Sooty mold

Capnodium spp. 

1. Identification

Sooty mould is a superficial disease caused by fungi of the genus Capnodium spp., which develop on the honeydew excreted by sucking insects. It is known internationally as “sooty mold”, or “fumagina” in Portuguese. Although it does not penetrate the tissues, it reduces photosynthesis and the vigour of the plants.

2. Causal agent

Ascomycete fungi of the genus Capnodium, described by Montagne, characterised by the formation of a black, sooty mycelium that develops on plant surfaces covered with honeydew. They are not direct parasites: they depend on the presence of insects that produce sugary exudates.

3. Main hosts

Sooty mould occurs in numerous plant species, especially:

• Citrus
• Olive tree
• Grapevine
• Various fruit trees
• Ornamentals
• Vegetable crops susceptible to the presence of honeydew

The disease is indirect, depending on the presence of honeydew-producing pests.

4. Symptoms

• Black, sooty coating, easily detachable
• Reduction of photosynthesis and vigour
• General weakening of the plant
• Soiled fruits and loss of commercial value
• In severe cases, stunted growth and lower production

5. Disease cycle

The fungus settles on the honeydew produced by:

• Aphids
• Scale insects
• Whitefly
• Psyllids

The honeydew serves as a nutritive substrate. The fungus does not invade the plant tissues: it develops superficially, forming a black film that expands as long as honeydew is available.

6. Favourable conditions

• High presence of honeydew-producing insects
• Moderate to high humidity
• Dense canopies and poor ventilation
• Weakened or poorly managed plants
• Urban environments or orchards with high pest pressure

7. Disease management

• Control of honeydew-producing pests (essential measure)
• Improvement of ventilation through appropriate pruning
• Washing of the plants in mild cases (when permitted)
• Integrated management with regular monitoring of pests
• Maintenance of plant vigour to reduce susceptibility
• Avoid excess nitrogen, which favours sucking pests

Sooty mould disappears naturally when the source of honeydew is eliminated.

Bibliographic references

• Agrios, G. N. (2005). Plant Pathology. Elsevier.
• EPPO. Guidelines for Integrated Pest and Disease Management.
• FAO. Integrated Management of Insect Pests Producing Honeydew.
• European Commission. IPM Principles for Fruit and Ornamental Crops.