Question
QUESTION: My plum tree is sick, the leaves are ghost leaves, not green.  What is this and how to treat it?

ANSWER: If this is a whitish-grey "dust" that you can smudge off, this is most likely a mildew infection which can be combated using a fungicide. If you have had a rainy Spring, this is most likely the problem.

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QUESTION: This is not mildew.  The leaves are brown, it looks like an xray of a leaf.

Answer
Okay I could only guess what "ghost leaves" meant. I don't know what is causing this. If your leaves are totally brown look for new buds right where your brown leaves emerge from the stem. If you see new buds your tree will re-leaf and hope is not lost.

sorry i can't help you further!