Fraxinus is a genus of medium to large, mostly deciduous ash trees native to Asia and North America. Ashes are common in forests of the eastern United States as well as in urban and suburban landscapes where they were widely planted to replace native elms killed by Dutch elm disease. In addition to their landscape value, ash trees are a significant source of timber for multiple uses. Diseases of ash include anthracnose and ash yellows. However, the most serious problem in both forest and landscape settings is the emerald ash borer.