Watch local variations
THE NATIONAL disease survey provides a general picture, but has its limitations, warns Cambs pathologist Bill Clark.
"Its only a single, late season snapshot." Its figures tend to mask high disease levels in local areas. The south-west regularly has higher levels of septoria in wheat and rhynchosporium and net blotch in barley, he points out.
Yellow rust position
Yellow rust was non-existent for the bulk of the country last season. But the disease hit several crops in south Lincs. "We got a 7t/ha yield response at Terrington," he says.
Admittedly the variety was the highly susceptible Slejpner. But with the new rust strain lurking to hit more widely grown varieties, growers need to be watchful, he suggests.
The extra output was achieved with only 0.75litres/ha of Folicur (tebuconazole) costing about £20.
Mr Clark is unable to account for the rises in sharp eyespot. "We know so little about the disease. Its very erratic." Changes in the variety mix are unlikely to be the reason, he says. "Its probably just a blip."
Main reason for the increase in BYDV in 1995 was that many growers omitted to re-treat crops invaded again by virus-carrying aphids in the relatively warm November after earlier sprays in October.
"It was fundamentally because of the mild winter," says ADAS entomologist Jon Oakley.
All the signs are that this autumn has been similar. "Anything that was treated before Oct 15 could need doing again," he says. "
If you can find any aphids at all you need to spray."