Question
I have 2 Norway maples that have developed a green fungus on the trunks of both trees. Is there a remedy or something I need to do for this? They both have about 6" trunks.

Answer
Hi Jim,

Most likely these organisms are not fungi, but rather algae or some type of moss.  These are common and do not harm the plants.  These most often appear on the shaded side of the trunk and persist in relatively moist environments (high humidity).  

If these are unsightly, you can scrub the trunks with a dilute solution of chlorine bleach (1 part bleach to 9 parts water = 10% bleach solution.)  Be sure to rinse thoroughly afterwards.

There are also fungal and algal associations (lichens) which may be associated with some tree species.  These are harmless as well.