Dry harvest and long storage raise potato disease risk

Low market movement of potatoes has left ware crops in store longer than usual, making store hygiene a key priority this summer.

The dry harvest conditions of 2025 increased tuber damage, creating entry points for diseases.

Together with slow market movement and longer storage times, disease risks are higher with the likes of fusarium dry rot, soft rots and silver scurf more evident this spring.

See also: Rising costs and policy fears dent potato grower confidence

Frontier seed treatment specialist Darren Wonnacott says the combination of increased tuber damage at harvest, extended storage and a market demanding only top-quality potatoes has created a “perfect storm” for storage disease pressure.

“There was a lot of damage last harvest and with a long storage season, you end up with more issues because you’ve given the pathogens time to develop,” he says.

Reduce disease inoculum for 2026 

The concern is not just the quality of crops still being marketed, but the risk that disease inoculum remains in stores providing a bridge to the 2026 crop.

The issue is most relevant to ware growers who have been forced to hold onto crop that would usually have been moved by Christmas or early spring because of suppressed retailer and processor demand.

Growers should assess risk on a store-by-store basis, considering how much crop damage occurred at harvest, how long crops were held and whether there were visible disease issues that have caused problems.

Where risk is identified, physical cleaning is key before using a wet fog disinfectant.

© Tim Scrivener

Soil, dust, old tubers and debris should be removed first but there is little value in disinfecting early if the store is then left open or used for other crops or machinery before potatoes return.

“I’ve seen cases in the past where we’ve gone in with JET5 fog disinfectant, then a week later the doors are open, and there’s dust – which could be carrying disease spores – blowing across the yard into the store. You’ve just wasted time and money.”

Darren adds that stores can be treated soon after emptying, with no need for a long resting period.

Boxes can be treated in store. Darren advises loading only half the store capacity as too tight packing restricts fog movement.

“We know 2026-27 is not going to be a bed of roses, so taking all the steps you can to reduce crop and financial loss is a sensible thing to do,” he says.