Since no one else has answered, I'll take a stab. A photo would be really helpful. It's possible your problem is aphids. They leave stuff called "sooty mold" on rose leaves. Without googling it I seem to remember that it comes from the aphids secretions?
Google "sooty mold" and see if that is your issue.
Best of luck,
Susan

My first thought were bugs of some sort too since it was just on the back of the leaves. I know Lace Bugs leave such spots (their "scat") on the backs of leaves, but they aren't known to infest Roses. Californians have a whole host of bugs that may infest roses that we don't have - much like rust (which is non existant to most of us). It could be the "leavings" of aphids too. If you have a reliable nursery or county Ag office, you may want to take a leaf in to them for analysis........Maryl

Without seeing it, I also suggest that you may have black sooty mould. See:

http://farmerfredrant.blogspot.com/2012/01/controlling-sooty-mold.html
and link, below.

"What is Sooty Mold?
Sooty mold is a type of plant mold. It is a type of mold that growing in the honeydew or secretion of many common plant pests, such as aphids or scale. The pests cover the leaves of your plant in honeydew and the sooty mold spore lands on the honeydew and begins to reproduce."

The causative agent, usually is aphids.

Jeri

Here is a link that might be useful: BLACK SOOTY MOULD INFO

Black Sooty Mold grows on the upper surfaces of leaves where other overhanging foliage above them have sucking insects on their reverses. As the insects suck the plant sap, they excrete sugar water which falls on the tops of the underlying foliage. Sooty, black mold grows in the sugar water making the surfaces black and 'sooty', but not in dots.

What you describe sounds like old rust where the orange pustules have lived their useful lives. Rust often turns black toward the end of the fungus' life cycle, and it can be "sooty" feeling. I agree, clear photos would certainly help. Here is an image I found on line of "old rust". Kim

Here is a link that might be useful: old rust

Kim, that looks like it! Though I have never seen this before in 35 years of growing roses (though I almost always have some rust.) What makes me favor this rather than the Black Sooty Mold is, as you say, 1) because it is on the UNDERSIDES of the leaves and does come in distinct tiny, individual, VERY BLACK, sooty pustules. I would upload a photo but I'm too ignorant and don't know how. But it would look a lot like the photo you linked me to.
Now, any advice for someone who tries not to spray? Could this be rust that's kind of been "stopped in its tracks/killed" by Green Cure, which I used?

Apologies to everyone who suggested Black Sooty Mold. I now see that I wrote in my original entry that the sooty black dots were all over the BACKS of my leaves, which is how I was referring to the UNDERSIDES. It would be easy to read that to mean the "tops". My bad.

You're welcome Bebba. Glad I could help. By the time the rust turns black, it's at the end of the cycle and may still be infectious. If you've already sprayed with something and you intend upon maintaining your garden hygeine, all you probably need to do is to do is just keep doing what you're doing. Rust this late in the season is likely nothing to worry about. Disease is, in my opinion, one way Nature "tells" the plants it's time to rest for "winter". Spraying now would probably just waste and pollute your garden needlessly. Good luck! Kim

deleted--somehow I missed a key post above.

This post was edited by michaelg on Tue, Dec 17, 13 at 12:06