How to identify and manage red spider mite

UK seasonality and monitoring

Red spider mite is most troublesome in warm, dry greenhouse or polytunnel weather.

During this period inspect Cucumbers, tomatoes, chillies and protected crops, 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 Cucumbers, tomatoes, chillies and protected crops. 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: Stippled leaves, bronzing and weakened plants in hot dry conditions. Match the symptom to a live pest, larva, egg or characteristic feeding sign before deciding that treatment is needed.

Damage and likely consequences

Stippled leaves, bronzing and weakened plants in hot dry conditions. 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 Cucumbers, tomatoes, chillies and protected crops, 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

Keep greenhouse crops evenly watered and check the undersides of leaves with a hand lens during hot, dry weather.

Control and integrated management

Rinse leaf undersides and consider an approved biological control only if mites are confirmed and protected-crop conditions suit it.

Natural predators and wildlife-conscious choices

Avoid broad insecticides that also kill predatory mites.

For red spider mite on Cucumbers, tomatoes, chillies and protected crops, 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

Remove badly affected foliage and avoid broad insecticides that also kill predatory mites.

For red spider mite on Cucumbers, tomatoes, chillies and protected crops, 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. These tiny mites are easiest to spot with a hand lens on leaf undersides. Fine webbing, pale stippling and later bronzing are typical in warm, dry protected spaces; webbing alone can be confused with ordinary spiders. Look for a matching live pest or fresh feeding sign before intervening.

Pale or stippled leaves can have several causes; confirm mites or eggs before treating.

If damage continues

Recheck Cucumbers, tomatoes, chillies and protected crops 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, remove badly affected leaves and use biological control where suitable.) 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