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Charcoal rot


© Iowa State University

Pathogen(s) causing disease:

Macrophomina phaseolina

Symptoms:

Irregular areas of wilting or premature death. Early season diagnosis is very difficult, but during the later stages of plant development very small black structures become evident as a grayish-black discoloration in the root and lower stem tissues. Cutting the lower stem will expose the discolored tissues in comparison to normally white tissues of healthy plants.

Conditions:

The disease develops when there is a high level of the pathogens in the soil and when plants are under stress. Hot, dry weather creates much of the stress. Infection occurs early in the season on seedlings and the fungus grows slowly in the plant until hot dry weather occurs after flowering. Soil populations increase when soybeans are grown continuously, allowing the disease to become more severe in successive soybean crops.

Management:

There are no fungicides available for effective disease control and genetic resistance is generally not available in cultivars. Crop rotation can prevent build-up of inoculum (microsclerotia) in the soil. Plant at recommended plant populations. Very high plant populations are prone to drought stress which favors disease development. Maintain adequate soil fertility levels to reduce nutrient stress and encourage vigorous growth. Select soybean varieties that are not highly susceptible to charcoal rot. Plants grown in conditions of high temperatures, drought or poor fertility (too high or too low) are most susceptible. Any cultural practices that minimize plant stress will reduce the risk of charcoal rot.

Sources:

Ohio State
WI

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