Q: I see whiteflies all over my gardenias in summer. What should I do to kill them?
A: If you see hundreds in spring, you’ll see millions by mid-summer! They suck plant sap and excrete a sticky honeydew that gets all over lower leaves. The honeydew supports the growth of sooty mold, which inhibits photosynthesis.
Whiteflies can be killed with most garden insecticides. But they reproduce so rapidly that if you don’t stay ahead of them, they become uncontrollable. Deltamethrin, permethrin and esfenvalerate are common garden insecticides. The key is thorough coverage. Spray the insecticide up, down and through the shrub. Repeat as directed on the insecticide label.
Another excellent option is to use a soil-applied systemic insecticide in spring. Imidacloprid (Bayer Advanced Tree & Shrub Insecticide) gives great results if applied at the right time.