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My plants are coated in a black substance PDF Print E-mail

Sooty mould is caused by a group of fungi which breed on leaf surfaces causing them to appear blackened as if covered with soot. They breed where there is a source of food, most commonly where sugar-rich honeydew is being secreted by sap sucking pests. Sooty moulds do not attack plant tissue but their presence impedes photosynthesis, the process by which plants generate food for growth. Severe outbreaks spoil the appearance of plants and fruit. In the long term sooty moulds can weaken plants and this in turn may cause stunting.

Common species of garden ants actively farm sap sucking pests, carrying them to new hosts and defending them from predators. Sap sucking pests excrete honeydew made from excess sugars harvested from sap. This sticky substance falls on and adheres to leaves below.

Control outbreaks by controlling sap sucking pests, such as aphid, scale and mealybug, and ants. Denied their source of food, sooty moulds slowly die and the mould crumbles off foliage. Alternatively sooty moulds can be hosed off or carefully wiped off foliage using a soft damp cloth moistened with soapy water.

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