9 June 1995

UK climate too harsh or not?

SOME growers doubt the value of containment. They believe the UK climate is too harsh for rhizomania to flourish.

Some evidence to back that exists. But the risks of removing restrictions are too high until resistant varieties are proven, says Dr Asher.

Cooler UK weather may reduce rhizomanias virulence, he explains. "In warm soils the disease can infect very young crops. That can cause up to 40% yield loss in France and Germany."

Holland has a similar climate to the UK, and soils warm too late for the disease to hit hard. "Rhizomania is quite extensive there, and sometimes locally damaging. But they still out-yield us nationally every year."

Although 15 new outbreaks were found last year in the UK, only 41 farms in total have become infected, all in Norfolk and Suffolk. If the trend continues, about 3000ha (7400 acres) across 100 farms will be affected by the end of the decade. But that is still under 2% of the sugar beet area, notes Dr Asher.

Prediction difficult

However, the industry would be foolish to rely on these figures, he warns. "Its very difficult to predict disease patterns accurately. It could take off as it has done in some other countries, especially if controls were dropped."

He believes many more fields could be carrying the disease at subclinical levels. "Infection probably occurred 10-20 years ago. Several beet crops may be needed to incubate the disease here. How much spread there has been in that time is difficult to say."

Continued containment means the UK can wait until resistant varieties that match conventional ones for yield and quality are bred, he says. "Some are doing well in Dutch trials, and could be commercially available in two years."

But they must not encourage the virus to multiply, he stresses. Disease would spread quickly and resistance could break down. Brooms Barn and ministry trials are screening new varieties now.

"Once we have suitable resistant varieties, we can say goodbye to containment. Until then, it should be maintained in a form that balances risk against growers needs," says Dr Asher.