How do I save my rosemary?

This rosemary was purchased at a local nursery in September. It's planted in a pretty copper pot and kept outside on the porch steps. I live in zone 7a and wasn't planning on bringing it inside. We've had pretty regular rain, so it's only received rain water. The soil mixture I used at the time had fertilizer mixed in, so I haven't fertilized it, either. I think it was MiracleGro potting mix.

Now it has a white substance on pretty much all of the leaves. Is this some sort of a fungal infection? What should I do? We haven't had a killing freeze here yet. Will the cold naturally kill this infection? Will the rosemary be edible at some point, or are the infected leaves no longer edible? Should I spray it with neem oil or another homemade mixture? Or do I cut all of it down and wait for new growth next year?

can you post a picture?

I can't get my camerphone to take a clear picture... I think it might be powdery mildew.

It kind of looks like this but less "fluffy" and more flat.
http://www.ppdl.purdue.edu/PPDL/images/PMrosemary.jpg

This summer, I had powdery mildew on my crape myrtle and roses.

Had the same problem with my rosemary this past summer-it was in a big pot with other herbs. It was infected with spider mites,which I had never seen before. I kept trying to cut out the problem thinking it was powdery mildew but by the time I found out what it was I had to toss all the plants and the dirt also. A friend said to plant in a dry area with good air circulation and add pea gravel to the soil. She also gave me a recipe for insecticidal soap which I will use if it starts this summer. Let me know if you want it- a fraction of the cost of buying commercial-

I potted this plant before I learned about using light, gritty soils for containers. The cold has not helped the rosemary, so I'm afraid I'll be tossing the dirt and the plant and starting over again.