Fungi Science
Downy mildew on roses is triggered by the pathogen Peronospora sparsa. As the illness progresses, the leaves take on a warped look with purple spots. These spots then sporulate and, in the final stages of the disease, turn light brown or white. Peronospora and Plasmopara species are specifically unsafe for most gardeners. Bremia and Basidiophora are also problematic, specifically...
