How to Manage Pests

UC Pest Management Guidelines

Dry Beans

Charcoal Rot (Ashy Stem Blight)

Pathogen: Macrophomina phaseolina

(Reviewed 8/07, updated 12/08)

In this Guideline:


Charcoal rot is most serious on common beans and then blackeyes; it also occurs on limas. Symptoms may appear after the pathogen, which can be soilborne, germinates and infects seedling stems near the soil line at the base of developing cotyledons. The fungus produces black, sunken cankers that have a sharp margins and often contain concentric rings. The plant's growing tip may be killed or the stem broken where it is weakened by the canker. Infection may continue into the hypocotyl and root region or the primary leaf petioles. Root infection causes a brown to black necrosis. If plants are grown under dry land conditions, young plants can be killed.

Infection of older seedlings and plants may cause stunting, leaf chlorosis, premature defoliation, and plant death, especially during periods of high temperature and particularly following drought stress. On older plants "charcoal dust" often appears on the surface of the stems and is diagnostic evidence for this disease. This charcoal effect is caused by the production of small, black microsclerotia just below the epidermis and in the vascular tissue. This symptom is also called ashy stem blight.


The fungus is pathogenic on many crops including corn and sorghum, and the disease tends to be worse on certain soils. Although the fungus is capable of infecting plants at all stages of growth, severe disease primarily occurs under conditions of drought stress and high temperatures, especially when a late irrigation is applied.


Avoid drought stress especially during periods of high temperature. A 3-year rotation with a cereal crop may help reduce soil inoculum.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446


R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County

Acknowledgment for contributions to Abiotic Disorders:
A. E. Hall, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to Diseases/Abiotic Disorders:
S. R. Temple, Plant Sciences, UC Davis
Acknowledgment for contributions to Diseases (viruses):
R. L. Gilbertson, Plant Pathology, UC Davis

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