Anthracnose is a severe, rapidly developing disease that can cause complete plant defoliation and extensive yield loss if plants become diseased prior to, or during pod fill. North Dakota State University Crop and Pest Report #13 (7-24-03) reported the disease on two dry edible bean samples received by the Plant Diagnostic Clinic during July (See the Cheryl Biller report on p. 6). The disease has been identified in Minnesota this year as well.

In early August a pinto bean grower near Argyle noticed plant symptoms such as brown lesions on leaf veins and dark, circular lesions on pods (Figure 1).

Figure 1. Bean pod showing anthracnose lesions. As disease severity advances, lesions coalesce into large areas of dead plant tissue.

The fungal pathogen (Colletotrichum lindemuthianum) infects leaves, petioles, stems, pods, and seeds of susceptible plants. Severe anthracnose symptoms were identified on plants in a limited area of the 90 acre field. Recent dry weather and hot temperatures likely reduced spore production and stopped the disease from spreading.

The pathogen produces spores that are carried to healthy plants during rain events. Likewise, field equipment, animals and insects that come in contact with wet, diseased plants can also spread spores to healthy plants. If anthracnose is present in a field, cultivation and other field work should be postponed until the plant canopy has dried.

Anthracnose is a seed and residue-born disease. Growers are urged to use reputable seed companies that sell certified anthracnose-free seed to prevent introducing the disease into their fields. Areas that already have the disease should be rotated out of susceptible dry beans for one or two years. Fungicides offer some control, but fields must be scouted often and timely applications made to prevent yield loss.

For more information on anthracnose see NDSU Extension Circular No. PP-1233 entitled “Anthracnose of Dry Beans” by Luis del Rio and Carl A. Bradley.