Maincrop potato prices have begun the season well ahead of last year with recent scorching weather raising fears over yields and quality.

Ex-farm average prices began at £150/t last week, £40/t above the same time last year. But values have since risen, with the free-buy market averaging £165/t while chipping varieties neared £200/t.

Recent isolated storms, forecast to continue, have meant a postcode lottery for crops, pushing irrigators to their limits in the driest areas.

British Potato Council market analyst Rob Burrow said the recently harvested early potato varieties had been hit worst by the heatwave.

“Early crop reports show a 12% fall in yields so far.

But it’s probably not too late for most of the maincrop if the weather does change.”

The BPC estimated 131,000t had been lifted from 5000ha (12,300 acres) since 1 May at an average of 200/t, a rise of over 50/t on a similar area in 2005.

Yields from non-irrigated crops in the driest eastern counties were as low as 15t/ha (6t/acre).

“Some yield reduction seems inevitable and there are prospects for strong prices this season,” reckoned Mr Burrow.

Reports of scab were on the increase and many farmers feared secondary growth should the weather bring a long period of rain.

Coupled with this, record temperatures for July had restricted tuber size and raised the danger of greening as canopies died off.

Farmers Weekly Barometer farmer Richard Solari, who grows 90ha (220 acres) of potatoes near Bridgnorth, Shropshire, reckoned prices could rise further.

“Consumer demand is lower at the moment, as people prefer lighter food like salads, and many are away holidaying.”

The level of irrigation taking place demanded an extraordinary uptake of water, he added.

“We’ve been luckier here.

Two big storms have brought about 30mm of rain each, while five miles away, farmers have had 90mm and that has damaged crops.”

Cambridgeshire, Herefordshire and Yorkshire have not fared so well. John Watkins, who grows 120ha (300 acres) for free-buy and contract markets near Ross-on-Wye, said the forecast rain just had not appeared.

“People are comparing temperatures with 1976. There was very little rainfall in the 1975/1976 winter and that has been the case this year, too.”

Heavy rains in late May had substantially weakened crops before the drought struck, Mr Watkins said.

“Three inches of rain on 20 May washed many of the headlands out on the heavier land round here, leading to poor, misshapen crops.

“If we get yields as low as 8-9t/acre – instead of 16t/acre – we will need prices between £200 and £300/t to break even.”

Cost-plus contracts left growers little scope to reinvest, he added.

Richard Marcroft, potato supply manager for McCain Foods, said its three factories had only started processing the 2006 crop and it was too early to gauge overall yields and quality.

“There will be some effect on supplies, but we will be working closely with our grower base.”

ian.ashbridge@rbi.co.uk