Scouting for Soybean Stem Diseases

Published: 05/31/2016

DOI: doi.org/10.31274/cpn-20190620-020

CPN-1002

The most effective management of soybean stem diseases starts with proper identification. Symptoms of soybean stem diseases typically appear in the mid to late reproductive stages of soybean.

Figure 1. Symptom key for stem diseases without external stem symptoms or signs

Figure 2. Symptom key for stem diseases with external stem symptoms or signs

Soybean stem diseases

Anthracnose stem blight (fungus: Colletotrichum truncatum)

Stems and petioles with red to brown irregular shaped blotches in early soybean reproductive growth stages and black fungal bodies near soybean maturity. Leaf symptoms include reddish veins and rolling. Infected petioles cause leaves to twist down into a Shepherd’s crook and can result in early defoliation.

Figure 3. Anthracnose stem blight stem symptoms

Figure 4. Anthracnose stem blight can cause shepherd's crooking of soybean foliage

Brown stem rot (fungus: Phialophora gregata)

Stems will have reddish-brown discoloration in the pith (center of stem), which may only be found at nodes. Although it appears healthy in most cases, the stem exterior of severely infected plants will look olive green and shiny. Leaf symptoms include interveinal chlorosis and necrosis of youngest leaves, symptoms may not occur on all plants. Root rot is typically not evident in plants with brown stem rot, unlike roots with sudden death syndrome.

Figure 5. Brown stem rot can cause pith discoloration at nodes

Figure 6. Brown stem rot foliar symptoms

Charcoal rot (fungus: Macrophomina phaseolina)

The lower stem and taproot appear light gray or silver and small, dark microsclerotia can be present. The interior of stems and taproot will be discolored with microsclerotia. Leaves yellow and die but remain attached to the plant.

Figure 7. Characteristic signs of charcoal rot include microsclerotia in the stem

Figure 8. Microsclerotia indicative of M. phaseolina infection

Fusarium wilt (fungus: Fusarium spp.)

The inside of the stem and roots will have brown vascular tissue. Upper leaves wilt and lower canopy leaves drop early. Roots are stunted with purplish-brown to black discoloration. If plant roots are incubated, there will be no purple/blue spore masses, unlike roots with sudden death syndrome.

Figure 9. Fusarium wilt stem symptoms

Figure 10. Fusarium wilt symptoms in the field

Phytophthora root and stem rot (oomycete: Phytophthora sojae)

A dark brown lesion beginning at the taproot and extending up several nodes on the stem can be observed. This lesion surrounds the entire stem. Brown internal stem discoloration can be observed on plants at any stage. Roots are discolored and leaves yellow and wilt but remain attached to the plant.

Figure 11. Phytophthora stem rot symptoms on soybean stem

Figure 12. Stem discoloration symptomatic of Phytophthora root and stem rot

Pod and stem blight (fungus: Diaporthe phaseolorum var. sojae)

Black, raised specks (pycnidia) in linear rows can be seen on mature soybean stems. Pycnidia can also be seen on petioles and pods.

Figure 13. Pod and stem blight pycnidia on soybean stem

Figure 14. Pod and stem blight pycnidia on soybean stem

Sclerotinia stem rot (white mold; fungus: Sclerotinia sclerotiorum) 

White, cottony mold can be seen on the lower stem and black, hard sclerotia may be present. These sclerotia can also be embedded inside the stem. Leaves wilt and turn grayish green between veins but remain attached to the plant.

Figure 15. Soybean stem with Sclerotinia stem rot

Figure 16. Soybean stems with fuzzy white growth and sclerotia

Sudden death syndrome (fungus: Fusarium virguliforme)

The stem interior shows brown or gray discoloration below the outer layer but pith is white (unlike brown stem rot). Leaves show interveinal chlorosis and necrosis and drop from the plant after they die. Root discoloration and rotting, along with internal browning of the taproot, can be observed.

Figure 17. Interior stem discoloration from sudden death syndrome

Figure 18. Sudden death syndrome foliar symptoms

Stem canker (fungus: Diaporthe caulivora, D. aspalathi)

A dark, red-brown canker forms at a node and can extend over several nodes. Lesions often do not entirely surround the stem. Inside the stem, there is discoloration or browning near the lesion. Leaves will have interveinal chlorosis and necrosis and remain attached to the plant.

Figure 19. Early stem canker symptoms on soybean stem

Figure 20. Stem lesions symptomatic of stem canker

Acknowledgments

Authors

Kiersten Wise, Purdue University; Carl Bradley, University of Illinois; Martin Chilvers, Michigan State University; Loren Giesler, University of Nebraska-Lincoln; Febina Mathew, South Dakota State University; Daren Mueller, Iowa State University; Adam Sisson, Iowa State University; Damon Smith, University of Wisconsin; and Albert Tenuta, Ontario Ministry of Agriculture.

Reviewers

Emmanuel Byamukama, South Dakota State University; Anne Dorrance, The Ohio State University; Doug Jardine, Kansas State University; Dean Malvick, University of Minnesota; Samuel Markell, North Dakota State University; and Laura Sweets, University of Missouri. 

Photographs

All photos were provided by and are the property of the authors except brown stem rot split stem by X.B. Yang, Iowa State University; brown stem rot foliar symptoms, stem canker images, and Sclerotinia stem rot images by Craig Grau, University of Wisconsin; charcoal rot left image and pod and stem blight right image by Alison Robertson, Iowa State University; charcoal rot right image by Tristan Mueller, Iowa Soybean Association; Fusarium wilt aboveground symptoms by John Kennicker, Iowa State University; and sudden death syndrome left image by Gary Munkvold, Iowa State University

Sponsors

The Soybean Disease Management series is a multi-state collaboration sponsored by the North Central Soybean Research Program (NCSRP) through the Soybean Checkoff. This project was funded in part through Growing Forward 2 (GF2), a federal-provincial territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario. The authors thank the United States Department of Agriculture - National Institute of Food and Agriculture and the Grain Farmers of Ontario for their support. Contributors to this series come from land-grant universities in the North Central states and Canada. 

This information is provided only as a guide, and the authors assume no liability for practices implemented based on this information.

Click the link below to download this publication.

Scouting for Soybean Stem Diseases [PDF]


This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/ private professionals that provides unbiased, research-based information to farmers and agricultural personnel. This information in this publication is only a guide, and the authors assume no liability for practices implemented based on this information. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer.

In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident.

Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, American Sign Language, etc.) should contact the responsible Agency or USDA's TARGET Center at (202) 720-2600 (voice and TTY) or contact USDA through the Federal Relay Service at (800) 877-8339. Additionally, program information may be made available in languages other than English.

To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at How to File a Program Discrimination Complaint and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information requested in the form. To request a copy of the complaint form, call (866) 632-9992. Submit your completed form or letter to USDA by: (1) mail: U.S. Department of Agriculture, Office of the Assistant Secretary for Civil Rights, 1400 Independence Avenue, SW, Washington, D.C. 20250-9410; (2) fax: (202) 690-7442; or (3) email: program.intake@usda.gov.

USDA is an equal opportunity provider, employer, and lender.

©2024 by the Crop Protection Network. All rights reserved.

We are extension logo

Related Resources

An Overview of White Mold

An Overview of Stem Canker

An Overview of Pod and Stem Blight and Diaporthe Seed Decay

Scouting for Soybean Stem Diseases

Soybean Stem Zone Lines: Fact and Fiction