Black pox is a fungus disease caused by Helminthosporium papulosum. It is considered to be of minor economic importance. When it occurs, the disease can affect apple bark, fruit, and foliage. It is more common from southern Virginia southward than in the northern mid-Atlantic region. The same fungus causes blister canker on pear.
Infection first appears on current season twigs as well-defined, conical, shiny black lesions, which enlarge by the end of the first season. Extensive secondary lesion enlargement may …