Question
I have some crepe myrtle that have black looking bark.  It looks like a tree that has been in a forest fire--black.  But it has not been in any fire.  I have several that look like this.  Is it a fungus or something else?  How do I treat it?

Answer
This is sooty mold growing on the excrement of an insect called aphids. The aphids suck the plant juices out of the plant and excrete a sugary substance called honeydew. The fungus is growing on the honeydew. The sooty mold is not damaging the plant but the aphids will.  Check the tree when it leaves out for aphids (the leaves will get sticky and wet looking) Spray an insecticide for the aphids and the sooty mold will go away. Check with your local nursery/garden type store for a systemic insecticide for aphids.