Hot and dry weather throughout much of July has reduced blight risk in many areas, but potato growers should not ease up on protection, experts have advised.

“Without the leaf wetness, we don’t really get the blight spread,” said Lincolnshire-based agronomist, John Keer. “Even if you’re irrigating, the heat and dryness mean the canopy will be dry within about 20 minutes.”

While conditions remain hot and dry, growers could save money by using slightly cheaper products, rather than extending spray intervals, he said.

“I don’t believe in extended intervals – it’s the sort of season you could get away with using cheaper products, such as Dithane (mancozeb) and still get a reasonable level of control. You don’t have to use the most expensive chemistry.”

But growers should be wary if the weather breaks (as forecasts suggest) and must also make sure they include products with enough zoospore active material to protect against tuber blight, he said.

“Action on tuber blight should not be left to the end of the programme, because low levels of foliar blight earlier in the season can lead to high incidence of tuber blight,” added Dow AgroSciences’, Andy Leader.

Repeat sprays of products with known zoospore activity (e.g. Zoxium – as in Electis) should be applied from stable canopy through to lifting to prevent zoospore formation and release, he suggested.

“Tubers with a thin coverage of soil, or those growing in cracked soils, or those brought into contact with zoospores during lifting are liable to infection. Once inside the tuber, fungal mycelium breakdown cellular tissue and symptoms are normally seen within one month of lifting.”