Winter weather ramps up light leaf spot risk

The risk of light leaf spot (LLS) in the UK has increased since the publication of the preliminary 2017/18 forecast last autumn.

AHDB Cereals said the risk has been fuelled by cold and wet conditions over the winter. The increased risk has been captured in the final LLS forecast for 2017/18.

Cold conditions favour the disease because it slows oilseed rape’s growth and wet conditions help distribute spores.

The elevated risk will not come as a surprise to many, as there have been numerous field reports of disease symptoms showing up in crops over the last few days.

Early control of LLS is important, with vulnerable crops benefiting from a well-timed autumn fungicide.

A second spray for at-risk crops is usually advised in February and March but field conditions have made it a challenge to meet this timing.

Where symptoms are found, this spray will need to be applied as soon as practically possible, as control levels will diminish rapidly.

The disease typically reduces yield by a third of the incidence (90% plants affected at early stem extension causes 30% yield loss) and on average, UK yield losses equate to £100-140M per year.

Issued in autumn, the preliminary forecast shows the proportion of the oilseed rape crop (disease resistance rating of 5) estimated to have more than 25 per cent of plants affected by LLS in the spring for the current season.

The forecast uses previous season pod incidence data, deviation from 30-year mean summer temperature data and 30-year mean rainfall data.

In spring, the forecast is updated to reflect deviation in actual winter rainfall data from the 30-year mean.