Fungal Disease
The African violet plant can develop spots on its leaves from being misted or splashed with water. The African violet’s fuzzy leaves can trap moisture causing fungal or bacterial leaf spot to form. To avoid this, always water your African violet at the soil level by carefully lifting the leaves or with the bottom-watering method, never on the leaves or the center of the plant. If you need to provide extra humidity do so by placing it over a pebble tray or putting a humidifier nearby instead of misting.
If the spots on your African violet are white and powdery looking, this could be a fungal disease called powdery mildew. Powdery mildew could have formed because the plant lacks air circulation in a hot and humid environment. When combined with a lack of light, these conditions create the perfect environment for powdery mildew to grow.
To help the plant, prune off the dead stems and leaves and isolate them from other plants since fungal issues can spread quickly between plants. Place the plant somewhere with more air movement and more light, and treat the plant with a copper fungicide. If not caught in time, powdery mildew is sometimes fatal to African violets and other indoor plants.
Overwatering
Overwatering an African violet can also cause spots to appear on the leaves. Too much moisture in the soil of a houseplant can sometimes cause edema. Edema shows up as spots most often on the underside of the leaves, but occasionally on the top. These spots have a reddish coloration and will luckily not spread once watering is corrected. Eventually, this dead plant tissue will fall away, or you can trim using sharp, clean pruning scissors.
Water when the soil volume is 25% dry. This plant likes to be kept moist, but does not like to sit in soggy soil. Avoid getting the leaves wet, and the bottom-watering method is recommended. Place your plant in a sink filled with 2-4″ of water. Leave the plant to soak for up to 45 minutes. Test the top of the soil for moisture. If it still feels dry water a little from the top. When your plant’s soil is evenly damp, drain the sink/tub and allow the plant to rest while it drains thoroughly.
Temperature
If your plant has been exposed to temperatures below 55°F, it can cause damage. On the other hand, exposure to direct sun can also cause spots. Be sure to keep the plant’s leaves from pressing up against window panes, which can become hotter or colder than the indoor air.
