Crepe myrtle diseases - My bushes have small white spots on the leaves and they are loosing their leaves, what should I do to help them?
The best solution is to get the plant in an area with good circulation and enough sunlight and hope for the best. You can also launch a preemptive strike of fungicides and pesticides. For more details, visit http://mycrepemyrtle.com/crepe-myrtle-diseases-and-pests/.
Sounds like you have scale insects they will suck the juices out of the leaves causing them to turn yellow and fall off. Spray with a good insecticide for plants.