Nematodes are the big problem in Florida, and cause them to turn yellow. Try fumigating the ground first with a diluted chlorine bleach mixture to kill the little buggers first. Will hold them off for quite sometime. Don't get any bagged fertilizer in the crown area, and even better use miracle grow sprayed on to fertilize. You can gas them to produce more fruit by putting calcium carbide or apple chunks in the crown. Clear plastic over the plants for a few days will help them gas. You can get calcium carbide off Ebay that they use for carbide cannons. Sometimes available in 1 pound boxes. Also, you can take the debris from up top of a Palmetto Palm(you know all that nasty crud thatr comes out of them when you trim them up)and put that in the crowns and when it rots it forces them to fruit quite nicely. Or you just knock back a bunch of beers, give up the idea of growing them, and go to Publix and buy them. So much easier Good Luck !