Question
Hello, I live in Northeastern Ohio and have a few black walnut trees in my yard. One of them has a greenish looking fungus on some of its branches. It is not moss. What could it be and what should I do? Thanks

Answer
Sounds like lichens. These are common and are not a problem to the health of the tree. Lichens are combination of a fungi and an alga. They are no threat to the tree so there is nothing to do. Here is a web link that will give you more information on lichens;  http://helios.bto.ed.ac.uk/bto/microbes/lichen.htm