Thanks for the responses. Yes, I am very excited to get the Sapote in the ground and hopefully taste the fruits in a few years.
CTMiami, thanks for checking in. I am in Palm Beach county, Royal palm beach. Deep, sandy soil as far as I can tell, definitely well draining. Have not seen any insects around the lesions. I did have quite a bit of purple queen as a groundcover around it but just mowed that down today, and also removed some of the lower branches close to the lesions in the hopes that better airflow will help (if it turns out to be a fungus). I will try and take better pictures tomorrow.