High soil moisture combined with full canopy crops could create microclimates ideal for potato blight development, irrespective of the weather, warns the British Potato Council’s (BPC) blight advisory team.
Adas blight expert Nick Bradshaw said that despite continued cooler, unsettled weather, conditions are generally unfavourable for blight development. But, he added that with the majority of potato crops now with a full canopy, high humidity could still develop within canopies, following the recent rainfall. This would pose a blight risk.
Bradshaw advised basing treatment decisions on accurate local knowledge of inoculum pressure to help risk assessment. “While there have been few full Smith periods recorded in England or Wales since the 14 June, blight has been confirmed in a crop of Shepody near Chester, and as isolated plants in two crops in Norfolk, but nothing to indicate a major upsurge in activity,” he said.
“There have been no reports from other areas where blight is almost conspicuous by its’ absence,” he added, urging growers, agronomists and formally-recognised ‘blight scouts’ to send suspect samples for confirmation. He said such data is very important for effective risk assessment to build up a picture of an epidemic, as part of the BPC’s awareness campaign.
Bradshaw notes that the weather pattern in the last week or so has often meant localised rainfall and so any decision to rely solely on protectant fungicides or to extend intervals must be locally based. “Where protectant products are being used, overextending intervals could allow blight infection to occur.” In this situation he recommends that products with known kick-back activity should be available.
Potato haulms are easily damaged in the continuing windy conditions, said Bradshaw, and will provide an entry for botrytis infection. It can be easily confused with blight and incorrect diagnosis often leads to unnecessary fungicide use, or may mask the presence of blight. “All the more reason to get suspect lesions correctly identified,” he concluded.
For regular potato blight updates growers can visit the BPC’s website www.potato.org.uk
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