Guy Padgett | 8/20/2011 12:55:30 AM
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Charcoal Rot (Macrophomina phaseolina)
Gerard T. Berggren
LSU AgCenter (retired)
Charcoal rot occurs worldwide and is common in the southern United States. Yield losses are difficult to measure, as there are no known resistant cultivars or fungicidal controls. The disease is most severe when plants are under stress from moisture or nutrient deficiencies, soil compaction, nematodes, or other pathogens. Overwintering inoculum survives as sclerotia on plant debris or in soil. Symptoms appear in hot, dry weather usually after flowering.
Charcoal rot is primarily a root and basal stem disease, but may be seen on above ground parts of infected plants. Diseased tissue in the taproot and lower stem develops a grayish discoloration. Eventually the lower stem is girdled, causing wilting and death. Infected soybean plants have many tiny, black specks (sclerotia) on the roots and lower stem just beneath the epidermis or bark. The sclerotia resemble a sprinkling of powdered charcoal, hence the name charcoal rot.
Since the disease is often associated with weakened plants, maintaining healthy, vigorous plants will reduce losses. Maintaining vigorous plants requires proper fertilization, weed management, and irrigation, where possible.
The LSU AgCenter and the LSU College of Agriculture