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Light leaf spot disease risk high, says forecast

The HGCA-supported light leaf spot (LLS) service forecasts a very high disease infection risk in all regions of the UK for the 2014–15 season.

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The HGCA-supported light leaf spot (LLS) service forecasts a very high disease infection risk in all regions of the UK for the 2014–15 season.

The current high-risk level is due to a combination of disease build-up over recent years and favourable weather for pathogen growth over the summer.

Where LLS is found in crops over the autumn/winter period, early treatment with a protectant fungicide is recommended to help growers get on top of the disease before it becomes established.

The regional forecasts are based on disease incidence on pods in the previous season combined with summer temperature and rainfall information.

Dr Neal Evans, plant pathologist at Weather INnovations, who put together the forecast, said: “As there were high levels of LLS on crops at harvest, there is a high potential for disease spores to disperse into the current crop of oilseed rape.

“On the weather front, summer conditions favoured development of the fungus that causes LLS and are factored into the forecast.

“The first half of July was warm and sunny for much of the UK. The second half was unsettled with cooler temperatures and characterised by thunderstorms with heavy local downpours, particularly in the south and the east.

“In addition, August was wet and cool for much of the UK, hampering harvest and also giving us the coolest UK-average August since 1993.”

As the current LLS disease risk forecast is high, more growers are likely to consider applying a protectant spray during November or early December.

Early detection and spraying before the disease becomes established are essential – particularly for varieties with moderate to low disease resistance.

The identification of the disease can be tricky, as symptoms are not always visible and are easily confused with other plant disorders.

Symptoms can be brought out by putting plant samples in polythene bags at 10–15°C for 4-5 days.

A second spray may be required early next year, if light leaf spot symptoms are found during field monitoring.

The full LLS forecast and information on sampling is provided on the LLS forecast page

The forecast information follows the release of the latest fungicide performance data by HGCA in October. For LLS, the results showed that several products achieve similar levels of control.

For full details, read the fungicide performance report and other useful disease control information at

HGCA’s Fungicide performance in oilseed rape publication will be updated this winter to include the latest information.

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