Question
I need to know why my crape myrtles leaves are turning black, and what can i do to fix this problem.
thanks
kevin

Answer
Sounds like aphids. These insect suck the plant juices for the plant and secrete a substance called honeydew. This is high is sugar content and a sooty mold will grow on the honeydew. Usually the leaves are sticky with this dripping. Control the aphids and you will see the sooty mold go away.

Spray the foliage and stems with an insecticide. Contact insecticides currently registered for aphid control include: acephate (Orthene),  bifenthrin (Talstar), chlorpyrifos (Dursban),  diazinon, malathion, nicotine sulfate, pyrethrum, , rotenone, resmethrin, and tetramethrin + sumithrin.

A systemic insecticide can be used that the tree takes the insecticide into the root system and to the leaves and twigs and kills the aphid when they suck the plant juices.
Imidacloprid (Bayer Advanced Garden Tree and Shrub Insect Control) is a newly available systemic insecticide that can provide aphid control on trees for several months following application to the soil.