Watch for red crown rot in soybean

COLUMBIA, Mo. – 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.

When scouting, growers should dig up plants and inspect the stem base and roots to differentiate RCR from SDS. RCR-infected plants can have reddish discolorations at the base of the stem near the soil line that become noticeable when soybean are in the vegetative stages. Red perithecia (tiny spheres) typically form at the base of the stem and root during late reproductive stages. At the end of the growing season, note any surprising low-yielding patches in the field. Research by University of Kentucky plant pathologist Carl Bradley shows the disease compromises nearly all yield components, including pod numbers and seed weight.

Splitting stems can also help distinguish RCR from lookalike diseases, such as brown stem rot. Once established, the disease remains in the field. Research shows seed treatments may help reduce early-season infections, but foliar fungicides are ineffective. There are no commercial soybean varieties with RCR resistance, however there are some variety differences, and farmers with RCR infestations should contact their seed dealers to learn what is known.

Bish says there is no “silver bullet” solution for RCR, but several management practices may help reduce severity. Bish recommends rotating to a non-host crop such as corn for two years to lower soil inoculum. Include a fungicide seed treatment labeled for RCR, and select a variety that is more tolerant when available. Cleaning soil from equipment before entering new fields and working infected fields last can also limit spread.

MU Extension researchers, including Bish and her plant sciences team, continue to study best management practices and collaborate with other land-grant universities to find solutions.

Contact the MU Plant Diagnostic Clinic to help with diagnosis of the disease. You also can follow the spread of red crown rot and other plant diseases at the Crop Protection Network.

Map

This Crop Protection Network map shows where red crown rot (RCR) has been confirmed. Missouri soybean growers should be alert for RCR in 2026, says University of Missouri Extension state plant pathologist Mandy Bish.