Modelling leaf wetness duration during the rosette stage of oilseed rape

In this paper, we develop a variant of the energy budget model approach, as presented by Pedro and Gillespie, to model leaf wetness duration for use in forecasting the oilseed diseases, stem canker and light leaf spot. The model overcomes three shortcomings of existing models: (i) the model includes rain as a source of leaf wetness, (ii) the model is simple enough to be integrated in disease forecasting systems and (iii) the model only uses meteorological measurements available from standard meteorological stations. The model is tested using two data sets from sites on the experimental farm at Rothamsted Research, UK. Model performance is discussed on basis of (i) the performance of the model for predicting consecutive multiple day periods of leaf wetness duration above a threshold and (ii) the percentage of days where the model correctly/incorrectly predicts whether or not infections could occur. These criteria are important for forecasting both light leaf spot and stem canker in oilseed rape crops.