Red crown rot (RCR) is a soybean disease caused by the soilborne fungus Calonectria ilicicola that is spreading to parts of the Midwest. There have been no confirmed reports of RCR in Ohio, but it has been detected in Kentucky and Illinois. Soybean growers should stay vigilant when scouting fields as RCR can be easily confused with other soybean diseases that cause similar foliar symptoms.
RCR can be misidentified as sudden death syndrome (SDS) or brown stem rot (BSR) as all three diseases can cause yellowing between the leaf veins or interveinal leaf chlorosis (Figure 1). Proper diagnosis will require digging up the plant, scraping the soil off, and inspecting for red discoloration on the outer stem (Figure 2). Also look for small, brick red perithecia (fungal sexual structure) on the lower stem or root crown area. These perithecia will be smaller than the tip of a pencil and more likely to be observed following wet weather.
In general, concentrate scouting efforts for RCR in low-lying, saturated areas of the field between the R3 (beginning pod) and R5 (beginning seed) growth stages. Keep an eye out for scattered patches of plants dying off early.
Ohio producers who suspect they may have RCR should contact their county extension office and submit samples for diagnosis at the Soybean Pathology and Nematology Laboratory in Columbus. To submit samples, dig out 3-5 symptomatic plants including the roots, place them in a plastic bag, and submit to the following address:
OSU Soybean Pathology and Nematology Lab
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
lopez-nicora.1@osu.edu