The findings of the 2025 Fight Against Blight (FAB) campaign, which monitors the spread of the late blight pathogen Phytophthora infestans, have underlined the importance of growing potato varieties with built-in resistance as the disease continues to evolve.
Dr David Cooke of The James Hutton Institute, who leads the monitoring programme, said the 2025 season started quietly.
“Dry conditions in April and May suppressed sources of primary infection,” he explained. “Some potato-growing areas in eastern England didn’t see conditions suitable for blight until mid-July, by which time early infections had largely been held in check.”
The first outbreak of the year was recorded in Ceredigion in mid-May, followed by outbreaks in Cornwall, Pembrokeshire, Perth and Kinross, and Aberdeenshire during June. Across the UK, Hutton scientists sampled 81 outbreaks, more than half of which came from volunteer potato plants rather than commercial crops, which persisted in warm and wet conditions from September onwards.
One strain, EU46, increased sharply, accounting for 23% of 300 FAB samples, though it was only found at seven sites, mostly in trial and organic crops. Outbreaks began in Wales and spread to the Midlands and Derbyshire, possibly aided by Storm Amy. Its presence in Wales suggests it may reappear in 2026.
Dr Cooke warned growers to stay vigilant: “EU46 has a known resistance to oxathiapiprolin, a key fungicide ingredient. All the FAB strains tested in 2025 were found to have the mutation that confers that resistance.
"However, unlike on the continent in 2023 and 2024, management failures were not reported which implies that growers are following industry and Fungicide Resistance Action Committee (FRAC) guidelines correctly when implementing their blight control programmes.”
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Other key 2025 findings included:
- EU36 remains the most common strain (over 40% of samples) and can overcome varietal resistance. Its distribution across the UK is wider than in previous years.
- EU37, resistant to fluazinam, has almost disappeared, detected at only two sites.
- EU13, resistant to metalaxyl, caused just two outbreaks, both on volunteer plants.
EU41 requires monitoring in Scotland due to reduced sensitivity to low doses of cyazofamid.
Fungicide efficacy testing by Hutton’s team showed:
- Oxathiapiprolin: EU36 and EU41 remain sensitive; EU46 is resistant.
- Mandipropamid: all UK isolates remain sensitive.
- Amisulbrom, propamocarb, and fluopicolide: all tested isolates remain sensitive.
Dr Cooke stressed that 2016 strategies must focus on:
- Rotating fungicides and avoiding repeated use of the same active ingredient, particularly with the loss of mancozeb.
- Choosing potato varieties with stronger blight resistance.
- Managing sources of infection, including volunteer plants, waste piles, and contaminated soil.
“These steps are crucial for a sustainable, integrated approach to blight control,” Dr Cooke added, “as the pathogen continues to adapt and evolve.”
The Hutton Institute, home to the National Potato Innovation Centre (NPIC), works with industry, government, and academia to safeguard the UK potato industry, supporting both economic resilience and sustainable crop production.
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