Potential two spray requirement for LLS at flowering in OSR - Cam Murray - The Scottish Farmer

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One who is advocating a twin-approach to OSR sprays (see story left) to beat the LLS disease risk, is Cam Murray, the northern regional technical manager for advice specialists, Hutchinsons.

Oilseed rape in many northern areas is expected to be at high risk from light leaf spot this spring, so crops must be fully protected throughout the crucial flowering period, he said.

An updated light leaf spot forecast, which takes into account the deviation of actual winter rainfall from the 30-year mean, went live on the AHDB website in early April and this suggested that certain areas of the UK are at particularly high risk of light leaf spot this season.

The risk of plants reaching 25% of plants infected this spring has increased in the east from 13% to 16% and from 66% to 78% in the north of Scotland.

"Our leaf analysis Last autumn showed no light leaf spot present at the time, but results from samples taken this spring show infection has come in over winter, as the cool, wet conditions really suited disease development," said Mr Murray. "Infection is very high in crops across northern England and Scotland."

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 the stems to pods.

It affects all parts of the plant and can result in yield losses of up to 50% if left uncontrolled. Curative treatments have little activity against either light leaf spot or selerotinia, so well timed protectant sprays are the only in-season way of reducing infection risk and protecting the developing pods.

A prothioconazole/tebuconazole-based fungicide at early stem extension is often the first line of defence to prevent disease travelling up stems, added Mr Murray.

This should be supported with two flowering fungicides - the first of which is best applied at early flowering followed by a second spray around three weeks later to safeguard crops throughout the flowering period, typically lasts around six weeks, but varies depending on conditions.

Prothioconazole is the strongest option against light leaf spot and should be applied at early flowering where the disease is prevalent on upper leaves and stems.