How to treat black sooty mould in plants and gardenias

Updated February 21, 2017

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.

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

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.

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.

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.


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.

Things You'll Need

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

Samantha Volz has been involved in journalistic and informative writing for over eight years. She holds a bachelor's degree in English literature from Lycoming College, Williamsport, Pennsylvania, with a minor in European history. In college she was editor-in-chief of the student newspaper and completed a professional internship with the "Williamsport Sun-Gazette," serving as a full-time reporter. She resides in Horsham, Pennsylvania.