By Linda Geist
Missouri soybean growers should be alert for red crown rot (RCR) in 2026, says University of Missouri Extension state plant pathologist Mandy Bish. The soilborne pathogen was confirmed in nine Missouri counties during the 2025 growing season after its initial detection in Marion County in 2024.
RCR can cause significant economic losses. In 2024, some Missouri fields saw yield declines of 50%-55%. Caused by the fungus Calonectria ilicicola, the disease was first identified on soybean in the U.S. in 1972 in North Carolina and later spread throughout the southeastern states and into the Midwest.
“The identification of red crown rot across nine Missouri counties in 2025 raises important questions,” says Bish. “We still have work to do to understand the extent to which the pathogen is actively spreading to new areas versus the extent to which increased awareness is allowing us to detect longer-standing infestations. Detections in areas with limited soybean acreage, such as Maries and Phelps counties, underscore the need to learn more.”
The RCR fungus survives in plant residue over winter and thrives in wet, warm soil conditions between 77 F and 86 F. The fungus usually infects seedlings, but the most obvious symptoms, which appear on the leaves, typically emerge after the R3 (beginning pod) growth stage, often appearing in low-lying or poorly drained areas. Leaf symptoms can initially appear as yellow spots that progress to larger yellow-brown areas between the veins and look very similar to symptoms of sudden death syndrome (SDS). Leaves with RCR will typically remain attached to the plant after death.
Source : missouri.edu