23 October 2001
ADAS issues phoma warning

By Tom Allen-Stevens

OILSEED rape growers have been warned that there has been an explosion of phoma, the yield-threatening disease that leads to stem canker.

A count of infected plants at ADAS Boxworth, near Cambridge, on Monday (22 October) revealed that 75% of plants are now infected.

This has risen from 1% just two weeks ago.

Latest counts from ADAS Terrington, in Norfolk show 40% of plants are infected while this figure stands at 12% for High Mowthorpe in Yorkshire.

To compound the situation, spore trapping at Boxworth shows that last weeks release of phoma ascospores has doubled the previous cumulative count.

These counts, which give about a 10-day pre-warning of future infection, show the disease is still increasing rapidly, said Iain Hamilton of Syngenta.

“Its not as high yet as the worst ever case we had two years ago, but it will catch up pretty quickly,” he told FWi on Tuesday (23 October).

The key worry for ADAS oilseed specialist Peter Gladders is the timing. “Usually were into November before the phoma explosion occurs,” he said.

“Its development is very dependent on temperature. The current mild conditions mean the disease is now growing rapidly down the stem.”

Growers in the south and east are urged to spray as soon as possible, while further west the signs are there that the disease is about to take off.

“Normally we recommend spraying at 10-20% plants infected, but Id say bring that nearer to 10% now,” said Dr Gladders.

He advises using a standard half rate of a chemical with kickback as well as protective activity, which may need to be repeated in December.

The typical response from treatments is 0.75t/ha, said Dr Gladders.

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