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Septoria tritici blotch update

Even though 2017 wasn’t particularly conducive to wet weather diseases like Septoria tritici blotch, there were still widespread reports of this disease in crops throughout southern Australia. ‘How we can therefore manage our fungicide use to reduce resistance risk’ was Nick Poole’s key message when he presented at the Adelaide GRDC Research Updates on a Septoria tritici update and latest developments in powdery mildew management’.

Three things continued to make Septoria tritici blotch problematic in 2017

  1. There is limited genetic resistance to the disease in the popular cultivars grown in southern Australia
  2. Sowing earlier, although giving productivity advantages, has increased disease pressure particularly where cultivars have limited genetic resistance
  3. Septoria tritici pathogen has acquired a number mutations that have been spreading through the population and which differentially affect some of the fungicides commonly used, the azole or demethylase inhibitor (DMI) Group 3 fungicides.

One of these strains, the R8 or isoform 11 strain carries a number of mutations and is now increasing on the mainland. In Tasmania where the strain is dominant in the population the field performance of some of the DMI fungicides are being affected, particularly flutriafol and tebuconazole.

Making sure we minimise the number of fungicides used, alternating between the Group 3 Azole fungicides, and limiting where possible the overall applications of the newer fungicides (SDHIs Group 7 and strobilurins Group 11) to one application per season (since these fungicides are at higher risk for fungicide resistance development) will help slow down the development of fungicide resistance.

For more information on Septoria tritici blotch and the latest developments in powdery mildew management, read Nick’s GRDC Updates paper ‘Septoria tritici update and latest developments in powdery mildew management’

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