It may be powder mold, Wait and see what the other members have to say. I will like to see what the cure will be. Good Luck..
Christine

If it's mold, mildew, fungus, you need a good fungicide, I'd recommend a metal based one.
In a pinch, cinnamon will knock it back...
I'm not sure that what your looking at, what's it feel like, does it wipe off, is the plant marked from it?

See my response to your other post. If you wipe them off the leaves now, you won't have any webby whitefly infestation later.

Sue

It turns out to be whiteflies. Little aphids that infest on the underside of plant leaves. They can lay up to 400 eggs at one time which hatch in a couple weeks. Once the tree becomes infested the white fly leaves a sticky substance called "honeydew" all over the leaf. This substance will collect dirt and mold over time and slow photosynthesis. My almanac says to wash the tree with antibacterial soap up to three times.... I will give it a try and post an update. Thank you for all your help !

Here's a picture of a leaf covered in "honeydew" : (

Thanks for posting the info on white flies,
Christine

Oh my!
I would have thought an infestation of that size would have been appearant!

That entire is black with it?