sandcherry trees have hard white caking on the bark

Question

Do you have any idea what it is?

Answer 1

This could be a fungus or even insects.
Treat with Neem Oil as this works as both an insecticide and fungicide.

Here are a few links for you with more information.
https://www.gardeningknowhow.com/ornamental/trees/sand-cherry/purple-leaf-sandcherry-info.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm