Please help! Japanese Pieris Mountain Fire dying!

[Jactaylor24]

Hello! I have 5 beautiful Japanese pieris mountain fires. They were growing beautifully, and all of a sudden the leaves started turning brown and then falling off on one plant. I wasn't worried until the others seemed to be doing the same thing- one after another. Please help! I love these little guys don't know what to do!

I've read some websites saying the soil may not be acidic enough and to add distiller vinegar, some saying to use soapy water for insects and others saying to add Epsom salt because they may be lacking in magnesium. I don't want to start adding things without knowing what's wrong. Does this look like a pest problem, root rot? Any ideas?

[rainbowgardener]

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