Sooty mold is the black stuff that is sometimes found on the tops of leaves on many plants.

Sooty mold is the result of insects feeding on leaves. Insects, such as white flies, aphids, scale and mealybugs, secrete a sugary substance called honeydew. Sooty mold grows wherever there is honeydew.

Honeydew contains sugars, amino acids, proteins, minerals and vitamins, which make a nice media for the sooty mold fungi. Sooty mold does not feed off of the tree or shrub. It can become a problem if it gets too thick and prevents light from entering the leaf. Certain plants seem to have more sooty mold than others.

Citrus trees commonly have problems with sooty mold because of aphids and scale insects. Sago palms sometimes have problems with mealy bugs and scales which cause sooty mold.

Crape myrtles commonly have sooty mold on their leaves because aphids are attracted to them. Much literature states that crape myrtles are relatively pest free, but aphids are a very common problem. They love the succulent new growth that occurs with fast growth.

By the end of summer many crape myrtles look bad if aphid populations are high. The only good thing about having sooty mold on crape myrtles is that the tree will lose its leaves soon and you can start over next year. However, the tree trunk will still be stained for a while.

Gardenias are another plant known for being covered with sooty mold. Aphids and white flies love to suck the juices from gardenia leaves. Since gardenias are evergreen, the layers of sooty mold can build up and be quite thick on these shrubs.

Sooty mold is more of a problem on evergreens because the leaves do not shed every year. Leaves will be replaced every couple of years, but new leaves will soon be covered with sooty mold if insects are not controlled.

Sooty mold can grow anywhere honeydew falls. If there are lawn chairs underneath trees with aphids, the mold can grow on the honeydew that has fallen on the lawn chair. Sooty mold can stain nearby plants that do not have problems with insect pests.

I have seen crape myrtles planted along downtown streets that were covered with aphids. The trees were not pruned away from the buildings and aphids became a problem on the trees. This led to a sooty mold problem which stained the awnings and brick.

Instead of controlling the insects, these crape myrtles were severely pruned, which stimulated more new growth and more aphids. A month later, the sooty mold was worse and ambrosia beetles attacked the trees because they were so severely pruned and stressed. Eventually all the crape myrtles were removed.

Sooty mold can be difficult to remove. Repeated applications of warm soapy water will help remove the mold. Sometimes when it is very dry, the mold will become dry and flakey and fall off.

The best way to prevent sooty mold is to control the insects. Populations of insects can build during the growing season so it is best to control them early while their populations are not out of control. Oils, soaps and insecticides can help control many of the leaf-sucking insects.

Jake Price is the University of Georgia extension agent/coordinator, Lowndes County. More information: Call (229) 333-5185, or email jprice@uga.edu.