Plant Problem Diagnostic
Whiteflies: How to Identify and Manage Them
The short answer
Whiteflies are tiny (about 1/16 inch) sap-sucking insects with white wings that rise in a cloud when you brush an infested plant. Their feeding stipples and yellows leaves, and the sticky honeydew they excrete grows black sooty mold. Start with the least-toxic steps: hose nymphs off leaf undersides with a strong water spray, hang yellow sticky traps to catch adults, and protect the natural predators and parasitoids that usually suppress populations as the season goes on.
If numbers keep climbing on a valued plant, insecticidal soap or horticultural oil applied to the leaf undersides (where the nymphs feed) is the next step. Coverage matters more than the product. If you are unsure the pest is whitefly, or damage is severe and spreading, send a photo or sample to your local Extension office before escalating.
How to identify whiteflies
Adults are roughly 1/16 inch long, yellowish with white wings, and gather on the undersides of leaves. Common hosts include tomato, bean, cucumber, squash, eggplant, potato, and cabbage-family crops.
- A white cloud flies up when you disturb the plant
- Leaves are stippled, yellowing, or dropping early
- Sticky honeydew and black sooty mold coat leaves and fruit below
Least-toxic management, in order
- 1Inspect and remove — Check transplants before buying, and pick off or prune the most heavily infested lower leaves.
- 2Water spray — Direct a strong stream of water at leaf undersides to knock off nymphs and adults.
- 3Yellow sticky traps — Place traps near plants to catch flying adults and monitor numbers.
- 4Protect natural enemies — Whiteflies have many predators and parasitoids; avoid broad-spectrum sprays that kill them.
- 5Soap or oil — For persistent nymph infestations, insecticidal soap or horticultural oil applied to leaf undersides with thorough coverage is the least-toxic product option.
When to escalate
Escalate if numbers keep rising despite sprays, if honeydew and sooty mold are spreading to fruit, or if you cannot confirm the identification. Your regional Extension diagnostic lab can confirm the pest and advise before you reach for stronger products.
⚠ Whiteflies can transmit plant viruses. If plants show mottling or distortion alongside whiteflies, contact your local Extension office rather than treating blindly.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Maryland Extension — Whiteflies on Vegetables — Whitefly size, hosts, honeydew/sooty mold damage, and management with sticky traps, oils, soap, and natural enemies
- UC IPM — Whiteflies (Home and Landscape) — Identification of adults and nymphs and least-toxic management guidance