Aphids: identify, prevent, control

Worst in spring and early summer flushes of new growth, September to December, with a second autumn peak.

Aphids are small sap-sucking insects that cluster on soft new growth and the undersides of leaves. They breed fast in warm weather and spread plant viruses, so we treat them early before colonies explode across a bed.

How to identify it

• Tiny green, black, grey or pink insects clustered on new shoots and leaf undersides
• Curled, distorted or yellowing young leaves
• Sticky honeydew on leaves below, often followed by black sooty mould
• Ants running up and down stems, farming the aphids for honeydew
• Winged adults appear once a colony gets crowded

How to prevent it

• Avoid heavy nitrogen feeding, which pushes soft sappy growth aphids love
• Encourage ladybirds, lacewings and hoverflies by planting alyssum, dill and yarrow nearby
• Inspect new seedlings before planting so you do not bring infestations in
• Keep plants well watered, as drought-stressed plants attract more aphids

Organic control, step by step

• Squash small colonies by hand or blast them off with a sharp jet of water
• Spray eco-oil or a soap spray (20ml pure soap per litre of water) directly onto colonies, covering leaf undersides
• Use eco-neem at label rate for heavier infestations, repeating every 7 days
• Pyrethrum knocks down severe outbreaks fast, but spray at dusk to spare bees
• Release or attract ladybirds and lacewings, which each eat dozens of aphids a day
• Control ants with a barrier band, since ants protect aphids from predators

Plants it attacks