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Symptom

Sticky leaves or black film

Honeydew is the sugary waste of aphids, whitefly, scale and mealybugs. It makes leaves shiny and sticky, attracts ants, and grows black sooty mould. Look above the sticky leaves for the source.

Look directly above the sticky patch, on stems and leaf undersides. The insect is always higher up.

Likely causes

Ordered from the usual answer to the less likely one. Each links to the full problem.

  1. A colony of green aphids on the underside of a leaf Pest Common

    Aphids

    Colonies on shoot tips and under leaves.
  2. Brown scale insects along a leaf midrib Pest Common

    Scale insects

    Immobile bumps on stems and veins.
  3. Tiny white whitefly under a tomato leaf Pest Common

    Whitefly

    Clouds of tiny white flies when disturbed.
  4. Citrus leaves coated with black sooty mould Fungal disease Common

    Sooty mould

    Black film on the honeydew.
  5. White cottony mealybugs at the base of aloe leaves Pest Possible

    Mealybugs

    White, cottony insects in joints.