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Can’t keep up control with just Tebuconazole

The first signs of a wheat powdery mildew mutation have now been observed in our laboratories, coming from samples collected across NSW and Tasmania.

Madeline Tucker of CCDM’s Fungicide Resistance Group seems to think that this mutation could limit the efficacy of the popular active ingredient tebuconazole for use on wheat powdery mildew. The discovery follows a similar discovery of resistance endowing mutations in barley powdery mildew some five years ago which led to reduced control by tebuconazole.

“It’s hard to be the bearer of bad news, but at least this information gives growers valuable time to act early before this wheat powdery mildew mutation becomes dominant in the field. Particularly in this coming season, with so much infected stubble around we expect it to be another big year for wheat powdery mildew,” Madeline said.

Having worked very closely on WA’s barley powdery mildew epidemic of 2009, Madeline said there were two mutations that need to occur within the pathogen before it becomes a significant issue in the field.

“The first mutation – referred to as the Y136F mutation – is quite harmless, however we now know it acts as a ‘gateway’ to the second mutation – S509T – which is much more serious, as the combination of which presents clear signs of tebuconazole resistance in the paddock,” Madeline said.

“Barley powdery mildew and wheat powdery mildew are similar diseases, differing only in the crops they infect. We’ve observed the first mutation (Y136F) in wheat powdery mildew, and it is feared that the second mutation (S509T) could also arise.”

 

PMW 2
Powdery mildew on wheat

How do we know this?

The CCDM’s Fungicide Resistance Group keeps a close watch on fungal pathogens across the country, testing different fungicides on different strains and watching to see if the pathogen survives.

When it comes to wheat and barley powdery mildew, we now know exactly where to look on the genome for mutations – it’s the same two locations for both pathogens.

dna with mutations
Powdery Mildew DNA carrying both the Y136F and S509T mutation will be resistant to tebuconazole.

While the wheat powdery mildew Y136F mutation was only found in Tasmania and NSW, it is quite likely resistant strains are in other states too – it’s just a matter of our time and resources to test more samples.


Where powdery mildew mutations have set in

Maps3


The way to get rapid tebuconazole resistance

Tebuconazole is accessible and cheap and as such its popularity is understandable. However using this active ingredient repeatedly, without rotating your fungicides between different modes of action, or using fungicide mixtures of different modes of action, will promote fungicide breakdown.

Planting susceptible wheat and barley varieties will also create an environment for the pathogen to thrive.


Speaking of varieties…

A large portion of the available wheat varieties in Australia are either moderately susceptible or worse. It is this lack of genetic resistance in popular varieties, planted over large areas, which contributed to a heavy season of wheat powdery mildew in 2015.


Introducing the 10 steps to success:

  1. Start with a clean workbench. Maintain good farm hygiene. Quickly dispose of crop debris and volunteer plants.
  2. Time is of the essence. Quick fungal disease identification allows rapid and effective intervention. Spray before the pressure of disease is high.
  3. Get your measurements right. Always follow the recommendations of the label. Doses above the recommended rate will increase selection for resistance.
  4. Use your mixtures. If possible, use fungicide mixtures formulated with more than one mode of action.
  5. Alternate to obliterate. If you can, alternate fungicides with different modes of action between each fungicide treatment within one season.
  6. Let the plant play its part. To prevent disease outbreaks, use resistant crop varieties. Resistant / moderately resistance varieties require less fungicide applications to protect yield.
  7. Break the disease cycle. Many fungal diseases persist on stubble between seasons. You can use crop rotation or pasture to minimise fungal carry over.
  8. Help out your mates. Report fungal disease by notifying your regional crop disease monitoring services, or report it to the CCDM. You can send in samples to the CCDM for research, and share this recipe with your neighbours. Together we can collectively manage crop disease outbreaks.
  9. Keep detailed records. Detail all crop rotations, disease reports and fungicide applications. Tracing the events prior to a disease occurrence will equip researchers in managing future outbreaks. This information helps us help you.
  10. Keep the recipe current. Stay up to date on the recipe for success and fungicide resistance messages by subscribing to The Spotlight.


Contact us if you suspect it!

Growers who suspect fungicide resistance issues can contact CCDM’s Fungicide Resistance Group at frg@curtin.edu.au for advice or instructions on sampling.

Lab Madeline 2

About Madeline Tucker

Madeline is at the finishing stages of her PhD, which confirmed the first case of fungicide resistance in a crop pathogen in Australia.

She has since continued to dissect the mechanisms of fungicide resistance in the barley powdery mildew pathogen population in WA and has used that information to help prevent fungicide resistance in other economically important fungal species in Australia.

 

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