shih tzu doesnt like puppies

Question
My Shih Tzu is a year old and mostly loves other dogs.  Right around the 10-mo. mark he met a puppy Puggle about 10 weeks old and started growling, snapping and lunging at her.  This was the first time ever that he reacted that way to another dog.  I've kept him away from her but other dogs, all kinds and sizes seem to be his friend, as long as they're not puppies.  I've taken him to small dog play time and he reacts that way only to puppies.  I've taken him to dog parks and he will play with the biggest dog there, no problem, but the first puppy he runs into, even if the puppy is larger (Labs, Goldens, Boxers) he will go after them.  I don't know what to do-- he's so loving and playful with people and most dogs.  The dog park is his favorite thing to do, but I have to watch him like a hawk-- and I'm so nervous that he'll go after a puppy and I won't be close enough to stop him.

Answer
Your dog might have been the only one in the litter and was never socialized to puppies properly; or, he may have had a very unpleasant experience as a pup with another his age; or, if the pup is very young, the lack of pheromones might be confusing him and making him fearful.  It's impossible for me to determine what sort of aggression he's demonstrating as I can't see it, but it "sounds" like fear.

First, no puppy of any age should be allowed to run with adult dogs; people who do this in dog parks are doing their pup a huge disservice, as one bad experience (or bullying experience, not uncommon between adult dogs and young pups) can seriously affect future dog to dog relationships.  However, you have no control over the mistakes made by other dog owners!  You do, however, have control over your own dog.  You must be vigilant and be certain that your dog does not interact with puppies.  Perhaps you can find (or organize!) a play group of dogs between 1 and 3 years of age.  You might also benefit from consulting a credentialed behavior expert who can observe your dog first hand and suggest rehabilitative exposure to pups (although how you would find people willing to allow their pups to participate is a whole new problem!)  If I were working with your dog, I would start by visiting a puppy kindergarten (with the agreement of the trainer conducting it) to observe exactly what's going on with your dog.  I think this CAN be rehabilitated.