‘FIGHT AGAINST BLIGHT’ FINDINGS ON UK POTATO GROWERS’ SAMPLES OFFER SURPRISES BUT A WELCOME POSITIVE
POTATO crops have endured long periods of weather conditions highly conducive to blight this season and reports of blight outbreaks submitted for testing with the Fight Against Blight campaign have now topped 135 incidences across the UK.
Of the samples submitted by the end of July to the ‘Fight Against Blight’ project for late blight strain analysis, none had been identified as being the fungicide-resistant EU_43 or EU_46 strains.
The first UK blight samples arrived at Hutton in April from outbreaks in Kent, with another six samples sent during May.
Senior Plant Pathologist at the James Hutton Institute, Dr David Cooke, said this is “one positive” from what has been a difficult season to control late blight in potatoes.
“That’s early for blight,” David said. “With a wide range of planting dates, primary inoculum from last season’s unharvested crops and dumps that survived over the winter, blight pressure has been high and made it a difficult season to manage because of crops at different growth stages.”
With dozens of samples arriving more or less every day through June, it has been one of the most intense for early-season outbreaks he has experienced while managing the Fight Against Blight project.
“To some extent, this will have been prompted by our plea for samples to monitor for the new CAA and OSBPI fungicide-resistant strains that have been found on the continent and in Ireland, but obviously, you can only sample blight if it is present,” he said.
Fight Against Blight is only funded to test 400 samples across the season, David explained, adding: “But we don’t like to say ‘no’ to samples, and you never know when new genotypes will arrive.”
Of the samples genotyped by the end of July, 72% of the population was the aggressive strain EU_36, which has consolidated and spread across much of the country, David reports.
“A further 22% is EU_6, which has been around a long time, while 3% is EU_13. That’s a little bit of a surprise as it has been on a gradual decline for years, to the extent that we only had one sample a few years ago with this strain.”
The only newer lineage found this year is EU_41. A Danish clone, it was previously found somewhat unexpectedly in a single outbreak in Scotland in 2021 in a Maris Piper crop with no obvious seed connection to the continent.
“This year, we’re finding it in a few outbreaks both in Scotland and south of the border,” David said.
Testing has found that it has insensitivity to metalaxyl fungicides, and there have been discussions about whether the strain’s appearance is linked with potato volunteers being sprayed with metalaxyl in carrots.
Metalaxyl is not used much in potatoes currently but could be an option once mancozeb’s approval lapses, David said.
Photo: Hutton Blightspy / Norwegian Meteorological Institute
