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Larry A. Sagers Regional Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved
Last week, a caller from central Utah wanted to know how to control whiteflies on tomatoes in his greenhouse. Since these pest are so troublesome and so difficult to control, I am including this as one of the tips.
Greenhouse whitefly (Trialeurodes vaporariorum) is a common pest of many houseplants such as poinsettia, ivy, Hibiscus, and Lantana. The pest is almost guaranteed to attack many greenhouse-grown vegetables but is particularly troublesome on tomatoes, pepper and cucumbers.
Insects damage the plant by sucking sap from the leaves and stems. Heavily infested plants drop their leaves prematurely and their vigor is drastically reduced. Whiteflies also excrete sticky honeydew during feeding. This detracts from the appearance of the plant and also allows sooty mold, a black fungus to cover the leaves.
Winged adults are the most commonly noticed stage. They look like tiny butterflies and covered with fine white wax. Adults lay their eggs on the leaves and the eggs hatch into the immature nymph stage in three to seven days. The nymphs cause the most feeding injury to the plant.
Whitefly nymphs are translucent in color and rather immobile. Because they feed on the underside of the leaves the whitefly, nymphs are often inconspicuous and easily overlooked. The nymphs feed for two to four weeks and then change into an inactive “pupal” stage that typically lasts one to two weeks, before adults emerge. Adults are active and lay eggs for two months if conditions are favorable.
The greenhouse whitefly is a tropical insect that is incapable of overwintering outdoors in Utah. Freezing temperatures or a relatively short host-free period eliminates greenhouse whitefly.
Although most houseplant problems originate from the purchase and movement of infested plants, some whiteflies can reproduce and infest new plantings during the warm summer months.
Use yellow sticky cards or tape to trap adult whiteflies. On small plants, eliminate adult whiteflies vacuuming.
Insecticides containing pyrethrums or related insecticides are the most effective chemical controls for adult whiteflies. Horticultural oils, neem insecticides, and insecticidal soaps control nymphs on leaves.
Whenever using insecticides, make three applications 10-14 days apart to control the lifestyles that develop from the eggs.