Gloomy, rainy skies bring blight infection risk

A pall of gloomy skies across large parts of the UK has left potato growers battling against blight infections and struggling to cope with big crop canopies in the run-up to harvest.

Reports of blight in crops had been widespread, with repeated warnings of high-risk conditions, according to Syngenta technical manager Jon Ogborn.

"Wet weather significantly increases the risk of motile blight zoospores infecting tubers and potentially ruining the value of the crop," he said.

"Infection can be hard to spot in the big crop canopies, with the potential for high levels of tuber blight from even relatively low incidences of leaf or stem blight lesions.

"It is imperative growers maintain tight fungicide spray intervals."

He suggested using zoospore-active Shirlan until all green material was destroyed by desiccation programmes. Many growers wanted to time programmes to optimise tuber numbers in premium-price size bands, at a time when crops still had large vigorous canopies, he pointed out.

"Where there is continued vigorous crop growth, growers need to plan how best to use the full five litres per hectare of Reglone available," he said, recommending a minimum of 1.5 l/ha to open up the canopy and stop further tuber development.

Reglone was the only diquat desiccant with a full 5.0 l/ha total dose approved on the label, he added. He advised growers to undertake a "smart" (soil moisture availability for Reglone treatment) test before applying.

He also advised growers to avoid flail haulm removal in wet conditions because it risked spreading blight and blackleg, with a potentially serious impact on stored crops and seed stock quality.

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