How to identify and manage greenhouse whitefly

UK seasonality and monitoring

Builds through warm greenhouse weather.

During this period inspect Tomatoes, cucumbers, chillies and ornamentals under cover, concentrating on the crop stage and plant parts described above. Note when and where fresh injury appears; old feeding marks can remain after the pest has moved on.

Crops and plants affected

The recorded hosts are Tomatoes, cucumbers, chillies and ornamentals under cover. This list identifies plants worth checking; it does not mean every crop is equally vulnerable. Start with the listed plants and inspect the tissue where this pest feeds.

Check affected crops for these signs: Honeydew, sooty mould and weakened protected crops. Match the symptom to a live pest, larva, egg or characteristic feeding sign before deciding that treatment is needed.

Damage and likely consequences

Honeydew, sooty mould and weakened protected crops. A small amount of old damage on a vigorous plant may be cosmetic. Continued feeding on roots, seedlings, growing points or edible parts can reduce establishment or yield.

On Tomatoes, cucumbers, chillies and ornamentals under cover, judge severity by checking whether injury is fresh and spreading, whether the plant is still growing, and whether the edible part is affected. Avoid removing a crop based on one ambiguous mark.

Prevention

Ventilate the greenhouse, inspect new plants and monitor leaf undersides before colonies build.

Control and integrated management

Wash small colonies from foliage or introduce a suitable biological control early under cover.

Natural predators and wildlife-conscious choices

Encourage parasitoid wasps and avoid unnecessary broad insecticides.

For greenhouse whitefly on Tomatoes, cucumbers, chillies and ornamentals under cover, use a barrier or hand removal only where it fits the crop and life stage. Keep any cover taut, inspect it for trapped wildlife, and remove it when protection is no longer needed.

Long-term management

Use monitoring cards and remove infested crop remains when the growing season ends.

For greenhouse whitefly on Tomatoes, cucumbers, chillies and ornamentals under cover, record the bed, crop stage and date when fresh damage first appears. Those notes help time protection and monitoring before the same crop stage is vulnerable next season.

Common mistakes

A symptom alone is not a diagnosis. Adult greenhouse whiteflies rise in a cloud from leaf undersides when disturbed. Eggs and scale-like nymphs remain on leaves, where honeydew can support sooty mould. Check new plants before putting them in a tunnel. Look for a matching live pest or fresh feeding sign before intervening.

Adults are conspicuous, but eggs and nymphs remain on leaf undersides; inspect both stages.

If damage continues

Recheck Tomatoes, cucumbers, chillies and ornamentals under cover where new injury is appearing, including the hidden feeding site: roots, folded leaves, leaf undersides, flowers or fruit as appropriate. If identification remains uncertain, photograph a live specimen alongside the damage and ask an allotment association or horticultural adviser.

If the recommended control (Wash foliage and use yellow monitoring cards or approved biologicals.) has not helped, confirm that it was fitted or applied at the right crop stage and that fresh damage is still occurring. Old marks do not heal when the pest has gone.

Frequently asked questions