Farmers are being warned to be on the lookout for areas of crop which appear to be ripening prematurely.

Neil Groom, technical director at Eye-based seed merchant Grainseed, said this could be a symptom of soil-borne fungal disease Verticillium wilt.

'If you have Verticillium in your soils, the only way to live with it is to grow a variety which has good Verticillium wilt resistance or tolerance,' he said.

'Using crop intervals or rotations is impractical, since the disease remains viable in the soil for over 20 years. Nor are there any approved chemical answers.

'In the East, Midlands and the West, 8% of crops had this disease last year according to Crop Monitor.

'If you don't grow a resistant variety, you will have to suffer the consequences. We suggest that those who are seeing Verticillium wilt now or in the past few years, make a proactive decision to grow a resistant variety this autumn.'