Red crown rot (RCR) of soybean was found for the first time in Wisconsin in 2025. Observed in a Columbia County soybean field August 25, this disease is caused by the soilborne fungus, Calonectria ilicicola. A plant sample collected by UW-Madison Field Crops Pathologist Dr. Damon Smith was confirmed positive September 4 using morphology and DNA sequencing.
Historically, RCR has been associated with peanut production in the southern U.S. It has been turning up in the Midwest since 2018, with the first case reported in Illinois, followed by finds in Indiana, Kentucky, Michigan, Missouri, and Ohio (Crop Protection Network distribution map). Minnesota, like Wisconsin, also confirmed its first detection of the disease in August 2025.
Red crown rot is spread locally by contaminated soil, crop residue, water, and via wind and farm equipment. Its pathway into the northern states remains unresolved, but likely causes are soil movement or unrecognized cases since symptoms are similar to those of sudden death syndrome, brown stem rot, and southern stem canker. Symptoms include leaf yellowing, early dieback, reddened lower stems, and rotted roots. The diagnostic feature that distinguishes RCR is the presence of tiny red fungal structures, called perithecia, on the crown and roots.
