The only known stage in all Alternaria species is the asexual stage. Conidia and mycelium overwinter in the soil and on crop residues and cause primary infection of the leaves. Survival can be several years, up to eight years for several Alternaria spp.
Typically, Alternaria causes early blight of potato and early blight of tomato, which presents itself as spots on leaves, petals and stems. These spots can be distinguished by the dark and brown concentric rings that are caused by sporulation. Species may differ in specific symptoms.