How to treat black sooty mould in plants and gardenias

Written by samantha volz
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How to treat black sooty mould in plants and gardenias
Gardenias are susceptible to black sooty mould, a fungus spread by insects. (Getty Thinkstock)

Gardeners use plants to provide bright, colourful life to the landscape, but this appearance can be ruined by a black scourge that infects plants and shrubs. Sooty mould is a fungus that grows in thin filaments. These filaments spread across leaves, fruits, branches and twigs, creating a charcoal appearance on the normally green plants. The moulds grow as a result of insect infestation; the moulds feed off the secretions of the insects. You must get rid of both the mould and the insects to completely restore the health of your plants.

Skill level:

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Things you need

  • Dish detergent
  • Water
  • Spray bottle
  • Soft-bristle brush or toothbrush
  • Pesticides

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  1. 1

    Mix 15 ml (1 tbsp) of liquid dish detergent in 4 litres (1 gallon) of water. Add the mixture to a spray bottle.

  2. 2

    Soak mould-infested leaves, fruit, twigs and other infected areas with the cleaning spray from the bottle. Allow the soap to dissolve the soot for 15 minutes.

  3. 3

    Rinse the sprayed areas with a squirt of fresh water from a hose, or from a spray bottle filled with clean water. Gently brush the loosened mould away with a soft-bristle brush or toothbrush.

  4. 4

    Treat infected plants with insecticides designed to kill aphids, whiteflies and other such insects. Treat all mould-infested plants, as well as any other plants that have shown even a hint of sooty mould or insect infestation, per the product instructions.

Tips and warnings

  • Contact your local garden centre, nursery or extension service if you have questions regarding types of pesticides that are safe for your plants.
  • Replace pesticides with horticultural oils if necessary. These oils can also soften sooty mould, but they can be dangerous if applied to young plants.
  • Follow all instructions and warnings on pesticide products when applying them to plants. These chemicals can be extremely dangerous to plants, animals and humans if used incorrectly.

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