Downy Mildew -- Peronospora sparsa
Host: Rose, alyssum, pansy, salvia, snapdragon, statice, stock
Symptoms: Downy mildew causes purplish-red to dark brown, irregularly shaped spots on leaves. Leaflets can turn yellow with ”green island” areas and leaf crinkling. If humid conditions persist, a white mass of spores can appear on the underside of leaves. Defoliation and stunting are common.
Conditions Favoring Disease: This disease readily occurs in conditions of high humidity and cool temperatures. The infection usually occurs on young plant parts, but flowers and leaves can be infected.
How Pathogen Survives/Disperses: The fungus typically overwinters as mycelium in stems or as oospores in leaf debris or stems.
Photo and write up provided by Syngenta Professional Products