That unappealing black coating on your tree is actually a harmless byproduct of a bug! The black substance is called sooty mold and grows on the waste product of an insect called scale. The mold itself is fairly harmless, more aesthetic than anything. It can even be washed off with a high-powered hose or wet sponge. However, the insect that causes the mold can be harmful to the health of your tree. Our advice? Get rid of the insect problem!
Crape Myrtle Bark Scale is a sucking insect that looks like a white bump/growth on the tree. It is stationary in its mature form, so you won’t see it moving around. The insect feeds on the nutrients of the tree and can sometimes be hard to get rid of. A DIY physical method of removal is simply to use a high-pressure hose or wet sponge with dawn dish soap to wash off as many of the insects as you can. If the infestation is high, contact a Certified Arborist or your local garden center about treatment options.