HPIPM:Black Leg

Author: Howard F. Schwartz and David H. Gent

Identification and Life Cycle

Black leg of brussel sprouts, broccoli, and cauliflower is caused by the fungus Phoma lingam. The disease occurs sporadically in the High Plains during extended periods of cool, moist weather. Infections often start at or below the soil surface when seeds are exposed to contaminated crop debris. The disease damages the water-conducting tissues, resulting in blackened streaks in stems. The pathogen survives between susceptible hosts in crop debris, contaminated seed, and soil.

Plant Response and Damage

Black leg can cause lesions on leaves and stems, above or below the soil. Infected stems have a characteristic semi-dry, blackened rot with small black fungal fruiting bodies (pycnidia) covering the infected area. Affected plants are often stunted and wilt. Blackened streaks are apparent when stems are cut in cross-section.

Biological Control

No biological control strategies have been developed for black leg.

Cultural Control

Plant seed free from the black leg pathogen. Practice a three-year or longer rotation to non-hosts. Deeply incorporate crop residues after harvest to reduce pathogen survival.

Chemical Control

Fungicides are most effective when used in combination with cultural control strategies. Fumigation provides effective control of black leg, but is rarely economical in the High Plains.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.