Phialophora resides on the old soybean residue. This fungus can build up on soybean residue and is more commonly reported from fields that are continuously cropped to soybeans. Symptoms typically appear one to two weeks before the leaves begin to yellow. Severe symptoms at the end of the season include dark brown discoloration between the veins of the leaves and premature defoliation. The key diagnostic feature of brown stem rot is the internal browning of the pith. Premature death of plants results in small lightweight seeds.
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| Figure 21. Brown stem rot. Note brown discoloration of the pith. In this plant, it is not continuous. | Figure 22. Brown stem rot. In this plant, the brown pith is continuous from the base of the plant up to the top. | Figure 23. Foliar symptoms of brown stem rot — large areas of brown edged with dull yellow. |
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