Which rhododendrons? While I suppose it could be mildew, you would normally see that begin when ground is dry and humidity in the air high - certainly the wrong time of year for it in my area :)

Glaucous coating is normal for some types.

Here is a link that might be useful: {{gwi:391411}}

thanks, yeah, the leaves look healthy and they do sort of look like that picture. Except they have more white than that. These are Yuko Princess? I think? does that sound right? maybe Yoku? Thanks, I guess I'll keep an eye on them and see how it goes. I just got freaked out because all of my rose bushes had powdery mildew and I let it go because I didn't know what it was, but I sprayed them and they're fine now.

I think you mean Yaku Princess. It is a great plant and relatively trouble free.

The glaucous coating which appears naturally is a waxy bloom or whitish material that appears on the leaves and buds and rubs off readily. Another possibility besides the normal glaucous coating and powdery mildew is thrips.

Thrips are characterized by a silvery white discoloration on the leaf's upper surface and silvery on the bottom with small black frass specks. The damage is similar to that from lace bugs. Thrips are a problem in warm and dry climates like California and New Zealand. Most of the standard insecticides and insecticidal soaps can be used. Control for thrips whether an insecticide or insecticidal soap is a contact control and must be applied on the adults. This is most likely done in May in California when they are visible. Locally, biological controls may also be available. It is best to remove infected flowers.

Here is a link that might be useful: How to grow rhododendrons and azaleas.