Order: Hemiptera (Homoptera)
“We’ve sprayed and sprayed, and it seems to just make them worse!”
Exasperated statements like this are often uttered by home gardeners attempting to control silverleaf whiteflies. Fortunately, infestations of silverleaf whiteflies are relatively uncommon in outdoor Mississippi gardens and landscapes. It is primarily more serious gardeners, gardeners who have greenhouses or a lot of house plants, that experience problems.
Silverleaf whiteflies do not survive Mississippi winters well outdoors, but they thrive in indoor settings. If you have whiteflies in your greenhouse or on houseplants, they are going to move onto your outdoor plants in the spring. Plants attacked include tomatoes, peppers, squash, melons, sweetpotatoes, cabbage, collards, lantana, hibiscus, roses, petunia, verbena, and around 500 more.
Adult whiteflies look a bit like tiny white moths and fly weakly when infested plants are handled. Immature whiteflies are immobile, oval-shaped, scale-like insects that feed on the undersides of leaves (see photo). Immature whiteflies are easy to overlook, but this is the stage that causes most damage. Whiteflies damage plants by sucking plant sap, producing honeydew, and causing sooty mold. They also vector several serious virus diseases, including tomato yellow leaf curl virus and cucurbit yellow stunting disorder virus.
Silverleaf whiteflies are difficult to control because they are resistant to many insecticides. Spraying with the wrong insecticide really does make them worse because the sprays kill tiny parasitic wasps and other beneficial insects without affecting the whiteflies. Silverleaf whiteflies are not controlled by the insecticides typically used by home gardeners. Familiar insecticides such as malathion, carbaryl, permethrin, zeta-cypermethrin and bifenthrin just don’t work on whiteflies.
Control: The best defense against silverleaf whiteflies in outdoor gardens and landscapes is to avoid getting them in the first place. Think twice before trying to keep those Christmas poinsettias until next year; they are also called poinsettia whiteflies for a reason. Watch for whitefly infestations on houseplants and control aggressively or discard infested plants. If you have a greenhouse, be sure to prevent and control whiteflies on your greenhouse plants, realizing that it may be necessary to have a host-free period in the greenhouse to achieve this. Carefully check plants for whiteflies at nurseries before you buy them and bring them home.
Homeowners have few good insecticides for controlling whiteflies. Some of the better options include: imidacloprid and dinotefuran, which can be applied as soil or pot drenches, especially on ornamental plants, though some formulations of imidacloprid are labeled on vegetables, and acetamiprid and azadirachtin, which can be applied as foliar sprays on both ornamentals and certain vegetables. Always read labels carefully before treating.
Commercial ornamental and vegetable growers have access to more and better products, but these are usually sold in large volume packages that make them inappropriate for home use. Many are not labeled for home use, or they are too costly, or the large packaging would result in having excess insecticide in storage. Certain parasitic wasps and other beneficial insects are used effectively in large commercial greenhouses, but these are impractical for outdoor use.
See page 3 of Insect Pests of the Home Vegetable Garden for more information on whitefly control in home vegetables.
See page 6 of Insect Pests of Ornamental Plants in the Home Landscape for information on whitefly control on ornamental plants.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
Mississippi State University is an equal opportunity institution.