5 September 1997

Potatoes on target but blight threatens

EARLY signs are that this years maincrop and late second early potatoes should yield on a par with last season.

But low tuber numbers, high dry matters and the continuing threat of blight could hit crop marketing.

After a season of extremes – a dry spring, sodden June and scorching August – many crops are much further forward than normal, according to the British Potato Councils Rob Burrow. "Early estimates from the field are for a pretty reasonable average of 41-45t/ha."

Summer temperatures up to 30C (86F), earlier than usual tin-based blight sprays and in places premature desiccation to contain the disease have all trimmed the potential of some varieties, especially Estima, say specialists. But blight-free crops of types like Cara still have plenty of growing to do.

Lower tuber counts caused by dry weather just before initiation are commonplace, says Anglian Produces Simon Bowen. This could be a benefit particularly in crops stressed during the August heatwave, he suggests. "It will increase their tuber size to get more baker fraction. Plants just shut down during the hot weather."

Mr Bowens main concern is for the excessively high dry matters and potential bruising in some crops. Some processors set an upper limit of 23-24%, he adds. "We have measured crops at 25%." Inevitably some growers may have to sacrifice yield by burning down earlier than normal to stay below the standard.

Suffolk-based BPC field manager, Terry Hunt, confirms the low tuber numbers, especially in shy-setting Romano. "But it is not universal." Estima at the councils autumn lifting demonstration north of Bury St Edmunds stood still for three weeks in the recent heat, he notes.

Tin-based sprays, which can check the growth of crops, have been extensively used up to a month earlier than normal in Lincs, says colleague Richard Spinks.

Trial digs in Desiree by March, Cambs-based MBM Produce agronomist Tim Berry, show nearly all the tubers in the correct size bracket for pre-packing (up to 65mm). "But the overall yield will be down at 13-14t/acre. We normally hope for 17-18t/acre."

Twelve hectares (30 acres) of Erntestoltz second early crispers lifted recently at Hook House Farm, Amcotts, near Scunthorpe, had a good dry matter, 21.5-22%, reports former barometer grower Guy Tindale. "They did about 16t/acre, which is a bit down on last year. But we did not get the tuber numbers."

Maincrop Shepody seems afflicted by the same problem, he says. "We could end up with deductions for over-size. But Maris Piper is shaping up nicely and a few less tubers in the Russet Burbank would be no bad thing."

Robert Belcher reckons yields of his Saturna, Record and Brodick on free-draining sand at Tibberton Manor, Newport, Shropshire, will be slightly lower than last year. The wet June has caused early senescence and shortened the growing season," he says.

Stressed Estima is unlikely to be a star performer on sandy loam for Bill Poortvliet at Stratton Streles Estate, Colby, Norwich. "But the more vigorous Cara and Fianna are still full of growth." Interestingly, he notes, tuber counts are higher in crops grown from once-grown seed than in those produced from Scottish seed.n

MAINCROP POINTERS

&#8226 Low tuber counts.

&#8226 Recent heat stress.

&#8226 High dry matters.

&#8226 Tin spray checks.


UK potato crop yields (BPC figures) (t/ha)

1994199519961997

Overall43.440.944.541-45?

Maincrop

only45.542.545.8??????