Symptoms: Common on many plants and easily recognized, powdery mildew is a fungal disease found through out the United States. It is caused by a variety of closely related fungal species, each with a limited host range. Low soil moisture combined with high humidity levels at the plant surface favors this disease. Powdery mildew starts on young leaves as raised blister-like areas that cause leaves to curl. Infected leaves become covered with white and gray powdery growth, usually on the upper surface; unopened flower buds may be white with mildew and may never open. Leaves of severely infected plants turn brown and drop. Fungal spores can spread to other plants in your garden.
Control: Prune or stake plants to improve air circulation. Keep the fallen and diseased foliage off the plant and from ground. Make sure to disinfect your pruning equipment after each cut. Applying sulfur or copper based fungicides weekly to prevent infection. Spraying neem oil on the plants will help prevent the diease. Water plants when lights go on so the water has all day to dry.