Identification

• Orchids are susceptible to sooty mold development. This disease is caused by fungi and is characterized by a smutty fungal growth on the outside of plants or other objects nearby. Sooty mold fungi adheres to surfaces with the aid of mucilaginous cell walls, where they grow and multiply. Some types of sooty mold causing fungi include Scorias, Capnodium and Antennariella.
  
  

Causes

• Orchids are vulnerable to infestation of scale insects, which causes sooty mold to develop. Several species of scale insects commonly attack orchids. These pests are small and have a waxy covering on their backs. Scale insects feed on orchids by piercing the orchid leaves with their sharp mouthparts, extracting plant juices and sap. After ingesting large amounts of sap, scale insects produce a substance known as honeydew, which is sticky and sweet. Honeydew causes sooty mold to develop on the orchid. Sometimes, honeydew drips onto the pot or the floor and sooty mold fungi begins to grow on these surfaces as well.
  
  

Cultural Controls

• If your orchid or orchid pot has sooty mold, you must eliminate insect infestations to get rid of the mold. Scale insects are often removed from orchids by spraying the plant with a hard stream of water. Repeat this action twice each week for best results. Scale insects are often removed by dipping a cotton ball in alcohol and rubbing it on the leaves, dislodging the insect. Washing your orchid with a soapy water solution can also eliminate scale insects, reducing sooty mold. Combine one quart of water with 1 tbsp. liquid dish soap and wash your plant and orchid pot with it. Repeat this once a week or as often as needed for insect control.
  
  

Chemical Control

• Horticultural oils are available at your local gardening supply center and are often effective in eliminating scale insect infestations and sooty mold. These oils work by coating the plant and disrupting the scale insects ability to breath. Horticultural oils also help loosen sooty mold fungi, making it easier to remove. Insecticidal sprays are also available to eliminate scale insects. Be sure to apply these products thoroughly, as they must come into contact with insects to kill them.