Q: At the end of last summer, we noticed our crape myrtles were covered with a black soot-like powder. It even discolored the pinestraw beneath. When we pruned back the trees recently we still noticed it. How should we treat?
A: Your problem is caused by what you just did: pruning back your crapemyrtles. The lush growth that results from a heavily pruned crapemyrtle attracts aphids, which produce honeydew, on which black sooty mold grows. Pruning crapemyrtles back to a knob is a great way to exacerbate problems with insects as well as powdery mildew. Consider applying a systemic insecticide (Bayer Tree & Shrub, etc) now to kill aphids in summer. I have pictures of correctly pruned crapemyrtles at http://xrl.us/PRUNECRAPE.