Whitefly is hard to keep under control once established on plants, so a preventative approach is good strategy. I recommend spreading worm castings around the plant to boost its immunity and to repel insects. Weak plants attract insect investations. The enzymes in worm castings break down exo-skeketons of insects and naturally repels them. I'm not sure if Arizona has adopted the same biological control of whitefly through the use of a parasitic wasp as we have in Calif. If so, even organic things like neem oil could interfere with the program. Actualy blasting undersides of leaves with water knocks off eggs and young flies and will eventually lessen populations. An even better option are whitefly sticky traps that have a pheromone attractant and disrupt mating. Since the insect produces a waxy substance to layer over eggs on leaf bottoms, irradicaton is tough. Good luck!