Potato late blight outbreaks confirmed
With growers struggling to get on the land due to heavy rainfall to apply timely blight fungicides in some areas, the number of confirmed cases of the disease is growing.
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Dr David Cooke, research leader at The James Hutton Institute, which is sponsored by AHDB to identify different genotypes (strains) of blight from samples sent in says there have been a number of samples submitted over the last week (w/c Jun 10). “We have four confirmed cases of blight and others pending. Of those pending, a few are definitely blight.”
Agronomist John Sarup of Spud Agronomy found his first blight outbreak of the season on June 20 in Maris Piper in Cheshire. “The pressure is on,” he says. “It is clear that spray intervals have been stretched as people have not been able to get on the land. Last year I saw no blight.
“Most crops are at 100 per cent ground cover so there is high risk in the local environment conducive to promoting leaf wetness.”
Dr Cooke says recent outbreaks have been in the Colchester area and Lincolnshire. “The early Hutton Criteria alerts are most important. There will have been a lot of alerts over the last two weeks with the heavy rain. But not every outbreak is reported and there is likely to be blight in other areas so it is as well to be cautious.”
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Robust programme
Mr Sarup says a robust fungicide programme is needed to keep on top of blight.
Where sprays have been postponed, a product with some curative activity, such as Zorvec (oxathiapiprolin) will help tackle any blight infection already developing in the crop, says Corteva Agriscience field technical manager Craig Chisholm. “Choosing an active ingredient with curative properties will ensure growers claw back some of the days of lost protection.”
Samples collected to date in the 2019 season from South East England have been genotype EU36_A2, according to Dr Cooke.
He says recent research results show that preventative treatments will be equally effective against all genotypes and this is the best form of management. “But once an infection has become established in a crop, genotype EU36_A2 appears to be a lot more difficult to suppress than other genotypes, even with products that are known to have some curative activity.”
Dr Cooke also advises growers to be cautious about using fluazinam in blight programmes due to insensitivity of the new aggressive blight strain EU37_A2 to the active.
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