It seems to me that crop dusting planes are no longer a viable option. The reason being, once one is spotted in an unusual area, the CDC and FBI will descend on that area so fast, and distribute antibiotics to everyone so rapidly, that few if any people will be infected.That's if anyone notices. If they can get the plane in the air from an abandoned airfield at night, they can spray all night long to their heart's content without being noticed. You can't really tell the difference between a crop duster and a single-engine plane when you're on the ground and the plane's way up there.
And dispersal is best done at night, preferably an overcast night. Exposure to sunlight can render the bacteria benign. If they do it that way, everybody wakes up and goes about their day like nothing happened.
Some good and scary points about using a cropduster even right now. Well, time for me to sleep. Lets hope we can wake up tomorrow and realize this was all a very bad dream. Its not normal when tin foil hatters like myself start sounding sane. Its just not the same world anymore.