There's bad news, good news/bad news coming my frustrated friend. That first bad news is that you have taught your dog this behavior by providing food for the bark. Your dog has made the connection. The good news/bad news is this behavior can be unlearned.
Check this link for the full story ... and good luck: http://www.quickanddirtytips.com/pets/dog-behavior/how-to-stop-demand-barking