Purple Seed Stain and Cercospora Leaf Blight


  • Purple seed stain reduces seed quality and is recognized as purple to pink areas on seeds ranging in size from small spots to large patches.
  • Infected leaves appear `sunburned".
  • Symptoms on leaves primarily occur in southern areas of the Midwest and begin after flowering.
  • Infected seeds do not always express symptoms.
  • Red-brown spots may develop on leaves, stems, and pods, and these spots may merge to form large lesions.

Pathogen Involved:

  • Cercospora kikuchii (a fungus).
  • Survives from year to year on infested debris or seed.
  • This fungus overwinters in soybean tissue and in infected seeds.
  • The same pathogen also causes Cercospora blight and leaf spot, which can reduce yields.

Time of Occurrence:

  • Flowering to maturity.

Conditions Favoring Disease:

  • High humidity and warm temperatures.

Disease Management:

  • Use pathogen-free seed.
  • Some varieties are less susceptible than others.
  • Rotation out of soybeans may be helpful.
  • Foliar and seed treatment fungicides may provide some control.