Worldwide distribution. On brassicas, crops, weeds and ornamentals. An important disease in sub-tropics.
Yellow to pale brown spots develop into irregular patches on upper surface of leaves, with growth of the water mould (oomycete) below. Seedlings stunted or killed. Damage on flower heads of broccoli and cauliflower greater than on plants used for leaves, e.g., cabbage.
Spread in wind and rain, and trade in seedlings.
Cultural control: weed; water early in day; avoid overcrowding; crop rotation, collect and burn trash after harvest.
Chemical control: copper, chlorothalonil, mancozeb (protectants); or metalaxyl, phosphorous acid (systemic).