ABSTRACT
Epidemiology is primarily concerned with epidemics but the term has a wide meaning and has come to include most field aspects of plant diseases. Epidemiology covers the effects of environmental factors on disease prevalence, incidence and severity, in addition, to survival and spread of plant pathogens. A proper understanding of epidemiology is necessary for prediction of plant diseases and formulation of effective control measures. Epidemic is a system. Analysis of epidemics is a modern approach in the study of epidemiology. Plants change in their susceptibility to disease with age. These are polycyclic pathogens that usually cause leaf spots, blights, rusts, mildews, and are responsible for most of the catastrophic plant disease epidemics in the world. The chief source for accumulation of inoculum for epidemics of such diseases is the diseased plant organs used for vegetative propagation and, therefore, the build-up of epidemic is comparatively slow. Most pathogens attack the plant at a particular stage of its growth.
