6 June 1997

Keep check on tuber initiation to beat scab

POTATO growers should check crops now for tuber initiation, warns Simon Bowen, field services manager for Norfolk-based Anglian Produce.

They may need to start irrigating to control common scab earlier than they expect as many crops are reaching that growth stage at quite low ground covers this season, he explains.

"Growers often use ground cover as a guide, usually associating tuber initiation with plants meeting along the rows," says Dr Bowen. "But many crops seem to be reaching that stage five to seven days early. To check growth accurately, you have to dig."

Many growers will struggle to maintain irrigation schedules to control scab, he suspects. "The aim is to keep water deficits below 15mm on light soils. But crops have grown quickly, and those at 50% ground cover will be using in excess of 3.5mm of water a day. If you are putting on 3⁄4in, it will only last four or five days."

A months irrigation is needed to ensure skins are sufficiently developed to ward off disease, but many growers may not be able to cover the ground every few days. With the tight scab tolerances for the pre-pack market it may pay to sacrifice a field for that market so the rest can be irrigated properly, suggests Dr Bowen.

"There are processing outlets for some varieties like Estima and Sante. If dropping a field from the schedule enables you to concentrate on getting the rest right, that may be the best thing to do." &#42