24 May 1996

Potatoes struggle to emerge in chill

A CHILLY May sees many potato crops struggling to come through, damaged by late frosts and at risk from rhizoctonia stem canker.

"Crops are taking a long time to emerge so are vulnerable to trouble," says agronomist Simon Bowen of Norfolk-based Anglian Produce. Many are taking five to six weeks to show instead of the more normal three to four, he says.

"Some varieties, such as Estima and Sante, seem more affected than others. Estima has variable emergence in a good season and does not like to go into cold soil, so this year it is worse than normal. Others, such as Cara and Fianna, seem to have coped better."

Small seed factor?

Mr Bowen believes small seed may account for the big range of emergence this season. With fewer reserves than larger tubers, seed in the 25-35mm size grade seems to be struggling.

"It is a season to show up the weakness of small seed. Where plants have emerged they appear to have weak stems. We have also seen a lot of secondary branching which may have been induced by the cold."

Early drought in the east is also worrying with many fields already having soil moisture deficits (SMDs) of 20-25mm (0.8-1in).

"SMDs are running away from us and if we do not get substantial rainfall soon huge deficits could build up," says Mr Bowen.

Emerged crops look reasonably healthy but are wide open to disease in the cold slow-growing conditions. A week of warmth will pull them together, he suggests. But the delayed emergence may upset tuber size and have a knock-on effect for early harvested bakers.

In Cambs, ADAS potato consultant Paul Dover has seen sandland crops of Estima suffering from late frosts.

"Growers cannot recall such a continuous run of cold weather in May and there has been widespread damage to crops," he says. "Many of the leading shoots have been burnt off. No crop has been sufficiently advanced to be badly compromised, but the damage has evened up the irregular emergence."

The latter could have been caused by sprout damage at planting, or putting seed in too deeply in friable seed-beds, he suggests.

Potatoes in Yorks and Lincs are suffering a 10-14 day delay.

"The cold has delayed emergence and plants are struggling with soil temperatures 4-5C below what they should be at this time of the year," says Denis Walsh of the Finningley-based Higgins Group which handles 150,000t of potatoes a year.

"There is nothing more sinister, although I am beginning to see the odd bit of rhizoctonia."

Ground frosts killed some early growth, but crops that had come through are now re-emerging. Potential yield has been lost but Mr Walsh is not too concerned about the long-term effects.

"The calendar is ticking over towards the longest day and crops have still not yet produced much of a canopy. Even so it is too early to worry."