Powdery mildew is a common disease on many types of plants. Contary to popular belief, powdery mildew generally does not require free water to establish and grow.
Infection can actually occur on dry leaves.
Warm temperatures and shady conditions encourage the fungus to grow and spread. However, the spores and mycelium are sensitive to extreme heat and direct sunlight. Symptoms Powdery mildew usually shows up on leaf and stem surfaces and does not directly affect most vegetable fruits. However, it can affect the flavor of melons and squash and reduce their yield. The young fruit of apples and grapes can also develop rough skin due to powdery mildew.