Pythium is a water mold. It needs water to form free-swimming spores (zoospores) that can then infect plants. The zoospores infect roots and colonize the plant, which results in a soft, light brown to tan discoloration.
The tissue, in advanced stages, collapses, and when seedlings are pulled from the soil, there are no visible roots.
Facts on Pythium
Poor stands, skips in rows, or larger areas with few plants are indications that pythium was active shortly after planting. Pythium also leads to yield reductions in severe cases.
Pythium produces swimming spores and flourishes in fields with standing water. It survives in soil and plant residue. There are several Pythium species capable of causing seed rot and damping-off, and they are active when soil conditions are wet and cool (55 F).
Management of Pythium
Infected seedlings rarely recover. Evaluating the stand that is left will be important to decide whether replanting is necessary. Do not replant back into the old row without stirring soil to dilute fungus. Seed treatments with active ingredients specifically targeting pythium can help control this disease.