The fungus shows a high degree of variability. Resistance acquired through plant breeding are frequently broken by the formation of new strains of downy mildew. Salad plants have a varying susceptibility.
Downy mildew (salad plants)
The fungus forms spores which adhere to the seed and are probably the primary source of infection. The main risk exists in late summer and fall, during periods with high humidity. The fungus mainly occurs on crops under glass.
Pattern of damage
Leaf salad: yellow spots appear on the upper side of older leaves, the underside shows a white spore lawn; later, the affected spots turn brown. Mache: yellowing from the edge, a gray, later violet mycelium on the underside of the leaf.