Plant diseases in the landscape and garden are very important and can be a significant source of frustration and loss to the gardener. There are about 30, 000 diseases of economic importance in the U.S. Plant pathology is the study of the biotic and abiotic agents that cause disease in plants, of the mechanisms by which these causal agents induce disease in pants and of the methods of preventing or controlling disease and reducing the damage cause. Plant diseases in the landscape and garden are very important and can be a significant source of frustration and loss to the gardener.