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Whiteflies

Garden pest · Aleyrodidae

Description​

Whiteflies are a family of tiny, sap-feeding insects that infest vegetables, ornamentals, and greenhouse plants. Despite their name and mothlike appearance, they are not true flies. Adults are usually about 1–2 mm long, with white, powdery wings, and gather on the undersides of leaves. They lay eggs there; the young settle onto the leaf and feed as flattened, nearly motionless nymphs. By removing plant sap, heavy populations can cause yellowing, weakened growth, and leaf drop. Whiteflies also excrete sugary honeydew, which makes leaves sticky and supports black sooty mold. Some species spread plant viruses, particularly in crops such as tomato and cucurbits. Infestations often build quickly in warm weather and protected growing spaces, where successive generations overlap. Light infestations may cause little noticeable damage, but an unchecked population can weaken a plant substantially.

Symptoms​

  • Yellowing leaves
  • Sticky residue on leaves
  • Black sooty coating
  • Curled or cupped leaves
  • Stunted growth
  • Leaves dropping
  • Insects visible on the plant

How to Identify​

Gently shake an affected plant: a small cloud of white, mothlike adults may rise from the foliage, then settle again. Check leaf undersides for adults, tiny eggs, and flat, pale nymphs that remain attached while feeding. Sticky leaves or black sooty mold strengthen the diagnosis, though other sap-feeding insects produce honeydew too. Aphids are larger and pear-shaped; mealybugs look cottony and do not fly up in a cloud. Fungus gnats are dark and usually hover near moist soil, while spider mites cause fine webbing rather than a burst of white insects. A hand lens helps reveal the nymphs.

Prevention​

Inspect new plants carefully, especially beneath leaves, and keep infested purchases away from healthy plants. Check susceptible plants regularly so small populations are caught before they multiply. Remove heavily infested leaves and nearby weeds that can host whiteflies, disposing of them rather than leaving them beside the crop. Avoid excessive nitrogen fertilizer, which encourages tender growth attractive to sap-feeding pests. In greenhouses, use insect screens where ventilation permits and monitor adults with yellow sticky cards; the cards help reveal an infestation but will not control one alone. Encourage natural enemies by growing a variety of flowering plants and avoiding unnecessary broad-spectrum insecticides. Space plants for easy inspection, and clean up infested crop remains at the end of the season.

Treatment​

Start by isolating movable plants and washing leaf undersides with a firm stream of water to dislodge adults and nymphs. Remove badly infested leaves if the plant can tolerate it. In a greenhouse, yellow sticky cards can catch some adults; a handheld vacuum can also remove adults from a small infestation. If numbers remain high, thoroughly coat leaf undersides with insecticidal soap or horticultural oil labeled for the plant. Follow the label, test a small area first, and avoid spraying during hot weather or when plants are water-stressed. Repeat as directed because eggs and emerging adults may escape an initial application. In protected growing spaces, the parasitic wasp Encarsia formosa can help when released early under suitable conditions. Preserve other beneficial insects wherever possible. Consider stronger, plant-labeled pesticides only if these measures fail; follow all label directions, heed pollinator precautions, and avoid repeated use of one insecticide class.

Plants Affected​

Gardenia, Geranium, Hibiscus, Jasmine, Moth Bean, Mung Bean, Okra, Passionflower, Rose of Sharon, Urad Bean

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