exudation of sap or gum from the bark. often in response to disease or insect damage.
Merriam-Webster Online Dictionary
gummosis (noun)a pathological production of exudate in a plant - gummy , also a plant disease marked by gummosis
gummosis (Wikipedia)
Canker-induced gummosis on a Tibetan cherry
Plant sap rises from the bark of a cherry tree
Gummosis is the formation of patches of a gummy substance on the surface of certain plants, particularly fruit trees. This occurs when sap oozes from wounds or cankers as a reaction to outside stimuli such as adverse weather conditions, infections, insect problems, or mechanical damage. It is understood as a plant physiological disease.