Whiteflies are hard to miss. Every time you water or walk by your gardenias, they fly up in pesky white swarms. Or, you may have noticed their eggs on the underside of your gardenia’s leaves. Whatever the sign, it’s important to kill white flies as soon as you notice them. These insects spread rapidly, especially in the warm southern areas, and can quickly overwhelm a gardenia bush. Large enough numbers of them will strip its foliage, potentially spread viruses and diseases, and maybe even kill a weakened plant.
Destroy any whitefly eggs that you may find growing on the underside of your gardenia's leaves. Prune the leaves and dispose of them. Crush the eggs or spray them with horticultural oil.
Suck large swarms of whiteflies up with the hose on your vacuum.
Spray the adult population. Whiteflies are quite susceptible to a number of controls: insecticidal soap, neem and horticultural oils, and pesticides like purethrum, permethrin and bifenthrin. The trouble lies in the application. All of these methods work by contact, and whiteflies are quick little blighters. Whichever method you choose, you will likely need to spray your gardenias once weekly for a month. And when you do spray, aim at the underside of your gardenia's leaves where the whiteflies live.
Release beneficial insects into your garden. Ladybugs (Delphastus pusillus), green lacewings (Chrysoperla spp.) and predatory mites (Euseius spp.) all feed on whiteflies. If you release beneficial insects, abstain from spraying your gardenias. The pesticides will kill the beneficial insects as well.