I live in Tucson, AZ, obviously a very dry climate. In late April this year, late to be planting in our climate, I planted two seven foot crape myrtles that I purchased from Lowes. In or around June, I noticed white dots on the stem of the tree and branches (not leaves). Since then, the white dots have travelled to every plant in my yard, all my photinias, my bougainvillea, my buddleia, even my texas sage.

I've tried to identify it so i know how to cure it. I've thought mealy bugs, but they don't appear to be insects (they don't move, they pop up in different places but don't appear to travel themselves). The picture you're looking at is of a Bougainvillea I pulled out of the ground because it was not doing well and potted to restablish its roots. It's the most recent plant to catch it. Ignore the leaves, which are brittle because it's still recovering, but look at the dots on the stems.

I tried sauteeing garlic in olive oil with a little cayenne pepper, mixed the oil with dish soap and sprayed and the infection seemed to abate. I've since started using a neem oil solution, but they keep seeming to spread.

What is it and how do I get rid of it? (I kind of ruled out mold because our climate is so dry, but I could be wrong.)