Whiteflies: Tiny Sap-Suckers That Spread Viruses

GardenDraft Team · June 24, 2026 · 5 min read

Part of: Plant Problems & Pest Guides

You brush a tomato plant and a little cloud of white specks lifts off and resettles. Those are whiteflies: tiny, moth-like sap-suckers that cluster on the undersides of leaves, weaken plants, coat them in sticky residue, and, worst of all, spread plant viruses. They're more of a problem in warm climates, greenhouses, and on houseplants, where they breed year-round, but they turn up in summer gardens everywhere.

What the damage looks like

Whiteflies feed by sucking sap from the leaf undersides, which yellows and weakens the plant. Like aphids, they excrete sticky honeydew that coats the leaves and then grows a black sooty mold, dulling the foliage and blocking light. On a heavily infested plant you'll see clusters of the white adults and their flat, scale-like nymphs on the leaf undersides. They favor tomatoes, peppers, cabbage, and many others. The honeydew and weakening are bad enough, but the real danger is that whiteflies transmit viral diseases between plants as they feed — reason enough to keep their numbers down.

Whitefly control: knock numbers down without nuking beneficials

Whiteflies are managed, not eliminated, and a few tactics do most of the work:

• Yellow sticky traps. Whiteflies are strongly drawn to yellow, so sticky traps set among the plants catch the flying adults and help you monitor numbers.
• Spray the undersides. A strong jet of water dislodges them, and insecticidal soap or horticultural oil, applied thoroughly to the leaf undersides where they live and repeated every few days, smothers adults and nymphs. Coverage is everything: miss the undersides and you miss the pest.
• Remove the worst leaves. Pick off and bag heavily infested lower leaves to remove a chunk of the population at once.
• Protect transplants with row cover early in the season, and inspect new plants (especially nursery and houseplants) before bringing them in, since that's how infestations usually arrive.

As with spider mites, avoid routine broad-spectrum insecticides — whiteflies develop resistance quickly and the sprays wipe out the tiny parasitic wasps and other beneficials that are your best long-term ally against them.

Keep an eye out, especially indoors and in heat

Whiteflies build up fast in warm, sheltered conditions, so check leaf undersides regularly on susceptible plants, and be especially watchful with greenhouse and indoor plants where they breed nonstop. Catching a small infestation early — a few traps, a soap spray, a couple of pruned leaves — is far easier than fighting an established cloud of them. Whiteflies are one of the spokes in the common garden pests guide.