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High Disease Risk Calls for Twin OSR Sprays - Cam Murray - Agronomy News

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The updated light leaf spot (LLS) forecast suggests certain areas of the UK are at high risk this season. Cold and wet weather over winter have been ideal for light leaf spot since cold conditions slow oilseed rape's growth and wet conditions increase LLS because it helps to distribute spores.

According to Cam Murray, Hutchinsons' northern regional technical manager, samples taken during the spring show infection has come in over the winter as the cool, wet conditions really suited disease development.

"As a result, infection pressure is very high in all oilseed rape crops across northern England and Scotland," he says.

Mr Murray warns that light leaf spot cannot be eradicated once in a crop, so the focus has to be on protecting fresh growth to prevent disease spreading up stems to pods. "Once light leaf spot reaches the pods, it's very hard to do anything about it and will cause real problems," he says.

In terms of yield loss, LLS affects all parts of the plant and can result in yield losses of up to 50% if left uncontrolled.

"Curative treatments are largely ineffective against the disease so well timed protective sprays are the only in-season way of reducing infection risk and protecting developing pods," he says. "A prothioconazole/ tebuconazole-based fungicide at early stem extension is often the first line of defence to prevent the disease travelling up the stems. This should be supported with two flowering fungicides - one at early flowering and the second about three weeks later," advises Mr Murray.