How to Cure Gardenia Mold

Prevent mold so gardenia leaves remain green and glossy.

The glossy green leaves and waxy white flowers of a gardenia bush provide a fragrant, attractive landscape plant until a mold problem develops. Sooty mold dulls the glossy leaves and gives the plant a blackened, dead appearance. Controlling the cause of the mold while removing any existing fungus improves both the appearance and vigor of the gardenia.

Causes

Sooty mold feeds upon the sticky, sap-like substance extruded by some insects as they feed. This substance, called honeydew, indicates an aphid, whitefly, mealybug, or other sap-feeding insect infestation. The mold forms a dark, sooty-looking coating on both the top and bottom leaf surfaces. Mold can also spread to the gardenia stems and flowers, although it primarily affects only the leaves. Aphids and whiteflies are the primary causes of sooty mold on most gardenia plants.

Concerns

The mold ruins the appearance of the gardenia, but light infections rarely affect the plant's health. Severe mold problems that cover the majority of the leaf surfaces can cause the plant to grow poorly because the mold blocks the leaves from absorbing sunlight. The mold also clogs the leaf pores so they cannot breathe properly. Sooty mold can spread quickly through a gardenia bush if the infection isn't managed properly, causing a mild cosmetic issue to blossom into one that endangers the vigor of the plant.

Insect Control

Eradicating the insects usually eliminates sooty mold issues. Inspect the plants closely to determine which insect pest is responsible for the honeydew and mold. Aphids tend to congregate on the bottom leaf surfaces. These small, soft-bodied pests come in colors including pink, green, white and black. Whiteflies are seen flying around the bush and settling on the leaf surfaces. Treat these pests with an insecticidal soap or an insecticide formulated to control the specific insect. Keep the area around the bushes clear of weeds and debris to reduce the chance of a further infestation.

Plant Maintenance

Wiping the leaf surfaces with a damp cloth removes sooty mold from the leaf surfaces. The leaf usually looks healthy beneath the mold, although a leaf that has been covered for some time may exhibit some yellowing. Pruning out the areas of the gardenia with the worst mold can quickly improve the bush's appearance and prevent the mold from spreading to unaffected parts of the plant. Rinse the plant periodically with a sharp spray of water to dislodge insect pests and rinse away the honeydew before it has a chance to attract mold spores.

References

• University of Rhode Island: Gardenia Care
• Clemson Cooperative Extension: Gardenia Diseases and Other Problems