Growers warned over black dot

Wet soils are posing a high risk of black dot on potatoes being harvested over the coming weeks, Dr Jeff Peters of Central Science Laboratory has forecast.

Peters told growers at the East Anglian Potato Event - held near Aylsham on 5 September and organised by Greenvale AP, Frontier Agriculture and Syngenta Crop Protection UK - that the saturated soils have been highly conducive to disease development, and every week's delay in harvesting with the wet conditions increases the risk.

Growers, he said, should be deciding now when to desiccate crops to minimise the risk of the skin disease reaching levels where retailers may start to penalise the quality of pre-pack samples.

Trials, funded by the Potato Council and the Scottish Government, have shown that maincrop varieties that are in the ground for more than 130 days from 50 per cent crop emergence to harvest have a significantly higher level of disease infection.

For second earlies, the risk increases after 120 days.

"If growers can lift before this time, then skin quality can be maintained with good storage," Peters advised. "Where there is a risk of black dot, tubers should be cooled to 3.5 degsC in store as quickly as possible.

"Typically, infection may be at levels growers would not even see at harvest, but will be clearly visible as the areas of skin with microsclerotia darken up over several weeks, or when tubers are brought out of cold store for packing."

He added that, although trials have shown no advantage of ventilation for black dot control, drying tubers will be highly important to minimise other storage rots this season.


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