Alternaria leaf spot is caused by the fungal pathogen Alternaria alternata. This is a minor disease of faba beans occurring late in the season. The main impact of the disease is confusion with the disease chocolate spot.

What to Look For

Dark brown leaf spots which often have a zoned pattern of concentric brown rings with dark margins. Symptoms can be confused with chocolate spot.

Alternaria lesions have concentric rings beans

Disease Cycle

Alternaria is a weak pathogen of many hosts and is usually a secondary pathogen that only attacks following damage by other fungi or insects. Alternaria leaf spot develops late in the season as the plants start to mature. The fungus probably survives on crop residues and on other hosts.

Management

Control of alternaria alone is usually not warranted.