Last week, signs and symptoms of red crown rot of soybean were observed in a few fields in Graves County, Kentucky by a local agronomist (Clint Gregory with Hutson Ag) who contacted the University of Kentucky. Samples were collected from the fields and submitted to the Plant Disease Diagnostic Laboratory, which confirmed red crown rot, caused by the fungus Calonectria ilicicola.
This is the first time this disease has been observed in Kentucky. Red crown rot has been present in states to the south of Kentucky (such as Louisiana and Mississippi) for several years. In 2018, the disease was observed for the first time in Kentucky’s neighboring state, Illinois.
The red crown rot fungus can survive in the soil for several years as structures known as microsclerotia. The fungus will infect soybean roots, causing root rot and dark-reddish discoloration of the area of the stem just above the soil line. Red-colored reproductive structures and white hyphae of the fungus may develop on the lower stem and root area. The fungus also produces a toxin that can accumulate in the leaves, causing interveinal chlorosis (yellowing of leaf tissue with main veins remaining green) and interveinal necrosis (dead leaf tissue between green veins).
These symptoms could be confused with those caused by other diseases that occur in Kentucky, such as sudden death syndrome and southern stem canker. Red crown rot generally appears in patches in the field as groups of affected plants.
Management of red crown rot in states south of Kentucky is done through rotating to non-host crops, planting less-susceptible varieties, and delaying planting in fields known to be infested with the red crown rot fungus.
Research will need to be conducted to determine the best practices for management of this disease here in Kentucky. Currently, the distribution of red crown rot in Kentucky is only known to be in a small area of Graves County, but could be in other areas.
If red crown rot is suspected, it is important to contact your local county UK Extension office to submit symptomatic samples to the UK Plant Disease Diagnostic Laboratory for confirmation.