Answer: There are several potential reasons for the fungus but without visually inspecting the tree, I can't really offer any control suggestions. Gummosis is common with cherry trees and the first symptom is a thick sap oozing from the branches or the trunk. There's another disease called black knot which can also produce a black jelly like substance. Bacterial canker is yet another malady of cherry trees. The diagnosis really depends upon whether you see cracking bark, cankers, other injuries, etc. under the black substance. I think your best course of action right now is to contact your local Cooperative Extension office and request a publication on cherry tree diseases. With color photos you can compare the disease symptoms with what you are seeing on your trees. Wish I could offer more help. Best wishes with your trees!
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