WATCH out, phoma is likely to threaten vulnerable newly-emerged crops from this weekend, following favourable conditions for the damaging disease.
Spore production on trash is highest when wet weather follows dry conditions, just what is forecast, warns fungicide supplier Syngenta.
Small leaved crops are most vulnerable, notes Norfolk-based Morley crop consultant Bill Barr. In warm weather phoma can spread down the leaf and onto the stem in just a few days, going on to form yield-sapping cankers later in the year.
"Growers have got to react quickly to the first signs of infection," says Mr Barr. In smaller-leaved crops he advocates an early application of 0.25litres/ha of Plover (difenoconazole) as soon as 10% of plants are infected.
Only add mbc to boost light leaf spot control on highly susceptible varieties or where the disease is identified, he adds.
ADASs Peter Gladders believes untreated phoma knocks 0.7t/ha off rape yields in the east, a two-spray programme recovering up to 0.5t/ha of that. *