Black rot is a fungus disease that can cause serious losses in apple orchards, especially in warm, humid areas. Three forms of the disease can occur:
- a fruit rot, which causes fruit to become unmarketable;
- a leaf spot known as frogeye leaf spot which, if severe, can result in defoliation which weakens the tree; and
- a limb canker which can girdle and eventually kill entire branches.
Read more and see images in this article, Black Rot of Apple.
Answer provided by Alan R. Biggs, West Virginia University.