What do dahlias require and what to do about leaf insects. Dahlias
Dahlias powdery and very sad looking
Ventura County California dahlias
Thank you for your question. Without having any images of the insects or powdery condition, it is impossible to tell you what you have or how to deal with it. However, here is a link to an Extension article on these plants. The list on the right has a variety of insect and disease subjects with photos, so perhaps you can find your problem(s) and know what to do. Good luck!