Management of Downy Mildew on Roses
Potted roses grown in U.S. greenhouses and nursery production facilities have been plagued since the 1800s by downy mildew, a highly destructive disease. It may occur sporadically in some areas of the country, but is a predictable pest in others. Peronospora sparsa, the pathogen that infects rose (Fig. 1A), is specialized and does not infect other ornamentals.
Source: • American Floral Endowment Special Research Reports #131