Anthracnose is a group of diseases found on many deciduous and evergreen trees and shrubs; some trees such as sycamore, ash, and evergreen elms can be noticeably blighted. Often called leaf, shoot, or twig blight, anthracnose results from infection by any of several different fungi, including Apiognomonia errabunda, A. veneta, Discula fraxinea, Glomerella sp., Gnomonia sp., and Stegophora ulmea, depending on the tree attacked. Infections on deciduous plants are more severe in areas where prolonged spring rains occur after new growth is produced. Anthracnose fungi need water to be disseminated and infect; they do not spread under dry conditions.
Anthracnose fungi occur primarily on leaves and twigs. On deciduous trees these fungi overwinter in infected twigs. In spring many microscopic spores are produced and spread by splashing rain or sprinkler water to new growth where they germinate; the fungus enters the leaves and newly expanded twigs. If moist conditions prevail, a successive generation of spores is produced in the infected parts of new leaves. On evergreen species such as Chinese elm, the fungus can occur year-round on leaves and twigs, but on most deciduous trees the progress of the disease slows and becomes negligible during the hot dry summer.