Coconut Palm problem

Can anyone tell me what might be wrong with one of my coconut palm trees? I noticed the middle (heart) has turned brown and looks like some sort of chemical burn. It has not had any treatment other than water from my well. I live in SE Florida and our water has lots of iron but my other plants don't show any damage. Has anyone else ever had this probllem?

Never grown a coconut (can't grow here in California... with very rare exceptions)... but lethal yellowing is a serious infection that kills Coconut palms (and many others) and it's common in Florida... not sure how to diagnose it, but you might contact your local nurseries or even the city... they would probably know. Hope that's NOT what you have, since it is quite contagious to neighboring palms, and 100% fatal once they get it.