By Blake Jackson
A soybean disease not previously confirmed in Wisconsin has now been identified in the state. In the fall of 2025, red crown rot (RCR) was discovered in a soybean field in Columbia County, according to Damon L. Smith, Extension Field Crops Pathologist with the University of Wisconsin–Madison.
Although the affected area was limited to a small patch near the edge of the field, laboratory testing and pathogen verification confirmed the presence of the disease.
Red crown rot is caused by the soilborne fungus Calonectria ilicicola. The pathogen attacks soybean roots, leading to stunted growth, declining plant health, premature death, and potential yield reductions. While soybeans are a primary host, the fungus can also infect crops such as alfalfa and peanut, along with several woody plant species.
Traditionally found in the southern United States, red crown rot has recently been observed farther north, including parts of the Midwest. Its appearance in Wisconsin suggests the disease may be spreading into new production regions.
The fungus survives in soil through durable structures known as microsclerotia, allowing it to remain viable for years. Infections typically begin shortly after seed germination and are most severe when plants become infected early in the growing season.
Warm soil temperatures between 77°F and 86°F favor disease development.
Field symptoms can resemble other soybean diseases, including sudden death syndrome, brown stem rot, and stem canker. One of the most reliable signs is the presence of small brick-red, pimple-like structures called perithecia near the base of infected plants.
Research has shown that infected soybeans often produce fewer pods and seeds, resulting in lower seed weight and reduced yields.
Growers are encouraged to monitor fields closely, seek laboratory confirmation when symptoms appear, rotate to non-host crops, consider effective fungicide seed treatments, clean equipment to reduce soil movement, and minimize plant stress.
Early detection and proactive management will be essential to limiting the impact of red crown rot in Wisconsin.
Photo Credit: istock-ds70
Categories: Wisconsin, Crops, Soybeans, Weather