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The 2017 season saw many growers reporting high disease pressure with some experiencing control below their expectations.

Evidence indicates the reasons for the high disease incidence are the result of a combination of factors, notably early onset followed by favourable weather, but also delayed fungicide application and use of varieties of low disease resistance.

For another year, powdery mildew failed to be the threat it can be with rust the principal disease to threaten crops.

Those able to drill early and achieve good establishment benefitted from rapid canopy growth in the early start to summer. The first case of rust was reported on the 7th June – one of the earliest cases to be seen in the UK – but with many crops still to reach canopy complete some growers decided to delay the first fungicide until July.

Such early disease onset poses problems. It came in before many crops had reached full canopy and a few growers experienced drought stressed crops too under the high temperatures experienced during June. However, where fungicides were applied at the correct time and followed up four weeks later most diseases were controlled well.

Late fungicide applications however, are only part of the explanation. In some cases, water rates were potentially too low to ensure full canopy penetration and the interval between applications too long to deliver continued protection.

The summer of 2017 also saw several instances of cercospora. In contrast to rust and powdery mildew, where no resistant strains have been detected in the UK, three cases of QoI-resistant cercospora were found by Bayer in 2016.

By late autumn most crops, particularly in East Anglia, had low levels of cercospora, and it was notable that some growers and agronomists were identifying differences with disease incidence between varieties.

The spread of cercospora is concerning and crops should be monitored closely for signs of disease but attempts to control it should not come at the expense of controlling rust or cause a delay to application timing.

Two well-timed applications of Escolta (cyproconazole + trifloxystrobin) can easily form the backbone of fungicide strategy for all crops lifted after mid-October. For cercospora, triazoles are useful, with epoxiconazole and cyproconazole showing some activity against.

If you have any questions, please contact your local CTM or Tweet @Bayer4CropsUK.

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