Washington (AFP) - Trick or treat! While youngsters dress up as ghosts and goblins and go door to door for Halloween, grown-ups across the United States are indulging in all things pumpkin spice.What started a decade ago as a seasonal Starbucks coffee flavor -- which curiously isn't made of pumpkin -- has blossomed into something of an autumn American obsession.Supermarket shelves are bursting with pumpkin spice cookies, chocolates, marshmallows, waffles, bagels, pasta, potato chips, Greek yogurt, hummus, granola and pudding, to name but a few.Trader Joe's, a hip grocery chain, features "pumpkin-spiced pumpkin seeds" among its arm's length list of edible Halloween offerings.Craft brewers are tapping into a growing market for limited-edition pumpkin-flavored beer.