Red crown rot causing losses in soybeans

Red crown rot (RCR) has been causing a stir in the Midwest in summer 2023, particularly in western and central Illinois. While it’s been found in southern soybean fields for decades, RCR was first confirmed in Illinois in 2018, followed by Kentucky in 2021. Although the distribution of the disease is spotty, yield losses can be substantial in areas where the disease is present. 

Carl Bradley, University of Kentucky plant pathologist, has recently gained some experience working with RCR in Illinois and Kentucky. “It can be a big problem in fields where the disease is present. In severe situations, there are big areas of fields that are affected severely and yields in those areas may be close to zero. So that’s pretty significant. It’s just not on a majority of acres right now.”  

RCR is caused by the fungus Calonectria ilicicola. Stephanie Porter, an outreach agronomist for the Illinois Soybean Association, says, “Foliar symptoms look similar to sudden death syndrome (SDS), stem canker, or brown stem rot where foliar symptoms are caused by a toxin produced by the pathogen in the root that is then sent to the leaves following a mid-season rain.”

Additional symptoms include a reddish stem, root discoloration, and root rot. Symptoms can be difficult to distinguish from other stem and root diseases like SDS, brown stem rot, and stem canker. Severely infected plants will senesce prematurely, with the leaves staying attached to the plant. In contrast, early senescence caused by SDS is characterized by leaves dropping from the plant.

“This disease is a lot like SDS,” Porter says. “However, it has distinctive bright red fruiting structures at the base of the stem called perithecia.”

Austin Rinker farms in Moweaqua, Illinois, and found RCR for the first time this summer. “We found it initially in a research plot and started scouting in nearby fields and found it there as well. We are still learning more about it and will formulate a plan to manage it for next year.”

There are no rescue treatments for root rot diseases, including RCR. Crop rotation to a non-host crop like corn or wheat may help reduce inoculum levels in the soil. Bradley suggests growers experiencing issues with this disease consider rotating away from soybeans for two seasons to help reduce disease pressure, versus the standard one-year corn / soybean rotation.

Using a labeled fungicide seed treatment can help protect against early infections. Saltro fungicide seed treatment has a special label for suppression of red crown rot in six states, including Illinois and Kentucky. If you do have RCR in your fields, preventing the spread from field to field is important.

“I know this is hard to do, but washing equipment before moving from one field to the next might help slow the spread,” Bradley says.

Soybean cyst nematode (SCN) feeding can provide an entry for RCR to enter the root, so managing SCN may also lessen the path for disease infection.

“There was a lot of work done on this disease at LSU in the 80s and 90s, and one of the things they looked at was the interaction between RCR and SCN,” Bradley says. “They did show that when the two pathogens were both present, the effect on the soybean was worse than either one on its own.”

Efforts are underway to track the distribution of RCR and farmers are encouraged to get out and take a look at suspect areas in fields.

“Send in samples to the lab to verify if it is RCR. We saw pressure show up in fields that looked like SDS. It’s important to ask questions and work with your agronomic advisor to understand what is going on out in the field,” recommends Rinker.

“If you have plants you suspect may be infected with red crown rot, work with your local Extension office and send a sample of the crown to your local diagnostic clinic,” Porter says.