My camellia plants have scales and look powdery. The branches also have the same look.
Camellia Scale on Leaves and Branches
Certified GKH Gardening Expert
If the powdery residue is black, this is sooty mold, and a byproduct of the scale. This article will help you with getting rid of it: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
Neem oil can help as well. In addition to treating the scale, it is also a good fungicide. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm