Illinois Soybeans See Rising Threat From Red Crown Rot Disease

Emerging in the Midwest as recently as 2018, the footprint of red crown rot of soybeans is expanding in Illinois, according to an agronomist. 

Besides Illinois, the disease has only been confirmed in a few more states. Neighboring Indiana, Kentucky, and Missouri have all reported positive cases. Beyond that, Louisiana and Delaware have reported cases of the disease, and Ohio is reporting it for the first time this season.

Positive Cases in Illinois

Of all top corn-growing states, red crown rot has had the largest impact on Illinois historically. The Crop Protection Network’s cumulative case map shows 34 counties have reported the disease in soybeans to date. Here’s an interactive map of where red crown rot has been reported in Illinois.

Syngenta Agronomist Phil Krieg, whose territory includes southern Illinois, shared that although the disease has been expected, it’s making a bigger mark this season.

“Red crown rot is showing up right on schedule where it is a problem,” Krieg said. “Overall, the footprint of red crown rot is expanding throughout the area — not an epidemic, but more is being found.”

What Farmers Should Do

While red crown rot cannot be diagnosed from the road alone, Matt Montgomery, agronomy education lead with Beck’s Hybrids, says there are signs that should make a farmer take a closer look. Sudden death syndrome (SDS) often wipes out soybeans in a sharp, uniform pattern, similar to a “lightning strike,” he said. 

“In contrast, with red crown rot, at least initially, you have this mishmash of yellow, brown, green all rolled together. Just dead plants next to live ones next to yellow ones.” That irregular mix of plant health should prompt growers to stop the truck, walk into the field, and investigate the lower stem for confirmation, Montgomery explained. 

To diagnose RCR in comparison to SDS or brown stem rot (BSR), farmers should stop and check the lower stem. “Look for red discoloration and, most importantly, the little red fruiting structures (parathecia) about an inch above and below the soil line,” Montogomery said, noting that these are easiest to spot in mid-August. Sending samples to a plant clinic is recommended for confirmation.

Management tools are still limited, and nothing can be done this growing season. “Saltro is the best seed treatment product currently on the market for RCR management, but in the face of intense pressure, it’s still not enough,” Montgomery said. 

Weed control is also important because the pathogen has many alternate host species. Because the fungus produces hardy survival structures (sclerotia), Montogomery cautions that once the disease is present, it is likely to remain in the soil indefinitely. This means rotation away from soybeans may slow symptom buildup but is unlikely to eliminate the pathogen.

Montgomery emphasized reducing stress-on-stress with sound agronomy and planning fieldwork carefully. “If you think you’ve got a field that’s got RCR, let’s work that piece of ground last,” he advised, to reduce the chance of spreading contaminated soil.

Illinois Weather

Besides the impact of diseases like red crown rot on Illinois soybeans, weather stress is taking a toll. Krieg ranked it as a top concern in his area: “Overall soybeans look good, finally, but dry and hot weather is taking yield away every day.” 

According to the latest U.S. Drought Monitor report, 4% of the state is in moderate and 22% is abnormally dry.

Illinois Crop Progress and Condition

The USDA released its latest Crop Progress report earlier this week. In Illinois, 94% of the soybean crop had reached the blooming stage by Aug. 17, behind both the five-year average and progress a year ago by 2 percentage points.

By the same date, 87% of the crop had reached the setting pods stage, which is ahead of the five-year average by 4 percentage points. Progress a year ago had reached 88%.

Illinois soybeans were rated 17% excellent, 43% good, 27% fair, 9% poor, and 4% very poor by USDA.

That’s worse than the national average: 15% excellent, 53% good, 24% fair, 6% poor, and 2% very poor.