Aphids on Plants UK
Greenfly, blackfly, and woolly aphids weaken plants and spread virus diseases. Here's how to identify and control them.
Pest control advice verified against RHS guidance by the SoilCommander Growing Team.
Identification
Aphids are tiny (1–3mm), soft-bodied insects found in dense colonies on new growth, stem tips, and leaf undersides. They come in many colours: green (greenfly on roses and vegetables), black (blackfly on broad beans and courgettes), grey (woolly aphid on apple trees). All excrete sticky honeydew that causes sooty mould and attracts ants.
Control Methods
- Blast with water: a strong jet knocks aphids off without chemicals; repeat every 2–3 days
- Squash by hand: effective for small infestations on broad bean tips
- Encourage predators: ladybirds, lacewings, and hoverflies all eat aphids — plant marigolds and fennel nearby
- Insecticidal soap: safe for bees when applied in the evening; coat all surfaces of the plant
- Pinch out broad bean tips once first pods form — removes the soft growth blackfly target
- Nasturtiums as trap crop: aphids prefer nasturtiums and can be concentrated there
When Are Aphids Worst?
Peak aphid season in the UK runs May–July. Warm, dry spells cause populations to explode. Blackfly on broad beans peaks in May–June; greenfly on vegetables and roses June–August. Cool, wet weather knocks populations back naturally.
Common Mistakes to Avoid
- Reaching for pesticide at the first sighting. Most pesticides, including organic ones, reduce garden biodiversity — many light infestations clear up naturally once predators become active.
- Treating the aphids but ignoring virus risk. Some aphids transmit plant viruses to tomatoes, strawberries and ornamentals like dahlias and tulips — destroy visibly virus-infected plants rather than just controlling the aphids on them.
- Letting ants run unchecked nearby. Ants farm aphids for their honeydew and will defend colonies from predators such as ladybirds — discouraging ants near infested plants helps natural control work.
Frequently Asked Questions
Do aphids spread plant diseases?
Yes — some aphids transmit viruses, particularly to tomatoes, soft fruit, and ornamentals such as dahlias and tulips. Destroy obviously virus-infected plants rather than trying to treat them.
Should I spray at the first sign of aphids?
Not necessarily. Aphid numbers rise in spring before natural predators are active in large enough numbers, but many light infestations are brought under control naturally within a few weeks — broad-spectrum pesticides kill the predators too.
Why are ants often found alongside aphid colonies?
Ants feed on the honeydew aphids excrete and will actively defend colonies from ladybirds and other predators — controlling ants nearby can help natural predators do their job.
Plan Smarter to Reduce Pest Pressure
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Last updated 4 July 2026
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