Another soybean disease is not what you want to worry about right now. However, if there is a chance to head it off before it becomes rampant, wouldn’t you want to know? If you learn to recognize red crown rot now, you can help keep it from spreading to other fields,

“Red crown rot of soybean has become a new concern in Indiana after a few localized occurrences have been found in previous years,” explains Darcy Telenko, Purdue Extension plant pathologist. “We also have reports of it in 2024 in Indiana.”

The disease isn’t limited to Indiana. “We have confirmed it in Marion County in Missouri, across the river from Pike County, Ill., where it is also confirmed,” explains Mandy Bish, Extension plant pathologist at the University of Missouri. “It is at the point where if you grow soybeans in the Midwest, it’s time to look for it. Be able to identify it if you see it, and then take samples to confirm it.”

Telenko notes that the disease is caused by the soilborne fungus Calonectria ilicicola. Because it is soilborne, plant pathologists believe it can overwinter and survive in the soil.

Red crown rot symptoms

Red crown rot may appear in patches in a field like other soilborne diseases, such as sudden death syndrome, better known as SDS, and brown stem rot, Telenko explains. Early foliar symptoms also may mimic these diseases, including chlorosis (yellowing) and necrosis (dying) of leaf tissue between leaf veins.

“It is important to take a few plant samples and check out the stem to verify the issue,” Telenko says. “Red crown rot will cause a red discoloration of the lower stem near the soil line. Red, spherical perithecia may be visible.

“If you cut open the stem, the central pith may have a gray discoloration. Roots are rotted and the plants are easily pulled up from the soil.”

CLOSE-UP LOOKS: Red discoloration at the crown of a soybean plant is shown in the picture on the left. In the center and right pictures, red, spherical perithecia have formed on the crown and stem of plants. (Darcy Telenko and John Bonkowski, Purdue Extension)

How to combat disease

The first step is to determine how widespread this relatively new disease is already, Telenko says. She encourages growers to study pictures of red crown rot. If you find similar symptoms on plants and suspect it may be red crown rot, send samples to your university lab for confirmation.

“We are working with our colleagues across the Midwest to determine how widespread this disease is so far,” Telenko says.

Right now, while there may be some tolerance to red crown rot among seed varieties, there is no known resistance. Bish notes that once you know red crown rot is in a field, the best thing you can do is contain it to that field.

“That is not a popular strategy, but it is important in limiting spread of a soilborne disease,” she explains. “Basically, it means working fields where it is confirmed last, and doing everything you can to avoid removing any soil from that field. You don’t want to spread it to other fields.”