Keep traps at least 50 feet from the crape myrtle tree or you may create more of a problem by attracting them to the area. Milky spore, Bacillus popilliae , is a disease-causing bacterium that is effective against grubs of Japanese beetles but not the adults. It is commercially available for homeowner use. As with all pesticides, read and follow all label instructions and precautions. Leaf and stem surfaces are covered with a black sooty substance, causing them to appear black and dirty.
Sooty mold indicates that there is an insect problem on the plant.
These common molds are caused by fungi that grow on the sugary substance, called honeydew, produced by various insects that suck sap from the plant. Aphids, scales, mealybugs and whiteflies most commonly cause this problem. Sooty molds are unsightly, but are relatively harmless, since they do not directly attack the plant. Controlling the insect problem can reduce excessive amounts of sooty mold. Reduce aphid numbers by allowing beneficial insects such as lady beetles to inhabit the plant.