Despite a bumper potato harvest in Switzerland this year, growers' joy is being spoiled by big retailers squeezing them on price and rejecting bigger-than-average spuds.

Charlotte shouldn't be bigger than size 60-120. Nothing to do with a farmers lonely hearts column, these are the accepted measurements of the Charlotte potato variety, reported swissinfo.ch.

In other words, Charlotte - a frequent visitor on Swiss plates "with its distinctive long, oval shape, white skin and moist texture" - shouldn't be more than 60 millimetres wide and 120 millimetres long.

If they are, they won't fit on the shelves of the big supermarkets - not to mention in the cooking pots of customers, who are increasingly asking for smaller varieties. Industry potatoes used to make chips or crisps can be a bit bigger.

The problem is that the dry spring and in particular the very warm autumn have conspired to increase both the number of tubers per plant and also their size.

Ruedi Fischer, president of the Swiss Potato Producers Association, is sceptical of "record years", preferring to talk about an "above-average crop", as in 2009. Many regions are reporting excess yields of 20 per cent or more, while elsewhere the crop is average.

"In addition to the large harvest, the market conditions are very tense. We're really feeling the struggle for market share," he told swissinfo.ch.