Soybean root and stem diseases are common across Minnesota where they kill and stunt plants and result in yield losses. This proposal is directed at Rhizoctonia root and stem rot and brown stem rot (BSR), two important and widespread diseases in Minnesota. The research goals are to identify and evaluate best management strategies for these diseases in Minnesota using replicated studies in the field and greenhouse, with a focus on seed treatment fungicides and resistant varieties. The final goal is to conduct diagnostic and extension education activities that address important and unusual soybean disease problems in Minnesota. The ultimate benefit to soybean growers will be increased yields and reduced risk of replanting and lost yields due to root and stem diseases.

1. Identify and refine management tactics for Rhizoctonia root and stem rot of soybean.
2. Improve strategies to manage brown stem rot of soybean.
3. Address special diagnostic needs and provide focused education on important diseases.

• Identify which seed treatments are effective for managing Rhizoctonia root rot.
• Determine the potential value of seed treatment fungicides for management of BSR.
• Identify resistance to both common types of the BSR pathogen in a selection of soybean breeding lines and varieties.
• Determine if new methods to evaluate soybean for resistance to BSR are more consistent and have higher throughput than current methods.
• Conduct specialized disease diagnosis for unusual soybean disease problems from Minnesota production fields.
• Develop and extend updated information on the management, distribution, and risks of key soybean stem and root diseases for Minnesota soybean growers.

Updated September 23, 2025:
Minnesota Soybean Research and Promotion Council
Research Action Team Project for FY26

Project update August 31, 2025

Project Title: Developing Answers for Managing Soybean Root and Stem Diseases
Project year: 2025-2026

Principal Investigator: Dean Malvick, University of Minnesota, dmalvick@umn.edu

Project Summary: This proposal addresses the priority area of Soybean Pest Management. It focuses on research into managing against yield and quality-limiting effects of root and stem rots in Minnesota. Soybean root and stem diseases are common across Minnesota where they result in stand and yield losses. This proposal is directed at Rhizoctonia root and stem rot and brown stem rot (BSR), two important and widespread diseases in Minnesota. The research goals are to identify and evaluate best management strategies for these diseases in Minnesota using studies in the field and greenhouse. The final goal is to conduct diagnostic and extension education activities that address important and unusual soybean disease problems in Minnesota. The ultimate benefit to soybean growers will be increased yields and reduced risk of lost yields due to these diseases.

Project Goals
1. Identify and refine management tactics for Rhizoctonia root and stem rot of soybean.
2. Improve strategies to manage brown stem rot of soybean.
3. Address special diagnostic needs and provide focused education on important diseases.

Project Updates for Period May to August 2025

Goal 1. Improve management of Rhizoctonia root and stem rot of soybean.
Background: Rhizoctonia root rot is frequently a serious early to mid-season soybean disease in Minnesota, especially in central and Northwestern regions.

Objective A. Determine efficacy of seed treatments for managing Rhizoctonia root of soybean. Soybean seed treated with different seed treatment fungicides are being evaluated for efficacy against Rhizoctonia root rot in inoculated and replicated field studies at a field location in Waseca, MN. The study was planted in mid-May 2025 as planned. Rhizoctonia root and stem rot developed to high levels in the study and resulted in stand loss. We have been measuring the effects of the treatments on plant population, and results suggest significant differences in plant populations based on treatment effects. Seed yield will be determined in October when the plants are ready for harvest.
Objective B. Determine if selected soybean varieties and breeding lines vary in susceptibility to Rhizoctonia root rot in replicated field studies. We planted a set of selected soybean varieties into inoculated and noninoculated plots at a field location in Waseca, MN. Disease developed to high levels in this study and resulted in significant stand loss. We will measure yield in October to determine if varieties vary in susceptibility and yield in the presence of Rhizoctonia root rot.

Goal 2. Improve management of brown stem rot of soybean.
Background. Brown stem rot (BSR) is a common and damaging soybean disease across Minnesota. BSR can be suppressed with crop rotation and resistant varieties however, neither method completely manages this disease. Given that BSR is a continuing problem for soybean production in Minnesota, more information is needed to understand and prioritize disease management options.

Objective A. Determine if seed treatments are effective for managing BSR. Soybean seed treatments containing a variety of fungicidal active ingredients were applied to soybean seed prior to planting. It was unknown if those fungicides can suppress development of BSR or growth of the BSR pathogen. Lab. experiments have been completed to determine if a range of different fungicides are effective in reducing growth of BSR and results are being summarized and analyzed.
Objective B. Evaluate soybean breeding lines and varieties for resistance to BSR. Advanced breeding lines from the U of MN soybean-breeding program, as well as selected commercial soybean varieties, will be evaluated in the greenhouse this winter for resistance to the A and B types of BSR in greenhouse studies. This work will be conducted in cooperation with Dr. Aaron Lorenz. Plants at the VC/V1 growth in the greenhouse stage will be inoculated in replicated studies with the BSR pathogen. We have also conducted more work to evaluate different methods to screen for resistance with the goal of validating a method that is simple, consistent, and has higher throughput for breeding and research.

Goal 3. Conduct diagnostic extension education activities that address important and unusual soybean disease problems in Minnesota.
Background: Each year there are unusual soybean disease outbreaks in fields across Minnesota that we are called upon to assist with, usually via specialized diagnosis and testing efforts that lead to discussion of disease management responses.

Objective: Perform specialized diagnosis and assist with identifying and responding to unusual soybean disease problems in Minnesota. Although a variety of different soybean disease samples have been received, the focus on this work has turned to the disease red crown rot. We have preliminarily confirmed red crown rot on soybean in Minnesota for the first time, and we are continuing the work to provide final confirmation that the disease is red crown rot. Red crown rot has been spreading in the Midwest in recent years, but we did not expect it to develop and be found in Minnesota this year.

The ultimate benefit to soybean growers will be increased yields and reduced risk of lost yields due to root and stem diseases. This proposed project will address the need for improved understanding and management of key soybean root and stem diseases that reduce soybean yields across Minnesota. Enhanced understanding of how to manage and reduce the risk of them should result in increased soybean yields. Results will be transferred through newsletters, production meetings and field days, scientific meetings, and news outlets.