What is White Mould?

Sclerotinia stem rot (Sclerotinia sclerotiorum), more commonly called “white mould”, is a very common and widespread soybean fungal disease. Yield losses from this disease can be extreme depending on the year and the amount of inoculum in the soil, and it can spread across fields if not managed properly. 

Because white mould symptoms aren’t prevalent until late in the season, it’s important to know the factors that encourage growth and when you’re likely to see it so you can manage it as early as possible.

Disease Development 

White mould infections occur at flowering in sustained wet soil or in high humidity, and thrive in temperatures lower than 29° Celsius, according to the Soybean Research and Information Initiative (2015).

Foliar symptoms (yellow or brown leaves) of white mould will not appear until the fungus has progressed enough to kill the plant. University of Wisconsin Extension recommends that growers examine stems for white mould fungus, appearing as gray to white lesions at the nodes.  

Common symptoms include:

• A white growth on stems that appears fluffy or cottony 
• Dark black sclerotia along the stem or bean pods
• Bleached or light-colored stems as soybeans become dry or die

Source: https://cropprotectionnetwork.org/encyclopedia/white-mold-of-soybean 

Management and Prevention

To get ahead of white mould in your fields, consider scouting your fields early and continue evaluating your soybean fields for damage. If your fields have a history of this disease or you experience consistent environmental conditions for white mould growth (cool, wet, and humid weather at flowering), you may need to consider a fungicide application. The timing of your application is critical for reducing the impact of white mould. Apply close to the R1 growth stage.

Cultural control for white mould may offer the best disease management if you experience persistent disease pressure year to year.

To reduce the prevalence of white mould:

• Plant a variety with built-in resistance
• Select management practices that work to reduce the fungal population in your fields including crop rotations and minimizing tillage when possible 
• Carefully consider plant populations and row spacing in the future. Lower plant populations and wider row spacing can lower your risk
• Consider a timely fungicide application if required

Additional White Mould Resource Links: Crop Protection Network 

Speak to your local NK^® Seeds Agronomist for more information, or join the conversation online – connect with us at @NKSeedsCanada on Twitter and Facebook.

These are general considerations. Always consider the specific situation on your field and exercise good agronomic practices.
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