John - Pa. wrote in message
...
That sounds like what they generically call "powdery mildew". I haven't
had a problem with it on my Phlox, but it does affect my Peony and it
is famous on Zinnia.

Yes, that's what I assumed it was.

My understanding is that although it looks bad, it doesn't usually hurt
the plant.

It doesn't seem to. If the plants died I wouldn't mind ...

I have read that good ways to reduce instances of this are full sun,
good air circulation and clearing out dead leaves and other Autumn
debris. I also think that there are potions that are supposed to deal
with it too.

It only gets late sun in the evening. I half expected that to be the
reason :-)

Thanks,

Mary

Here are several remedies.
http://www.rnzih.org.nz/pages/powdery-mildew.htm

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Travis in Shoreline Washington