7 June 1996

Clamps at risk from increase in violet root rot

Root rots have thrived in recent warm summers. In the absence of fungicides for control, how can growers prevent such late season diseases?

VIOLET root rot, known since the 1940s, has been causing increasing problems in recent years.

Violet strands of fungal growth often appear on the root surface in mid- to late summer. Early and severe infections can decrease both root yield and sugar content. But the main damage occurs after lifting.

Richard Cogman, agronomist based at British Sugars Ipswich factory, says diseased roots deteriorate quickly in the clamp.

"If you carry on lifting and clamping infected material, it wont be long before affected roots rot to unacceptable levels. But rejection is not inevitable if you seek advice from the factory field staff as soon as you see the first symptoms."

The disease seems to be encouraged by warm, moist summers. But its response to climatic conditions is not really understood, says Mike Asher, plant pathologist at Brooms Barn. For that reason, the threat is difficult to predict.

"Sugar beet grown in rotation with other root crops, which act as alternative hosts, are at high risk. But it is not just root crops which harbour violet root rot – those with large roots such as parsley and certain weeds, for example thistles, can exacerbate its spread."

Fungicides offer no hope of control. So the best defence lies in extending the beet rotation to one year in four or five, or omitting other root crops. But that is often uneconomic, Dr Asher admits.

Controlling weeds may help prevent inoculum build-up. But realistically growers may have to wait until resistant varieties can be found, he says.

Clamp collapse culprit ‚ violet root rot.