If not powdery mildew, I suspect aphids, in particular rosy apple aphids.
Try a Google image search for pix and see how you think it compares.

Good luck!
Suzy O

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powdery mildew dosent typically show up as a series of specks like
that, and is usually much more opaque. Rub the white spots and see
what happens. If it rubs off, you have powdery mildew. If it dosent,
check the bottom of the leaves for insects. It looks to me like you
have leafhopper damage, though the picture isnt very close up.

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