Pathologist: Red Crown Rot Spreading
Published: Friday, August 28, 2026
With a new disease threat emerging in Indiana soybean fields this year, a Purdue University Extension field crop pathologist is urging farmers to scout their fields and send in samples if they find it.
At the Pinney Purdue Ag Center in Wanatah, where Purdue's Darcy Telenko spoke last Wednesday, the research farm and surrounding areas are free of red crown rot. But she said soybean growers should be vigilant.
She held up a map of Illinois showing where the disease has been found so far this year. The map shows a high concentration of the disease in the central and southern parts of the state.
"I suspect we mimic Illinois," Talenko said. "We just haven't documented it. It's not going to move like tar spot moved—on the weather and spores. It's going to move on soil and debris. So, whenever we're moving soil around, it's going to move this pathogen."
Talenko said red crown rot can resemble SDS, or sudden death syndrome. Like SDS, red crown rot will cause the leaves to turn yellow.
To correctly identify it, growers need to pull back the canopy and look at the crown of the plant. If they see a red discoloration, that's a sure sign of red crown rot. She urged farmers to bag the roots and send the sample to her laboratory.
"I really want you to go out and look for it," she said.
The Indiana Soybean Alliance and the United Soybean Board are sponsoring this sampling effort. The root samples will assist Talenko in determining the distribution of red crown rot and guide future research.
Talenko said a grower in Rush County had red crown rot. His soybean yield dropped from 80 bushels per acre in 2018 to 49 bushels per acre last year. He has since rotated those fields to corn.
According to the Purdue plant pathologist, the good news is that growers can plant varieties that are partially resistant. Seed treatment is another tool to fight red crown rot.
"We just need to make sure we're targeting the right pathogen, SDS versus red crown rot," she said.
Talenko was asked if red crown rot can be spread by combine residue.
"That's the question we're looking at," she said.
She is also looking at the effect tillage and tiling equipment might have on the disease's spread.
Because red crown rot is a soil-borne pathogen, it attacks the roots. Foliar symptoms are similar to SDS or brown stem rot, so the only way to identify red crown rot is by looking just above the soil line, where the crown is located.
"It's very, very red," she said.
When the stem is split open, the central pith may appear gray to brown, the roots are often rotted, and affected plants are easily pulled from the soil due to root deterioration.
With SDS, only the vascular tissue is affected, she said. Eventually, the leaves will drop to the ground. SDS tends to occur in cool, moist soils, whereas red crown rot thrives in hot soils. In some cases, red crown rot has been spotted along tile lines and other places where water has collected.
"It does follow the water," she said.
Another important point: red crown rot can survive in the soil for multiple years.
"If you had it two years ago, it's going to be in the beans next year," she said.
As for tar spot, Talenko said Indiana isn't seeing a large outbreak this year. The growing season began with high-risk conditions in April and May, but hot weather in June reduced the risk of tar spot in corn.
"It really hasn't blown up," she said. "The disease that blew up in my plots was gray leaf spot."
Untreated sections in her research plot had significant gray leaf spot infections, especially in the lower canopy.
"I would say gray leaf spot is the foliar disease that's most active here in Indiana," she said. "And I've heard reports of northern corn leaf blight in pockets, too. Tar spot really didn't happen. It's here, but it's in pockets."
For those who want to spray for tar spot, Talenko recommends a single fungicide application between the VT and R3 stages. However, she said growers won't have a good return on investment if tar spot infection exceeds 5% or more of the ear leaf.
Also speaking at the Pinney Purdue field day were Dan Quinn and Shaun Casteel, Purdue specialists for corn and soybeans, respectively.
Under Quinn's supervision, Purdue conducts between 10 and 15 trials every year at the Pinney Purdue research farm. One of those trials examines nitrogen (N) stabilizers and how nitrogen is managed in corn. The three-year trial involves three locations with pre-plant applications, split applications and single side-dress applications.
"What is unique about this trial is we're pretty much tracking every way you can lose nitrogen and seeing how the stabilizers perform," Quinn said. "So, we're looking at ammonia losses, we're looking at N2O losses, we're looking at leachate and water samples, we're looking at soil samples down to 2 feet and different increments. Those are the big ones. We're looking at N uptake in the plants. We're going to look at yield, obviously. Grain nitrogen. Plant nitrogen. Kind of the whole system."
Nitrogen is expensive, Quinn said, and the challenge is that it can be lost.
"And a lot of it is environmentally dictated," he said.
Nitrogen can be lost through leaching, volatilization and denitrification. Stabilizer products target these three factors, each with different active ingredients. Products include nitrification inhibitors, urease inhibitors and combination products.
"Pay attention to the active ingredients and pay attention to what they target," he said.
Quinn pointed out that nitrogen inhibitors aren't perfect. They don't work every year in every field. After application, they remain effective for about 10 to 14 days on average. Quinn said they can provide "small windows of protection."
"Stabilizers work when you have N-loss conditions," he said. "When you give them a reason to work, they work."
When used in the right situation, nitrogen stabilizers can make a big difference, according to Quinn. At Pinney Purdue, a stabilizer product was side-dressed just before a heavy rain event. The result was a 17-bushel response.
"That's been the more surprising piece that I've seen over the last few years working on this," he said. "We often look at stabilizers, typically, for fall application or early spring applications. The last few years when we've done these trials, it's been pretty dry. We haven't seen a lot of response. I'll be curious this year, because we had similar type of treatments. We had side-dress in June, and then in June we got smoked with rainfall. Then we saw that response to those nitrification inhibitors."
Quinn was asked a more general question about this summer's heavy rainfall and what impact that will have on the corn crop.
"That's the million-dollar question," he said. "I do think in the areas where they had 12 to 15 inches of rain, it's not good. I've found that when you have waterlogging or flooding, like R3 or R4, if that goes longer than about five or six days, that is when we start seeing the yield go down—specifically grain fill."
He is also concerned about root rots, stalk rots, ear rots and mold issues.
For soybeans, Casteel shared the latest research about residue management, early planting and row spacing.
Studies have shown that early planted soybeans yield better. Residue management, especially after corn, can impact the emergence of newly planted soybeans.
"We want to have good soil moisture, good soil temperatures during our planting season so the beans can get up out of the ground," Casteel said.
Farmers can manage residue in various ways, but reducing the size of the corn residue as it moves through the combine is the goal. Tillage is an option, but Casteel said that could delay planting in the spring.
Most soybeans are planted with no-till drills, but emergence usually takes about a week longer compared to strip till. Heavy residue keeps the soil from warming up as quickly, Casteel said, and cooler soils prevent mineralization.
"Temperature is a good part of this," he said, "because you've got the residue until that day of planting. You move it (the planter) across. You think about the strip till. It's already got the berm. It's already had time to warm up. So, the question is, does that seven-day delay cause a difference in yield? Usually, we're about four bushels off."
Casteel said residue management begins this fall.
"I bring this up especially as we go into harvest," he said, "to set our combines. It has a huge effect on what the following crop is going to do."
Looking at row spacing, the sooner the soybean plant reaches full canopy, the better. Casteel shared information showing that soybeans planted on 15-inch rows will develop more pods and close the canopy sooner compared to 30-inch rows.
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