How Can I Control Whiteflies?

Do you want to control whiteflies using the biological control method?

Do you want to control whiteflies using traps?

Do you want to control whiteflies using reflective mulches?

Do you want to control whiteflies using low-risk (organic) insecticides?

Do you want to control whiteflies using synthetic insecticides?

Do you want to use residual, foliar sprays?

General predators of whiteflies include lacewings, big-eyed bugs, and minute pirate bugs. Several small lady beetles including Clitostethus arcuatus (on ash whitefly) and scale predators, such as Scymnus or Chilocorus species, and the Asian multicolored lady beetle, Harmonia axyridis, feed on whiteflies. Several naturally occurring parasites can be very important in controlling whiteflies. Encarsia spp. parasites are commercially available for release in greenhouse situations. However, they are not generally recommended for outdoor use because they are not well adapted for survival in temperate zones.

In vegetable gardens, yellow sticky traps can be posted around the garden to trap adults. Such traps won’t eliminate damaging populations but may reduce them somewhat as a component of an integrated management program relying on multiple tactics. Whiteflies do not fly very far, so many traps may be needed. You may need as many as one trap for every two large plants, with the sticky yellow part of the trap level with the whitefly infestation. Place traps with the sticky side facing plants but out of direct sunlight.

Shiny metallic-coated construction paper or reflective plastic mulches can repel whiteflies, especially away from small plants. Alternatively, you can spray clear plastic mulch with silver paint. Reflective plastic mulches are available online and in some garden stores. In addition to repelling whiteflies, aphids, and leafhoppers, the mulch will enhance crop growth and control weeds. Reflective mulches have been shown to deter pests that transmit viruses in commercial vegetable crops.

Most less-toxic products such as insecticidal soaps, neem oil, or petroleum-based oils control only those whiteflies that are directly sprayed. Therefore, plants must be thoroughly covered with the spray solution, and repeat applications may be necessary. Be sure to cover the undersides of all infested leaves. Usually, these are the lowest leaves and the most difficult to reach. Use soaps or oils when plants are not drought-stressed and when temperatures are under 90°F to prevent possible “burn” damage to plants.

Avoid using pesticides other than soaps and oils to control whiteflies. Not only do most of them kill natural enemies, whiteflies quickly build up resistance to them, and most are not very effective in garden situations.

The soil-applied systemic insecticide imidacloprid can control whitefly nymphs. Imidacloprid can have negative impacts on natural enemies, honey bees, and other pollinators in the garden, especially when applied as a foliar spray or as a soil application to plants that are flowering or soon to be flowering. It can also cause outbreaks of spider mites. Reserve its use for special situations where these problems can be avoided.

Hand removal of leaves or plants heavily infested with the nonmobile nymphal and pupal stages may reduce populations to levels that natural enemies can contain. Remove and destroy whitefly-infested vegetable plants after harvest. Always inspect new plants for whiteflies and nymphs before introducing them in the greenhouse or garden. Water sprays (syringing) may also be useful in dislodging adults. Watering can also reduce the hot, dry dusty conditions that favor whiteflies and inhibit their natural enemies.