What is downy mildew?
Downy mildew of brassicas is a disease of seedlings and also mature plants. It is caused by a fungus-like organism, Peronospora parasitica, that penetrates the tissues under wet conditions and grows out to produce fuzzy whitish patches. These infections in turn release spores and spread to other brassicas by wind and rain. Expect damage in spring in young plants especially in greenhouses and other propagation environments and in summer and early autumn in maturing crops outdoors. This disease is specific to brassicas; both vegetables, including: cabbages, cauliflowers, Brussels sprouts, radishes, swedes and turnips; and some ornamental and wild relatives, including: horseradish, Cheiranthus (wallflowers), Matthiola (stocks), Aubrieta (aubretia) and Capsella bursa-pastoris (shepherd’s purse). Brassica downy mildew often occurs together with brassica white blister (Albugo candida), another foliar pathogen.
