How to identify and manage black bean aphid

UK seasonality and monitoring

Black bean aphid colonies usually build from late spring into summer.

During this period inspect Runner beans, French beans and broad beans, 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 Runner beans, French beans and broad beans. 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: Curled shoots, sticky honeydew and weak flowering tips. Match the symptom to a live pest, larva, egg or characteristic feeding sign before deciding that treatment is needed.

Damage and likely consequences

Curled shoots, sticky honeydew and weak flowering tips. 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 Runner beans, French beans and broad beans, 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

Inspect broad-bean and other bean shoot tips from late spring; avoid excess nitrogen and provide flowering habitat for predators.

Control and integrated management

Pinch out a heavily colonised tip only when healthy growth remains and predators are not already reducing the colony.

Natural predators and wildlife-conscious choices

Ladybirds, hoverflies and lacewings often control colonies naturally.

For black bean aphid on Runner beans, French beans and broad beans, 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

Encourage ladybirds, hoverflies and lacewings, and check new tips again after warm weather.

For black bean aphid on Runner beans, French beans and broad beans, 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. Dense, shiny black colonies cluster on broad bean, runner bean and French bean tips. Ants may attend the colonies for honeydew. The first small colonies are easier to manage than curled, hardened shoots. Look for a matching live pest or fresh feeding sign before intervening.

Removing every infested tip can remove flowers and beneficial insects as well as aphids.

If damage continues

Recheck Runner beans, French beans and broad beans 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 (Squash small colonies, wash shoots and pinch out badly infested tips where practical.) 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