Whitefly
Small white moth-like insects on the undersides of leaves that rise in a cloud when the plant is disturbed — a sign so distinctive that it settles the identification on its own. The scale-like immature stages stay fixed to the leaf and are what actually does the feeding.
Caused by: Trialeurodes vaporariorum · also called glasshouse whitefly
Described view
The underside of a tomato leaf held up to the light showing both culprits at once: a dense cluster of soft-bodied green aphids along the midrib, and separately the tiny flat white-winged adults and pale scale-like nymphs of whitefly, with the sticky honeydew shine visible on the leaf surface below them
What brings it on
Warm protected growing: greenhouses, conservatories and indoor plantings, where breeding continues year-round rather than being interrupted by winter.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Glasshouse whitefly
Checked 2026-08-13
Usually seen: May, June, July, August, September, October
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Inspect the undersides of leaves on incoming plants. A greenhouse cleared and cleaned over winter starts the season with a far smaller population.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Glasshouse whitefly — prevention
Checked 2026-08-13
Dealing with it once it is there
- Yellow sticky traps catch the flying adults and, more usefully, tell you whether numbers are rising or falling. They do not control an established infestation on their own.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Glasshouse whitefly — control
Checked 2026-08-13
- The parasitic wasp Encarsia formosa is the standard biological control under glass and works only in warm conditions with a population already present to parasitise.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Biological control
Checked 2026-08-13
Signs that lead here
Each of these lists the other things that produce the same sign, and how to tell them apart.
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.
Plant-specific guides
Where this is one of several causes that look alike on a particular plant, GrowingHQ publishes the differential rather than the general answer.