Answer: There isn't an insecticide that targets true whiteflies. They are able to reproduce very quickly, so it is essential to keep after them to get their numbers under control. Continue wiping them away as soon as you see them. Whiteflies are attracted to the color yellow. You can purchase or make yellow "sticky" traps from yellow cardboard smeared with petroleum jelly. They fly to it and get stuck.
Spraying daily with a forceful blast of water is helpful. I realize this is more problematic when the tree is indoors than outdoors. Soapy water sprays are another possibility. Use 1 teaspoon to 2 tablespoons of liquid detergent soap per gallon of water. Use regular, not concentrated soap. Don't use soaps with lemon, as the citric acid can burn plants. Start with the lower amount and work up as needed. Spray as often as needed. As with any spray you might wish to test it on a few leaves first before you treat all your plants. Next on my list would be an insecticidal soap spray. The insecticidal soaps are made from plant-derived fatty acids and target soft-bodied insects.
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