Citrus & Black Mold

Citrus trees such as lemons and oranges are susceptible to black mold or sooty mold problems. Black mold is a symptom of an insect infestation. Gardeners control the mold by eradicating the insects.

Features

Insects such as aphids, whiteflies, scales and mealybugs have piercing and sucking mouthparts. They attach their mouths to plant tissue, pierce the surface and suck the sap from citrus leaves and stems. As they feed, they exude copious amounts of a sticky-sweet liquid called honeydew that drips down on the surrounding foliage and fruit.

Effects

Honeydew acts as a growing medium for sooty mold spores. A thick, velvety-black fungus forms on the honeydew, covering leaves, stems and fruit in unsightly mold. The fungus does not invade the plant tissues or harm citrus trees in itself, but heavy deposits of black mold can interfere with photosynthesis, stunt plant growth and reduce plant vigor. Weakened trees are susceptible to attacks from other insects and diseases.

Control

Gardeners use horticultural oils to control whiteflies and scale insects. They treat aphids and mealybugs with insecticidal soaps. The University of Florida Lee County Extension warns that although chemical sprays such as imidacloprid will kill the insects, the poison cannot be used to treat food crops such as citrus. A steady stream of water or a mild mixture of water and dishwashing soap dislodges the buildup of black mold.

References

• Clemson University: Chewing Insects vs. Sucking Insects
• Ohio State University Extension Fact Sheet: Sooty Molds on Trees and Shrubs
• University of Florida Lee County Extension Service: Causes and Control of Sooty Mold