Question
Hi Jim,

I live in California in the desert region.  We have an old fruitless mulberry that seems to have been infected.  The bark on the infected area was peeling away. Underneath the peeling it had turned black as coal. If you touch it, the black stuff will come off on your hand. It looked like it was spreading down the branch towards the trunk of the tree.

Do you know what's causing it, and whether there is anyway we can treat it (perhaps cut off the infected branches or something?)  Thanks in advance.

Answer
I am not real sure what this could be but I lean toward a disease called Black Knot. The best control is pruning the branches that have the disease and destroy the pruned branches. There are some fungicides that can be sprayed also. Here is a web link to Black Knot from it you should be able to determine if in fact this is what your tree has.
http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/fd4.htm