Severe blight alert

25 May 2001




Severe blight alert

BLIGHT inoculum from unprecedented numbers of abandoned potato fields is a real danger to this seasons crop, warns the British Potato Council.

With much of this springs late planted crop still only just emerging, blight from an estimated 8000ha of unlifted and poorly harvested potatoes from the 2000 campaign will be a potent source of early disease, unless managed correctly.

"It is a significant extra threat," says the BPCs Mike Storey. Warm, humid conditions mean newly emerged foliage in nearby crops will be at particular risk.

Despite warnings every year initial infections often come from uncontrolled growth in dumps of waste tubers. "Dumps should not be a problem, but every year without fail, they cause trouble," says Mr Storey.

This season there are effectively whole fields ready to act as dumps, says agronomist colleague Rob Clayton.

"The key is to prevent any volunteers from developing, which probably means repeated use of herbicides."

Simply ploughing down lost crops will not avoid the risk of blight arising. Several treatments of glyphosate at 14-day intervals will be needed to deal with emergence from tubers at different depths, he advises.

For volunteers on truly waste ground Casoron G (dichlobenil) is a more effective controller, but nothing may be sown or grown for over a year thereafter, notes former BPC R & D committee chairman, John Chinn.

Main problem on his Herefordshire farm, where he grows about 320ha of potatoes, are widespread volunteers in subsequent peas and sugar beet drilled after two fields of potatoes went unlifted.

Most buried tubers rotted. But after a light cultivation in February those near the surface were only partially killed by frosts.

"It is a big worry. Are we going to have to put a fungicide in with the sugar beet spray every time we go through?"

To minimise the threat from unlifted areas of particularly blight-prone varieties on farms with a history of the disease it may be sensible to include a fungicide with the herbicide used to destroy them, says Dr Clayton.

"But you need to get MAFF permission to do so on the grounds of plant health risk." &#42

BEWARE BLIGHT

&#8226 Big unlifted potato area.

&#8226 Potential source of disease.

&#8226 Repeat herbicides needed.

&#8226 Add blight fungicide too?

BEWARE BLIGHT

&#8226 Big unlifted potato area.

&#8226 Favourable weather.

&#8226 Potential source of disease.

&#8226 Repeat herbicides needed.

&#8226 Add blight fungicide too?


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