This white objects might be Crapemyrtle Bark Scale, though some look too large and lumpy to be scale alone. There are some ladybug larvae that happen to look nearly identical to the scale  (though slightly larger) which might be present and feeding on them; the linked page provides photos and information. Some of the lumps might be dried sap, but we don't know from what, since it's not typical for Crapemyrtle plants to ooze sap that congeals and looks like this.

If scale are confirmed to be present, you can use the information in the linked page for managing the population. It does not look that heavy, at least from this photo, so intervention might not even be needed at this point, especially if you find lady beetle larvae hunting scale.

Miri

Thank you for your quick response!

You're welcome.