Q: I notice that most crape myrtle trees are topped and pruned. Is that how they should be done or would selective pruning be a better alternative?

A: Selective pruning is much better for the health of the plant. Although crapemyrtles will bloom even after being pruned to an ugly knob, the knobbing is done by landscapers more interested in lowering labor costs than in preventing powdery mildew and aphid attack in summer. I have several references and pictures at Crapemyrtle Pruning