There are a number of fungi that can attack indoor plants. Over-zealous watering and misting of plants are two of the main causes of fungus outbreaks. Other causes include poor air circulation and introducing an already infected plant into the indoor garden. Often drying a plant out will cure the problem, however in some cases, fungicide does have its place in the indoor gardener's toolbox.
Botrytis blight, also known as gray mold, attacks a plant's soft tissues, according to the University of Illinois Extension. There are more than 50 different types of Botrytis fungus, including Botrytis cinerea, which causes a host of diseases, including stem canker; stem, bud, cutting and crown rot; and blossom and leaf blight. The affected area will first turn brown, then a fuzzy gray mold will appear. Isolate the affected plant, removing any affected leaves and stems and increase air circulation to dry any lingering wet patches. Ensure that the plant is not misted and that only the soil surrounding the plant receives water. Use a fungicide specific to Botrytis on a routine basis to prevent another outbreak.
Fungal Leaf Spot
Fungal leaf spot shows as spots on leaves, which can vary is color, shape and size, according to Purdue University's Department of Botany. The spots may also have small black dots inside them and larger spots can connect, causing widespread discoloration over the leaf. Fungal leaf spot is caused by over-watering and can spread to healthy plants. Isolate the affected plant, remove leaves that show leaf spot and keep the foliage dry, only watering the soil. Fungal leaf spot will likely clear up on its own.
Powdery mildew is the name given to several different types of fungi that present as a white or gray powdery coating on the leaves and stems of a plant, according to Cornell University. The mildew is spread by spores between plants in the same species and the fungi growing cycle is nonstop because of the favorable indoor climate. To treat, isolate the plant, remove the affected leaves and spray with a fungicide specifically made for powdery mildew.