how is your humidity/RH ?
in veg keep it around 50-60% in flowering try to keep it under 40% .. 30% is perfect ..
you did`t provide mouch info or pictures .. so hard to help .. but if it is powder mildew ther is diffrent stuff you can buy to spray it with to keep it under control/remove it .. do some research/google it ..
if your close to harvest you can clean em after so you don't have to smoke the damn thing:
[video=youtube;S7jE7qzfgQs]http://www.youtube.com/watch?v=S7jE7qzfgQs[/video]
hope this help .. try to post some pictures .. Ppl. tent to be more helpfull and can give better advice ..