Sounds like Scale to me. If it is small white specks on leaves or black brown bumps on the stem that are hard to scrape off. Squeeze the specks with your finger nails, If a yellow juice squeezes out it is Scale most likely.
It either case scale or powdery mildew, Ultrafine Oil will cure it. Follow the directions on the bottle.
Insecticidal soap and horticulture oil will cure about 90% of the problems on ornamentals. They act as insecticide, fungusicide, miteicide, bacteriaicide, all rolled into one. In the heat of summer they can be sprayed on at dusk and washed off in the morning. These products are pretty friendly to our environment. Unless you get sprayed in the eyes or soaked with 100% pure, they have little danger to human or animal.
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