DELAWARE, Ohio – Since 2018, red crown rot (RCR), caused by the fungus Calonectria ilicicola, has been spotted in Illinois, Indiana, Kentucky and Missouri. Now, add Ohio to that list.

RCR was confirmed in Ohio soybeans for the first time in Delaware County earlier this summer. RCR presents a significant threat to Ohio’s soybean crop, with potential yield losses exceeding half.

“This confirmation is a critical first detection,” said Dr. Horacio Lopez-Nicora, Ohio State University Extension soybean pathologist and nematologist. “Once established, this pathogen is nearly impossible to eradicate, so integrated management is the only sustainable path forward to reduce its impact on Ohio’s soybean crop.”

The issue is significant, considering that soybeans are Ohio’s top crop by acreage and value.

In states where red crown rot is established, yield losses have reached as high as 80 percent in severely affected fields, Lopez-Nicora said. Even under moderate disease pressure, farmers often see losses from 15-70 percent.

“For Ohio, if the disease spreads unchecked, growers could face persistent yield reduction and higher production costs year after year, threatening the profitability of the state’s most widely planted crop,” he added.

Red crown rot can be mistaken for sudden death syndrome or other common soybean diseases because all cause yellowing and browning between the veins of leaves during pod fill. But the two can be distinguished by careful inspection.

“With red crown rot, we see red to orange discoloration at the crown of the stem and the presence of perithecia (small, red fungal fruiting bodies) on the lower stem or crown,” Lopez-Nicora said. “Plants often die quickly, and dead plants usually retain their leaves attached to stems.”

Lopez-Nicora urges farmers to dig up plants, not pull them, and submit samples for confirmation to the OSU College of Food, Agricultural and Environmental Sciences (CFAES) Soybean Pathology and Nematology Laboratory, 110 Kottman Hall, 2021 Coffey Rd., Columbus, Ohio 43210.

Red crown rot has been in the United States since the 1960s, first affecting peanuts. The exact path red crown rot took into the north-central United States remains unclear. However, the exchange of used equipment is thought to play a major role, as soil clinging to machinery from infected fields can easily introduce the fungus to clean fields.

“From an epidemiological perspective, red crown rot’s emergence highlights the challenges affecting Ohio agriculture,” said Pierce Paul, professor and chair of the CFAES Department of Plant Pathology. Paul is also an epidemiologist and OSU Extension specialist.

“It’s soilborne nature, long-term persistence and ability to mimic other soybean diseases make it difficult to detect and manage,” Paul said. “The emergence and spread of a new disease like RCR are the result of three major factors: weather conditions favorable for its development, the presence of the pathogen in our fields and our cultivars being susceptible or only partially resistant.”

Lopez-Nicora and Paul both urge farmers and consultants to take immediate action to limit the spread of RCR. They advise to scout systematically, dig up whole plants, sanitize equipment and submit samples to the CFAES laboratory.

“Farmers should check low-lying or compacted areas where symptoms often appear first,” Paul said. “Prevent soil movement from infested to clean fields and harvest suspect fields last. Integrated management will be critical. Practices such as crop rotation with nonhost crops, improving drainage, using seed-applied fungicides and managing soybean cyst nematode populations will be important to protect yields in affected areas.”

Paul said that RCR develops most severely in warm, wet soils, particularly when soil temperatures are from 77 to 86 degrees Fahrenheit, adding that the planting date and associated soil temperatures can influence disease severity.

“RCR is especially challenging because it can survive in soil for many years, even without soybeans, allowing it to persist and infect future crops,” Paul said. “Fields with a history of soybeans or other susceptible legumes, such as clovers, vetch, or lupine, are at higher risk.”

Lopez-Nicora advises farmers to avoid planting soybean or other legume hosts for at least two years in infested fields. He adds that rotation to non-host crops such as corn or small grains can reduce inoculum but may not eliminate it.