the science of plant diseases, means and methods of their prevention and elimination. Divided into General and private. F. exploring common diseases, the causes and conditions of their occurrence, the patterns of development and distribution, especially mass outbreaks (epiphytotics (Cm. Epifitotia)), anatomical and physiological abnormalities in diseased organisms, issues of immunity and quarantine of plants, develops forecasts of disease, means and methods of protection of plants; also includes the doctrine of the deformities. To private, or special, are referred S. F.-X. F., which explores the disease of agricultural crops; F. forest – the section on diseases of trees and shrubs, on the destruction of dead wood; F. ornamental plants. F. use of the achievements of the anatomy and physiology of plants, Microbiology, Mycology, genetics, plant breeding, plant cultivation, chemistry, physics and other Sciences. The results of phytopathological studies are the theoretical basis for the construction of systems of plant protection from diseases, has especially great practical importance in agriculture.