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Using different fungicide modes of action as resistance management in wheat

Using different fungicide modes of action as resistance management in wheat

Using different fungicide modes of action as resistance management in wheat

Fungicide resistance is not a new concept, especially in the main wheat disease Septoria tritici. So when resistance presents, it can happen quickly as seen with strobilurin chemistry here in New Zealand.

Resistance occurs via different paths:

  1. A change in inhibitor site.
  2. Reduced uptake or accumulation of active ingredient.
  3. Detoxification of the fungicide.
  4. Development of override pathways.
  5. Increase in virulence.

If a fungicide with the same mode of action (MOA) is continually used over time, the number of susceptible isolates decreases and is replaced by resistant strains as illustrated in Graphic One.



The current fungicides available need to be preserved as new MOAs can take up to 10 years to come to market. The key to this strategy is alternating the MOA applied to wheat to combat Septoria.

The fungicide, Questar™ with Inatreq™ Active by Corteva Agriscience, features a new MOA with no cross-resistance to existing MOAs. This means it controls Septoria strains that are otherwise resistant.

Questar provides a flexible application window and has a favourable mammalian and environmental profile with Inatreq produced by the fermentation of a naturally occurring soil bacterium. This active is the first member of a new class of cereal fungicides, the picolinamides (Group 21), which have a different target site to other fungicides currently applied for Septoria control in wheat. Questar is an advance in fungicide resistance management in wheat and provides Septoria and rust control when tank mixed with an appropriate fungicide.

Apply Questar only once per season at either T1 or T2 depending on the Septoria pressure. This helps prevent the development of resistance and using the new MOA also slows resistance to other fungicide groups.

Advantages of Questar

  1. Unique site of action.
  2. Active on triazole and SDHI shifted strains of Septoria.
  3. Inatreq active offers good retention and redistribution, spreading up and down the leaf via the cuticular waxes.
  4. Performs in low water volumes or through low drift nozzles.

Use integrated pest management (IPM) strategies within a crop disease control programme to reduce the reliance on fungicides. By using IPM, the longevity of all fungicide groups is extended. Strategies includes crop rotation, destruction of green bridges, use of resistant varieties, avoiding large areas of the same variety, rotating MOAs, timely applications, adhering to recommended doses and the use of multi-site fungicides. 

To discuss using Questar™ within your spray programme, contact your local PGG Wrightson Technical Field Representative.