Practical solutions for powdery scab control

SCOTTISH potato growers had a difficult year in 2011 for several reasons, but one of the most significant was the cool, wet conditions, which were ideal for powdery scab to spread.

At the SAC Association of Potato Growers conference, Alison Lees of the James Hutton Institute and SAC consultant, Stuart Wale told delegates about the most recent research on powdery scab and the control measures available for the disease.

Nine trial sites had shown a similar pattern of disease and data had been analysed to establish links between infection and environmental variables.

Dr Lees said a soil test would not predict the disease, but the more inoculum found in the soil, the greater the incidence of disease - providing climatic conditions were favourable.

Dr Wale said planting resistant varieties would go some way towards reducing the incidence of powdery scab, but even varieties with a susceptibility rating of 8 were at risk under cold, wet conditions.

He told the conference that in six out of seven trials the fungicide fluazinam worked, but only if applied properly as a downward drench and evenly distributed through the soil just before planting. He recommended a combination of the two, plus taking into account the history of the field.

Planting healthy seed was crucial, but he said: “There has been a bit of powdery scab about this year, and even when graded out, tubers showing no symptoms can still be carrying spores and infect the crop.”

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