THE EU Court of Justice (ECJ) recently overruled a lower court decision on mancozeb’s non-renewal in the EU, citing various procedural errors. It challenged the decision of the EU General Court, which supported the European Commission’s decision to withdraw the authorisation of mancozeb in 2020.
Although this ruling is independent of the UK’s approval process, and it is still not known what it will mean for mancozeb approval in the EU, it raises hopes that we might see a return of mancozeb in the future.
UPL confirmed that this ruling is independent of the UK’s approval process and that it continually monitors the situation within the EU.
For now, the UK has side-stepped a major outbreak of the new fungicide-resistant blight strains that have challenged the European potato industry, according to Dr David Cooke, research leader at the James Hutton Institute.
The emergence of widespread outbreaks across Denmark, the Netherlands, Belgium, and Germany in 2023 caused by EU_43_A1 (EU43) and EU_46_A1 (EU46) shaped UK blight programmes last season. Despite Fight Against Blight monitoring detecting two cases of EU46 in Wales and Scotland, the spread was contained, and we have seen the incidence of EU43 and EU46 reduce in Europe.
Senior Agronomist at Scottish Agronomy, Eric Anderson, said we should take confidence and applaud the fact we haven’t found EU43 in the country, and the two cases of EU46 were found at the tail end of the season.
“Had we not undertaken an alternation and mixing strategy, then I would have predicted we should have seen EU43 and EU46 coming in long before the end of the season, given the inoculum pressure on the continent,” he said.
A measure of how intense the blight pressure was last season is that Fight Against Blight ended up analysing double the samples it was contracted to do, according to David Cooke. “Especially toward the end of the season when we had the two findings of EU46. Blight pressure was still high, and we wanted to sample the late outbreaks to predict what would be around in the spring,” he said.
It was Eric Anderson who sampled the EU46 discovery in Angus. “We can categorically say there was no association with any contaminated imported seed within the vicinity,” he said.
“The crop didn’t receive any oxathiapiprolin. It received two applications of mandipropamid, but on both occasions, it was mixed with another mode of action at full rate. Therefore, we can also say no selection pressure was applied during the season. This means it could have happened to anyone.”
David and Eric hypothesise that an unusually strong eastern wind in September may have carried spores from the continent and caused the Scottish outbreak. The timing correlates with when the lesions become visible, and Eric says that the lesions were only present in the top of the crop on the newest leaves, indicating a new infection.
If correct, the same mass airflow event would have brought spores to the entire Eastern coast. “It would be a very brave person to say that because EU46 hasn’t been found in the rest of the country means it isn’t there,” surmises Eric.
“This theory doesn’t tie in with the Welsh outbreak. Inevitably, people are saying it blew across from Ireland, but we haven’t found any samples of EU46 there,” David added.
Resistance testing by James Hutton Institute on behalf of Fight Against Blight paints another promising picture for the UK blight population. David says that apart from oxathiapiprolin resistance found in the two isolates of EU46, all testing on contemporary lineages of EU41, EU6, and EU36 showed sensitivity to the other tested actives: mandipropamid, propamocarb and cyazofamid.
Despite the understandable focus on EU43 and EU46, the prevalence of EU_36_A2 (EU36) continues to grow in the population, now making up almost two-thirds of the total. Its virulence and ability to withstand early-season temperatures mean that growers must maintain vigilance, even on resistant varieties.
“Unless we go back to spraying single modes of action and EU43 comes in, I can’t see a major shift in the population. EU36 is difficult to manage, but it’s the case of ‘better the devil you know’,” David said.
Mancozeb, which European growers have been without for three seasons, has been a key tool for UK potato growers in the fight against fungicide resistance. As on-farm stocks are used up this year, 2025 is an opportunity to experiment with alternative programmes.
Mixing multiple modes of action in each application is essential to halting the spread of carboxylic acid amide (CAA) and oxathiapiprolin resistance. According to Dr Cooke, discussions within the EuroBlight community have attributed reductions in the prevalence of EU43 and EU46 in the Netherlands and Denmark to switching from single-product sprays to mixing modes of action.
“It is no longer a nice to have, we must have robust strategies of alternating and mixing,” states Eric “As (on-farm) mancozeb stocks start to dwindle and are depleted, what are people going to mix with single-site mode of action products?”
“Once you start to rationalise how many products you can use of each of the modes of action, and where you are going to sequence those, the complexity of blight programmes this season is daunting.”
For growers with mancozeb to use up, Geoff Hailstone, Potato Technical Specialist at UPL recommends prioritising their remaining stocks where blight or resistance pressure is greatest.
“It’s difficult to know how much mancozeb is out on farm,” said Geoff. “The likely answer is that some may have an entire season’s worth, and others will have none.
“An obvious place to use mancozeb is with CAA-containing fungicides and oxathiapiprolin to help protect them from EU43 and EU46. It will also be a valuable tool to reduce fungicide programme costs since they have become more expensive as more products are tank mixed.”
When looking at potential mancozeb replacement in programmes, Geoff advises growers to consider Proxanil (propamacarb + cymoxanil), which he says is an ideal tank mix partner for more expensive single-site chemistry.
“Propamocarb is the only reliable anti-sporulant remaining,” he says. “It has good movement in the plant and is in a unique resistance group. Additionally, cymoxanil is known to be one of the few actives with kickback activity and has a very low risk of developing resistance.
“When tank-mixed with a single site protectant fungicide such as cyazofamid, Proxanil strengthens the activity and gives excellent resistance management.”
Fight Against Blight is still seeking support for its 2025 programme. Get in touch to find out more about how you can help.
Photo, From left: David Cooke, Eric Anderson and Geoff Hailstone
