Blight affected potato foilage.

Mixed weather patterns across many regions in the UK and Ireland is leading to localised outbreaks of late blight in potatoes.

Main-crop varieties are closing in on the burndown phase, but much of the planted area has up to three weeks left and growers need to ensure they take clean crops into store.

The Blightwatch alert system, hosted by AHDB and the MET Office, has displayed red warnings – indicating the highest level of blight threat ­– for key potato-growing regions.

The counties with Blightwatch red alerts in England include Lincolnshire, Yorkshire and Lancashire. Forfar and Ayr in Scotland have had a similar level of threat indicated, as does Wales.

Corteva Agriscience’s field technical manager for potatoes, Craig Chisholm, said the crop protection and seed company had received a flurry of calls from growers and advisers on how to protect crops late in the season.

“The risk is that tuber blight could be carried into store, caused by temperatures falling and rain washing zoospores into the soil,” he said. “Catchy weather may well extend the intervals between spraying blight fungicides, so we’re advising growers to use a product that’ll protect the canopy for 10 days.

“Some growers have the added complication of managing a stop-start cereal harvest at the same time as timing preventative blight sprays. Because of this, a product with some curative activity on blight will prove useful.”

Craig Chisholm of Corteva Agriscience.

Mr Chisholm said Corteva’s blight fungicide co-formulation Zorvec Endavia – launched this year – can play an important role in providing late protection.

“Zorvec has very good activity on the leaf surface and within the plant so acts to prevent the production of zoospores that cause late blight,” he said. “The Zorvec AgPack containing Zorvec Enicade + amisulbrom will add additional activity, as amisulbrom is generally used to prevent zoospores in the latter part of the programme.”

Rainfastness is another concern as showers appear hugely localised, making it difficult for sprayer operators to plan applications.

“Zorvec is as rainfast as any active ingredient available to UK growers,” Mr Chisholm said. “There’ll be some variability with different levels of leaf wetness, canopy structure and leaf surface, but growers will favour a robust fungicide that’ll protect their investment so close to the end of the season.”

See for the latest blight disease threat warnings.

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