Black Spot Plant Disease on a Houseplant

Fungal Leaf Spot

• Several different fungi can cause leaf spotting, but generally the symptoms are the same. Spots range in color from tan to yellow or dark brown to black. Often, lighter colored splotches will have a fine black speckling indicative of fungal fruiting bodies. As spots enlarge they can engulf leaves, causing them to drop from the plant. Trim infected leaves and move the plant away from any others to prevent spread and increase airflow. Avoid getting foliage wet. If necessary, thin dense foliage to increase airflow to the center of the plant. Fungicides are not typically needed if proper cultural care is provided.

Air Pollutants

• Plants "breath" air in through their leaves so they can be highly sensitive to pollutants in the home environment. Aerosols, like hairspray or cooking spray can cause spotting and discoloration of leaves. A houseplant in the kitchen can be burned by grease spatter. Even natural gas from a gas stove can cause leaf spots. Be mindful of where your plants are located and move them out of high traffic areas or areas where they are exposed to any chemicals.

Bacterial Infection

• Much like fungi, bacteria can infect the leaves of houseplants. Initial symptoms are dark brown, mushy spots that may have a yellow halo. Depending on the bacteria the spots may ooze. If allowed to dry out bacterial spots may turn reddish brown. Move infected plants away from other plants. Trim infected leaves and thin dense foliage to improve airflow. Avoid getting foliage wet when you water. Bactericides are generally not necessary and infections will clear up if you follow good cultural practices.

Fluoridated Water

• According to the Washington State University extension service, using fluoridated water to irrigate houseplants can cause brown or black leaf spots. Check with your local municipal water supplier to see if your water is fluoridated. Flush your houseplant with distilled water, allowing water to run from the bottom of the pot for a minute or two. You can continue to water with fluoridated water and flush the pot occasionally, or just water with distilled or bottled water. Spider plants, Dracaena and palms are most sensitive to flouride.