Dusty Leaves?

Hi Guys
I'm about 1 - 2 weeks away from cropping and some of the smaller more shaded lower leaves have what looks like a fine coating of dust.
I worried it might be mildew perhaps?
The humidity is up around 70% after feeding/watering ( Coca + Cana A-B )
Lowest readings are around 46% during rest.
Temp is a nice 18 degrees resting and 25 degrees lit up.
Buds seem nice and healthy although not too smelly from a distance and doesn't seem bothered by it's few manky leaves..
Anything to worry about?

Dave

nothing to worry about my friend, it happens when theres not enough air flow and some dead leaves at the bottom,

all is fine as long as its dead leaves at the bottom

I found it.
Powdered mildew. I'm cropping soon so it's not too much of a problem.
Just fire a sulpur bomb off before I do my next grow.
Yes we tracked down the problem as to not enough air exchange and too high humidity.
Won't happen next grow.

I just bought a product called Serenade, it came highly recommended at the hydro store here. I got it for rust spots but says powdery mildew on it.