Hi- I'm posting again about another shrub at our new home. I decided to prune to the ground our three loropetalums, since they looked very unhealthy and gangly. After cutting, I noticed that the trunks toward the bottoms of the plants were turning black with a rough texture. Unfortunately, the previous owner had mulched around the trunks. Here is a pic:

Is this some kind of root rot or other disease? (If the pic is too sunny, I can take another later in the day).