Answer: Based on your description, I suspect this is a fungus growing on honeydew secreted by aphids or other insects that are sucking plant juices from an overhanging tree and dripping onto the azaleas. If this is the case, you should be able to rinse the powder off with water from the garden hose. If not, I would suggest you consult with your local Penn State county extension to obtain a more specific diagnosis of the problem and based on knowing that, decide how to proceed. If it is something that requires a chemical control, they will have the most up to date information on what to use and how/when is best to apply it for maximum results.
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