UK Growers Must Adapt to New Regulations and Fungicide Resistance Challenges
With the withdrawal of mancozeb set for later this year and confirmed resistance to other fungicides on the continent, UK potato growers will need to develop new strategies for controlling potato blight in 2025 and beyond. Recent regulatory changes add complexity to this challenge.
Mancozeb, a mainstay multi-site fungicide for potato blight control, will see its approval expire on May 31, 2024. Sales and supply of products containing mancozeb will end on November 31, 2024, with the final storage, disposal, and use-up period concluding on November 31, 2025. Consequently, growers must adjust their blight protection programs accordingly. While alternative active ingredients exist, the regulations surrounding their use are intricate, compounded by confirmed resistance to some key actives in Europe.
“For example, instead of applying three consecutive applications of CAA (carboxylic acid amide) fungicides, the latest FRAC (Fungicide Resistance Action Committee) guidance limits these to a maximum of two consecutive applications,” explains ProCam agronomist, Harry James. This recommendation arises from the loss of efficacy of CAA fungicides on the continent, with crop protection manufacturers like Syngenta advocating the alternation of mandipropamid with fungicides of different modes of action.
Resistance to oxathiapiprolin (Zorvec) has also been confirmed in parts of northern Europe, including the Netherlands, Belgium, and Germany. As a result, the post-Zorvec application interval has been reduced from 10 days to 7, necessitating its use in alternation with non-CAA chemistry.
“This will make it more labor-intensive and time-consuming to keep crops clean,” James describes, “especially as this key active no longer provides a curative effect and can only deliver preventative activity. This means sprays must be applied on time, every time, to ensure crop protection.
“To avoid confusion with the new rules and prevent the same resistance issues faced by European counterparts, UK growers should seek professional advice to devise suitable blight programs for the upcoming season and beyond,” James advises.
Growers must also recognize the high risk of fungicide resistance in the UK, exacerbated by the shortfall in British seed potatoes, increasing the likelihood of resistant strains introduced by imported seed stock. The high incidence of foliar and tuber blight in continental seed crops presents a significant risk of resistance impacting British crops. Thus, anti-resistance strategies—alternating modes of action and limiting exposure to any single active ingredient—must be followed from the outset.
Monitoring resistance updates throughout the season and consulting professional advice for spray programs will be crucial due to the evolving legislative landscape and resistance scenarios. Despite these challenges, with careful planning, growers and agronomists can achieve effective blight control and stay ahead of resistance threats. Reliable control hinges on adapting programs to weather conditions and using forecasting tools to identify peak blight threats. Additionally, selecting varieties with better natural blight resistance and removing volunteer potatoes from dumps and other crops in the rotation should be considered.
“Ultimately, getting into the field to assess crops and disease pressure remains irreplaceable,” James concludes.
