The 2025 findings from Fight Against Blight (FAB) — an industry-sponsored monitoring campaign — track the emergence and spread of Phytophthora infestans (the late blight pathogen) clones. The results underscore the value of choosing potato varieties with built-in resistance to help safeguard future crops as the disease continues to evolve.
Dr. David Cooke of the James Hutton Institute, who leads the monitoring programme, reported that the 2025 potato season started quietly for FAB scouts — the nationwide network of agronomists, growers, and industry representatives who submit field samples from suspected late blight outbreaks across Britain. Exceptionally dry weather in April and May suppressed sources of primary infection. In some potato-growing areas in eastern England, conditions suitable for blight did not occur until mid-July, by which time early infection sources had largely been kept under control.
The first outbreak was recorded in Ceredigion in mid-May, followed by further outbreaks from mid- to late June in Cornwall, Pembroke, Perth and Kinross, and Aberdeenshire, according to a press release.
The James Hutton Institute — home to the National Potato Innovation Centre (NPIC) — partners with academics, industry, and government in the UK and internationally to deliver research that helps future-proof the potato sector and supports economic resilience and growth. Its work focuses on practical solutions to keep potatoes sustainable, profitable, and widely available as a nutritious food crop that also contributes to the British economy.
Across the UK, Hutton scientists sampled 81 outbreaks in 2025, with more than half linked to volunteer potato plants growing outside commercial crops. These volunteers persisted in the warmer, wetter conditions from September onwards and became a major source of samples.
One pathogen strain, EU46, increased sharply and accounted for 23% of the 300 FAB samples. However, it was detected in only seven locations—just two of which were conventional commercial potato crops — while the remaining detections came from trial sites and organic crops.
EU46-associated outbreaks began in Wales and later appeared in the Midlands and Derbyshire, potentially aided by Storm Amy. Its apparent establishment in Wales suggests it may re-emerge in 2026.
Cooke said that growers must stay alert.
“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.
Cooke said the absence of EU43, in which resistance to mandipropamid has been widely reported, was good news for the British industry, though the prevalence of the EU41 clone at multiple sites in Scotland will need to be closely monitored given last year’s reports of it having reduced sensitivity to low doses of cyazofamid.
“Despite the doses in question being well below field rate, it does flag the potential for population shifts through selection. Bearing in mind that the effective dose in the crop progressively reduces in the intervals between applications, growers need to avoid consecutive applications of any fungicide product, particularly those with only a single active ingredient.”
Other key findings from 2025 were:
- EU36 was again the most common strain, making up over 40% of samples. It is known for breaking down resistance in potato varieties and has shown signs of fungicide resistance in parts of Europe. In the past this clone was more prevalent in the east, but it has now spread more widely across the UK than in previous years.
- EU37, which is resistant to the fungicide fluazinam, has almost disappeared, being found on just two sites in 2025, an encouraging sign that careful fungicide management is working.
- EU13, resistant to metalaxyl, caused only two outbreaks, both on volunteer plants
Although this year’s campaign received far fewer samples of suspected late blight than usual, Cooke warns against complacency. “It remains crucial that growers continue to alternate the actives in their spray programmes to reduce the threat of resistance developing. There is no place for block spraying.
“Cultivar resistance has become increasingly important to complement fungicides, and care should still be taken to maintain long rotations to reduce the numbers of long-lived sexual oospores in the soil plus managing other key sources of primary inoculum such as cull piles and potato volunteers.”
James Lynott, research assistant on the Hutton team tested several fungicides for their efficacy against current strains and found that:
- Oxathiapiprolin: EU36 and EU41 remain sensitive; EU46 is resistant.
- Mandipropamid: all UK isolates (the cultures grown from samples of late blight) remain sensitive, unlike some resistant strains found in Europe.
- Amisulbrom, propamocarb, and fluopicolide: all UK isolates tested remain sensitive.
Lynott also expanded DNA-based fungicide resistance testing throughout the season, reporting any issues as soon as they were identified to provide growers with real-time guidance. This supported more effective Integrated Pest Management (IPM) of late blight, in line with the UK Pesticides National Action Plan for 2025.
“Care must be taken in 2026 to ensure that industry continues to follow FRAC guidelines on mixing and alternating active ingredients, in particular considering the loss of multi-site mancozeb products, Cooke said.
He emphasised three key actions for 2026:
- Rotate fungicides and avoid repeated use of the same active ingredient, especially with the loss of mancozeb from the market.
- Choose more blight-resistant potato varieties to reduce reliance on chemicals.
- Manage sources of infection such as volunteer plants, waste piles, and oospore contaminated soil.
These measures, which promote a more sustainable and integrated approach to blight management, are increasingly important as the pathogen continues to adapt and evolve.
Launched in 2006, the Fight Against Blight (FAB) scheme monitors Phytophthora infestans populations through a nationwide network of agronomists, growers, and industry representatives known as FAB Scouts. Each year, the network submits up to 1,500 field samples from suspected late blight outbreaks across Britain. The programme includes annual outbreak sampling, characterisation of pathogen populations, and fungicide sensitivity testing on industry-prioritised active ingredients.
