Pathology is the study of the diseases and disorders of plants.
Disease can be defined as a harmful deviation from normal functioning of the physiological processes caused by an infectious agent. In the case of plant diseases, the causal agent maybe a fungus, virus, bacterium or a parasitic flowering plant. Top, an example of a rust fungus on a bean leaf. At right, an example of a parasitic flowering plant, bloomrape. Much of the time plant pathologists study diseases of crop plants.