Reviewed October 2001
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Figure 1
An adult whitefly.
Managing Whiteflies on Indoor and Outdoor Plants
Bruce A. Barrett
Department of Entomology
Whiteflies are closely related to aphids, mealybugs and scale, all of which feed by sucking sap from plants. Whiteflies can be found on the undersides of leaves and are active during the daytime when it is warm. When a heavily infested plant is disturbed, white clouds of winged adults fly into the air.
Some species of whiteflies can become serious pests of certain vegetable crops, greenhouseplants or ornamental plants. Two of the most important species are the greenhouse whitefly, Trialeurodes vaporariorum, and the sweet potato whitefly, Bemisia tabaci. In colder climates whiteflies die outdoors, but in warmer climates and indoors and in greenhouses, they can reproduce throughout the year with several overlapping generations.
Biology
Adult whiteflies are about 1/10- to 1/16-inch long and look like tiny moths (Figure 1). They have four broad, delicate wings that are held rooflike over the body and covered with a white, powdery wax. Adult females usually lay between 200 and 400 eggs. Sometimes the eggs are deposited in a circular pattern in groups of 30 to 40 because the female will often keep her mouthparts in the plant to feed while moving her abdomen in a circle.
Within about a week, the eggs hatch into flattened nymphs, called crawlers, that wander about the plant. Soon, they insert their mouthparts into the plant and begin to feed. After their first molt, the nymphs lose their legs and antennae. They attach themselves to the undersides of leaves with several waxylike rods coming from their bodies, giving them the appearance of small, white, oval scale. The nymphs remain fixed to the plant and feed for about four weeks. After a pupa stage, the adults emerge and live for about one month. Within a population, all life stages are present, and generations often overlap.
Damage
Whiteflies damage plants by sucking out plant juices. Because large amounts of sap can be removed, primarily by the developing nymphs, heavily infested plants can be seriously weakened and grow poorly. Leaves often turn yellow, appear dry and drop prematurely (Figure 2).
Figure 2
Whiteflies suck out plant juices. This seriously weakens the plant.
Also, because whiteflies suck out more plant juice than they can digest, the excess is excreted as a sweet, sticky substance called honeydew. The honeydew covers leaf surfaces and acts as a growth medium for a black, sooty mold. Both the removal of plant juices and the presence of the black, sooty mold growing on the honeydew can interfere with photosynthesis.
In some parts of the country, some species of whitefly can transmit several plant viruses.
Control
Cultural control
Ornamental plants in or around the home and plants in greenhouses or gardens often become infested with whiteflies through the introduction of infested plants. A slight infestation from one plant can quickly spread to other plants. Inspect all new plants thoroughly, and isolate them for a few days before placing them among established plants. During this isolation period, inspect the plants and treat those infested.
Inspect plants regularly, and remove by hand older leaves that are heavily infested with whiteflies in the nonmobile nymphal and pupal stages.
Biological control
Whiteflies have many natural enemies in the garden setting, such as spiders, lady beetles and lacewings. However, these predators are not effective in controlling whitefly populations if there is frequent or widespread use of insecticides to control other garden pests.
A tiny parasitoid, Encarsia formosa, has been successfully used in managing greenhouse whitefly populations in greenhouses and conservatories for many years. E. formosa is available from commercial suppliers. (See below.) However, in an outdoor setting where favorable temperature and light conditions cannot be maintained, use of E. formosa is limited.
Mechanical control
The use of traps can be very helpful in controlling light infestations of whiteflies in greenhouses. You can make a trap, 12-by-6 inches, from cardboard or strong poster board and paint it bright yellow. Then coat it with a sticky substance, such as Tanglefoot, petroleum jelly, petroleum jelly/mineral oil mix, mineral oil or a heavy- grade motor oil (SAE 90). Hang the trap vertically or support it on stakes just above the plants. The adults are attracted to the yellow color and become trapped on the sticky substance. Whitefly traps are available commercially, also. (See below.)
The use of yellow traps outside may have limited value because of the large number of traps required. One trap for every two large vegetable plants is recommended. Clean the traps periodically to remove insects and other debris, and apply fresh adhesive to the yellow surface. In order to avoid trapping too many of the whitefly's natural enemies, use traps when whiteflies first start to appear, but remove them when the whitefly population seems to be decreasing.
Another mechanical technique that can be helpful to control whiteflies is a small, hand-held vacuum cleaner. Vacuum the adult whiteflies in the early morning when it is cool and they are slow-moving. Put only the vacuum bag with the insects (not the vacuum) inside a large plastic bag and freeze for 24 hours to kill the insects. Vacuuming adults is most helpful and effective when an infestation is just starting and when the adults have not laid many eggs.
Chemical control
It many cases it has been difficult to control whiteflies with insecticides because they have developed resistance to some chemicals. Because of this resistance, a certain product may work well in one area but not in another. Resistance may be delayed by alternating the types of chemicals used. In addition, the egg and non-feeding pupa stages are generally not as susceptible to insecticides as are the adults and nymphs. Consequently, eradication of a whitefly population usually requires four to five applications of a registered insecticide at five- to seven-day intervals. Be sure that the applications are made to the lower leaf surface, and apply as soon as whiteflies are detected. Do not wait until populations become severe.
Some of the conventional and alternative insecticides that are available for control of whiteflies are listed in Tables 1 and 2. Some of the chemicals listed are registered only for indoor use (greenhouse included), outdoor use (ornamental) or vegetable plants. The "Plant and site uses" column lists the type of plants (vegetable or ornamental) and sites (indoor or outdoor) where the insecticide may be used. Some insecticides may be phytotoxic to some plants.
Table 1
Conventional whitefly insecticides
| Common name | Examples of trade names | Plant and site uses |
|---|---|---|
| Over-the-counter insecticides | ||
| diazinon | Ortho Diazinon Plus Insect Spray | Outside ornamental plants, Vegetable plants |
| Super K-Gro Fruit and Vegetable Insect Control | Vegetable plants | |
| Spectracide Lawn and Garden Insect Control | Outside ornamental plants | |
| acephate | Ortho Isotox Insect Killer | Outside ornamental plants |
| Ortho Orthene Systemic Insect Control | Outside ornamental plants | |
| malathion | Ortho Malathion 50 Plus Insect Spray | Outside ornamental plants, Vegetable plants |
| Dragon 50 percent Malathion Spray | Outside ornamental plants, Vegetable plants | |
| K-Gro Malathion 50 Insect Spray | Outside ornamental plants | |
| endosulfan | Dragon Thiodan Insect Spray | Outside ornamental plants, Vegetable plants |
| resmethrins | Dragon Whitefly and Mealybug Spray | Houseplants, Outside ornamental plants |
| permethrin | Spectracide Lawn and Garden Insect Control | Houseplants, Interiorscapes, Greenhouse plants, Outside ornamental plants |
| Nonrestricted-use insecticides | ||
| acephate | Orthene Turf, Tree and Ornamental Spray | Greenhouse plants |
| bendiocarb | Dycarb | Interiorscapes, Greenhouse plants, Outside ornamental plants |
| cyfluthrin | Tempo 2 | Interiorscapes, Greenhouse plants, Outside ornamental plants |
| fenopropathrin | Tame 2.4 EC | Greenhouse plants |
| fluvalinate | Mavrik Aquaflow | Interiorscapes, Greenhouse plants |
| bifenthrin | Talstar 10 WP | Greenhouse plants, Outside ornamental plants |
| naled | Dibrom 8 | Greenhouse plants |
| imidacloprid | Merit 75 WSP | Interiorscapes, Outside ornamental plants |
| Marathon 1 percent G | Greenhouse plants, Outside ornamental plants | |
| endosulfan | Thiodan 50 WP | Vegetable plants |
| Restricted-use insecticides | ||
| permethrin | Ambush 25W | Outside ornamental plants |
| Pounce 3.2 EC | Outside ornamental plants | |
Table 2
Alternative whitefly insecticides
| Common name | Examples of trade names | Plant and site uses |
|---|---|---|
| Botanical insecticides | ||
| pyrethrins | Dragon Rose and Garden Insect Spray | Houseplants, Outside ornamental plants, Vegetable plants |
| pyrethrins and | Dragon Gentle Care Houseplant Spray | Houseplants |
| piperonyl butoxide | Ortho Tomato and Vegetable Insect Killer | Vegetable plants |
| Yarden Insect Spray | Greenhouse plants, Outside ornamental plants, Vegetable plants | |
| Scotts Bug Spray | Houseplants, Greenhouse plants, Outside ornamental plants, Vegetable plants | |
| Schultz-Instant Houseplant Insect Spray | Houseplants, Greenhouse plants, Outside ornamental plants, Vegetable plants | |
| Ortho Rose and Flower Insect Killer | Outside ornamental plants | |
| Safer Garden Insect Killer | Outside ornamental plants, Vegetable plants | |
| pyrethrins and rotenone | Dragon Tomato and Vegetable Insect Spray | Vegetable plants |
| Natur-Gro Triple Plus WP Insecticide | Outside ornamental plants, Vegetable plants | |
| azadirachtin | Margosan-O | Houseplants, Interiorscapes, Greenhouse plants, Outside ornamental plants |
| Insecticidal soap | ||
| M-Pede | Houseplants, Interiorscapes, Greenhouse plants, Outside ornamental plants, Vegetable plants | |
| Safer Insecticidal Soap | Houseplants, Interiorscapes, Greenhouse plants, Outside ornamental plants, Vegetable plants | |
| Ortho Insecticidal Soap | Houseplants, Vegetable plants | |
| Ringer Attack | Vegetable plants | |
| Safer Aphid, Whitefly and Mealybug Killer | Houseplants, Outside ornamental plants, Vegetable plants | |
| Petroleum oil | ||
| Ortho Volck Oil Spray | Houseplants, Greenhouse plants, Outside ornamental plants | |
| Ortho Horticultural Spray Oil | Houseplants, Greenhouse plants, Outside ornamental plants | |
| Sunspray UltraFine Spray Oil | Houseplants, Greenhouse plants, Outside ornamental plants, Vegetable plants | |
| Saf-T-Side for Vegetables | Vegetable plants | |
| Insect growth regulator | ||
| kinoprene | Enstar II | Interiorscapes, Greenhouse plants |
Note
Before you use any insecticide for whitefly control, please make sure that the site and target plant are both listed on the label. Follow label directions carefully
Sources
Some of the insecticides listed in the tables and the yellow sticky cards used for trapping whiteflies can be obtained from the following (and other) horticultural supply companies.
- Hummert International, 2746 Chouteau Ave., St. Louis, MO 63103
800-392-9113. - E.C. Geiger, Inc., Box 285, Harleysville, PA 19438
800-443-4437. - Florist Products, Inc., 2242 N. Palmer Drive, Schaumburg, IL 60173
800-828-2242. - Siemer Distributors, 6300 Collinsville Road, East St. Louis, IL 62201
800-593-3030.
The following are some of the comapnies that rear E. formosa commercially for whitefly biocontrol.
- Beneficial Insectary, 14751 Oak Run Road, Oak Run, CA 96069
800-477-3715. - Gerhart, Inc., 6396 Avon Belden Road, North Ridgeville, OH 44039
216-353-9457. - IPM Laboratories, Inc., Main Street, Locke, NY 13092
315-497-3129. - Natural Pest Controls, 8864 Little Creek Drive, Orangeville, CA 95662
916-726-0855. - Nature's Control, P.O. Box 35, Medford, OR 97501
503-899-9121.
G7275, reviewed October 2001