By Blake Jackson
University of Missouri Extension specialists have identified red crown rot (RCR) in soybean fields in Maries and Phelps counties, marking a growing concern for Missouri soybean producers.
State plant pathologist Mandy Bish confirmed the presence of the disease in early August. RCR is a potentially devastating fungal disease that can reduce soybean yields by as much as 80% in severely affected areas.
This discovery follows the state’s first confirmed case of RCR in Marion County in northeast Missouri during the summer of 2023.
Bish urges farmers to begin scouting now. RCR typically appears in irregular patches within fields, often in wetter, low-lying areas. The disease is caused by the soilborne fungus Calonectria ilicicola, with symptoms typically showing during the soybean reproductive stages, usually at R3 or later.
Leaf symptoms include yellowing between the veins, also known as interveinal chlorosis. However, Bish cautions that “checking leaves is not enough,” because RCR symptoms closely resemble those of sudden death syndrome (SDS).
As the disease progresses, leaves may turn necrotic and die. A key difference, Bish explains, is that RCR-infected leaves tend to stay attached to the plant's petioles, while SDS-infected leaves often fall off.
To accurately diagnose RCR, farmers should dig up affected plants and examine the roots and stems. RCR-infected plants will show red discoloration at the stem base, severe root rot, and small red reproductive structures (perithecia) near the root crown. In some cases, plants may be infected with both RCR and SDS.
“Once red crown rot spreads, you cannot unspread it,” Bish warns. There is currently no cure for RCR. Foliar fungicides are ineffective, though some seed treatments may reduce the severity of infection.
Management strategies include planting into cooler soils, cleaning equipment when moving from infected fields, and rotating to non-host crops like corn for at least two years. No fully resistant soybean varieties exist, though some may show better tolerance.
Research on RCR is being supported by the Missouri Soybean Merchandising Council. MU Extension is working to culture the pathogen to better understand its infection process and to screen soybean lines for potential resistance.
Photo Credit: gettyimages-gilaxia
Categories: Missouri, Crops, Soybeans