Scouting for Soybean Seed Diseases

Published: 11/07/2016

DOI: doi.org/10.31274/cpn-20190620-018

CPN-1001

Scouting for Common Soybean Seed Diseases

Soybean diseases affect seed quality that results in economic losses. Food grade or specialty soybeans require blemish-free seed coats and are at the highest risk of economic losses due to seed diseases. This publication describes signs and symptoms of soybean seed diseases that are observed in the late reproductive stages of soybean through harvest.

Healthy soybean seed (center) surrounded by seeds with various diseases

Seed Disease Management Strategies

Plant pathogen-free seed of resistant varieties in areas with a history of the disease.
Fungicide seed treatments may reduce seed to seedling transmission of fungal diseases; foliar fungicides may reduce seed infection by some fungi.
Tillage and crop rotation can reduce the amount of residue-born disease inoculum available to infect soybean.
Controlling bean leaf beetle, aphids, and other insect vectors will reduce virus infection and can reduce pod injury that could result in fungal infection.

Seedling diseases

Diaporthe seed decay (fungus: Diaporthe spp.)

Diaporthe (formerly Phomopsis) seed decay is characterized by cracked, shriveled seed with chalky mold present on the seed surface. Black fungal specks (pycnidia) may also be present on seed. Diaporthe seed decay can affect yield, grade, food quality, viability, and vigor of infected seed.

Diaporthe seed decay in the field

Diaporthe seed decay signs and symptoms

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

Infected stems and pods are discolored and white, cottony mold and black fungal bodies (sclerotia) are present. Infected pods can result in seed infection, and sclerotia can contaminate seed lots.

Soybean seeds with sclerotia and symptoms of Sclerotinia stem rot

Sclerotinia stem rot cottony growth and sclerotia in pod

Soybean viruses (bean pod mottle and soybean mosaic)

Infected seeds have brown to black streaks extending from the hilum. Virus symptoms on leaves are often confused with growth-regulator herbicide injury. Virus infected plants are scattered in the field or may be found along the edge where insect vectors enter the field. One way virusessurvive from season to season is in infected seed. The viruses are transmitted from plant to plant by insects such as bean leaf beetle and aphids.

Symptoms of bean pod mottle virus on soybean seed

Symptoms of soybean mosaic virus on soybean seed

Cercospora purple seed stain (fungus: Cercospora kikuchii)

The pathogen that causes purple seed stain also causes Cercospora leaf blight of soybean. Infected seed varies from pale to dark purple discoloration of the seed coat. In most cases, the seed embryo is not affected, but germination of infected seed may be reduced.

Soybean seed in pod showing symptoms of purple seed stain

Purple seed stain symptoms on soybean seeds

Downy mildew (oomycete: Peronospora manshurica)

The foliar phase of downy mildew results in pale yellow-green lesions on leaves in the upper canopy. Infected pods may not show symptoms, but the seed and inner pod will have a white crust that is made up of a mass of spores. Infected seed can be cracked and small and have reduced quality.

Downy mildew foliar symptoms

Downy mildew seed symptoms

Other seed diseases

Seed can be affected by several other fungi such as Alternaria, Macrophomina (charcoal rot), Penicillium, Fusarium, Colletotrichum (Anthracnose), and bacteria such as Pseudomonas (bacterial blight). These issues are often more problematic on previously damaged seed.

Penicillium-infected seed

Fusarium-infected seed

Acknowledgments

Authors

Albert Tenuta, Ontario Ministry of Agriculture; 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 Kiersten Wise, Purdue University.

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.

All photos were provided by and are the property of the authors except bean pod mottle and petri dishes with diseased seeds by Craig Grau, University of Wisconsin; downy mildew diseased seeds by X.B. Yang, Iowa State University; downy mildew leaf symptoms by Alison Robertson, Iowa State University, Penicillium and Fusarium diseased seedlings from Dennis McGee and Robert Nyvall, 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.

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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.

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