It works anywhere. Remove the affected parts and get on a treatment schedule. Next year, try a mold-resistant outdoor strain like Island Sweet Skunk.
You can get it at hardware stores and walmart too, but I keep hearing rumours that b. subtilis is being taken off the market in some places, anyone see it disappearing off shelves yet? It's a red bottle shaped like a small laundry-soap jug, that says 'Serenade' and has a pic of hummingbird on the label.