Best care for butterfly bush

Question

Leaves will sometimes shrivel and a gray dust occasionally forms on new leaf froth

Answer 1

This sounds like Downy Mildew; which can be common on Butterfly Bush.
This article will help you.

https://www.gardeningknowhow.com/ornamental/shrubs/butterfly-bush/butterfly-bush-diseases.htm
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm