ESTIMATION OF YIELD LOSS CAUSED BY FUNGAL DISEASES ON WINTER-WHEAT - CONSTRUCTION AND VALIDATION OF A MODEL TAKING INTO ACCOUNT THE EFFECTS OF THE CROPPING SYSTEM

The risk of yield loss caused by fungal diseases on winter wheat has always been believed to be a limiting factor that farmers could only eliminate by using fungicides. These chemicals now represent about 25% of the supply costs in France. In order to grow winter wheat with low fungicidal inputs we must take into account possibilities other than fungicides to reduce the damage caused by disease. A statistical linear model of prediction that estimates the yield loss caused by fungal diseases has been built. The important variable is the percentage of the yield obtained without disease. The effects of the climate and various elements of the cropping system on yield loss were quantified: previous crop type; variety; and planting date. In this paper, we develop a model obtained from 454 fungicide trials in Haute-Normandie and Picardie (in northern France) from 1978 to 1991. The various steps of the conception of the model of prediction are discussed. Its validation is discussed together with its importance for the construction of new methods of growing wheat with low fungicide inputs.