Sounds like a tough problem, if you can't use a systemic and spraying with Neem Oil or Safer is out of the question (didn't really seem to help with my trees anyway). Most solutions I've seen involve either a systemic or a combination of systemic and just spraying with a strong jet stream of water. You might be down to that and ladybugs. They have become a real problem. In my neighborhood in Boca Raton, they are everywhere. My neighbor's gumbo limbo has taken on a silver hue, as have my other neighbor's coconut palms and all the christmas palms are turning white and black from the sooty mold. I have them on my hurricane palms and lemon tree (I even saw eggs on a lemon). Good news is that they don't seem to be killing anything - yet.