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Blackfly
Aphis fabae
PestMedium impact
The black bean aphid is one of the most common and visible bean pests. Dense black colonies establish on growing tips and shoot undersides from late spring, weakening new growth and transmitting viruses. Particularly troublesome on broad beans.
Key facts
- Type
- Pest
- Affects
- Bean
- Active season
- May - Aug
- Peak season
- Jun - Jul
- Vulnerable stages
- Growing · Harvesting
- Spread rate
- fast
- If confirmed
- Act soon
Signs & symptoms
- -dense clusters of tiny black insects on growing tips and young shoot undersides
- -distorted, curled leaves at the plant apex
- -sticky honeydew and sooty mould on leaves below the colony
- -ants farming the colony on stems
Management
Do now
- -Pinch out the top 5-10cm of heavily infested shoot tips and bin - this removes the bulk of the colony at once
- -Squash remaining colonies by hand on accessible stems
- -Spray with a strong jet of water to dislodge insects
- -Encourage predators - avoid broad-spectrum insecticides
Prevention
- -Pinch out the growing tips of broad beans after 4 sets of flower clusters, before blackfly arrive
- -Avoid excessive nitrogen feeding, which promotes the soft lush growth that pests favour
Further reading
- -Blackfly overwinter as eggs on spindle tree (Euonymus europaeus) and migrate to beans as winged adults in May and June
- -Pinching out growing tips is highly effective for broad beans and is best done before colonies establish