3 November 1995

Ideal conditions raise rot risk in potatoes

WATCH out for in-store rotting. Thats ADASs advice to potato growers as warm weather and poor skin set prove ideal for bacteria to cause tuber breakdown.

The speed of deterioration in some stores has been "remarkable", says Graeme Byers of ADAS Leeds. The plant clinic there reports more than a dozen "serious" cases. Some apparently sound crops have been unloaded within a fortnight of storing to prevent further losses.

So far it seems the worst hit tubers are those which started to set skins, but still managed to absorb early September rains. None of the affected crops were burnt off until after the rain and dry matter levels fell dramatically, he notes.

Late maincrops escaped because they had not begun to set, and second earlies had senesced too far to make use of the rain.

Another common theme is a high level of common scab or mechanical damage allowing soil-borne Erwinia bacteria to gain hold.

"I dont think were so badly affected in the east," says ADAS Huntingdon-based senior potato consultant Paul Dover. But lack of cool air for ventilating stores has been a big problem, he adds.

Tim Berry, agronomist with March-based MBM Produce, reports above average levels of pink rot but little concern except in a couple of stores. "Its not an imminent disaster, but it needs watching."

Keep tubers dry

The key, he maintains, is trying to keep tubers dry. "Even if you cant get the temperature right down you need to get them dry as quickly as possible."

David Hudson of the PMBs Sutton Bridge producer group comments: "Theres more rotting than we like to see, but no horror stories yet." The long hot summer followed by a wet back-end encouraged pink rot and watery wound rot, he explains. "Bacteria are then getting in behind the fungus."