Definition of apple rust in English:

apple rust

noun

  • Any of several rust fungi of the genus Gynosporangium, especially G. juniperivirginianae, which alternately infects red cedar (Juniperus virginiana) and the apple; the disease caused by this, resulting (in the apple) in lesions on the leaves and distorted fruit.

Origin

Late 19th century; earliest use found in The Botanical Gazette.