The finding of septoria mutants in Irish fields that are quite resistant to SDHI fungicide actives heralds a potential inevitability – resistance.

However, the majority of speakers at the Teagasc septoria conference this week were of the view that we still have potential to slow this threat with the help of the best variety resistance, alternating the use of azole actives to exploit incomplete cross resistance and the use of mixtures with different modes of action (to include a multisite active).

Together, these can help to slow the rise of the mutants.

The conference was told by Neil Paveley of ADAS that the best way to drive and select for resistance is through the intensive use of high rates of fungicide and prolonged exposure to the same mode of action. The more often an active is used on its own, the more it will leave behind those which it cannot control. This is the path to exposing resistance. Mixtures of different modes of action help to slow this process.

Economically viable

Striving for crops to be cleaner than is economically viable is also a driver.

We know we do not need perfect cleanliness, therefore the challenge is to know the levels of disease varieties can cope with while still delivering maximum yields. The more intensive the fungicide use the greater the selection pressure.

The cleaner we try to make our crops the quicker field control failures are likely to appear.

Maximising the use of the available genetic resistance and delaying sowing dates are useful husbandry tools to help slow disease development and the lower the level of infection the lower the chance of either new mutants being produced or of those present being able to multiply and dominate.

While we have a number of new chemical modes of action in the pipeline to come to the market in the coming years, we must hope that the current efforts of wheat breeders to produce more robust multigene genetic resistance will be rewarded.

Strong multigene resistance has the potential to reduce the amount of fungicide needed to secure adequate septoria control and it might even allow for fewer applications – both are key to reducing selection pressure over time.

This was an important gathering of experts and growers with a very international mix. it was noted that a signification proportion of the UK acreage was represented in the room as they realise the good research that takes place here and the fact that our problems become their problems very quickly.

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