Initial symptoms appear on the bark of 2- to 3-year-old trees as pustules or pox-like vesicles. Tissues beneath the affected area become black and necrotic. No gum formation appears and eventually the underlying tissues collapse. Dark, dead tissues become brittle and peel. Individual pockmark depressions or, if tissues coalesced, large cankers can form.

Fruit and leaves develop no diagnostic symptoms in most apple cultivars.

Summary: Nemeth 1986