Charcoal Rot - Symptoms

Plants infected by the charcoal rot pathogen may have premature yellowing of the top leaves. Symptoms usually appear first in the driest parts of the field. Photo © Doug Jardine, Kansas State University

The small, black microsclerotia produced on soybean roots and stems are released into the soil as these tissues decay. Photo © Doug Jardine, Kansas State Universi

Symptoms of charcoal rot most frequently begin in the driest areas of the field such as sandy or compacted areas, or the tops of terraces.

Plants infected by the charcoal rot pathogen may have premature yellowing of the top leaves and premature leaf drop. This is easy to mistake for normal maturity.  Plants wilt in the midday heat, recovering at night until the permanent wilt point is reached. Look for unfilled upper pods and general low plant vigor. In some cases, the upper one-third of the plant may have only flat pods without seed.

Beginning at flowering, a light gray discoloration develops on the epidermal and sub epidermal tissues of both tap and secondary roots and lower stems. Scrape the outer tissues and look for the presence of the black, dusty microsclerotia - a diagnostic symptom of charcoal rot..

Increased susceptibility to root rot

In some cases, charcoal rot symptoms may appear in lower wetter areas of the field. In these instances, the soybeans usually will have symptoms of root rot from a previous infection of Pythium, Phytophthora or Rhizoctonia. The damaged root system decreases the ability of the roots to move water from the soil to the plant, putting the plant under moisture stress. In these situations, the charcoal rot fungus can be considered a secondary invader.

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