Damage symptoms
Downy mildew pathogens infect mostly the leaves but occasionally also stems and fruits. They cause lesions on the upper leaf surface, bordered by the veins, which are first yellow and then turn brown. On the underside of the leaf fluffy growth appears which is first white and later turns grey-brown. This is, in fact, the sporulation of the pathogens extruding from the stomata. In lettuce, the foot is infected first and this causes the plant to fall over. In cabbage the stem is also infected in severe epidemics. In blackberry, red stripes may occur on the stems and petioles due to systemic infection. Early fruit infection may cause early reddening, after which the fruits die and shrivel. Later infections cause the berries to split and one or both parts to possibly shrivel.
