Answer: Whitefly is one of the most difficult pests to control. The little fly-like insects with white wings hang out on the undersides of leaves where they multiply rapidly in warm weather. Whiteflies damage leaves and suck sap from the plant; if the infestation is severe, this can lead to death in young plants and decline in older ones.
Persistence is the key to control. I have had good luck controlling these pests by spraying them with a mixture of dishwashing liquid, such as Palmolive with lemon, and water. A good squirt of soap to a gallon of water should do the trick. Place the mixture in spray bottle and spray leaves, both sides well, at least twice a week when the flies are active. You may need to continue this treatment for many weeks. Spray on an overcast day, in the very early morning or late afternoon to avoid damage from the sun.
Also worth a try:
Yellow sticky tape placed near plants -- Yellow colored traps that attract insects with their color and snare them with a sticky substance. Can make your own with yellow paper and Tanglefoot pest barrier.
Release Encarsia Formosa, a tiny parasitic wasp which will eat them. Available from some nurseries and seed companies.
Pyrethrin spray -- an organic pesticide made from chrysanthemums.
Encourage Hummingbirds. They love to dine on whiteflies. Hang feeders and keep them clean and full of simple syrup (a mixture made from 1 part sugar dissolved in 4 parts hot water). Plant flowers they adore, those with tubular flowers such as fuchsia, foxglove, salvias, bee balm.
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