apple rust

noun

: any of several diseases caused by fungi of the genus Gymnosporangium

especially : a destructive fungal disease especially of the apple but also attacking pears and quinces that is caused by a rust (G. juniperi-virginianae) having its pycnial and aecial stages on the leaves and fruit of the apple and the telial stage on species of Juneperus, especially a common red cedar (J. virginiana)

: the fungus causing apple rust

called also cedar apple rust, cedar rust

compare cedar apple