Agronomic approach: cropping systems and plant diseases.

This paper deals with the effects of agronomic practices on parasite life cycles, and the design of integrated crop protection strategies. Cropping systems have a large effect on the size of the primary inoculum and its localisation, on the development and spread of epidemics, and on the coordination of the life cycle of cultivated plants and that of their parasites. They can disrupt ecological equilibria, either favouring or disfavouring the pathogens. By combining information concerning the effects of agricultural techniques on diseases and the physiological effects of diseases on growth and crop production, it is now possible to develop new crop management systems, in which the use of non-chemical methods for preventing diseases is a priority. However, the current knowledge need to be completed by studies on other scales, particularly of the effect of cropping systems on the genetics of disease populations integrating more completely the 'long-term' dimension of sustainable agriculture.