I have a lavender star flower that became infested with whiteflies at the end of warm weather last fall. I tried everything--Garden Safe spray, dish soap in solution, even Sevin. Nothing stopped the little monsters from coming back. I finally wrapped the pot with saran wrap to keep the soil in, and put the tree in the kitchen sink. I used a toothbrush and the spray nozzle, and scrubbed the entire tree clean. Then neem oil every other day for two weeks, since I was told that if they lay eggs before you kill 'em, their progeny will be back before you know it. So far, so good. It suffered a considerable amount of leaf drop, but is now shooting new growth and forming numerous blossoms [which I can't help but think has to be a good sign.]