If i were to guess, and I live in FL, that anyplace with hot and wet weather could breed blackhead. That said not everyone has problems with it, bad thing is you normally have to have a turkey come down with it before you know you have it.... I am careful about introducing new chickens, I always keep meds like Fishzole on hand encase I have problems, and I've had a few. I try to avoid keeping chickens and turkey penned togther. I raise poults off ground until about 3 months old. I worm chickens with safeguard liquid goat wormer, as it helps kill off the host parasite that carries balckhead.