Downy Mildew is a fungal disease that affects a variety of plants, particularly those in the grape, cucumber, and lettuce families. It thrives in cool, moist conditions and is characterized by yellow or white spots on leaves, which can eventually lead to wilting and decay. The disease is caused by different species of the Peronospora genus and can spread rapidly in humid environments. Effective management includes proper spacing of plants for air circulation, avoiding overhead watering, and using resistant plant varieties when available.