Poinsettias (Euphorbia pulcherrima), so familiar during the winter as houseplants, grow as perennials in U.S. Department of Agriculture plant hardiness zones 9 through 11. These plants produce colorful bracts and brighten rooms for the holidays, so it can cause concern when whiteflies infest a poinsettia. Whitefly adults look like tiny, delicate moths that are covered with a powdery white wax. An immature whitefly, or nymph, is flat, oval and mostly immobile where it feeds on leaf undersides. Both adults and nymphs feed on poinsettias, stunting plant growth when an infestation is heavy. Typically more troubling is that whiteflies produce honeydew, a sugary substance, as a byproduct of feeding. Honeydew gives surfaces it drips onto a shiny look and supports the growth of the unattractive sooty mold fungus.
Pinch off, bag and dispose of the oldest leaves on the poinsettia that are heavily infested with immature whiteflies and eggs. Always wear gloves when touching a poinsettia because the sap can irritate skin.
Shake the poinsettia gently and vacuum up whitefly adults that fly into the air above the poinsettia using a small, hand-held vacuum. Place the vacuum bag in the freezer overnight before disposing of its contents.
Wipe the leaves of the poinsettia down with a moist sponge or cloth, concentrating on leaf undersides. This may control the pests.
Smear petroleum jelly onto a small piece of yellow cardboard or buy yellow sticky traps and place one or more near the poinsettia. Keep the yellow sticky traps out of the reach of children or small pets to avoid a sticky mess.
Blend 2 tablespoons of mild dish washing detergent with 1 gallon of lukewarm water. Pour the solution into a spray bottle and spray a small, inconspicuous section of the poinsettia. Rinse the soap spray off of the plant after a few minutes. Monitor the area you sprayed for about a week to make sure it didn't damage the poinsettia. If the sprayed part of the plant was damaged, decrease the concentration of the soap or use a different soap and test again. If no injury occurred, spray the entire plant thoroughly, wait a few minutes, then rinse off the soap. Spray a week later, if needed.