I'm not sure where you live and the status of EAB in your area.  But I am confident that EAB is still present - there are enough young ash and untreated ash trees around to support EAB populations pretty much everywhere this invader has become established.  I also do not know how your tree is being treated.  A trunk injection of an insecticide with emamectin benzoate (e.g., Tree-age or Mectinite) does not need to be treated more than once every 3 years.  Other products such as TreeAzin or Azasol (azadirachtin) likely need to be injected every 2 years.  Products with imidacloprid or dinotefuran need to be applied annually.  

If there are very few live ash trees in your area, you can consider extending the treatment interval by a year.  For example, maybe you can get away with injecting an emamectin benzoate product every 4 years.  A healthy ash tree can handle a few EAB galleries and  EAB is unusually vulnerable to Em Ben.  

We have a big bulletin about using systemic insecticides to protect ash trees.  The url is below.  It includes pros and cons of various treatments, FAQs and so forth.  I think you'll find some useful info there. 

Multistate_EAB_Insecticide_Fact_Sheet.pdf (emeraldashborer.info)

Deb