Hi Stewies Mom:
My comet used to eat grass alot also. The advice that I've gotten which you probably already know is that dogs eat grass to make themselves vomit. Perhaps Stewie is probably trying to clean his own system out? Maybe he ate something that didn't agree with him?
Comet ate grass alot and eventually lost interest. Now he only sniffs and digs through it. I realize that I was also feeding him Science Diet at the time. Now that he's eating Innova, he leaves the grass alone. I'm sure that Stewie will eventually wean his way off on his own.
Comet is 5 months old now. How old is Stewie?