Worldwide distribution. On members of the brassica family, e.g., broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, radish, and cruciferous weeds. Another species attacks sweetpotato. White rust reduces market value.
A water mould, an Oomycete, not a fungus is the cause. Spread by rain-splash, wind, insects, and on plants and seeds.
Cultural control: good quality, reputable seed; long crop rotations; drip rather than overhead irrigation early in the day; use wide plant spacing; optimise plant nutrition; collect and burn debris after harvest; tolerant varieties (except broccoli).
Chemical control: alternate copper or mancozeb with systemic metalaxyl or phosphorous acid.