Mold and mildew have many similar characteristics, but they are different types of fungi, and are often different in color and texture. Usually mentioned together, mold and mildew grow in many of the same moist and warm locations. Mold and mildew can sometimes be difficult to tell apart, as both spread out from spores. Mold is often black, green, red or blue in color while mildew is usually gray or white.
Gray mold, or Botrytis blight, is caused by the Botrytis species of fungus. Plants growing in damp, cool conditions are very susceptible to gray mold. Plants that are already in distress are even more susceptible. Once gray mold is in an area, it can spread quickly to healthy plants and rot the plant tissue.
Early signs of gray mold are circular spots on the plant that can be brown or gray. As the mold progresses, the spots turn fuzzy. Aging flower blossoms and leaves of the plant will exhibit a fuzzy gray coating. When the affected flower or leaf is removed, the spores can often be seen as a grayish white cloud.
Remove the leaves and flowers affected by the gray mold and dispose of in a plastic bag. When watering the plant, avoid getting the leaves or flower head wet. Make sure there is enough room in the pot for air circulation.
Powdery mildew is another pest of houseplants, especially grape ivy and African violets. Poor air circulation and humidity encourage the growth of powdery mildew. It shows up as a white or gray dusty growth on the surface of the leaves. Powdery mildew can also affect the stems and buds of houseplants. If caught early, it can be rubbed off the leaves, as long as the pathogens don't spread. Otherwise, remove the affected leaf and discard it in a plastic bag.
Don't mist the plant if powdery mildew is present---and try to reduce the humidity in the area of the plants. Move the plant to an area with more ventilation.
Sooty mold can be identified by the black buildup on the flower-plant tissue. It isn't caused by the condition or location of the flower pot, but is caused by an infestation of aphids or scale. Both scale and aphids secrete sugary waste called honeydew, which encourages growth of the black sooty mold. When the mold spores germinate, mycelia threads (black fungal strands) cover entire areas of the plant. The sooty mold can be washed off the plant, but unless the insect pests are controlled, the mold will come back.