Anthracnose is a worldwide disease of beans caused by the fungus Colletotrichum lindemuthianum. Common bean is very susceptible to this disease, as is tepary bean. Scarlet runner bean, lima bean, and mung bean are somewhat susceptible. Anthracnose is one of the most important bean diseases. It is worse in temperate regions. Under cool (60° F), wet conditions, the disease can cause complete loss. It can cause disease at all stages of plant growth, from seedlings to growing pods.

Symptoms. On seedlings grown from infected seed, symptoms start as small dark brown to black spots on the seed leaves. Rust-colored specks appear on the hypocotyl and enlarge along, and sometimes around, the stem. If the spots grow completely around the stem, the seedling is killed. The spots become sunken and fill with a salmon-colored ooze, which consists of millions of spores.

On established plants, the veins on the underside of the leaves and the petiole can become infected with elongate, somewhat angular, brick-red to purple spots that soon turn dark-brown to black. Spots may sometimes occur on the upper sides of leaves.

On the pods, symptoms begin with small tan to rust-colored spots which enlarge to dark sunken areas surrounded by a slightly raised black ring with cinnamon-colored border. In the center of the spots, there is often a tan to salmon-colored ooze, which consists of millions of spores. Ooze dries to gray-brown to black granules. On the seeds, large or small yellowish-brown sunken spots may form, which turn brown to black. Pods may shrivel and die if infection is severe.

Similar Diseases.  Anthracnose is similar to bacterial blights, which may have yellow or white ooze exuding from the spots on the pods, rather than the tan to salmon-colored ooze of anthracnose. Leaf symptoms are different as well.

Prevention. The fungus survives in the seed, so it is important to use certified disease-free seed, or seed that has been hot water soaked or fungicide treated. Use of a three-year crop rotation is recommended. Keep the fields weed free for good air circulation during the season. It is important to plow under bean refuse immediately after harvest as the fungus survives in debris as well. Resistance is available for this disease, but there are several races of the fungus, and it is important to know which races are in the area before varieties are selected for planting.

Contact your local Cooperative Extension center or refer to current recommendations for chemical control measures in the latest New England Vegetable Management Guide.

References.

• Ntahimpera, N., et al. 1997. Influence of Tillage Practices on Anthracnose Development and Distribution in Dry Bean Fields. Plant Diseases 81:71-76.
• Schwartz, H.F. 1991. Anthracnose in Compendium of Bean Diseases. R. Hall, ed. APS Press, St Paul, MN. pp. 16-17
• Sherf, A.F. and A. A. MacNab. 1986. Vegetable Disease and Their Control. John Wiley and Sons, New York.

This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

By: Pamela S. Mercure, IPM Program Assistant, University of Connecticut, 1998, Reviewed 2012

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