Too much water, such as flowing water or rain, destroys spores by causing them to burst. The fungus does not grow in a leaf but rather across the surface. ... Symptoms White or grayish patches on leaves, stems and sometimes closed delphinium buds late in summer.

How do you get rid of powdery mildew on delphiniums?

Two organic sprays have been proven to work in the treatment of powdery mildew. The first is a mixture of milk and water (one part milk to nine parts water) sprayed on the plants in the morning of a warm and dry day. Don't spray the plants with any liquid in the evening.

What can you do for mold on delphiniums?

Use neem oil, a commercially available organic treatment. This both treats existing powdery mildew and protects the plant against further infection. Apply a milk spray to your plants as a preventative measure.