My zinnia leaves have a something on them that looks like a white powder. Does anyone know what type of disease this is and what do you use to treat this organically?

Sounds like powdery mildew. The cornmeal treatment works well for this. Mix 1-2 cups of cornmeal with a gallon of water, allow to sit for an hour or so, stirring occasionally. Strain off the solid material, which will leave a rather milky water and spray with that. Then water the plants with the rest of the mix and the cornmeal you soaked. This works very well with almost any plant I've ever treated. Good luck and let us know how it goes. In any case, zinnias are at the end of their growing season since they are hot weather types, so it might help them limp along but they will go soon anyway. The cornmeal will help your soil to improve over the winter so I'd give it a shot as it is so inexpensive and beneficial.

Hope this helps!

Kathe, I have a question about preparing a planting bed for zinnias. This weekend I began preparations for a large area in full sun to plant zinnia and cosmos seeds. Hoping the deer leave the zinnias alone. This area is about 5' wide and 133' long and it gets full sun. I incorporated a very generous amount of compost this weekend after plowing up the original area. Was wondering--should I add cornmeal to the soil and any other amendments you might suggest? Would appreciate any suggestions.

Thanks - Susan

_________________
"Life ain't in holding a good hand, but playing a good hand well." - William Smeathers