When leaves are covered with a blackish substance, similar to black soot that would have collected overnight, it is a sign of sooty mold.
This fungal disease is well-known to gardeners, and in itself isn’t particularly dangerous. However, it usually appears in tow of parasite infestations that are much more serious, like aphids or scale insects.
The Latin name of the fungus that develop are Capnodium oleaginum, or Fumago salicina. Spores from these strands develop on sweet honeydew produced by the parasites described above.
Sooty mold symptoms, black powder on leaves
These parasites produce honeydew, which is a sweet and sticky substance. Air-born sooty mold fungus attaches to this honeydew and develops quickly into a black layer that covers leaves.
Although this doesn’t kill the plant, sooty mold does nonetheless reduce photosynthesis when it covers all leaves with a thick black layer. That is when it suffocates leaves that wither and die.
When sooty mold only spots a few leaves, damage is very limited.
Preventive treatment against sooty mold
There are a few things to do that can reduce the likeliness that this disease would appear.
- Ensure your plant has sufficient nutrients and is well watered. A plant weakened by poor soil or lack of water is a vulnerable plant.
- Increase the diversity of plants and flowers in your garden, it is the best way to protect them naturally from their predators.
Effective treatments against sooty mold
The only effective treatment against sooty mold is to first treat the insects that are the cause of it.
Here is our advice to avoid or fight them off:
Once the plant is treated and these invasive pests have been removed, clean the leaves so that they may again perform their life-giving function.
Cleaning is easy with a damp cloth or rag dipped in lightly soapy water, which you can then rinse with clear water.
Using organic treatments to treat sooty mold protects the ecosystem that surrounds the plant, most especially bees that come pollinate the flowers.
Plants impacted by sooty mold
Sooty mold appears on a great number of plants, such as fruit trees (apple tree, pear tree, olive tree, etc…), heath plants (rhododendron, camellia, hydrangea, etc…), plants in the vegetable patch (tomato, etc…), decorative shrubs (oleander, rose tree) and citrus (orange tree, lemon tree, grapefruit tree, bergamot, etc…)
Smart tip about sooty mold
As you deal with the insects themselves, remember to wipe the sooty mold off the leaves, too. Indeed, even if the pests are gone, that dark layer will still block light out, which isn’t good!
Sooty mold on a citrus tree, Prem Kumar by U.S. Department of Agriculture under Public Domain
Black dust on croton by Scot Nelson under Public Domain
Aphid with honeydew by Scot Nelson under Public Domain
Mock orange with black dust on leaves by Scot Nelson under Public Domain