The reduction of powdery scab brought about by two consecutive dry summers should not lead seed potato growers to forget that the pathogen Spongospora subterranean is still the most significant threat to their crops.
That was the message from Stuart Wale of SAC, who added that although cool wet conditions at tuber initiation are the normal indicators of a bad year for powdery scab infection, even after a dry summer powdery scab can still be found in fields where soil contamination elves are high.
As many as three-quarters of varieties are regarded as being susceptible or highly susceptible to powdery scab, with SAC estimateing that seed growers’ losses in Scotland alone could top £7m a year in a favourable year for the disease.
Wale is advocating the use of Shirlan, a product for which SAC gained a SOLA last year, not just for Scottish seed growers but also those in other high risk situations. The SOLA permits the soil application of Shirlan at 3l/ha and incorporated into the soil immediately prior to planting seed crops.
Monitoring of diseases in seed stocks across England has revealed the incidence of powdery scab was highest in seed to be planted in the south east and west midlands, with 50% of stocks in the south east affected.