With the rise of resistant blight strains on the continent in the last few years, coupled with exceptionally wet weather at the end of last year, potato growers have had a very tough time of late.
There doesn’t look to be any let up soon.
Potato blight control will continue to be a big challenge for growers across the country throughout 2024.
We’ve spoken with experts in the fields of blight research and fungicide application to help you know what to look out for, minimise risk and enhance your blight control programme this year.
The key blight strains to monitor
At present, the dominant blight strain in the UK is EU_36_A2, according to research and analysis conducted by the James Hutton Institute, which runs the Fight Against Blight monitoring service.
Researcher leader Dr. David Cooke, says this is largely good news:
“This doesn’t mean blight is easy to manage, but at least we don’t have resistance issues. All the fungicide testing has shown that the UK isolates are sensitive to all the main actives, apart from the known fluazinam issue with EU_37_A2.”
But in Europe, blight resistant strains are now dominant. EU_43_A1 (EU43) and its related strain EU_46_A1 (EU46), account for almost 40% of the samples analysed across Europe by EuroBlight, a consortium of organisations studying late blight across Europe.
It’s proven to be resistant to both mandipropamid (widespread) and oxathiapiprolin.
EU43 has been found in Ireland too.
In 2023, it accounted for:
• 52% of samples in the Netherlands
• 52% of samples in Germany
• 36% of samples in Belgium
• 24% of samples in Denmark
In 2022, EU43 accounted for 64% of samples in Denmark. That big decline gives growers a glimmer of hope. There’s a potential fitness penalty, and the sensible use of carboxylic acid amide (CAA) fungicides could reduce the selection pressure for this strain.
That’s why experts are in agreement:
• Use CAA-containing fungicides judiciously
• Rigorously follow FRAC CAA working group guidelines
Want to hear from the experts? Join our free webinar on potato disease control.
The risk to British growers
While EU43 wasn’t detected in the UK in 2023, there continues to be a big risk to growers this year, especially with the findings from Ireland.
“The EU43 found in Ireland is a concern because of the prevailing wind. Our view is once it has been found, there must be others; they just haven’t been sampled. Early potato crops in Pembrokeshire and Cornwall will be of interest and should be monitored closely,” says Dr Cooke.
Testing will be key as soon as this strain is identified, as some variants are resistant, some aren’t.
The James Hutton Institute has been developing genetic markers for mandipropamid and oxathiapiprolin resistance as part of Scottish government funding. These should help determine whether any field samples of EU43 in the 2024 season have the mutations associated with fungicide resistance.
Avoiding seed imports
Along with the threat from the prevailing wind, EU43 or EU46 could also reach our shores through imported seed potatoes, given the potential supply problems this season.
A 7% reduction in the Northern Europe seed area in 2023, coupled with losses from downgrading and poor yield, means growers could turn to imports from crops that are infected.
“Imported seed is more of a potential issue than anything else,” says Denis Buckley from Highfield Lodge Agronomy.
“I have been advising my clients not to buy it, but the problem is that many are already committed and can’t source it from anywhere else.”
This is the most likely cause of EU37 arriving in the UK, as it was first detected in a distinctive node in the Midlands.
The importance of mancozeb
The increased resistance pressure and the continued threat of new strains means a robust programme of systemic fungicides has never been more important.
Mancozeb, despite its proposed withdrawal, remains central to that.
“Mancozeb is the only potato blight fungicide we have access to with true multisite activity, meaning selection for resistance is highly unlikely,” says Denis.
That’s why at UPL - alongside the wider industry - we’re continuing to lobby for the maintenance of mancozeb.
“It has a critical role to play in resistance management and control,” says Geoff Hailstone, UPL’s potato technical lead in the UK. “It’s likely that its loss in mainland Europe has been an important contributory factor in the increase of resistant strains.”
Geoff’s advice for 2024’s blight control programme? Continue to prioritise mancozeb.
Whatever happens with regulatory review, we’ll have the supply of NAUTILE DG (cymoxanil + mancozeb) and MANZATE 75 WG (mancozeb) that growers need this year.
Even if the withdrawal goes ahead with the current proposed timelines, the sale of mancozeb products will be permitted until October 31st this year, and its use will be allowed through 2025.
We’ll be talking all about the mancozeb withdrawal and what you can expect in our expert-led webinar on Tuesday 30th April.
Increasing use of propamocarb
Moving forwards, growers will need to rely on products like PROXANIL (cymoxanil + propamocarb), which has actives from two different chemistry groups with no reported resistance issues at present.
Cymoxanil:
• One of the few actives with kickback activity
• Has a very low risk of developing resistance
Propamocarb:
• Has strong anti-sporulant activity
• Good movement in the plant
• The only active in the carbamate resistance group
Propamocarb could be more important than ever, as Geoff notes:
“With two different blight strains in Europe showing resistance to Zorvec products (containing the OSBPI fungicide oxathiapiprolin) and the likelihood that the strains will make their way to us (if they are not here already) PROXANIL is left as the only reliable anti-sporulant available.”
It’s also worth noting that Albert Bartlett have recently lifted their restriction on using propamocarb on potatoes grown for them, because of the severe threat from blight. They need to do all they can to ensure a good supply of potatoes.
As such, Bartlett growers across the region can now use PROXANIL. This announcement gives distributors the confidence they need to stock up and makes planning a lot easier.
Join our upcoming webinar to find out more about MANZATE 75 WG, NAUTILE DG and PROXANIL to support your blight control programmes this season.
