This drooping is a way for the plant to save water during the hot times. Hydrangeas do it as well. It will not kill the Shasta Daisies but if you want to avoid it you should work more organic matter into the soil so that the roots have extra moisture during the heat of the day. You can also try watering in mid morning so the roots are filled with moisture by afternoon - but even if you do this on a hot day you may still see the Shasta wilt. Keep cool this summer and Keep growing, Marianne Binetti