The Avocado tree (Persea americana) is best grown in U.S. Department of Agriculture plant hardiness zones 9B through 11. This oval-shaped evergreen tree can grow to 40 feet tall with a spread of up to 35 feet. The avocado fruits are dark green to purple, and are often used in salads or to make dips. If you have an avocado tree, you'll need to keep an eye out for whiteflies. Whiteflies damage avocado trees when they deposit honeydew on the fruit, according to the University of California Integrated Pest Management Program. This sticky substance collects dust that eventually grows a mold fungi.
Verify that you do indeed have a whitefly problem by turning the foliage on your avocado tree upside down during the daytime. If whiteflies are present, you'll see either 30 to 40 tiny eggs that are arranged in a circular patter, or 1⁄16 inch long adults that will quickly fly away from the foliage when disturbed.
Release whitefly predators near your avocado tree. Your choices include parasitic wasps, green lacewigs, pirate bugs, bigeyed bugs and lady beetles. These natural predators will get rid of the whiteflies for you.
Control ants and caterpillars. This is necessary to stop the ants and caterpillars from preying on the whitefly's natural predators. Ants can be stopped with insecticidal baits, while an application of the all-natural bacillus thuringiensis will work to kill the caterpillars.
Spray the underside of the avocado's foliage with an all-natural neem oil insecticide if the natural predators aren't enough to completely eradicate the whiteflies. You can get this insecticide at most gardening centers, or from an online vendor. Always follow the application instructions listed on the product label.