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Dark leaf spot

Dark leaf spot is a fungus that mainly infect most Brassica species.

recognize spores of fungus Alternaria brassicae
Spores of the fungus, photo: S. Seemadua - CC BY 3.0 au

Dark leaf spot (Alternaria brassicae) is a fungus that primarily affects brassicas, but roses can also be infected. Cruciferous plants are the host plants of this fungus.
After infection, round, gray to dark brown spots up to + 1 cm in size appear on the leaves. On the veins, these spots are oval and sometimes deepened. Cauliflower shows black spots.
Alternaria brassicicola is related to A. brassicae but causes more damage.. The fungus survives on seeds. On infected plants, the same gray to dark brown pale spots are formed as on A. brassicae but often have a broad yellow band around the spots.
Plants are infected through stomata. On the infected spots, spores are formed causing further spread. Warm and humid weather often lead to rapid expansion.

Where to find

  • Cruciferous plants
    • Cabbages
    • Rapeseed
  • Rose

Control

Remove affected crops; cut away affected branches (roses).

Prevention

Damaged crops from storms or hoeing, for example, are susceptible to this fungus. Keep crops literally out of the wind.