The fungi that cause anthracnose are microscopic members of the class Ascomycetes, spore-sac fungi, and Deuteromycetes, imperfect fungi.
They produce thread-like tubular mycelia that form fructifications producing sexual or asexual spores, depending on weather conditions and the fungus genus.
Ascomycetes produce two types of spores: conidia (asexual) and ascospores (sexual). The latter are usually arranged in groups of eight in an ascus, a small sac inside which meiosis occurs.
Deuteromycetes have no known sexual form, but they do produce large numbers of asexual spores (conidia).
The fungi overwinter on dead leaves, infected branches, gaps in bud scales and small cankers in the form of mycelia, conidia or ascospores, depending on the species.
In spring, overwintering spores often cause an initial infection when they are dispersed by wind and rain.
During the growing season, cool, rainy weather promotes the development of mycelia and the production of large numbers of asexual spores (conidia). These are dispersed and quickly form fructifications, spreading the infection to new tissues. Spots appear on leaves about ten days later. The fungi continue to multiply as long as weather conditions remain favourable.
In late summer, some genera also produce ascospores, sexual spores that are able to survive drought and winter cold and serve to maintain the genetic diversity of the species.