Whitefly
Whitefly adults and their scale-like young feed under leaves, weakening plants and coating them in honeydew that turns black with sooty mould. Glasshouse whitefly plagues tomatoes and peppers under cover; cabbage whitefly lives on brassicas outdoors all year.
Pests
What it looks like
Shake a plant: whitefly lift off like dust.
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Flying cloud Adults 1 to 2 mm long fly up when disturbed and settle again. -
Scales under leaves Flat, pale oval young stuck to the underside of leaves. -
Sticky leaves Honeydew coats leaves and fruit below. -
Black film Sooty mould grows on the honeydew.
How to confirm it
Check leaf undersides with a hand lens.
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Tap the plant
A white cloud confirms whitefly.
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Turn leaves
Eggs and pale scales sit under the upper leaves.
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Yellow sticky trap
Adults collect on hanging yellow traps.
What to do
Break the breeding cycle.
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Hang yellow sticky traps
They catch adults and show how numbers are changing.
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Use Encarsia
Release the parasitic wasp Encarsia formosa in the greenhouse once temperatures stay above about 18 °C (64 °F).
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Hose or wipe leaves
Wash young off leaf undersides; remove the worst leaves.
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Net brassicas
Fine mesh keeps cabbage whitefly off outdoor crops.
Prevent it next time
- Check bought plants carefully; whitefly arrive on them.
- Clean out the greenhouse in winter.
- Remove old brassica stumps that carry cabbage whitefly over winter.
What not to do
Do not rely on sprays alone; whitefly quickly become resistant and sprays kill Encarsia.
In the growing guides
Where the guides mention it, with plant-specific advice.
Sources
- Glasshouse whitefly, Royal Horticultural Society
- Cabbage whitefly, Royal Horticultural Society
- Whiteflies on vegetables, University of Maryland Extension