Could be spider mites,, Look at the crinkled leaves really good and check for fine webbing, and tap the top of a leaf and see if tiny black spects falls on your hand under the leaf, My crepe myrtles especially the ones on the side of the yard get them bad around early summer,, I cut them back a bit and spray with neem oil ( organic),, once a week for 3 weeks or so and they came back and give full blooms no problem!
Neem oil is good for a lot of what ills a plant or blooming tree,