I live in northern California.
My orange has been having this problem since I bought this house two years ago.with white cotton-shaped thing on the back of the leaves and black "dusts" on the front of the leaves that are infected.
The tree still bore oranges every year since I moved in but I would like to get rid of the problem since it's spread to my lemon tree nearby.
I tried safer Insect Killing Soap but it didn't help.
Could someone please help me identify the disease and recoommend a solution?