Inherited two rhododendron bushes (Vancover Island). Top leaves covered in white fur like texture. The plants look sad.
This could be Powdery Mildew or even Mealybug.
Neem Oil is a treatment, as it works as both an insecticide and fungicide.
Trim away the dead and damaged material and dispose of.
Here are some links for you that may help you pinpoint issues and care information.