Mildews are a type of fungus that thrive in warm, damp environments. They often appear as a thin, powdery coating on surfaces like plants, fabrics, and walls. Mildew can cause discoloration and damage to materials, making it important to address moisture issues in homes and gardens. There are two main types of mildew: powdery mildew and downy mildew. Powdery mildew typically appears as white or gray spots on leaves, while downy mildew has a more fuzzy texture and can be purple or yellow. Both types can affect a variety of plants, leading to reduced growth and yield.