25 April 1997

Less risk of sclerotinia

CONTINUED drought could ease the threat of sclerotinia in winter oilseed rape, according to ADAS.

But growers should be on their guard and ready to apply a petal fall spray if significant rain falls before the end of flowering, advises pathologist Peter Gladders.

"Dry conditions are keeping things fairly quiet at the moment." Although the funguss fruiting bodies began germinating in March, many subsequently shrivelled in parched soils, he says.

"It needs fairly substantial rain from now on to wet the ground again to about an inch to promote a fresh flush of germination. Effectively we would need two good spells of rain."

For farms where the sclerotinia risk is known to be low, there could be a case for withholding treatment until later than normal, he says. Where drought persists it might even be omitted altogether.

But watch out for advice. The results of more widespread petal testing on 350 farms this season should provide a good guide to the threat in specific areas, he says.

Most farms with a history of severe disease would be unwise to change tactics, he adds.n