Storage Diseases Move From Background Risk to Seed Priority

Tuber diseases rarely make headlines the way late blight or aphids do. They don't announce themselves in the field, and by the time symptoms appear, the crop is often already in store — or already planted on a customer's farm. That lag is exactly what makes them dangerous for seed producers, whose entire value proposition rests on the health of the tuber they hand over.

A tuber disease workshop hosted by Fortrie Farms near Ellon, Aberdeenshire, organized for members of the SAC Association of Potato Producers (SACAPP), brought researchers, industry specialists and growers together to look at exactly this problem, as covered in British Potato Review News. Fusarium dry rot, gangrene, silver scurf and skin spot were named as the diseases most affecting crop quality, storage performance and next-season establishment.

Darren Wonnacott, a tuber seed treatment specialist with Frontier Agriculture, has tracked rising Fusarium and dry rot issues over 23 years in the trade, particularly in ware crops. He points to variety choice as one driver: many newer processing varieties are thin-skinned and prone to damage, and that damage creates entry points for pathogens.

Two other trends compound the problem. Storage periods have lengthened as challenging market conditions keep crops sitting longer, giving latent infections more time to surface. And dry harvest conditions — 2025 was cited as a clear example — worsen bruising and skin damage, adding further infection opportunities. None of these factors acts alone; together they describe a system where risk accumulates quietly across the season rather than announcing itself at any single point.

Despite that rising pressure, relatively little seed actually receives post-harvest fungicide treatment. Kyran Maloney of SAC Consulting, drawing on SASA's Pesticide Usage Survey, found treatment use lower than many in the industry might assume, even though Fusarium and silver scurf turn up regularly in seed crops.

That gap isn't necessarily a failure — Maloney was careful to frame treatment as a risk-management tool rather than a default requirement, valuable where disease pressure or conducive conditions are already present rather than applied routinely. Part of the practical difficulty, per Wonnacott, is timing: treatments are commonly applied at first grading, by which point tubers may have already spent weeks in store, and most seed businesses aren't set up to treat before store entry. Seed treatments themselves are protectants, not eradicants — they guard fresh wounds from grading and handling but cannot reverse infections already established.

Work underway at SAC Consulting is sharpening the picture of what's actually present in stores. SAC's Verena Schmidt described growers commonly dealing with several pathogens at once rather than a single problem — Fusarium species as a leading cause of tuber rot, silver scurf as one of the most common skin blemishes, and black dot, skin spot and bacterial rots appearing regularly in samples with symptoms that often look alike.

That overlap matters practically: not every pathogen responds to the same chemistry, so correct diagnosis shapes which management strategy actually works. Schmidt's broader point was that no single measure solves every disease problem — handling, hygiene, storage conditions and targeted treatment each play a role.

A separate strand of work, run with Certis Belchim, looked past the potatoes entirely and examined the stores themselves. Dust and debris samples collected from two commercial stores were analyzed for pathogen DNA, and the results turned up several important potato pathogens — evidence that stores can carry disease inoculum over from one season into the next, even after a crop has been removed.

The findings stop short of proving disease will develop from that residual material, but they reinforce hygiene as a core, and comparatively cheap, line of defense: removing debris, cleaning ventilation, and running thorough disinfectant programs with products like Jet5 before a new crop goes in. For growers already facing prolonged storage or recurring disease, hygiene may be one of the more cost-effective interventions on offer.

Where treatment is used, imazalil and thiabendazole-based products remain the established tools against Fusarium dry rot and silver scurf. Gavel is widely used for general protection during prolonged storage, while Storite Excel offers an alternative mode of action that can broaden control or support resistance management.

Wonnacott argues that in genuinely high-risk situations there's a case for using both actives together, building resistance management directly into the program. Maloney agreed, noting documented resistance issues in some Fusarium populations historically, which strengthens the argument for including thiabendazole alongside other chemistry when risk is high. But both were consistent on the underlying principle: treatment decisions should follow risk assessment, not routine or habit, since not every stock needs both actives, one active, or any fungicide at all.