It’s not too late to act on fungicide resistance

After spring finally arrived, crops moved fast and fungicide programmes have now started. Though the cold end to winter seems to have suppressed disease, the increasing presence of fungicide resistance in some diseases could present challenges in the field this year and the recent weather hasn’t helped.

The main challenge is that the situation is dynamic – several diseases are developing resistance to different fungicide groups at varying rates – and it can be difficult to keep up. And then there’s the science, which is not always easy to understand. The temptation for many could be to carry on as normal or increase dose and hope for the best, neither is a good option.

This is why we are working with industry, through the Fungicide Resistance Action Group UK (FRAG–UK), on the Fungicide Futures initiative, to provide clear science-based information to help farmers implement good anti-resistance strategies to slow resistance spread while also maintaining effective control.

Though evolving resistance is a concern, results from industry and AHDB-funded research show there are several practical things that can be done. With this in mind, Fungicide Futures has three key tips for you:

  1. At T1 in wheat, only include an SDHI if the disease pressure warrants it. In varieties with greater septoria resistance, especially if sown later, an azole plus multisite may be sufficient.

Moderately SDHI resistant septoria isolates are now present over much of the UK, though often at low frequency. Using an SDHI at T1 will select for these, potentially making the population harder to control in future. The balance of this risk has to be weighed against the risk of poor disease control due to missing the SDHI at T1. For varieties with good septoria resistance ratings, especially if sown later, the balance is probably in favour of dropping the SDHI at T1 in many cases, though with many T0s missed this year, decisions really will need to be made on a field-by-field basis.

  1. Include a multi-site at T2 in wheat to protect azoles and SDHIs from resistance. However, be aware chlorothalonil can antagonise partner product curative activity when timings are delayed.

Survey data suggest that less than half of T2 sprays on wheat include a multi-site, exposing the SDHI and azole to selection for resistance. However, chlorothalonil can antagonise partner product curative activity, so when in a curative situation, particularly when timings are delayed, an alternative multisite should be considered. In addition to better resistance management, inclusion of a multisite can also improve septoria control, bringing yield benefit too.

  1. Include chlorothalonil at T2 in barley. This is particularly important at sites with a history of ramularia, as this disease is likely to be resistant to azoles and SDHIs, as well as strobilurins.

Resistance to strobilurins, azoles and SDHIs in ramularia is now widespread and at a high frequency in the UK – so it’s too late to stop it and now it’s all about disease control. Ramularia can rob half a tonne of yield at the end of the season and chlorothalonil is the only option to control it at the moment.

Looking ahead to autumn, growers need to consider making the most of varietal resistance. The key question to answer is: Are high-yielding varieties with poor resistance ratings really worth the risk anymore? Such crops often rely heavily on the protection from fungicides, which will help push selection for resistance harder and if pathogen resistance shifts significantly, these varieties will be the first to suffer.

Fungicide resistance means we all need to work together to crack the problem, we can’t leave it up to the few. Everyone needs to pull together. Choosing more robust varieties and relying less on fungicides will help the UK manage the risk over the shorter and longer term. With hindsight, we should have started years ago. But it is not too late to act.

cereals.ahdb.org.uk/fungicidefutures

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Paul Gosling

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