Honeydew is a fabulous food for black sooty mold

Q: My crape myrtle’s bark is black. What should I do?
A: Black bark, black leaves, and black lawn furniture under a crape myrtle are ultimately caused by sucking insects in the tree, probably crape myrtle aphids. They suck more sap than they can digest and excrete the rest. The excess that is excreted is called honeydew. Honeydew is a fabulous food for black sooty mold. The honeydew dripped out of your tree and coated the bark. Black sooty mold soon followed. The cure for this situation is to control insects in the tree. The easiest way to control them is to apply a systemic insecticide when the tree is not blooming. Go to a garden center, buy a product that contains imidacloprid, and follow the directions for applying.