Crop diseases are known to be caused by various abiotic and biotic agents. Diseases in plants are as similar as diseases in animals and human. We cannot see the actual organism responsible for disease but we feel and see the symptoms. Disease can be described as "any deviation from the normal behavior in a living organism is called a disease", different living organisms have different diseases and different microbes cause different diseases." Horticultural plants grow in response to their environment. Plants are cultivated from many areas of the world. Each has a different set of environmental conditions to which the plant has become adapted. Much of horticulture is concerned with modifying plant environments to enhance growth. This book covers several of the major environmental factors that influence plant growth, managing diseases, diseases control and the influence of climatic variations on horticultural plants and crops. Graduating students, researchers and teachers desirous of updating the information on different aspects of microbial plant pathogens and the diseases caused by them, will find this book to be useful.