Black Sooty Mold, Sooty Mold are common names used to describe several species of fungi that only grow on the honeydew secreted by soft-bodied plant pests. The most common producers of honeydew are aphids, leafhoppers, mealybugs, psyllids, soft scales, and whitefly.
These soft-bodied pests suck the sap out of plant leaves and whatever sugars their bodies cannot use are excreted as honeydew. This creates the perfect growing environment for the dark, threadlike growth of the mycelium that is known as black sooty mold. This fungi doesn't kill the plant but it reduces sunlight penetration and can reduce the ability of the plant to photosynthesize. This can stunt plant growth.
The sooty mold is easily washed off plants, fruits and vegetables with a mild solution of soap and water. Food crops remain edible.
A strong consideration for removing the sooty mold is that it attracts ants. The ants protect the pest insects that produce the honeydew – keeping the predator and parasitoid beneficial insects at bay. Another issue with ants, especially in citrus trees, is that they can ruin the fruit. Either themselves or taking advantage of bird-pecked holes. Either way, these spoiled fruits become an invitation for bigger issues to develop.