Black Soot on Rhododendrons

Question

My beautiful, healthy, prolific 22-year-old rhododendrons, in the past month or two, suddenly developed this thick black soot on the branches. The leaves turned brown and fell off and the buds never developed into flowers. It may be too late to save one of them, but this blight seems to be spreading to all of my rhododendrons. Any idea of what this is and how I can get rid of it?

Answer 1

This is sooty mold, usually an indication of pests like aphids. Treat the shrubs with neem oil, which will take care of both the sooty mold and whatever pest may be affecting them. Here is more information:
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm