8 March 1996

Dont let late blight play havoc in store

IN a dry season stem blight infection can go unnoticed and develop into trouble before routine spraying starts. The result is late blight which can cause havoc in store.

"Stem and leaf blight are different phases of the same disease," says Nigel Hardwick, ADASs national specialist for diseases on non-cereal crops. "If infected seed is planted emerging shoots carry the fungus which, in favourable conditions, later moves from stems to leaves. It is not always easy to see stem blight – normally trouble is only noticed when it reaches leaves."

The disease is most likely to be masked in a dry year as a humid micro-climate under the canopy allows fungal development when upper foliage is clean.

Dr Hardwick warns of the dangers of assuming a crop is blight-free. "At harvest growers lulled into a false sense of security by a clean looking crop may be tempted to cut corners and start lifting when there are green stems around. A month later rotting occurs in store and in extreme cases the crop can run out of the doors."

At the other end of the season fear of blight often forces growers to start spraying whether or not fungicide is needed. This can be a waste of money and reduce the flexibility of the programme. Blight monitors in the crop should improve spray timings for more economical fungicide use.

ADAS is working with the Central Science Laboratory to establish the in-crop criteria needed to forecast localised infection risks.

"The aim is to use the best bits of Smith periods and forecasting systems used in USA and on the Continent to provide blight warnings specific to individual crops for the year 2000 and beyond." &#42

There may be few signs of blight on the leaves. But stem lesions beneath the canopy can pose a hidden threat to tubers in storage.