Posted: 10/08/2013 at 20:43
Looks like powdery mildew, which is caused by dryness at the roots. If it is newly planted then it probably needs a good watering. Amazing how long it can take for a plant to send out rooys from the original compost and of course the top growth stops rain from getting to the roots.
Cannot help with the Sunflowers, never bothered growing them.