Red crown rot emerging in Illinois

JOHNSTON, Iowa — Red crown rot, a common southern U.S. fungal disease, made its way into Illinois soybean fields over the past few years.

First detected in 2018 in a single soybean field in Pike County, red crown rot has currently been confirmed in 14 counties and is suspected in another three counties in the Prairie State.

“It’s as far north as Bureau County, as far south as St. Clair County and has a pretty good distribution east to west across the state,” said Robert Bellm, retired University of Illinois Extension crops systems educator and agronomist in southern Illinois.

Bellm participated in an informational podcast on the disease along with Pioneer field agronomists Crystal Williams, northern Illinois; Brad Mason, western Illinois; Cody Pettit, eastern Illinois; Matt Montgomery, west-central/central Illinois; and Scott Eversgerd, western-southern Illinois.

Bellm’s first experience with red crown rot was in 2019.

“I had been scouting for sudden death syndrome in the Madison County area in Illinois and I texted Nathan Kleczewski (then-U of I plant pathologist) about seeing some sudden death syndrome in a field in that area,” Bellm noted.

“He responded back and asked if I’d seen any red crown rot. My immediate response was what the heck is that, I’d never heard of it. He gave me a description of it and when I was in a field I thought I was looking at rhizoctonia.”

Bellm sent photos of the infected soybean to Kleczewski and he confirmed it to be red crown rot.

“It’s an emerging disease that we are still learning about, but it can be significant in those fields that are heavily infested,” Bellm added.

Pike County is included in Mason’s agronomy area and he has been near the field where it was originally discovered.

“The way I’ve framed up the area of distribution for this disease, we’ve got it up to the suburbs of Chicago and all the way to Kentucky,” Mason said.

“Some people in Indiana are suspecting that they might have spotted it. That’s quite a bit of rapid distribution of this new disease.”

Misdiagnosis

Due to its misdiagnosis the last few years, its spread may be broader than known at this point.

“That’s probably one of the big things moving forward. Is it SDS? Is it brown stem rot? Is it red crown rot? The correct identification of this disease is going to be a big deal as we try to manage it and get a hold of it,” Eversgerd said.

“This is a real SDS look-alike. It’s going to have that interveinal chlorosis. It’s going to have that real distinct SDS pattern that a lot of people are used to. It’s going to be a real dead-ringer for it,” Montgomery added.

“There are some subtle differences in the way the leaf symptomology kind of manifests itself. For the most part, most people are going to think it looks like SDS.”

“The subtle difference that I have seen is with SDS typically the leaf falls off the plant as the disease progresses, leaving the petioles on the stem. On red crown rot, I see more symptomatology of the leaves just turning brown and hanging on the plant. It manifests more like southern stem canker in that respect than it does SDS,” Bellm said.

“The question of misdiagnosing it with the SDS disease, as far as I can read and find it, it’s strictly a soil-borne disease. I’ve got a field in this area that’s basically 100% infested on a 60-plus acre field. This disease has been around here for a long time in order to get that degree of infection, and we haven’t identified it properly.”

Yield Losses

Red crown rot’s impact on yields in Illinois is still being determined. However, yield losses of 25% to 30% have been documented in Louisiana and Mississippi where the disease has been present for years.

Bellm said he doesn’t have a good handle on yield hits yet, but from what he’s observed on plants “20% yield losses would not be unheard of in those areas heavily infected.”

“A lot of growers are not good at calibrating their yield monitors and the disease is sort of sporadic through the field,” he said. “It’s hard to guess.”

“Pike County has been dealing with it for quite a bit now. Last year, we had some historic 60-, 70-bushel fields yield 16 bushels per acre. Once it gets established, it can be really devastating,” Mason added.

Diagnosis

For those who haven’t had experience with identifying the disease, Eversgerd recommends sending samples to a lab for the correct diagnosis.

“Make sure you know exactly what you’re dealing with because it is (an SDS) look-alike and until you really get your eyes calibrated and your mind calibrated to what it looks like, you’ll run yourself in circles trying to figure out what it is. A lab can really help with that,” Eversgerd said.

“One thing I have noticed is it can coexist with SDS. When I was first finding it, it was in areas that had a history of SDS. I’d get out and I could pull up 20 plants and see the typical blue mycelia from SDS and then all of a sudden you pull a plant up and see one with red perithecia all over the base of the stem and it’s red crown rot,” Bellm said.

“It’s a root rot, so the infection occurs at the root at the very lowest portion of the stem at about the time the soybean plant reaches R3. So, I typically don’t see symptoms much before the first of August down in this area.

“When you pull plants up, the bottom maybe one inch of the stem above the ground line and even below the ground line will have. It kind of progresses. As the perithecia form you’ll see small round bigger than a soybean cysts — round balls on the base of the plant. The perithecia is very obvious. Even before those form at the base of the plant will become a very bright red. If perithecia is there, it’s red crown rot.

“One thing I have seen in areas where they’re heavily infected is the plants lodge very quickly. This thing is a true root rot and you can literally pull a plant out of the soil with two fingers. They’ll break off just below the ground line and SDS doesn’t seem to do that quite as much.”