13 October 2000

Phoma spray threshold is breached in Notts

PHOMA in NIAB/DuPont oilseed rape monitoring plots in Notts merited spraying by the start of the week. But elsewhere in the country levels remained below spray triggers.

At the Notts site 16% of Apex plants had spots, notes NIAB pathologist Jane Thomas. "It is essential to spray when no more than 10% of plants are infected," according to DuPonts Andy Selley.

"This site was one of the earliest to show high infection levels last year," says Dr Thomas. "And the monitored variety, Pronto, gave a 0.6t/ha yield response in HGCA-funded Recommended List trials."

With no leaf spots yet at the Kent and Gwent sites and only traces found in Hants and on an irrigated trial in Cambs phoma does not seem to be hitting quite so early as last year, she says.

"Cooler weather will help slow growth of the fungus from spot to stem base, but any return to warmer conditions will speed things again and give growers only a small spraying window."

For more resistant varieties such as Escort it may be possible to delay treatment, she notes.