CPN 1001 — 2015
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 scouting card describes signs and symptoms of soybean seed diseases that are observed in the late reproductive stages of soybean through harvest.
Phomopsis seed decay is characterized by cracked, shrivelled seed with chalky mold present on the seed surface. Black fungal specks (pycnidia) may also be present on seed. Phomopsis seed decay can affect yield, grade, food quality, viability, and vigor of infected seed.
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.
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 viruses
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.
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.
Seed can be affected by several other fungi such as Alternaria , Macrophomina (charcoal rot), Penicillium (right image), Fusarium (left image), Colletotrichum (Anthracnose), and bacteria such as Pseudomonas (bacterial blight). These issues are often more problematic on previously damaged seed.
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 and Adam Sisson, Iowa State University; Damon Smith, University of Wisconsin; Kiersten Wise, Purdue University
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; 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
The Soybean Disease Management series is a multi-state collaboration sponsored by the North Central Soybean Research Program (NCSRP). This project was funded in part through Growing Forward 2 (GF2), a federal-provincial territorial initiative. The Agricultural Adaption Council assists in the delivery of GF2 in Ontario. Contributors to this series come from land-grant universities in the North Central states and Canada.
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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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