Guide
Dealing with aphids
Aphids multiply fast but are rarely fatal if caught early. The response should be proportionate - low numbers often resolve without intervention.
Identify before acting
Aphids are small, soft-bodied insects found in clusters on growing tips and the undersides of leaves. They may be green, black, grey, or white depending on species. Check for sticky honeydew residue on leaves below the colony, which often also develops sooty mould. A few aphids on a healthy plant is not an emergency.
Assess the infestation
Light infestation - a small colony on one or two growing tips - will often be controlled by natural predators within a week or two if you leave it. Heavy infestation - covering multiple stems, causing leaf curl, or spreading between plants - warrants direct action. Decide based on what you see, not a fixed threshold.
Physical removal first
For light to moderate infestation, knock aphids off with a strong jet of water from a hose. Repeat every two to three days. Pinch off and bin heavily infested growing tips - this removes the colony and the most congested plant tissue in one step. Do not compost heavily infested material.
Encourage natural predators
Ladybirds, lacewings, parasitic wasps, and hoverflies all feed on aphids. Avoid broad-spectrum pesticides that kill these too. Leaving some flowering plants (e.g. phacelia, calendula, fennel) near the vegetable patch significantly increases predator populations. Patience during a low infestation is often the best strategy.
Soft soap spray
Insecticidal soap spray (diluted soft soap, not detergent) suffocates aphids on contact without persistent residue. Spray directly onto colonies, covering undersides of leaves thoroughly. Repeat every three to four days until the colony collapses. Effective for heavy infestation where physical removal is impractical.
Beans and blackfly
Broad beans are especially susceptible to black bean aphid (blackfly). Pinching out the top 10 cm of the plant once enough flowers have set removes the soft growing tip that blackfly prefer. This is both a prevention and control measure and is standard practice for broad beans.
Relevant to