Production is also down. In 2004 it was 47,828 tonnes, the smallest crop in 86 years. The latest crop is estimated at 90,000 tonnes, almost double that of last year, but still 48% smaller than the pre-2004 five-year average.
But the prune industry still has a lot to cheer about. More than 60% of the world's prunes originate from California and the state's growing conditions and agricultural practices mean it still has an advantage over many other prune-producing countries.
California leads the way in terms of quality because of its rich valley soil, long warm growing season, abundant supply of irrigation water and modern agricultural practices, according to Richard Peterson, executive director at the California Dried Plum Board.
Mark Dalrymple, president of Sunsweet Dryers, adds that California has some of the highest standards of prune drying and processing in the world. All Californian prunes are dried using dehydrators, he says. In other countries, many are still sun-dried, which causes them to pit badly.
Grower practice also helps California's prune industry stay ahead of the pack. Chile had a bumper prune crop last year, but farmers didn't 'mitigate' - cut back on fruit during early growth - meaning the size of the fruit was much smaller. Californian prunes, by comparison, are much larger.
The health credentials of prunes means that they could become the next superfruit in the UK. They have an ORAC - antioxidant rating scale - of 5,770, compared with 1,260 for spinach and 980 for brussel sprouts. They contain more potassium than bananas and more iron than broccoli. Yet consumer acceptance of prunes is low.
Dane Lance, vice president of global marketing and sales at Sunsweet Growers, which supplies half of total prunes in the US, says: "People in the UK know that prunes are healthy, but they hark back to school dinners. It is frustrating for us as nutritionally we are off the charts, but the laxative stigma still turns people off."
In a bid to change perceptions, Californian prunes have become the official snack of the England Netball team in a campaign fronted by model Nell McAndrew.
Lance hopes that new products to the UK will help. Prunes with fruit essence are popular in the US, and he highlights these as a key opportunity for growth in the UK.
Even organic prunes are being grown, with eyes on the UK market. Taylor Brothers was the second organic prune company in the US. President Richard Taylor says: "We saw there was a demand and felt that the industry had shifted too far with the use of pesticides."
The organic prune business has grown annually by 20%, says Taylor. Recent low crops means that the company has had little activity in the UK so far. It does supply prunes for the Crazy Jack brand and, with a new facility in Poland, output to the UK is likely to rise.
Yet both companies are aware of the challenges of the UK market. Says Lance: "UK buyers are buying cheaper and cheaper. Own label is much more developed, so it's hard for a brand to eke out a living."
Taylor says: "UK buyers have figured out how to squeeze producers until they die." n