Gummosis
Gummosis is a plant disease that is characterized by the discharge of a gummy substance on the surface of branches or trunk of certain trees.
This physiological or parasitic disease affects more particularly certain deciduous trees, in particular the stone fruit trees of the genus Prunus (cherry, plum, apricot and peach trees) and some others, such as citrus fruits.
The infamous black goo! I have heard some mighty fine conspiracy theories about from people who jump to crazy conclusions when they find this on trees.