Cercospora blight on soybeans

Cercospora blight on soybean

Photo credit: Daren Mueller, Iowa State University, Bugwood.org

COMMON NAME: Cercospora Blight of soybean

SCIENTIFIC NAME: Cercospora kukuchii



Cercospora leaf spot and blight are common problems among field crops, amaranth vegetables, ornamental plants, and shrubs in the southern and midwestern regions of the U.S. The disease is caused by the Ascomycete fungus Cercospora kukuchii. The disease primarily effects foliage in the form of leaf spots and blight, but can also cause spots or discoloration on shoots and seeds.



Symptoms of Cercospora leaf spot occur after pollination and during pod fill. The disease is characterized by small, brown spots encircled with bronze-purple borders on the surface of the leaf. Often the spots will coalesce to form large blighted areas. As the disease develops, the spots will become necrotic, grey and brittle, and eventually fall out of the leaf surface leaving jagged holes.



Cercospora blight of soybean

Stem lesion on soybean caused by C. kikuchi. Photo credit: Gail Ruhl, Purdue University, Bugwood.org

Cercospora kukuchii overwinters in infected seed and plant residue from the previous harvest. Fungal spores development on the surface of the residue when the weather becomes humid and temperatures hit 75-80°F. The spores disseminate via wind or rain, and begin to infect soybeans during flowering. The fungus then invades the pod, travels through the upper vein, and infect the hilum and seed coat of the developing seed. When an infected seed is planted, the fungus will grow through the cotyledon, into the stem, and infect the foliage. Cercospora kukuchii does not typically kill soybeans, but will reduce the value of the grain.



The most effective methods for managing the disease is to plant resistant soybean varieties and practice crop rotation to minimize the inoculum in the soil. Selecting disease-free seed is also an important practice for preventing the introduction of the fungus into a clean field. Fungicide applications are available to treat diseased fields, but are not as effective.



BugWood Wiki. Cercospora leaf blight and purple seed stain



University of Minnesota Extension: Cercospora leaf blight and purple seed stain on soybean



Soybean Research & Information Network. Soybean Diseases: Cercospora Leaf Blight



Farmers Business Network. Overview of Cercospora



This factsheet is authored by 

Rachael Sampson
pursuing a Masters in Horticulture

Factsheet information for the plant health issues represented by the images on the 2020 TPDDL calendar were written by graduate students enrolled in the Department of Plant Pathology & Microbiology  DR. DAVID APPEL’s Graduate level Introductory Plant Pathology course (PLPA601) in the 2019 Fall semester.  This exercise provides an opportunity for a high impact learning activity where the students are tasked with producing an informational output directed to the general public.  This activity provides an opportunity for the students to write and produce a  (hopefully) useful product to communicate information on plant health issues to the public. 




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