Potato growers are being warned to change their blight control strategies to combat the spread of an aggressive fungicide-resistant strain of the disease which has reached Suffolk.
The dark green 37_A2 form of Phytopthora infestans has quickly spread across Europe, reaching England two years ago when five cases were reported.
Around 20 cases were officially recorded in 2017, mainly in the West Midlands, Yorkshire and Kent, and more recently in Suffolk.
However, Darryl Shailes, root crop technical manager at agronomy firm Hutchinsons, believes the actual figure could be higher, with crops everywhere potentially at risk.
The new strain is at least, if not more, aggressive than the dominant blue 13 and pink 6 forms of blight, but the crucial difference is that it appears equally aggressive on foliar and tuber blight, he said.
In addition, the dark green 37 has reduced sensitivity to fluazinam, which features in many fungicides often used towards the end of the season to reduce tuber blight.
'There was a massive failure of fluazinam at the Eurofins blight trials last year and dark green 37 was implicated in several cases of store breakdown,' said Mr Shailes. 'Fluazinam has been a cost-effective option for tuber and foliar blight, especially against the blue 13 strain, but until we have access to real-time information to determine the exact genotype of blight spores present in the field, we have to question its position in blight programs.
'The yield loss from foliar infection of blight is often very small except in the worst years but the consequential losses from tuber blight can be massive.'
Mr Shailes added that the aggressiveness of new blight strains, combined with the fact that, in certain weather conditions, blight can be present as crops emerge, means it is vital to manage risk from the outset.
'There is a myriad of materials growers can use instead of fluazinam,' he said. 'As with any fungicide strategy, alternate chemistry so you're not relying on any one active ingredient or mode of action.'
Dark green 37 is thought to have reached the UK in imported seed, but it also spreads via airborne spores.
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