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Disease risks associated with cool soil temperatures.

Field soils are anything but sterile environments and there are many organisms that have the potential to help or harm our crops and the many microbial and chemical processes on which they rely.  Oomycetes are a group of plant pathogens that have some fungus-like and some algae-like characteristics. Oomycetes produce swimming spores called zoospores and oomycete growth and the production and release of zoospores is favored by free water and either warm or cool soil conditions.  Disease caused by the Pythium species of oomycete pathogens are favored by cool wet soil conditions (Figure).  Symptoms caused by Pythium infection can include rotted seeds or roots and pre- or post-emergence damping off.

Figure. Preemergence damping-off, characteristic of Pythium daming-off and root rot (Pythium spp.). Image: Courtesy M. V. Avanzato; Reproduced, by permission, from Hartman, G. L., et al., eds. 2015. Compendium of Soybean Diseases and Pests. 5th ed. American Phytopathological Society, St. Paul, MN.

Some farmers either request treated seed or purchase seed that comes pre-treated with one or more seed treatment fungicides.  If your soybean seed doesn't come pre-treated there are several factors to consider before using a soybean seed treatment (Wise et al. 2018). While these treatments can provide protection when conditions favor disease, they are unable to provide protection indefinitely (Wise et al. 2016).   Additional information about seed and seedling pathogens and diseases as well as the environmental conditions that tip the scales in their favor can be found on UMN Extension’s Soybean Seed and Seedling Diseases webpage or a publication called "Scouting for Soybean Seedling Diseases or Disorders" (Giesler et al. 2015).


Giesler, L. et al. 2015. Scouting for soybean diseases and disorders. Crop Protection Network.

Malvick, D.M. 2018. Soybean Seed and Seedling Diseases. University of Minnesota Extension. Online at {URL accessed April 2019}.

Wise et al. 2016. Soybean seed treatments: Questions that emerge when plants don't. Crop Protection Network. CPN 1016.

Wise et al. 2018. Factors to consider before using a soybean seed treatment. Crop Protection Network publication CPN-4003-W.

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