Forecast development

The light leaf spot forecast has been developed using the Defra-funded Winter Oilseed Rape Pest and Disease Survey results. The forecast is based on crop and weather factors. At the start of the season, a prediction is made for each region which takes account of the average weather conditions expected for that region. This forecast is then updated periodically to take account of deviations in actual weather away from the expected values.

The factors important in predicting spring light leaf spot are:

  1. The amount of pod disease the previous summer. It is thought that the summer pod disease produces innoculum to start the autumn epidemic.
  2. Summer temperatures. Warmer summer temperatures appear to be associated with lower levels of light leaf spot infection the following spring.
  3. The number of winter rain days above the regional average. Wetter winters appear to be associated with higher levels of light leaf spot infection the following spring.

These factors are combined to produce a forecast for each region. Individual crop factors also influence the disease levels. Earlier sowing and use of susceptible varieties also increase the risk of the disease and these factors are taken into account by the interactive model following grower input.