Dude, sounds like PM, Powdery Mildew...You can spray the shit outta your plants right now, but in a week or 2 longer and the buds might be affected...Get something serious for PM, cause you're gonna be fighting it all through flower and I tell you it's a pain in the ass. It goes away after you treat it for a few days and starts creeping back. Really, you wanna try to control it as best as possible now. There's a guy on here who swears by this stuff, but I've never used it so I can't make any recommendation for or against it, but it's supposed to be systemic so you treat the plant once or twice and the problem is gone...
http://www.dowagro.com/turf/prod/eagle.htm
Good luck dude, definately try to take care of that shit ASAP, it's a big pain when you have thick buds on the plants.