Some of the branches on my pomegranate bush have died. The bark turns dark and falls off. What is it and how do I treat it?
If the tree is experiencing wet conditions is can become susceptible to several different fungal diseases.
If is difficult to say from your description which fungus could be the issue.
The link below has detail on the most likely conditions and treatment.
If the tree is suffering from Root Rot, it can be very difficult to correct the situation.
Make sure the soil is properly draining.