How to Control Aphids

Aphids – greenfly, blackfly and their relatives – are among the most common garden pests. They suck sap from plants, spread viruses, and excrete sticky honeydew. Here is how to keep them under control.

Recognising aphid damage

• Clusters of small insects on shoot tips, buds and under leaves.
• Curled, distorted or yellowing leaves.
• Sticky honeydew on leaves, often with black sooty mould growing on it.
• Ants farming the aphids for honeydew.

Physical control

• Squish them: For small infestations, simply squash aphids between your fingers. Check plants regularly and deal with them before numbers build up.
• Blast with water: A strong jet from a hose knocks aphids off plants. They rarely climb back.
• Prune out: Remove heavily infested shoot tips and dispose of them.

Encourage natural predators

Many creatures eat aphids. A healthy garden ecosystem keeps aphid numbers in check naturally.

• Ladybirds: Both adults and larvae are voracious aphid eaters.
• Lacewings: Their larvae consume huge numbers of aphids.
• Hoverflies: The larvae eat aphids; adults need flowers for nectar.
• Blue tits: Feed aphids to their chicks in spring.

Avoid broad-spectrum insecticides which kill predators as well as pests.

Organic sprays

• Soap spray: Diluted washing-up liquid or insecticidal soap. Spray directly onto aphids – it works on contact by blocking their breathing pores.
• Neem oil: Disrupts aphid feeding and reproduction. Needs repeated applications.
• Pyrethrum: Derived from chrysanthemums. Kills on contact but breaks down quickly.

Spray in the evening to avoid harming bees, and cover all surfaces where aphids are present.

Chemical insecticides

For severe infestations, systemic insecticides are absorbed by the plant and kill aphids when they feed. However:

• They also kill beneficial insects.
• Do not use on flowering plants where bees are active.
• Follow product instructions carefully.
• Consider whether the damage justifies the treatment.

Prevention

• Healthy plants: Strong, well-fed plants are more resistant to aphid damage.
• Avoid excess nitrogen: Lush, soft growth is more attractive to aphids.
• Companion planting: Some gardeners plant marigolds, chives or garlic near susceptible plants.
• Check new plants: Inspect plants before bringing them into the garden.

Living with aphids

Some aphids are inevitable in any garden. A few aphids on a healthy plant cause little harm and provide food for beneficial insects. Only take action when numbers are high enough to cause visible damage.