Whiteflies
TreatablePest · spreads to other plants
Whiteflies are unmistakable because of how they behave — brush the plant and a small snowstorm lifts off it. Like aphids they suck sap and excrete honeydew, so the same stickiness and sooty mould follow. They are far more of a problem in greenhouses and indoors than outside.
What it looks like
Tiny white moth-like insects, about a sixteenth of an inch, that rise in a cloud when the plant is disturbed and settle again immediately. Undersides of leaves carry scale-like immature stages and a scatter of white specks.
How to confirm it
- A cloud of tiny white insects that flies up when you shake the plant.
- Immature stages fixed to leaf undersides, looking like tiny translucent scales.
- Sticky honeydew and eventually black sooty mould.
- Concentrated on the youngest leaves for egg-laying, older leaves for feeding.
What to do
- 1Yellow sticky traps catch adults and tell you how bad the population is.
- 2Vacuum adults off in the early morning when they are sluggish. This sounds absurd and works well.
- 3Insecticidal soap or neem on leaf undersides, repeated weekly — the eggs are not killed by most sprays.
- 4Remove the worst-infested lower leaves entirely.
What it gets confused with
One observation settles each of these.
Fungus gnats are dark, fly around the soil rather than the leaves, and do not cluster on leaf undersides.
Aphids do not fly up when disturbed.
Preventing it next time
- Inspect the undersides of new plants before bringing them home.
- Keep greenhouse vents screened and use sticky traps as an early warning.
Plants affected
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.