Also curious if using Serenade has been helpful for anyone.
The biological product that works best for me is called Actinovate. It's Streptomyces lydicus.
Erwinia is not one of the diseases listed on its label. But, it does list many other problematic species like Botrytis and Fusarium as well as various leaf spotting diseases so it's a useful product just from that standpoint. Despite not being officially listed, I've found Actinovate to be very effective for control of Erwinia in my collection. It doesn't mean I don't still get the occaisonal Erwinia rot on susceptible plants, but I have seen a dramatic improvement.
Actinovate has one (in my opinion) major advantage over Serenade and the stuff that Ray sells (both of which I have tried multiple times): I can use it more preventatively on my indoor collection than the other products, which might explain why I have more success with this product than the others.
Actinovate is completely odorless (it's a powder you mix with water), whereas the awful smell of the other products I've tried make them unsuitable for me to use. I can handle the stench, but the other members of my household cannot, and it's frankly embarassing to have guests over when my house smells like stinky athletic sneakers (Serenade) or putrid garbage funk (Ray's product).
The main downsides to Actinovate for me, are the fact that it's expensive and it can sometimes be hard to find for sale, as many vendors run out of stock on a somewhat frequent basis. As for the expense, it's actually not terrible when you consider it on a per dose / per application level, but the stuff is fairly expensive to buy by the packet.
The reason I tried Actinovate (whether scientifically solid or not): Agricultural streptomycin (antibiotic) is very effective at controlling Erwinia. I have used it in very limited quantities in my collection as a last resort, but I was not really comfortable using an antibiotic indoors like this. My theory was, since Actinovate contains a species of Streptomyces (the genus for which streptomycin is named), there was a chance that it would provide more targeted and "natural" antibiotic control of gram negative bacteria like Eriwnia.