Small flying insects on and around your citrus, tomato, crepe myrtle, roses, squash, etc., are most likely whiteflies.

In addition to clouds of the mature flies, you may also see:

• Deposits of white wax (with certain species).
• Tiny nymphs, the immature stage, which are oval, legless and immobile, and can range in color from transparent yellow, to whitish to black with a white fringe.
• Sticky honeydew on backsides of leaves or on fruit.
• A coating of black sooty mold on leaves, stems and/or fruit, a fungus that grows on the excess honeydew excreted by insects.

Whiteflies are not true flies, but are related to aphids, scales and mealybugs. They develop rapidly in warm weather and populations can build up quickly. The colonies usually develop on the underside of leaves. They breed year-round if conditions are warm, moving from one host plant to another. There are at least 10 different varieties of whitefly, with different or similar hosts and slightly different characteristics.

Are they dangerous to my plant?

While low levels of whiteflies are not usually damaging (but can be unsightly!), large populations can cause leaves to turn yellow, look dry or fall off the plant. They can cause significant damage in vegetable crops; for instance, the immature sweet potato whitefly can cause plant distortion, discoloration or silvering of leaves and plant loss.

What should I do about my infestation?

The best strategy is to prevent the development of large numbers of whiteflies in your garden. Below are prevention tips:

•  Whiteflies like dry, dusty conditions, so hosing down known host plants throughout the dry season can help keep populations low.
• Use yellow sticky traps to help monitor and catch them.
• Look for infestations and remove leaves harboring whiteflies.
• Control ant populations, which protect whiteflies from their natural predators, in order to feed on whitefly honeydew.

If you choose an insecticide, use insecticidal soap or neem oil, as directed, which can reduce but not eliminate populations. Systemic insecticides should be avoided in the home garden. They may be more effective but can have negative impacts on beneficial insects and pollinators.

Whiteflies do have natural enemies. General predators include lacewings, big-eyed bugs and minute pirate bugs. There are some varieties of small lady beetles (bugs) that also feed on whiteflies. Remember, using any insecticide can reduce populations of beneficials.

For more information on this or any other garden pest, visit the UC Integrated Pest Management website at http://ipm.ucanr.edu.

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Written by UC Master Gardener Julie Taylor