Blight protection must be maintained after desiccation and right up until harvest, potato growers have been reminded.

Although the viability of blight sporangia begins to decline after desiccation, they can remain active and infective in the soil for up to eight weeks after, said the Scottish Agricultural College’s Ruairidh Bain.

“…It’s imperative that growers don’t skimp at the end [of the season], when they think the crop may be safe. Preventing foliar blight in the crop is essential to minimise spore production, but they must also look for soil zoospore activity for as long as possible.”

Sporangia and zoospores can be washed down into the soil by rain or irrigation and growers should use products with strong zoospore activity – such as fluazinam (as in Shirlan), he said.

Lifting crops as soon as skins have set and soil conditions allow will also help reduce infection risk, but growers must make sure the haulm has been completely dead for at least two weeks, he advised.

More information on controlling blight can be found on the British Potato Council’s website, www.potato.org.uk