 It is most serious on the flowerhead types (cauliflower, broccoli), less serious on the leaf brassicas (cabbage, Brussels sprouts, and least serious on the root brassicas (turnips, swedes) and oil brassicas (rape).The pathogen persists as oospores in the soil.Attacks are most important in "Brassica" seedbeds, with infection appearing as yellow speckling of the upper surface of seedling leaves, and white mildew on the lower surface.