Red crown rot (RCR), caused by the soilborne fungus Calonectria ilicicola, is spreading across the United States and becoming an increasing threat to soybean crops. According to Carl Bradley, Plant Pathologist the University of Kentucky, RCR can cause defoliation, early plant maturity, and significant yield losses ranging from 15% to 70%. The fungus thrives in warm, wet conditions and typically infects soybean roots shortly after planting. The disease is particularly severe in a heavy soil type that contains at least 30% clay particles or in fields prone to flooding.
Like other soilborne diseases, such as sudden death syndrome (SDS) and brown stem rot, RCR often appears in patches within a field. Early foliar symptoms also may mimic these diseases, including chlorosis (yellowing) and necrosis (dying) of leaf tissue between leaf veins (Bechman, 2024).
Figure 1: Map of the reported incidence of RCR of Soybeans
Source: The Crop Protection Network
RCR Symptoms
- Red discoloration: The lower stem of the plant will appear red near the soil line.
- Perithecia: Bright, reddish-orange reproductive structures may be visible on the stem just above the soil line.
- Leaf symptoms: Yellow flecks will appear between the veins of the leaves, which can develop into interveinal chlorosis or necrosis.
- Rotted roots: The roots of the plant will be rotted, and the plant will be easy to pull up from the soil.
- Gray pith: If the stem is cut open, the central pith may appear gray.
RCR Management Strategies
- Seed treatment: Use a fungicide seed treatment labeled for red crown rot to help protect against early infections.
- Crop rotation: Rotate to a non-host crop for at least two years to help reduce the amount of the fungus in the soil. Avoid rotating to peanuts and alfalfa as they share a pathogen with RCR.
- Field drainage: Improve field drainage to help manage disease development.
- Weed control: Control weeds to help manage disease spread.
- Equipment cleaning: Clean equipment thoroughly when moving from an infected field to an uninfected one to prevent the spread of the fungus.
- Nematode control: Control the population of root-damaging nematodes to reduce the severity of infection.
From a seed treatment perspective, using a fungicide seed treatment that's labeled for red crown rot is an option. Talk to your local CHS account manager to understand what options are available in your market.
Controlling nematodes and limiting the infection vectors for RCR is also important. Trunemco® is a seed treatment for use on Soybeans that should be considered to protect the plant from 14 different parasitic nematodes, including soybean cyst nematodes. Trunemco works in combination with all the base level seed treatment combination of fungicides and insecticides. It activates natural enzymes in the soybean plant to provide a high level of protection as soon as the plant germinates. The biological mode of action in Trunemco colonizes around the newly established roots, providing nematode protection to the plant when nematodes cause the greatest plant damage, early in the life cycle of the plant. Along with this protection, Trunemco has been shown to increase plant vigor, helping plants stay one growth stage ahead, and allow for higher yields at the end of the season.
The season ahead offers an ideal opportunity to invest in a technology tool that can help increase your soybean yield potential. By incorporating Trunemco into your seed treatment program, you can protect your crops from multiple threats, improve plant health and increase profitability. Contact your local CHS account manager to explore how Trunemco can benefits your operation in 2025.
References
Bechman, T. J. (2024, Sept 5). How to identify red crown rot in soybeans. Retrieved from
https://www.farmprogress.com/soybean/how-to-identify-red-crown-rot-in-soybeans
