The announcement of mancozeb's withdrawal at the conclusion of the 2025 season marks the conclusion of a longstanding era for a multi-site fungicide that has been instrumental in safeguarding potato crops against late blight (Phytophthora infestans) since its introduction in 1961.

This decision, disclosed shortly after the start of the new year, comes in the wake of a review by the Health & Safety Executive (HSE) initiated in September 2021. The review identified mancozeb as a potential hazard to human health due to its classification as an endocrine disruptor, with operator exposure surpassing safe levels.

As of the current moment, DEFRA is expected to announce timelines for the sale and disposal of mancozeb-containing products, based on documents published by the World Trade Organization (WTO), indicating the following probable dates:

• Extension of active substance expiry until 30th April 2024;
• Cessation of sale and supply of mancozeb-containing products by 31st October 2024;
• Termination of storage, disposal, and use of mancozeb-containing products by 31st October 2025.

The discontinuation of mancozeb poses various implications for crop protection strategies, according to Nick Winmill, Agrii's head of potato R&D.

"Mancozeb's absence will undoubtedly leave a void. As the sole fungicide with multi-site activity, it stands as our best mixing partner, relatively inexpensive to incorporate into programmes, and offers incidental control of Alternaria species. None of the alternatives possess these characteristics," comments Mr Winmill.

Agrii's trials have explored potential substitutes for mancozeb since its EU ban at the close of 2020. While none provide a direct replacement, several products exhibit promise.

"The key observation is that programmes will need adjustment, likely becoming more intricate and costly," he notes.

For concerns regarding Alternaria, growers may consider applications of Narita (difenconazole), Amistar (azoxystrobin), Signum (boscalid + pyraclostrobin), or Caligula (fluopyram + prothioconazole), although these products vary in protective efficacy.

Of the active substances evaluated in Agrii's trials as mancozeb alternatives against late blight, two have demonstrated value. Potassium phosphonates have shown effective control levels but are presently only available as a co-formulation with ametoctradin, limited to three applications per crop.

"Innocul8," a foliar fertiliser incorporating PREtec technology, has also shown promise. However, while trials data support its inclusion in programmes, it cannot serve as a direct replacement for mancozeb due to its role as a plant health promoter.

"Biological crop protection products and enhanced nutrition will play an increasingly pivotal role in disease mitigation. However, while they may reduce the reliance on fungicides, they cannot fully replace them. Innocul8 exemplifies their potential utility, but they must be integrated into a broader IPM strategy encompassing variety selection and enhanced plant health," remarks Mr Winmill.

As long as mancozeb remains available and approved by processors or end-users, its continued use remains prudent, given its acknowledged value to crop protection programmes.

"Maintaining a balanced programme that considers the proliferation of resistant strains is imperative. While the CAA-resistant strain 43_A1 may have already spread to GB, mancozeb has helped impede its advancement. Removing it prematurely from a programme while it remains authorised for use would be ill-advised," he concludes.