22 May 1998

Management minefield…

Extreme conditions and planting dates have complicated

management for potato growers this season.

Andrew Swallow reports timely advice from experts

gathered at last weeks Potato Technology 98 event

CROPS fall into two groups – those planted before the April deluge, and those after. Add in high early season blight pressure, rapidly increasing aphid numbers, and in many cases a shortened growing season, and the challenge to meet market requirements for ware and processing is greater than ever.

"The late crops are late, very late in some cases, but the earlies were early," comments ADAS National Potato specialist Denis Buckley.

Early planted maincrops are on course for normal yields. But later planted crops are bound to have lost yield potential, and nitrogen rates need tweaking, he says.

More mineralised nitrogen is available from soil reserves for later plantings, points out Mark Stalham, research associate at Cambridge University Farms. This combined with the shorter growing season means 20-30kg/ha (16-24 units/acre) less nitrogen is required on all late planted crops for ware or processing.

"Extra nitrogen to compensate for yield is not going to be beneficial. The crop will produce extra foliage rather than tubers, delaying crop maturity and tuber bulking", he says.

Processing crop specialist Tom Dixon of MBMs Beeson group also stresses the need to reduce nitrogen rates on late planted processing crops, but says varietal characteristics should be into account.

"Crops must be allowed to grow to maturity to reach target dry matters. Growers should consider reducing nitrogen on late maturing varieties to ensure quality targets are met."

Hermes or Saturna pose potential problems, says Mr Dixon. But high dry matter varieties like Rosetta are less of a risk.

"Saturna is a specialist crisper. If growers dont get it right for crisping then its good for nothing else," he warns.

He also urges growers to be aware of the implications of seed management. Late planted mature seed with large apically dominant sprouts will throw fewer stems and tubers. There is a risk of potatoes growing too big, he warns.

Conversely de-sprouted seed may result in more stems and high numbers of late small tubers. All growers can do to increase tuber size is keep the top growing as long as possible he says. "Keep on top of blight – get in early and keep going."

Remember varietal needs when planning cuts in N, advises Tom Dixon,

1998 POTATOES

&#8226 Prolonged plantings.

&#8226 Heavy blight pressure.

&#8226 Irrigation messages.

&#8226 Early aphid activity.