Keep my tree alive
I have a plum tree that is about 17 years old. For the past 2 years, the tree has, what I think, a fungus. Prior to this fungus, it was growing well. It is a flowering plum tree, not fruit bearing. All the pictures are of it current state. There are pieces that look like fungus. What can I do to save my tree. Please help me and Thank you in advance.
Unfortunately, ornamental fruit trees are not terribly long-lived. At about 15 years most begin declining from multiple issues.
Here is a publication that covers those issues: http://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs/...
At this point we don't recommend any treatment. It it looks like you have a good amount of dead limbs. You should prune all of that out and see what you have left. It may be that it is time to remove and replace.
The things that you are seeing on the bark look like forms of lichens, which are harmless to trees.
They simply grow on slow-growing wood, dead wood and even stones.
Here is a page about them: http://extension.umd.edu/hgic/topics/lichens
Here is our publication on pruning ornamental plants if you need it: