The idea that the coyote population increases with the available food would make me think that making available plum or other food for them would not be a good idea. If researchers could develop a way to preserve the parvo (or other deadly disease to coyotes) virus so that you could take dead cows or deer carcass and infect the bait so that the coyotes would contact the disease thru ingesting it. Almost all dogs are treated for it, although I don't know if other wild animals contact the disease.