6 October 1995

Tuber disease is on the rise

POTATO tuber necrotic ring disease is on the rise, hitting five crops in Yorkshire, Norfolk and the West Midlands already this season.

The new disease is a strain of aphid-transmitted potato virus Y, explains ADAS Cambridge-based potato pathologist Mike Foley. In some crops up to half the tubers can be afflicted.

Best seen after washing

The small necrotic rings on the skin surface, with healthy tissue inside, are best seen after washing tubers. Initially they appear pale brown/orange, just beneath the surface, but later can eat up to 1.5cm (0.5in) into the tuber, causing problems for chippers and crispers.

"We think growers may be missing this, or confusing it with other conditions. After a period of storage the rings can darken, fill-in and crack to look more like fusarium dry rot," comments Mr Foley.

Control demands seed free from virus Y and good aphid control. Some varieties are worse affected than others, and crops which appear clean at harvest can develop symptoms in store, adds Mr Foley.