Growing blackleg threat to seed potatoes

Waterproofs were definitely required for a visit to this year’s Potatoes in Practice event at the James Hutton Institute’s Balruddery Farm, Invergowrie, near Dundee. Teresa Rush reports.

CONCERN is growing within the seed potato industry over the extent of blackleg disease being seen in this season’s crops.

Anecdotal evidence that levels of blackleg were significantly up on recent seasons appeared to be confirmed at Potatoes in Practice, when representatives from the Scottish Government’s Science and Advice for Scottish Agriculture (SASA), said 8 per cent of this season’s seed crop had been downgraded as a result of blackleg infection – double last year’s figure in percentage terms.

A further 1.5 per cent of crops have been rejected. About two-thirds had been inspected when the figures were collated.

However, putting the figure into context, SASA bacteriologist Dr Gerry Saddler said 2010 had been the only year since 2003 in which blackleg levels had fallen.”We have been seeing a building of blackleg since 2003,” he said.

Higher disease levels this season are believed to be linked to weather conditions favourable to the development of blackleg.

Contributory factor

SASA scientists were unconvinced by suggestions blackleg was increasing due to the withdrawal of sulphuric acid as a desiccant.

“Some growers stopped using sulphuric acid years ago. It could be a contributory factor, but we can’t say one way or the other at this stage,” said Dr Saddler.

“The sulphuric acid ban may be a contributory factor, but I don’t think it’s the sole cause,” said Dr John Kerr, head of potato branch.

According to Sutton Bridge Storage Research pathologist Glyn Harper, there were a number of measures growers could take to manage blackleg risk.

Advice included identifying at-risk stocks and dealing with them separately; harvesting as early as possible, and good machinery hygiene. Once in store, crops needed to be kept dry and cool.

“Aim to ventilate during early storage using dry air. Crops need to be dry and as cool as possible. Below 10degC disease development is slowed,” said Dr Harper.

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