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Potato Blight Challenge Amplified by Probably the UK’s Most Aggressive Strain Ever – Arable Farming – Darryl Shailes

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Darryl Shailes HLH. jpegIt has been an interesting and challenging spring and early summer, both in the fields and the garden.

Despite the deluges of last week, the water isn't much higher than normal in the River Waveney and certainly not as high as it was in June 2016 when the Waveney Valley flooded, including the gardens at the Open Gardens event which, as I write this, is approaching rapidly.

We are also seeing how nature changes, adapts and evolves in our potato crops.

Now, we probably have the perfect storm brewing for potato blight, with rapidly growing canopies, where blight is always more difficult to control, and plenty of rain to provide the leaf wetness blight needs but also keeps sprayers from travelling in crops.

The blight season would be challenging anyway, but this year it is combined with probably the most aggressive strain of blight we have ever seen in the UK.

So far this season, all the infections I am aware of that have been genotyped have been confirmed as the new Light Pink 36_A2. These findings have come from the AHDB Blight Scout samples, demonstrating the importance of the project.

This new strain has been mapped and has caused concern in Europe over the last few of years – and has been increasing in the UK. Light Pink 36_A2 first appeared in the UK in 2017 and went from 2% to 18% of the samples genotyped last year – although 2018 produced such low numbers the data may have been skewed.

Dominating

This season, it appears to be dominating so far. So, while we were mainly considering Dark Green 37_A2 and its insensitivity to fluazinam and adapting blight programmes to take this into account, Light Pink 36_A2 has slipped into the fray.

While not being identified as resistant to any chemistry, this strain is more difficult to control across the board, as demonstrated by tests conducted by AHDB at the James Hutton Institute. Work done at INRA in France has also demonstrated this new strain is able to develop the largest lesions and the greatest number of spores when compared to the older genotypes, demonstrating its ability to spread rapidly.

There is light at the end of the tunnel, however, as the rain has stopped for the time being. The sprayers can now travel and we have oxathiapiprolin from Corteva as the most active blight fungicide we have ever had at our disposal. So, for the present, programmes should be heavily weighted towards this new active, then managed according to risk for the rest of the season with the other excellent actives at our disposal, developing not only an effective programme, but also one that is demonstrating a good anti-resistance strategy.

In the beet crop, the heat and thunderstorms forecast for the last week of June and beyond may also play into the hands of another of the continent's most damaging diseases.

Last season, we had the heat but no rain, so the threat of cercospora in beet did not appear until much later, where it did not cause too much damage. This season could be different, so we need to be on our guard.

Cercospora can be resistant to strobilurins and less sensitive to the DMI chemistry which are the mainstays of the fungicide programmes in the UK. So we need to be able to adapt our programme to manage it if the weather becomes suitable for infection, as is forecast while I write this.

Finally, we must congratulate the all-factory finalists in the Beet Yield Challenge and the overall winner, Mark Means, of JS Means, who achieved 97% of his potential with a 107.9 tonne/hectare crop in what was another very challenging year. Well done, Mark.

Note: Darryl Shailes is Root Crop Technical Manager for Hutchinsons, with a nationwide remit. He has been working in potato agronomy for more than 20 years.