Locust tree fungus (0/1)

[intercon at cybermesa.com]

Hi,
I have a couple of groves of flowering locust trees (don't know there
official name).  I was just noticing that the north side of this grove
of trees is covered in a greenish/yellowish fungus or mold.  I took
some digital pictures that I am attaching to see if anyone can tell me
whether this is a benign fungus or something to take action on.  If I
am to take action, what should I do?
Thank you....