Experts and BHG readers answer.
Trumpet Plant-white flies
Thanks for writing. That's a tough one --- whiteflies are some of the hardest pests to deal with because while you can spray the ones that are on your plant, there's not much you can do to prevent new ones from attacking.
For that reason, you might consider trying to attract more beneficial insects to your garden; they'll attack the whiteflies and bring the population in balance. You'll always have some whiteflies, but they shouldn't be very noticeable.
Otherwise, you can also try looking for a systemic insecticide. These products are absorbed by the plant and kill insects that feed from the plant.
---Justin, Senior Garden Editor, BHG.com