Gummosis can result from environmental stress, mechanical injury, or disease and insect infestation.
Cytospora canker, the fungal cause of gummosis, affects stone fruit trees like apricot, cherry, peach, and plum. Cytospora infection is distinguishable from insect damage and mechanical injuries because sawdust or pieces of bark are not mixed in the sap, as it would be with insect or mechanical damage. Cytospora canker is also known as perennial canker. On trees infected with cytospora new shoots or leaves may turn yellow or wilt. Sunken lesions develop on the bark.