Tommy: Check with your local County Extension Office. They usually sponsor at least an annual training course in Pesticide Application. At the completion of the course you will be awarded a Georgia Pesticide Applicators License.
This enables you to purchase Restricted Pesticides and apply them in your own operation (farm, tree farm, game mgt. etc).
A professional applicators license requires more intensive study.
I have used Garlon and found it to be an excellent brush and weed killer. I believe it to have been Garlon-4 that I used.