Why are the leaves on our crepe myrtle turning yellow and falling off?

Question

We have 6 of the myrtles (3 on each side of the driveway), not all the same variety. We have noticed a curious “sap” falling on the cars this year that we have never had before. Now the leaves on some are yellowing and falling off. What could be causing this?

Answer 1

Crepe myrtles normally don't drop sap, so this is likely honeydew from a pest infestation. The most common is aphids. I would treat the tree with neem oil. This will kill the pests without harming people, pets or beneficial bugs. Here is more information:
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm