Cercospora leaf blight and purple seed stain are caused by the fungus Cercospora kikuchii.
This is a widespread disease, but yield loss is rarely observed.
Presence of Cercospora leaf blight, does not guarantee purple seed stain, even though they are caused by the same organism.

Identification

Foliar symptoms begin in the upper canopy on leaves exposed to the sun.
Symptomatic leaves are purple to bronze and may become leathery (Fig 1).
Discoloration from purple seed stain can be on small spots or the entire seed (Fig 2).

Fig 1: Cercospora leaf blight symptoms on soybean leaves

Fig 2: Soybeans with purple seed stain

Management

Varieties with resistance to Cercospora leaf blight are available.
Fungicides are registered for use on Cercosporabut are not usually needed.
Purple seed stain may result in dockage or denial of seed certification but does not reduce yield.

References

Crop Protection Network (2022, Jan 27). CercosporaLeaf Blight of Soybean. Retrieved from: https://cropprotectionnetwork.org/encyclopedia/cercospora-leaf-blight-of-soybean

Crop Protection Network (2022, Jan 27). Purple Seed Stain of Soybean. Retrieved from: https://cropprotectionnetwork.org/encyclopedia/purple-seed-stain-of-soybean

Authors: Madeline Henrickson and Dr. Alyssa Koehler

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