I have a tree in my front yard that is probably at least twenty years old, but it's not a tall tree (I'm not sure of the species). Anyway, it has a large branch that is turning black and also there is a lot of green flaky material that is starting to cover a lot of the branches and a lot of branches seem to die off every year.
It is hard to say what is causing the limb to turn black. If it is dead, it could be decay. If it is still alive, there may be insect activity that is causing sooty mold to form. The green flaky material on the bark sounds like Lichen. This organism usually does not cause any major health issues.
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