By Scout Nelson
Soybean farmers should watch for red crown rot, an emerging disease that can cause early yellowing, root damage, and lower crop yields. The disease may look like sudden death syndrome (SDS), making it difficult to identify through leaf symptoms alone.
Learning how to recognize the signs and report suspected cases can help experts track the disease and improve future management plans.
Connie Strunk, SDSU Extension Plant Pathology Field Specialist, and Madalyn Shires highlighted the importance of monitoring soybean fields for red crown rot. The disease is spreading across parts of the United States, including the Midwest.
Although South Dakota has not yet confirmed a case, two credible suspected reports have been received. Farmers should remain alert and report unusual symptoms to support early detection.
What is Red Crown Rot?
Red crown rot (RCR) is a fungal disease that affects soybeans and can damage plant roots and lower stems. It was first identified in North Carolina in 1972 and later spread across the southeastern United States and parts of the Atlantic Coast. The disease was first linked mainly to peanuts.
In 2018, red crown rot was detected in soybeans in Illinois, marking its first reported appearance in the Midwest. It was confirmed in Rock County, Minnesota, in 2025 and in Iowa in 2026. Reports from other Midwestern states also raise concerns about its spread.
These developments make field monitoring important for South Dakota farmers. Identifying where the disease occurs helps experts understand its spread and develop suitable management plans.
Signs of Red Crown Rot
Red crown rot symptoms often appear during the reproductive stages of soybean growth.
Farmers should examine both the leaves and the lower parts of plants to look for signs of infection.
Aboveground Symptoms
One early sign is interveinal chlorosis. This occurs when the leaf tissue between the veins turns yellow while the veins remain green. As the disease progresses, yellow areas may turn brown and die.
These symptoms can look similar to those caused by sudden death syndrome. Infected plants may lose leaves early, show poor growth, and produce lower yields. Symptoms may appear in patches across a field, especially when warm, wet conditions support disease development.
Belowground Symptoms
Farmers should also examine the roots and lower stems of plants with unusual leaf symptoms. Infected plants may have rotting roots and discoloration near the base of the stem.
One of the clearest signs of red crown rot is the presence of small, reddish-orange fungal structures called perithecia. These structures may form near the soil line and look like tiny red "crowns" around the lower stem. They give the disease its name.
However, these structures are not always visible. They may appear for only a few weeks during the growing season before disappearing. Their absence does not rule out infection.
Why Accurate Diagnosis Matters
Several soybean diseases can cause symptoms similar to red crown rot. These include sudden death syndrome, brown stem rot, and southern stem canker. Other diseases, such as charcoal rot, Rhizoctonia root rot, and Phytophthora stem rot, may cause similar damage to roots and lower stems.
Because of these similarities, visual checks alone may not provide a reliable diagnosis. Farmers should collect suspected plants and submit them to a plant diagnostic laboratory for testing.
Accurate identification helps experts confirm whether red crown rot is present and determine its distribution. This information supports research and the development of future disease management practices.
What Farmers Should Do in 2027
Although the 2026 growing season is too far along for timely soybean diagnosis in South Dakota, farmers should watch for the disease during the 2027 season.
The expected timing of symptoms in South Dakota is not yet known. Based on current estimates, symptoms may begin appearing around August 1, 2027, to August 15, 2027. Farmers should inspect fields during this period and report unusual plant symptoms.
Suspected cases can be reported through Crop Lookout or by contacting Connie Strunk or Madalyn Shires. Early reports help plant health experts monitor the disease and learn more about its spread.
How to Collect and Submit Samples
Farmers who suspect red crown rot should collect whole plants, including the roots and lower stems. Place the plants in a plastic bag, keep the samples cool, and submit them as soon as possible.
Photos of affected plants and details about the field's history can also help experts with the diagnosis.
Samples can be delivered to the SDSU Plant Diagnostic Clinic at Berg Agricultural Hall, Room 203. After-hour drop-off is available at Berg Agricultural Hall, Room 001. Samples can also be mailed to the clinic. Farmers should complete the required diagnostic form available on the SDSU Plant Diagnostic Clinic website.
Early detection helps experts track the spread of Red Crown Rot and confirm whether the disease is present in South Dakota soybean fields.
Photo Credit: South Dakota State University
Categories: South Dakota, Crops, Soybeans