The text provides an account of the major diseases of important crop plants caused by various taxonomic groups of plant pathogens and the environmental factors. It is not possible to include all the crop plants being grown world over and also all the diseases of a particular crop plant in any one textbook. This text book is structured as per to 5th Dean committee B.Sc. (Ag) course. This book contains the disease of major crop plants, the cereals, vegetable, fruits, pulses, oilseed, fiber, sugar and plantation crops. Similarly for a particular crop plant, major diseases of international importance responsible for appreciable yield losses have been selected.