The price of potatoes rose by 21 per cent between the end of June and the end of July and contributed substantially to the 1.2 per cent inflation rate in July.

Mr John Barry, of the Irish Farmers' Association, said yesterday the increase was caused by the introduction of new potatoes.

He said last year's potatoes had been particularly plentiful, resulting in low prices and continued availability until the end of June. Italian and Cypriot new potatoes became available in June, and Mr Barry said the increased price still gave a poor return to the growers. The IFA expects prices to drop again over the coming months.

A spokesman for Superquinn said the increase was due to a problem called blackleg in Irish potatoes. Blackleg is a fungus, prevalent in wet weather when potatoes rest too long in damp ground. It causes them to rot soon after harvesting, and Superquinn said this had resulted in an increase in the price of good quality potatoes. However, Mr Barry of the IFA said there had been no scarcity of new potatoes, and blackleg had not affected prices.