The emergence of a potato late blight strain resistant to key fungicides is prompting concern among growers in Europe, with the first UK case confirmed in Suffolk. The strain, identified as EU_43_A1, exhibits resistance to both carboxylic acid amide (CAA) fungicides, including mandipropamid, and oxysterol binding protein inhibitors (OSBPIs) like oxathiapiprolin.
Dr. David Cooke of the James Hutton Institute confirmed the finding following digital droplet PCR testing of blight-infected volunteer potatoes sampled in November . The late-season testing was added to the Fight against Blight program due to unusually warm and damp conditions in October and November, creating ideal conditions for late blight development.
While the EU_43_A1 strain has not previously been detected in routine sampling by the Fight against Blight program in Great Britain, its increasing presence on the European continent has been a growing concern. Preliminary information from Euroblight indicates difficulties in controlling the strain in several countries. A single case was also confirmed in Ireland at Teagasc’s research station in Carlow, further fueling concerns about its spread.
The discovery comes as growers are already facing challenges with another resistant strain, EU46, identified in west Wales and found at trial sites in Shropshire and Derbyshire during the summer. EU46 is also resistant to OSBPIs. However, the recent volunteer sampling did not reveal the presence of EU46, with most samples identified as the more common EU36 strain.
EU36 remains the dominant strain in the UK, accounting for 51% of samples in . It is described as aggressive and linked to the breakdown of varietal blight resistance. While some signs of reduced sensitivity to OSBPIs have been observed in parts of Europe, testing in the UK currently indicates it remains susceptible.
European data shows that strategic use of alternating actives and mixing modes of action has had some success in managing the spread of EU_43_A1. Between and , the incidence of the strain decreased from 23% to 12% across Europe, with Denmark seeing a particularly significant reduction to just 4%. However, France has experienced a sharp increase, from 10% to 25%, and is suspected as a potential source of the infection found near Halesworth in Suffolk.
Experts emphasize the importance of cultural practices in mitigating the risk. Geoff Hailstone, UPL’s technical potato lead, highlighted the need to remove volunteers and potato dumps to prevent the build-up of inoculum. He noted that dry conditions and a lack of hard frosts may have contributed to an increase in small tubers remaining in fields, and the potential for dumped potatoes, particularly from the continent, to serve as a source of infection.
While existing mixing and alternation tactics are generally considered sufficient, the upcoming loss of mancozeb as a fungicide option may complicate matters. Hailstone anticipates increased use of fluazinam and phosphonate products as a result. He also cautioned against overuse of fluazinam, given the emergence of resistance in the EU37 strain, which currently accounts for only 3% of samples but can spread rapidly with improper application.
Propamocarb, available in a mix with cymoxanil as Proxanil, is being positioned as a valuable tool in resistance management. Both actives represent unique modes of action with no known cross-resistance to other fungicide groups. Proxanil’s curative activity is particularly useful early in the program, potentially addressing infection from seed potatoes, while its anti-sporulant properties and ability to check mycelial growth are beneficial later in the season. It is also effective against tuber blight when mixed with cyazofamid.
Growers are advised to check with their buyers regarding potential restrictions on propamocarb use due to concerns about residue levels in potatoes. However, Hailstone noted the active has a short half-life and should not accumulate in tubers when used according to label instructions and with appropriate spacing between applications.
The situation underscores the ongoing need for vigilance and proactive resistance management strategies in potato cultivation. The spread of fungicide-resistant blight strains poses a significant threat to crop yields and requires a coordinated effort from growers, researchers, and industry stakeholders to protect potato production across Europe.
