Q.azalea
Black covering on leaves.

Downtoearthdigs
Answered on March 12, 2017
This could be Sooty Mold.
These articles will help you with this issue, caused by pests.
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
https://www.gardeningknowhow.com/ornamental/shrubs/azalea/common-azalea-problems.htm
https://www.gardeningknowhow.com/ornamental/shrubs/azalea/azalea-lace-bug.htm
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