The common name white mold typically refers to Sclerotinia stem rot that mainly affects field crops. If you have white mold on your succulent, you are more likely dealing with powdery mildew, a common houseplant ailment that is easy to treat. It can live on both stems and fleshy leaves of succulents.
Powdery mildew likes the same type of habitat that succulents like, warm and relatively dry areas. Because succulents and powdery mildew thrive in similar living conditions, succulents are the most infected types of plants. Your infection may look like the classic white, powdery coating. It can also take on a gray appearance with round yellow, brown, or black growths. The powdery mildew can appear in just one spot, but more commonly, it spreads to other leaves, stems, and buds of your plant.
At first, powdery mildew may seem harmless. Your succulent may be able to live with the white, moldy-looking disease, and even thrive, for some time. As the infection spreads and gets worse, you may notice deflated, damaged, or deformed leaves. The leaves and stems may also turn pale green and then yellow. If your succulent has a severe infection, it may lose leaves, fail to flower, or even die. Once one of your plants has powdery mildew, the infection can spread to others.
To treat powdery mildew, gently remove any infected leaves and stems that have begun to show signs of damage and then apply a fungicide. The fungicides that contain sulfur, neem oil, or triforine may effectively kill powdery mildew on healthy leaves, stems, and buds. Also, apply the fungicide to nearby plants as a preventative measure. Some gardeners have reported success with baking soda mixed with horticultural oil.
Separate your infected plants from your healthy plants, if possible. Next, work to increase air circulation to help slow spore production. Do this by selectively pruning plants, moving them to windier locations, or using fans to circulate more air in your home. Spores need some humidity level, so switching to early morning watering can help slow or prevent powdery mildew spread.