Oidium is a type of fungus that affects plants and crops, causing white powdery patches on the leaves and stems. Some synonyms for Oidium include powdery mildew, white mold, or white rust. These terms are often used interchangeably to describe the same type of fungal disease that affects a wide range of plants, including grapes, roses, cucumbers, and potatoes. Oidium is a common problem in humid climates where the temperature and moisture levels are just right for the fungus to thrive. Gardeners and farmers use various methods to control and prevent Oidium, including removing infected plant parts, using fungicides, and maintaining optimal growing conditions for plants.