Cut garlic scapes off once they start to curl. They're great chopped up in a stir fry or sauteed. Also good for pesto. Cutting them off sends the plant's energy into the bulbs instead of the seeds.
And don't forget they need water while developing, and there's 2 schools of thought on scapes. Some say leave them on, others say take them off. I've never did a real comparison. I do harvest some after they curl when they can be snapped off. I leave some on and let them develop. I've heard some people say leaving them on takes away from the bulb, since they are going to make seed, but you can also plant those. I plant a whole bunch together and just leave them year after year and cut some of the greens. One more thing. Don't forget to leave a few onions in the ground to flower and seed next year