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Forecast says oilseed rape crops are at risk from phoma disease

PUBLISHED: 08:56 12 October 2015 | UPDATED: 08:56 12 October 2015

Phoma on oilseed rape leaves

Phoma on oilseed rape leaves

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Oilseed rape growers should brace themselves for a "mass eruption" of the spores which cause one of the crop's most damaging diseases, according to experts.

The warning was issued alongside the critical October update of the phoma leaf spot forecast, funded by sector levy board AHDB (Agriculture and Horticulture Development Board) Cereals and Oilseeds.

Hosted by Rothamsted Research, the forecast uses temperature and rainfall data from summer to early autumn to provide information on potential disease pressure and to guide spray decisions against phoma.

With plenty of rain throughout August and unsettled conditions predicted for the foreseeable future, all regions are forecast to be at risk from a mass eruption of airborne spores during early to mid-October.

However, due to the localised influence of rain, the timing of visible leaf spot symptoms is expected to vary tremendously across the UK.

Dr Neal Evans, of Weather INnovations Consulting LP, advised growers to monitor the phoma leaf spot forecast website to track local risk.

“The UK forecast map is based on more than 80 sites and is updated daily to show when each site is predicted to have 10p leaf spotting, which is the established threshold for treatment,” he said. “Thus, the map can guide spray decisions but, as localised rain events play such an important role, nothing beats walking the crop and inspecting the leaves.”

Phoma stem canker is caused by two species of fungi, whose spores are released from infected crop stubble in autumn. The spores infect young susceptible leaves, which then develop the characteristic leaf spot.

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