Mold on Orchids

Orchids are susceptible to sooty mold development.

Orchids provide color and add interest to any home or garden. These flowers are often used as an indoor plant or placed outside in the landscape. Orchids are susceptible to insect infestations, which place it at risk of developing sooty mold. This condition is not usually damaging to orchids, but it is often unsightly.

Identification

Sooty mold is the development of a black fungus on the surface of plants, trees and flowers. The black fungal coating is easily removed with your fingers, but soon grows back. Sooty molds do not invade or feed on plant tissue and live only on the surface of the plant. This type of mold is considered to be primarily cosmetic, although very heavy coverings of sooty mold can cause some adverse effects in host plants.

Causes

Orchids infested with thrips, scale insects or mealybugs often develop sooty mold, as a result. These insects feed on plant leaves and stems and produce honeydew, which is an excrement that is rich in sugars. Honeydew falls on the leaves, stems and flowers of the orchid causing sooty mold fungi to stick to it.

Effects

Orchids with sooty mold develop a velvety fungal coating on leaves, stems and flowers. This fungal coating is black in color and resembles chimney soot, which is where the condition received its name. If drought conditions are present, plants with sooty mold tend to wilt more rapidly than plants without the condition. If the affected plant experiences reduced vigor, it may place it at risk for serious diseases or damaging insect infestations. Orchids that develop severe sooty mold, may receive less sunlight as a result. This may cause the orchid to have less intense color and smaller flowers.

Control

Controlling sooty mold requires the elimination or control of honeydew-producing insects. Spraying your orchid with a hard stream of water can knock insects from the plant. This process should be repeated twice each week for continued control. Horticultural oils are also effective in controlling insects such as mealybugs and aphids. These products smother the insects by coating the air holes they use to breath. Spraying your orchid with soapy water may remove sooty mold. Add 1 tsp. of liquid dish soap to 1 gallon of water and spray your plant. Always test your plants for damage before applying soapy water solutions.

References

• MOBOT: Kemper Center Factsheet: Orchids: Problems
• Ohio State University; Sooty Molds on Trees And Shrubs; Stephen Nameth, Jim Chatfield and David Shetlar