Report on Red Crown Rot in Missouri Soybeans

The agricultural community in northeastern Missouri is facing a new challenge as Mandy Bish, a state plant pathologist with the University of Missouri Extension, has confirmed the first incidence of red crown rot in Marion County’s soybean fields. This is the first time the disease has been reported in the state, following its earlier identification in Illinois in 2018.

Impact on Soybean Yields

Red crown rot is a serious soybean disease that can significantly affect crop yields, particularly when conditions are favorable for the disease. In the affected areas, yield losses can range from a moderate 15% to a devastating 70%, depending on the extent of the infection and field conditions. The disease tends to be more severe in fields with high moisture levels and warm temperatures, which are ideal for the fungus to thrive.

• The disease causes sudden death syndrome-like symptoms, where yellow spots appear on the upper canopy leaves, which then progress into larger yellow and brown spots that spread between the leaf veins.
• As the disease advances, infected plants may exhibit wilting, and ultimately, plant death occurs.
• The most distinct symptom is the reddish discoloration at the base of the stem and root near the soil line. In addition, white fungal growth (mycelia) and red spheres (perithecia), which are reproductive structures of the fungus, may be visible on the roots.

Strategies for Management and Prevention

Managing red crown rot in soybeans is challenging, especially since no commercial soybean varieties are resistant to it. The management strategy focuses on preventing the spread of the disease and reducing the fungal population in the soil:

• Crop rotation: Rotating soybeans with non-host crops such as corn for at least two years can significantly reduce the presence of the pathogen in the soil.
• Minimizing the movement of soil and plant debris by machinery between fields can prevent the spread of the fungus.
• Fungicide seed treatments: Although over-the-top fungicide applications are ineffective because the fungus resides in the soil, fungicide seed treatments labeled for red crown rot can protect young plants during critical early development stages.

Local Response and Farmer Adaptations

Local farmers like Zach Burch from Palmyra are on high alert due to the recent disease confirmation. They are actively participating in educational events such as the Marion County Ag Update to learn more about this and other emerging threats like tar spot. “Every time we think we’ve got it figured out, there’s a new disease,” Burch remarked, highlighting the ongoing challenge of managing crop health.

Agronomists like Rusty Lee are advising on cost-saving measures that also benefit crop health. For instance, applying nitrogen to pastures now can improve winter feed availability and reduce costs. This proactive approach not only saves money but also supports better pasture management, which can indirectly help manage soilborne diseases by improving overall plant health.

Diagnostic Efforts and Support

The University of Missouri Plant Diagnostic Clinic plays a crucial role in helping farmers identify and manage plant diseases. This year, the clinic has reported an increase in the number of samples submitted for disease diagnosis, particularly for soybeans and corn. This uptick in diagnostic activity is a positive sign that farmers are taking an active role in monitoring and managing crop health.

Farmers are encouraged to send both digital and physical samples for analysis. The clinic provides detailed guidelines for sample submissions on their website, ensuring that diagnoses are accurate and helpful.

Looking Ahead

As red crown rot continues to pose a threat to soybean production in Missouri, ongoing vigilance and adherence to recommended management practices will be key. The agricultural community is encouraged to stay informed, share knowledge, and adopt integrated pest management strategies to mitigate the impact of this and other crop diseases.

For more information or to submit a sample, contact the University of Missouri Plant Diagnostic Clinic:

• Email: plantclinic@missouri.edu
• Phone: 573-882-3019
• Twitter: MUplantclinic