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PestLeavesStemsFlowers

Aphids

Sap-feeding insects that cluster on soft growing tips and leaf undersides, distorting new growth and leaving sticky honeydew that blackens with sooty mould. Most garden infestations are transient and end when predators catch up.

Caused by: Many species, including Aphis fabae on broad beans and Myzus persicae · also called greenfly, blackfly

Described view

Two tomato shoots in one frame: one with thick, firm, evenly green leaves rolled upward into tubes along their length and otherwise undamaged, and one with thin, puckered, unevenly expanded young leaves carrying a visible colony of green aphids on the growing tip and the leaf undersides

What brings it on

Warm spring weather and soft, sappy growth. Heavy nitrogen feeding produces exactly the growth aphids do best on.

source

Sourced guidancehigh confidence

  • Royal Horticultural Society: Aphids
  • UC Statewide Integrated Pest Management Program — University of California Agriculture and Natural Resources: Aphids — biology and management

Checked 2026-08-13

Usually seen: April, May, June, July, August

Preventing it

Ordered by how much difference each measure actually makes, not by how often it is repeated.

  • Pinch out the growing tips of broad beans once the lowest pods have set. The tips are where blackfly concentrate, and removing them takes the colony with them.
    source

    Sourced guidancehigh confidence

    • Royal Horticultural Society: Blackfly on broad beans

    Checked 2026-08-13

  • Grow flowers that support hoverflies, lacewings and parasitic wasps near vegetable beds. Their larvae are the reason most aphid outbreaks collapse by midsummer.
    source

    Horticultural consensusmoderate confidence

    • Garden Organic — Garden Organic (Henry Doubleday Research Association): Encouraging natural enemies

    Checked 2026-08-13

Dealing with it once it is there

  • Rub or wash colonies off by hand. On a garden scale this handles most infestations, and it does not touch the predators.
    source

    Sourced guidancehigh confidence

    • Royal Horticultural Society: Aphids — control

    Checked 2026-08-13

  • Tolerate more than feels comfortable. An aphid colony is what predator populations build on, and clearing every one in May leaves nothing to eat the ones that arrive in June.
    source

    GrowingHQ editorial positionmoderate confidence

    An editorial position on threshold rather than a claim about the insects. Stated as a judgement because a grower with a small crop may reasonably weigh it differently.

    • GrowingHQ editorial synthesis — GrowingHQ

    Checked 2026-08-13

What it affects

Signs that lead here

Each of these lists the other things that produce the same sign, and how to tell them apart.

On sprays and treatments

GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.

Plant-specific guides

Where this is one of several causes that look alike on a particular plant, GrowingHQ publishes the differential rather than the general answer.