Question
What sites or professional organizations do you recommend for a tree service professional to become more familiar and involved with in order to offer special services for the customers tree needs.  Example.. I would like to purchase some Ethephon or "Florel Brand Fruit Eliminator" and need assistance with locating a supplier.  I have customers who are considering removing large beautiful oak trees because they are tired of dealing with the acorns by swimming pools or other high traffic areas. I would like to help the tree have a chance to continue to live if the fruit production can be drastically reduced.  Thanks for your time and shared knowledge.  Sincerely,  Luis  aka The Young Pro

Answer
In most states in order to charge to apply pesticides one would need to be certified or licensed. Usually this is the State Agriculture Department or some times the State Extension office. Usually the Extension hold training for the test and the Agriculture Department gives the tests. I would suggest that you contact these folks in your state. As far as organizations to join I would suggest looking into becoming a Certified Arborist this would give you more clout as a tree "expert". The organization  that handles this is the International Society of  Arborculture. Here is a link to their web site.  http://www.isa-arbor.com/home.aspx