Increased costs, complexity and market risk combine to deliver a triple treat for UK potato growers. CPM weighs up current industry concerns.
“Some of the mancozeb alternatives lack the persistency required for a seven-day interval, so the issue is performance, not managing resistance.” ERIC ANDERSON
By Rob Jones
After a tumultuous season where market prices fell by more than half on the previous year, irrigation demand and virus pressure were high but late blight pressure was low, many growers may find themselves at a metaphorical crossroads, believes Scottish Agronomy’s Eric Anderson.
As ever, decisions regarding what to do this season depend on money and attitude to risk, says Eric. He adds that the greatest challenge facing growers is the soaring capital requirement – for example, applying 150mm of water is now more than £900/ha.
“A typical 120ha ware crop enterprise represents an annual investment in the region of £1.4M. For those reliant on surface water to meet their irrigation requirements, or with ageing machinery and stores, this represents a considerable risk.
“Virus too is a greater threat than just five years ago – there’s no guarantee that seed is virus-free, so even a ware crop could be subject to a compulsory burn down if infection is assessed as beyond the statutory limit,” he says.
For growers in England, the statutory limit is 10% (of crop infected) while Scotland’s status as a seed producer means the limit is just 4%. Although the potato sector isn’t alone in facing such woes – all fresh produce growers face similar challenges – some have made progress on aspects where potato growers have struggled.
“We desperately require longer term contracts like the five-year arrangements available to carrot growers. These would go a long way in overcoming the greatest barriers to progress: a lack of business confidence and a reluctance to invest,” suggests Eric.
Arguably, falling prices make the increase in growing costs hard to accommodate, but of greater concern is the impact prolonged drought has on access to water, he highlights. By mid-summer 2025, dry weather across much of England resulted in 814 hands off flow restrictions in force. These are in-built conditions that require abstractors to either reduce or stop abstraction when flows fall below a predetermined level set out in the licence, thereby limiting crop irrigation.
The situation reveals a wider problem facing growers – poor water resilience, believes Eric. “This is a problem more growers have to face up to, but many can’t afford the investment in a bore hole or reservoir.”
Then, in weeds, pests and diseases, developments are likely to shape crop protection strategies, and influence both yield potential and quality. The most significant being the spread of oxathiapiprolin-resistant EU46_A1, and the implications for fungicide programmes following the end of mancozeb, explains Eric.
EU46 was the second most prevalent strain (23%) identified in Fight Against Blight (FAB) monitoring in 2025, although sampling was biased towards the West and Midlands where it was first detected.
Eric says finding a suitable replacement for mancozeb poses several questions – what to use in its place as suitable tank-mix partner? Then what level of threat, if any, should be ascribed to alternaria, and if so, how to respond?
Finding answers will take time, he believes. “Some of the possible mancozeb alternatives lack the persistency required for a seven-day interval, so the issue is one of performance rather than ensuring compliance with resistance management guidelines.”
A specific concern, raises Eric, is how to protect the efficacy of oxathiapiprolin given it’s available in a mixture with amisulbrom, meaning a third, non-CAA mode of action is required. The worry is that in the presence of EU46, and without a third mode of action, Qil amisulbrom (FRAC Group 21), will be fully exposed.
QiIs such as amisulbrom and cyazofamid are single-site, so if the efficacy of Ranman Top (cyazofamid) and Shinkon (amisulbrom) is to be preserved, another partner is required. Eric says fluazinam is an obvious choice given it’s reasonably inexpensive.
Equally, the prevalence of EU41 in Scotland also requires monitoring given reports of reduced sensitivity to low doses of cyazofamid.
One positive from the past few years – during which strains resistant to either oxathiapiprolin or mandipropamid have emerged in northwest Europe – is that the performance of Infinito (fluopicolide+ propamocarb) remains unaffected, highlights Eric.
“Given the situation with oxathiapiprolin, only fluopicolide and propamocarb offer any meaningful activity as an anti-sporulant, while the systemic and protectant properties of fluopicolide mean the two combine to deliver excellent foliar protection and tuber blight control.
“As there’s no need to add another tank-mix partner, it’s often less expensive to apply than RanmanTop plus a mixer,” he says.
As for alternaria, the truth is currently unknown, warns Eric. For many growers, mancozeb provided incidental control, and while it may take several years before alternaria represents a widespread threat, where a field has a known history of the disease, it should be monitored closely, he says.
“Should symptoms appear, a suitable fungicide should be applied, but growers have to be mindful of strobilurin- and SDHI-resistant strains of A.solani [to date, SDHI resistance has only been confirmed with boscalid]. Ideally, samples should be sent for testing,” comments Eric.
In fields with a history of alternaria, he advises using a product with specific activity such as Caligula(fluopyram+ prothioconazole) or Belanty (mefentrifluconazole). “These are the best means of protection. Caligula gives marginally better alternaria protection and has the advantage of not requiring a tank-mix partner if applying alone,” he explains.
According to Eric, alternaria control differs from that for late blight, in that it’s often easier to achieve. However, as with late blight, modes of action must to be interchanged (see table).
“Fungicide treatments should commence when symptoms are first observed or there’s a high risk of infection from early canopy development. Two to three treatments applied at fortnightly intervals are typically, but it can be more when the risk is high,” he adds.
| Fungicides for alternaria control | |||||
| Product (FRAC Group Code) | Max no applications | Recommended dose/ha | Comments | EuroBlight efficacy rating (14-day interval)* | EuroBlight efficacy rating (7-day interval)* |
| Vendetta (fluazinam+ azoxystrobin) (29+11) | 3 | 0.5 l | Also have activity against late blight; use as part of a late blight programme. | – | 3.6 |
| Carial Star (difenconazole+ mandipropamid) (40+3) | 3 | 0.6 l | 3.3 | – | |
| Belanty (mefentrifluconazole) (3) | 3 | 1.25 l | Specific alternaria product to tank-mix with blight programme. | 4.3 | – |
| Caligula (fluopyram+ prothioconazole) (7+3) | 3 | 0.5 l | 4.5 | – | |
| Signum (boscalid+ pyraclostrobin) (7+11) | 4 | 0.25 kg | Not described | Not described | |
| * EuroBlight assessments published 31 May 2022 | |||||
Finally, virus protection remains a challenge; Scotland recorded its highest vector pressure for 10 years in 2025, led largely by Peach-potato aphid (Myzus persicae). Given the pest’s significance in transmitting persistent viruses such as Potato Leaf Roll Virus (PLRV), this has led to fears that the virus epidemics of the 1970s and early 1990s might be repeated, suggests Eric.
As groundkeepers often emerge before planted seed-potatoes, it’s believed these are the most important virus sources in early spring. Because aphid flights occur earlier in the year, and aphids occur in higher numbers due to milder winters, the chance of early infection of the young and susceptible potato plants before roguing is considerable, he warns.
“Mild conditions enable aphid populations to overwinter in larger numbers leading to early migration and colonisation. This raises the risk of PLRV transmission from groundkeepers or infected tubers before symptoms appear, makes roguing less effective and potentially increasing the proportion of infected seed planted the following season.
“Without planting as clean a seed as possible, combined with implementation of multiple layers of mitigation, an epidemic is increasingly likely,” concludes Eric.
This article was taken from the latest issue of CPM. Read the article in full here.
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