News that mancozeb is to be withdrawn at the end of the 2025 season marks the end for a multi-site fungicide that has played in integral role in protecting potato crops against late blight (Phytophthora infestans) since its introduction in 1961.
The news, announced shortly after the new year, follows a review by the Health & Safety Executive (HSE) that began in September 2021. The review found that mancozeb represented a threat to human health on the grounds that it is an endocrine disruptor, and that operator exposure was beyond a level deemed to be safe. At the time of writing, timelines for the sale and disposal of mancozeb-containing products were still be announced by DEFRA, but based on the documents published by the World Trade Organization (WTO), the body to which notification must be issued, the following dates seem likely:
· Active substance expiry to be extended to 30 April 2024;
· Sale and supply of mancozeb-containing products to end on 31 October 2024;
· Storage, disposal and use of mancozeb-containing products to end on 31 October 2025.
The loss of mancozeb has several implications for crop protection strategies, says Nick Winmill, Agrii head of potato R&D:
“Without doubt, mancozeb will be missed. As the only fungicide with multi-site activity it is the best mixing partner we have available, it is relatively inexpensive to incorporate (into a programme), and it provides incidental control of Alternaria species. This cannot be said of any of the alternatives,” says Mr Winmill.
Agrii trials have considered the possible replacements for mancozeb since the EU called time on it at the end of 2020. None can be considered a like-for-like replacement, but several products have shown promise.
“The principal observation is that programmes will have to be adapted, but they are also likely to be more complex and costly as a result,” he says.
Where Alternaria is a concern, growers can apply Narita (difenconazole), Amistar (azoxystrobin), Signum (boscalid + pyraclostrobin) or Caligula (fluopyram + prothioconazole) though these products vary in the level of protection afforded. Across continental Europe, isolates showing reduced sensitivity to fungicides belonging to the Quinone outside Inhibitor (QoI) mode of action group – namely pyraclostrobin and azoxystrobin – are widespread. In recent years, isolates with reduced sensitivity to some SDHI active substances, namely boscalid, have also been detected.
Of the active substances considered in Agrii trials as a replacement for mancozeb against late blight, two have shown value. Potassium phosphonates has shown good levels of control but is currently only available as a co-form with ametoctradin and limited to three applications per crop.
“We have looked at two potassium phosphonates-containing products over several seasons. Only one has delivered the high-level protection expected and it is not currently authorised for use, but we are prepared to submit an application for emergency authorisation if other avenues fail,” says Mr Winmill.
The other product to have shown promise is Innocul8, a foliar fertiliser containing PREtec technology, a form of peptides derived from naturally occurring proteins that elicits a response against crop threats. Agrii says that trials data support its place in a programme but as a plant health promoter, it cannot be considered as a replacement for mancozeb.
“Biological crop protection products and better nutrition will have a greater role to play in helping to reduce the damage caused by disease, but while these may serve to reduce the amount of fungicides needed, they are not a replacement. Innocul8 is one example of how these products can be useful, but they need to be seen as part of a wider IPM strategy that considers variety choice and better plant health,” says Mr Winmill.
While mancozeb remains available and is approved by processors or end-users, it makes sense to continue using it given its acknowledged value to crop protection programmes.
“We also need to be mindful of maintaining a balanced programme that considers the spread of resistant strains. It may be that the CAA-resistant strain 43_A1 has already spread to GB, but mancozeb has helped keep it at bay. It would be premature to remove it from a programme while it remains authorised for use,” he adds.
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