Cabbage downy mildew is caused by the parasitic fungus Peronospora. This fungus thrives in warm and humid environments, spreading through intercellular spaces and using haustoria to extract water and nutrients from the host cells. The sporangiophores emerge from the stomata, and during germination, the sporangia produce germ tubes, which can directly infect under suitable conditions.

Symptoms of Cabbage Downy Mildew

Infected cabbage primarily exhibits symptoms on the leaves, followed by the stems, flower stalks, and seed pods. Initially, leaves display indistinct yellowing spots along the edges, which expand into yellow-brown, polygonal lesions restricted by the leaf veins. The undersides of the lesions are covered with varying densities of white downy growth. In severe cases, the lesions merge, causing the leaves to yellow and wither, rendering them inedible.