Aphids
TreatablePest · spreads to other plants · also called greenfly, blackfly, plant lice
Aphids are the most common garden pest anywhere, and they concentrate on the softest new growth because that is what their mouthparts can penetrate. The sticky honeydew they excrete is often noticed before the insects are, and black sooty mould growing on that honeydew is often noticed before either.
What it looks like
Clusters of small soft-bodied insects, usually green but also black, grey, pink or white, packed along new shoots and the undersides of young leaves. Leaves curl and pucker, and everything below becomes sticky with honeydew.
How to confirm it
- Dense clusters on new shoots and flower buds rather than scattered individuals.
- New leaves curl, pucker and distort while older leaves stay flat.
- Sticky shine on leaves, and on anything parked under the plant.
- Ants patrolling the stems — they farm aphids for the honeydew and will defend them.
What to do
- 1Blast them off with a jet of water. Repeated every few days this alone controls most infestations.
- 2Squash small colonies by hand. On a rose bud this takes seconds.
- 3Insecticidal soap or neem if numbers are overwhelming, applied to the undersides where they actually sit.
- 4Leave them if ladybird larvae are present — those alligator-shaped grey-and-orange larvae eat hundreds each and will clear the plant for you.
What it gets confused with
One observation settles each of these.
Whiteflies fly up in a cloud when the plant is disturbed. Aphids stay put.
Drift distorts new growth with no insects present and no stickiness.
Preventing it next time
- Avoid heavy nitrogen feeding, which produces the soft growth aphids prefer.
- Grow flowering plants nearby to support ladybirds, lacewings and hoverflies.
- Check new growth weekly in spring; small colonies are trivial to remove.
Plants affected
Most garden and container plants can be affected.
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.