Wanted: spot form net blotch samples

Centre for Crop and Disease Management fungicide resistance group leader Fran Lopez-Ruiz.
Centre for Crop and Disease Management fungicide resistance group leader Fran Lopez-Ruiz.

A Group 3 resistance finding in barley of spot form of net blotch (SFNB) in Western Australia should act as a reminder to growers and advisers that it is best practice to implement a fungicide application plan.

Analysis of 2017 crop samples detected the resistance in the fungus pathogen Pyrenophora teres f. maculate to some Group 3 DeMethylation Inhibitors (DMI) fungicides.

Centre for Crop and Disease Management (CCDM) fungicide resistance group leader Fran Lopez-Ruiz said more research with GRDC investment would be carried out into SFNB fungicide resistance and growers and advisers were encouraged to submit stubble and green plant samples of net blotches from all growing regions across Australia this season.

“Collectively we all have a role to play in protecting the longevity of our fungicides by using them responsibly, regardless of whether fungicide resistance is present in our own backyards or not,” he said.  

“So far, the resistance in spot form of net blotch has been found in WA only. However, the barley cropping area in Australia is huge and we can’t be absolutely sure that resistance is nowhere else.

“For this reason growers should keep an eye on the performance of their treatments and send in samples as soon as they notice a slight shift in disease sensitivity.”

For growers with DMI resistance – or suspected resistance – in their paddocks, Dr Lopez-Ruiz recommended avoiding the application of two consecutive applications of the same Group 3 fungicide active (either as a foliar or seed dressing) in one season, unless these were used in mixture with a different mode of action. 

He said a Group 7 (SDHI) seed dressing could be used as a preventative measure, but advised strict adherence to recommended label rates and application methods to achieve adequate fungicide coverage. 

Dr Lopez-Ruiz also provided the following guidelines for fungicide use: 

  • Choose mixtures with different modes of action if available 
  • Alternate fungicides and never apply the same fungicide twice in a row
  • Avoid applying the same mode of action twice  
  • If resistance is present or suspected, avoid or minimise the use of that mode of action as this will only further select for resistance 
  • Rotate crop types 
  • Grow resistant barley varieties to reduce disease pressure
  • Use label rates to ensure adequate spray coverage

Sampling is best carried out through local plant pathologists and for more information, email the CCDM Fungicide Resistance Group directly at frg@curtin.edu.au or visit http://ccdm.com.au/


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