Black Fungus on Ferns

Cause

• Black fungus, often known as sooty black mold, is a type of fungus known as Capnodium. The black fungus is often noticed during the summer and can appear on ferns and many other plants. Black fungus grows on a special substance known as honeydew, which is excreted by insects such as whiteflies, aphids and soft scales. These insects use their mouth to pierce plant tissues and suck out the juices. The excreted substance is sticky and sugary, coating the stems, leaves and fruit.

Effects

• Black fungus can be unattractive on the fern's fronds but doesn't harm the plant directly. But if the fungus becomes thick enough, it can block sunlight from the leaves and interfere with photosynthesis. This can cause slower growth in the fern and reduce its overall long-term vigor. Black fungus is not a disease and does not infect living tissue.

Management

• Ferns are not the only plants subject to sooty black mold. Shrubs, trees, indoor plants and palms are susceptible to developing it, as well. Sooty black mold is an indication that insect activity is present. Treatment should focus on controlling the offending pests. If the problem is minor, the mold will gradually disappear during dry weather. It may also be washed off small plants. Before resorting to chemical treatments, identify the pest to determine the proper treatment.

Prevention

• If you notice honeydew-producing insects on nearby trees or shrubs, take action to ensure that the insects don't spread to your ferns. One way to prevent black fungus is to control the insects. During the growing season, inspect all nearby plants for aphids, whiteflies and other insects. As soon as you see evidence of an infestation, treat the problem with an appropriate insecticide following package directions for best results. While the fungus can be washed off the fern's fronds, it will reappear if the insect population is not controlled. Another way to prevent black fungus on ferns is to avoid high humidity. A dehumidifier can be used indoors. In regions where humidity is high during the summer, ferns may fare better if brought indoors. Provide adequate air circulation between plants by not overcrowding. Ceiling fans can also help circulate air around the plants.