Whiteflies Management Guidelines--UC IPM
Traps
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.
Traps are most useful for monitoring and detecting whiteflies rather than controlling them. Commercial traps or sticky cards are available in stores and online. Additionally, you can make traps out of 1/4-inch plywood or masonite board, painted bright yellow, and mounted on pointed wooden stakes. Drive stakes into the soil close to the plants that are to be protected. Although commercially available sticky materials such as Tanglefoot are commonly used as coatings for the traps, you might want to try to make your own adhesive from one-part petroleum jelly or mineral oil and one-part household detergent. This material can be easily cleaned off boards with soap and water, whereas a commercial solvent must be used to remove the other adhesives. Periodic cleaning is essential to remove insects and debris from the boards and maintain the sticky surface.
Insecticide Sprays
Whiteflies can be difficult to control with insecticides. 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 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. Early evening, when there is enough light to safely apply products but when the sun is not shining directly on plants, may be a good time to spray.
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. Avoid using other 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.
