During the last years begins to spread dangerous diseases of tree species caused by microscopical fungi living in vascular bounds of wood and certain infections caused by bacteria. The complex of diseases, the so called “mass decline of oaks“ is spreading again on which participate the fungi of close relationship with the originator of graphiosis of elms and always appear further diseases of vessels caused by fungi (tracheomycosis) in beech, ash, alder, birch, poplar trees and in pine and spruce. From bacterial diseases it is first of all “scarlet fever“ of Rosacea and apple trees and shrubs, European decline of cherry and sour cherry trees and the so called Přerovian disease of poplars. The genus Ceratocystis, Diplodia and Verticillium belong to the most dangerous fungi causing tracheomycosis. The phycomycetous fungi Phytophora cinnamomi brings on a new type of tracheomycosis causing the decline of horse-chestnut. Especially man brings on the spreading of tracheomycosis and bacteriosis by the traffic of plants and wood and also by weakening of plant resistance against infections that are reproduced in wastes from logging. Also chemical spray is used in combination with fertilizers.