A surprising variation in the emergence of beet crops has been reported by many growers to the Norfolk-based British Beet Research Organisation.

While no immediate common factor has yet been established, lead scientist Dr Mark Stevens has been told in the last 72 hours of varying performance and vigour in at least six varieties.

He suggested that it was not just a simple a matter of timing – for example early versus middle or late drilling. 'It is a combination of a number of factors, that includes soil temperature, time of drilling and conditions at drilling,' said Dr Stevens, who is based at the Norwich Research Park.

'It is far from straight-forward. There are crops drilled in the window between March 5 and March 7 which don't have issues. There are some crops drilled around Easter and after Easter, March 31, when soils were starting to warm up which have not emerged evenly.

'There are some fields where a grower has two varieties; one has a plant population in excess of 100,000 and another with 40,000 to 60,000 plants per hectare. We have seen some fields with even lower plant populations.'

Dr Stevens said that it had been a difficult season, probably the worst year for 50 years and similar concerns had also been raised in northern Europe, notably in Belgium.

The emergence also seemed to vary across Norfolk and further afield. A British Sugar spokesman said that plants in East Norfolk had emerged well by the bank holiday but generally the beet crop was probably three weeks later than last year.

This was confirmed by former Norfolk farmers' leader, Richard Hirst, who said: 'I'm not aware of any problems in our part of the world.' However, performance has been variable.

One large beet grower, Poul Hovesen, who is estate manager for Sir John White's Salle Farms, near Reepham, has noticed some differences in emergence. 'There's no doubt that the early-drilled Cayman has been slower to develop,' he said.

At Salle, where about 700 acres of beet is grown, he said: 'We finished the last field of Cayman and filled up with another variety and moved two or three miles up the road.

'You can see a clear difference between the two.'

In west Norfolk, farmer John Darby, of Methwold Hythe, said that his 110 acres were also variable but he was more immediately concerned at the prospect of fen blow. 'I'd say that the 50pc early drilled beet are variable while the late drilled are small and all there. We are lucky because we're all relatively late-drilled. These are definitely the best,' he added.

Beet growers' leader, William Martin, and fellow members of the sugar board, who had discussed the concerns, were also puzzled. 'That's what is so frustrating... I don't think that anyone can say that it is a particular variety or a particular drilling date.'