Help! Our tree is covered in....cocaine?

Often times I write 'how to' posts, sharing things I've learned while working on our house. However, this time I'm asking for help. Our crape myrtle is covered in cocaine. Ok, so it's not really cocaine... but it is a fine white powder! See?

Don't see it? Let me give you a closer look:

What. The. Heck. If you touch the tree it comes off on your hands.

At first LJ and I were clueless as to what this was, so we did what any first time home owner would do; we googled it. Apparently it's mold. Isn't that gross? And it's definitely trying to take over our tree. The solution suggested online was this stuff:

You hook your hose up to the top and spray the tree down with water. You supposedly only need to use this stuff a few times and it does the trick... but it's been about a month and the mold is still there. I think the spray has helped some, but it is not the quick and easy solution it claims.

Any other bright ideas out there? Anyone?