Cylindrosporium disease [Cylindrosporium concentricum]
Oilseed rape in Germany's northern cultivation areas.
As a rough, thick-walled mycelium, the fungus survives up to 9 months on crop residues. Conidiospores are produced asexually there. The ascospores represent the sexual form, which is spread with the wind and is considered the main cause of primary infection. Primary infections and secondary infections of the crop are caused by conidiospores, which are formed in the gray leaf spots and are spread by wind and raindrops. The disease develops best during long rainy periods and temperatures between 14 and 20 °C.
Pattern of damage
Round, greenish-bronze colored spots develop on the leaves (Picture 1). These spots can reach 1.5 cm in size and change color to become whitish to gray with a dark green, purple or brown edge (Picture 2). Necrotic leaf tissue becomes torn. In the case of a severe infection, the spots grow together and the leaf dies. On the shoots there are delineated, elongated, slightly sunken-in spots with a blackish-brown edge, which become gray to purple in color. Pods exhibit slightly sunken-in spots with a blackish edge. Dark mottling (the conidia) can be seen in the center of the infected areas. There are similarities with light leaf spot, Phoma leaf spot, downy mildew, annular spot disease, Verticillium wilt, Phoma stem rot, black spot and gray mold.