Soybean flowering is getting into full swing around the state and this usually triggers many questions around white mold and the potential for disease development. White mold, also referred to as sclerotinia stem rot, can be a devastating pathogen that can cause significant plant mortality and yield loss. Once white mold has taken hold in a plant it can be very difficult to stop.

White mold is caused by the fungus Sclerotinia sclerotiorum which favors lower temperatures, especially below the soybean canopy and moisture from rain, fog, dew and/or high relative humidity. Infection of white mold spores occurs when we have the aforementioned environmental conditions, plus white mold spores present in the field and soybeans that are flowering as the spores infect through the senescing flower of the soybean plant. As the infection develops, you will notice the stem start to develop a water-soaked appearance that will progress up and down the stem of the plant. As the disease continues to develop you will notice plants that wilt and lodge. You will also start to find a white moldy type growth known as mycelia as well as dark hard masses (sclerotia) on the inside and/or outside of the stem.

White mold is a disease that can be managed especially if a field is known to have had this disease before. Cultivar selection for resistance to this pathogen is the best long-term strategy to combat this disease. No-till practices and crop rotation to a non-host crop are also viable options for reducing the number of viable sclerotia near the soil surface. Lastly, fungicides are an option for control of this plant pathogen, but timing of application is critical and often different from normal fungicide application recommendations. Fungicide applications for white mold need to be made during early flowering (R1) to early pod development (R3) growth stages. Choosing the right fungicide is also important as ratings for control differ among the different fungicides. Please refer to the link below for fungicide ratings on white mold and also consult your local FS crop specialist for more information on products if you think white mold is a concern.

As with any disease consider the disease triangle (host present, disease present, and weather conditions conducive for disease development) to better understand if your field may be at risk.

Originally published in Spokesman. Tim Berkland serves the FS System and GROWMARK’s strategic agronomy marketing manager. He can be reached at [email protected].