If my neighbor poisoned my trees who do I report to? I'm in Florida, do I contact the dept. of agriculture? How do I fight back?

You may have various causes of action, but it is impossible to determine what those might include or your chances of prevailing. Hire a lawyer to review your facts with specificity and advise you. This response does not create an attorney-client relationship. Unless you are already a client of the Mallory Law Group, pursuant to an executed employment agreement, you should not use, interpret, or rely on this response as legal advice or opinion. Do not act on any information in this response without seeking legal advice. Earl K. Mallory

If they poisoned your trees they committed a crime. Make a police report, but I doubt they will make those admissions to the police. You can sue for the value of the trees, but how are you going to prove they did it?

Intentionally poisoning your trees is a criminal act, so you should make a police report first to document the alleged act. Second, in addition to various other possible actions, you probably have a civil right to pursue the neighbor for damages in trespass to your property.