African Violets are prone to powdery mildew. You can recognize powdery mildew as a fine white powder that covers the plant and the flowers. If you blow on it, it will come off the plant. Powdering mildew is a fungus caused by poor air circulation. If you get it on your African violets, you have two options to get rid of it.

You can either use Lysol, or a product called Fung Away made by Green Light. The Fung Away product is a better, but more expensive, option since it will not damage the flowers; Lysol will damage the flowers if you plant is blooming. In either case, you want to remove the plant from the growing area. Spray the plant completely and let the spray dry completely before returning the plant to the growing area.

As powdery mildew tends to be caused by poor air circulation, if you start to get it, you should consider increasing the air circulation in your growing area. If you do not, then you are likely to get the mildew on your plants again.