Seed Treatments: Questions that Emerge When Plants Don’t

***Updated in 2025, this version replaces the previous 2016 Seed Treatments: Questions that Emerge When Plants Don't publication.***

Poor soybean stand establishment is frustrating, especially considering all the time and money spent on seed, planting, and maintaining fields. This is particularly true when farmers have also invested in seed treatments designed to prevent crop loss due to seedling diseases. However, every product has limitations and may not always work as intended. Conversely, a user may expect a product to work in a manner it was not designed for. In this publication, we answer some common questions that emerge when soybean plants do not.

Is disease actually causing poor stand establishment?

Stand establishment issues can be caused by many factors besides seedling diseases, including soil conditions (compaction, crusting, sidewall compaction, crop residue level), environmental issues (flooding, cold/heat stress, drought), planting issues (seed placement error, planter malfunction), insect injury, poor seed quality, etc. Making the proper diagnosis is the first step toward determining if seedling diseases are to blame for poor stand establishment. If seedling disease is the major cause of a problem, it is important to determine the causal pathogen and disease. As noted below, seed treatment and management practices can vary and depend on the diseases present. See Resources at the end of this document for information on seedling disease identification.

If a seedling disease is to blame, could the choice of seed treatment be the problem?

Choosing the proper seed treatment is important since certain fungicide active ingredients work against specific pathogens. For instance, metalaxyl and mefenoxam have activity against seedling blights caused by the Pythium and Phytophthora pathogens, but do not have efficacy against Fusarium and Rhizoctonia pathogens. Additionally, although most seed treatment packages have efficacy against these major pathogen groups, fungicide efficacy can vary for a given species within a pathogen group. See Resources at the end of this document for information on fungicide efficacy.

If the fungicide has activity against the causal pathogen, could the fungicide rate be incorrect?

Possibly. In certain fields with a history of soybean seedling blights such as Phytophthora root rot, higher rates of metalaxyl or mefenoxam may be required.

If a seedling disease is to blame, and the fungicide rate was correct, is fungicide resistance the issue?

Fungicide resistance is one of the factors that may come to mind when a fungicide fails to manage disease. Although possible, treatment failure due to fungicide resistance is not a common problem in seed treatments, and additional issues may be at play. Misapplication of the seed treatment, a low or reduced rate of the treatment, lack of combining other management strategies with the seed treatment, variety susceptibility, and environmental interactions all play a role in the success of using seed treatments to manage seedling blights and improve stand establishment. The only way to determine fungicide resistance is to have the causal pathogens isolated and examined in a laboratory. Although there are examples of pathogen resistance to fungicides used in seed treatments, these occurrences are generally rare and localized. The development of fungicide resistance is complex and influenced by fungicide's mode of action, pathogen biology, and other factors. 

Can the environment magnify disease issues?

Field environment conditions can have a significant impact on fungicide seed treatment efficacy. If the targeted planting date is early or conditions are cool and wet, seed treatments may not be enough to protect against certain pathogens, especially if emergence is slow/delayed. Additionally, seed treatments generally only protect seeds and seedlings for approximately 3 weeks after planting, depending on the product and the pathogen. If environmental conditions conducive to disease do not occur until after the initial 3-week time period on a susceptible variety, a farmer may see disease and think the seed treatment failed. It is always good to remember that seed treatments have a limited period of activity after planting.

What else can be done in combination with seed treatments to manage seedling diseases?

Fields with a severe history of seedling diseases may need to combine seed treatments with other management tactics, including improving drainage, longer crop rotation, reducing compaction, and avoiding planting before heavy rains or into cold soils. No single strategy will completely manage a particular seedling disease. Therefore, farmers are encouraged to incorporate an integrated approach to managing seedling diseases. For example, by combining tile drainage, genetic resistance, AND seed treatments, a farmer may observe better seedling diseases management and improved stand establishment compared to using seed treatments alone.

Resources

• Fungicide Efficacy for Control of Soybean Seedling Diseases

• An Overview of Soybean Seedling Diseases

• Scouting for Soybean Seedling Diseases

• Factors to Consider Before Using a Soybean Seed Treatment

• How Seed-Applied Nematicides Work

• Scouting for Soybean Seed Diseases

Acknowledgments

Authors

Kiersten Wise, University of Kentucky; Daren Mueller, Iowa State University; Carl Bradley, University of Kentucky; Martin Chilvers, Michigan State University; Horacio Lopez-Nicora, The Ohio State University; Dylan Mangel, University of Nebraska-Lincoln; Adam Sisson, Iowa State University; Damon Smith, University of Wisconsin-Madison; and Albert Tenuta, Ontario Ministry of Agriculture, Food and Agribusiness.

Reviewers

Tom Allen, Mississippi State University; Mandy Bish, University of Missouri; Maira Duffeck, Oklahoma State University; Travis Faske, University of Arkansas; David Langston, Virginia Tech; Dean Malvick, University of Minnesota; Madalyn Shires, South Dakota State University; Edward Sikora, Auburn University; Darcy Telenko, Purdue University; and Richard Wade Webster, North Dakota State University.

Sponsors

The authors thank The United Soybean Board, Grain Farmers of Ontario, and United States Department of Agriculture - National Institute of Food and Agriculture for their support.