Top Soybean Disease Scouting Tips

(“Soybean Field Guide 2nd Edition,” Iowa State University)
Soybean disease scouting tips

Sudden Death Syndrome (SDS):

  • Best time to scout – Look for symptoms of SDS during R1-R6 growth stage.
  • Environment – SDS is most likely to develop after significant rainfall during the reproductive growth stages of soybeans.
  • Scouting tip – In scouting for SDS, check plants in areas with high soil moisture. Fields infested with Soybean Cyst Nematode (SCN) are especially prone to development of SDS under the right conditions.

Soybean Cyst Nematode (SCN):

  • Best time to scout – Look for signs of SCN between 6 weeks after planting and up until 3 to 4 weeks prior to harvest.
  • Environment – Weather conditions that favor soybean growth – 85 degrees with ample moisture - also favor SCN development.
  • Scouting tip – Because SCN is primarily spread by human activity involving equipment and vehicles, SCN may first appear near field entrances, in flooded areas, weedy areas or high pH spots and low-yielding areas.

White Mold:

  • Best time to scout – White mold may begin to develop on soybeans during the R2-R6 growth stage.
  • Environment – Development of white mold is most likely to occur during rainy, cool temperatures, high humidity, with moist soil, with a closed canopy during flowering, and early pod development
  • Scouting tip – Plants in areas where moisture collects due to fog or extended dew periods are susceptible to white mold development. The disease may also start in in plants where there are pockets of low air movement, such as along tree lines.

Frogeye Leaf Spot (FLS):

  • Best time to scout – FLS can strike soybeans during the R3-R6 growth stage.
  • Environment – FLS is most prevalent in warm, humid weather conditions.
  • Scouting tip – Lesions are often seen in “layers” in the soybean canopy, corresponding to alternating wet and dry periods.  Young leaves are more vulnerable to infection, but infected leaves may not be obvious initially, as lesions take two weeks or more to develop after infection.

For additional details on soybean disease, scouting and treatment, consult these online publications:


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