Black leg (Leptosphaeria maculans, anamorph
Phoma lingam) – Seedborne
The disease is caused by Phoma lingam.
Symptoms are light-brown, oval to round spots
that enlarge to become grayish-tan, frequently
occurring near the bases of stems. Small black
dots (fungal fruiting bodies called pycnidia or
perithecia, depending on the stage of the fungus
that is developing) form in the centers of spots
(lesions); identifying these fruiting bodies is
important for diagnosis of this disease, as this
disease can readily be confused with ring spot,
another pathogen of crucifer crops caused by
Mycosphaerella brassicola. Black leg affects both
foliar and crown tissues; wilted leaves are often a
secondary symptom of severe stem and crown
lesions. The fungus overwinters in crop debris or
infected seed, with dissemination of spores
occurring through splashing rain, irrigation, or
wind. The fungus can survive for up to three years
in the soil and can be seedborne. Disease
development is favored by moist conditions, with
greater severity in years with frequent rainfall in
late spring and early summer. Avoid planting next
to a field that has had crucifers in the past year;
remove cruciferous weeds; incorporate crop