the problem.

The mutation – G143A – is well known in wheat powdery mildew across other parts of the world but until now was previously undetected in Australia.

With only two modes of action currently registered for wheat powdery mildew control, which are DMIs – group 3 (such as tebuconazole) and the strobilurins – group 11 (such as azoxystrobin and pyraclostrobin), Fungicide Resistance Group leader Dr Fran Lopez-Ruiz said this mutation is not good news for regions prone to wheat powdery mildew.

“Formulations containing strobilurins in mixtures will be compromised in areas where the resistant populations are found, and their use will potentially add more pressure on the group 3 fungicides,” Fran said.

“Such fungicide formulations include azoxystrobin and epoxiconazole.

“DMI fungicides are already under pressure – with a gateway mutation for DMI resistance already detected in samples from Tasmania, Victoria and New South Wales.

“To be frank, the situation is extremely fragile, but if we are mindful of how we manage this pathogen, we will have more chances of maintaining the efficacy of both groups of fungicides for as long as possible.”


How we can delay fungicide resistance for wheat powdery mildew

A maximum of one strobilurin spray per year is the only way forward in keeping disease populations from developing widespread resistance outbreaks to this mode of action.

If the crop requires additional sprays, Fran recommends using a DMI formulation that was not in the previous fungicide application, even if that DMI was in a DMI and strobilurin mixture. For a full list of registered fungicide formulations, visit www.apvma.gov.au.

“To protect our fungicides we need to make sure we are rotating them between different modes of action,” he said.

“We also need to incorporate IDM strategies as additional measures to reduce powdery mildew 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.

“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.”


We want your stubble

Fran said the frequency of the strobilurin resistant populations in Australia is unknown.

“So we are urgently calling on growers and advisors to send us a stubble sample infected with wheat powdery mildew, so we can rapidly put together a map of where strobilurin resistance occurs.

If you have any stubble infected with wheat powdery mildew, please drop us a line at frg@curtin.edu.au so we can send you a sample kit.

Or alternatively you could follow these instructions:

  1. Get a zip lock sandwich bag.
  2. Collect a small piece of wheat stubble from a paddock that was severely infected with wheat powdery mildew. Look for small dark coloured dots on the stubble. These dots are the WPM fruiting bodies and are especially abundant on leaf tissue.
  3. Email us (frg@curtin.edu.au) for an electronic copy of our import permit. We will inform quarantine your sample is on its way.
  4. Pop it in the zip log bag, wipe the outside down (alcohol wipe works great), then pop it into another two zip lock bags, and then into an envelope with a copy of the import permit and address it to:
    Belinda Cox
    Centre for Crop and Disease Management
    Department of Environment and Agriculture
    Curtin University
    GPO Box U1987
    Perth WA 6845
  1. Don’t forget to tell us where you got it from, so we can map it.

Too easy! We will then let you know what we find.

 

About Fran Lopez-Ruiz and the Fungicide Resistance Group

Since joining Curtin University in 2012, Fran has led CCDM’s Fungicide Resistance Group which works towards understanding how fungi are able to develop fungicide resistance and how management of diseases in the field can be improved to reduce losses.

Since the group’s establishment in 2012, they have contributed to the discovery of 10 of the 11 fungicide resistance/tolerance cases in Australia. For more info about the group, visit www.ccdm.com.au/FRG.

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