Prior to 2017, soybean red crown rot was not something Midwest farmers worried about. However, in the years since, the soil-borne disease has spread across Illinois and into Kentucky. Fields with low-lying and poorly drained areas are most susceptible, as are areas with warm soil temperatures – especially between 77°F and 86°F.
Red crown rot is often detected after the R3 stage with the appearance of yellowing on the leaves. However, root and stem rot can occur without producing any foliar symptoms. Severely affected plants will deteriorate, or senesce, prematurely, with the leaves staying attached to the plant. Another key distinguishing characteristic is the presence of perithecia, or tiny red balls, on the crown and roots just below the soil line.
“Late in the season you’ll find root rot on your soybeans,” said Matt Montgomery, Pioneer Field Agronomist. “It’s identified by red cankers that turn into red fruiting structures. Not too long after the rot takes hold, the plants tend to die away.”
In southern states, such as Louisiana and Mississippi, where red crown rot has been well established, yield losses of up to 30% have been documented. Red crown rot typically only affects patches within a field, but severely infected areas can be significantly impacted.
“Just last year in Illinois we had examples of 60-to-70-bushel fields historically that dropped down to 16 bushels due to red crown rot infestation,” Montgomery said.
Unfortunately for growers, management options for red crown rot are limited. No rescue treatments are available to mitigate plant damage and yield impact once infection has been detected.
Delayed spring planting can help reduce the severity of infections. Additionally, crop rotation out of soybean for at least two years can reduce disease-causing inoculum. Farmers may also want to manage pathogenic nematodes, which damage roots and create access points for soil-borne pathogens like red crown rot.
Lastly, improving drainage in areas where pooling is problematic and avoiding excessive organic matter in soils can help reduce red crown rot issues.