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Authors
Introduction
Symptoms/Signs
Causal Organism
Disease CycleDiagnostic Methods
Disease Management
Other Resources

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Figure 1. Pod Lesions.

Figure 2. Closeup of external pod lesion showing sporulation.

Figure 3. Internal pod decay and seed infection (insect).

Authors

B.A. Edmunds, Former Graduate Student, Plant Pathology
G.J. Holmes, Former Extension Plant Pathology
Department of Plant Pathology
North Carolina State University
Raleigh, North Carolina

Introduction

Anthracnose on common bean occurs throughout the world and is especially devastating in temperate and subtropical areas.  Yield losses can reach 100% if the disease is not managed.

Symptoms/Signs

Anthracnose affects all above ground parts of the plant including leaves, petioles and pods.  Seedlings can also be affected.  Lesions on the leaves and petioles can occur on both sides of the leaf surface and may appear to be elongated and/or form along the leaf veins.  The lesions start as reddish-purple specks that progress into brown-black lesions.  Symptoms on pods are reddish rust colored lesions or specks that develop into sunken tan colored lesions surrounded by black rings.  Lesions on pods range from 1-10 mm in diameter.  In humid weather masses of tan or pink colored spores may form in the center of the lesions.

Causal Organism

Anthracnose on beans is caused by the fungus Colletotrichum lindemuthianum.

Disease Cycle

C. lindemuthianum overwinters in crop debris and conidia are spread through seed, wind and rain.  C. lindemuthianum is also seedborne.  The temperature range for infection is 55-80°F and high relative humidity (>90%) is also required.

Diagnostic Methods

In the field: Look for characteristic lesions as described in the symptoms section.  In moist weather, a pink mound of spores may be present in the center of the lesion and can be seen using a hand lens.

In the lab: Look for lesions as described in the symptoms section.  Place sample in moist chamber to induce sporulation within the lesions.  Wet-mount spores onto a microscope slide.  C. lindemuthianum conidia are unicellular (no cross walls), clear to light tan, and cylindrical with rounded ends or with a narrow base).  Size range for conidia is 2.5-5.5 X 9.5-22 Ám.

Disease Management

Other Resources

Schwartz, H.F., Steadman, J.R., Hall, R., and R.L. Forster.  2005.  Compendium of bean diseases.  APS Press, St. Paul, MN.

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August 2007