Symptoms and Signs
This anthracnose fungus infects leaves, stems, and pods of common bean plants. The most characteristic symptom of the disease is the black-red sunken cankers or spots that develop on infected pods. As these spots become older, the edges develop a black ring with a red outer border and may show a pink ooze in the center, which contains the spores of the fungus. Similar spots may develop on seeds. Red-brown spots and streaks also develop on stems, petioles, and leaves. A characteristic symptom of the disease occurs on the underside of infected leaves: veins turn brick-red to purple and eventually black.
Comments on the Disease
Anthracnose develops under cool moist conditions, and thus is rarely a problem under dry, warm California conditions. The fungus overwinters in bean debris in the field or in association with seed. Young bean plants are infected from spores carried on seed or spores splashed from debris or nearby infected plants. The spores are then spread throughout the field by machinery, wind-driven rain, and irrigation water.
Cultural practices can be effective in managing this disease:
- Plant certified disease-free seed that was grown in areas unfavorable for anthracnose (e.g., California or Idaho).
- Plant resistant varieties, when possible.
- Use furrow rather than sprinkler irrigation because of the importance of water for disease development.
- Plow under bean debris in infected fields immediately after harvest.
- Use crop rotations of 2 to 3 years because the fungus is primarily a pathogen of common bean (but also infects lima bean and scarlet runner bean).