Bleached soybean stems infected with white mold.

In a recent Twitter poll to determine the soybean disease most concerning to growers going into the 2018 season, it’s no surprise 62% of respondents selected white mold (Sclerotinia stem rot). White mold results in significant yield loss if left unchecked, especially in susceptible varieties. That’s not a loss anyone wants to experience this season.

Disease development:

Because most white mold symptoms aren’t prevalent until late in the season, it’s important to know the factors that encourage growth and when it’s likely to pop up so you can manage it early.

White mold infections occur at flowering in sustained wet soil or in high humidity, and information shared by the Soybean Research and Information Initiative shows white mold thrives in cool temperatures lower than 85° Fahrenheit.

Symptoms include but are not limited to:

• White fungal growth on and inside bleached soybean stems
• Black fungal clusters on soybean stems

However, knowing the symptoms to look for isn’t enough to tackle this disease. If you are seeing these symptoms, it may already be too late to manage the disease effectively. White mold management plans should focus primarily on prevention and early management.

Prevention and management:

There are several steps you can take to help prevent or manage the severity of white mold:

1. Manage row spacing – if concerned about white mold, the American Phytopathological Society recommends a row-width that promotes air circulation to help dry plants and soil. Soybean rows that are too tightly-packed reach canopy closure early, creating an environment that holds in moisture and shuts out sunlight, perfect for white mold development.
2. Carefully consider your plant populations – similar to the concerns with too narrow row-spacing, denser soybean populations create conditions more conducive to white mold development. Michigan State University Extension recommends a uniform plant population of 100,000 soybean plants per acre.
3. Plant resistant varieties – the fight against disease often begins with your soybean variety. If white mold is a concern, be sure to plant a variety with built-in resistance.
4. Make a timely fungicide application – if your fields have a history of white mold or you experience persistent conditions conducive to white mold development, you may need to consider a fungicide application.

When it comes to controlling white mold with a fungicide, timing is critical. With other soybean diseases, such as frogeye leaf spot, fungicides can be applied later in the year during the R3 growth stage. White mold, on the other hand, requires a fungicide application at flowering for the fungicide to be effective.

If you’re not ready, white mold can sneak up on you and steal yield. Take steps early to prevent or manage this disease in your field.

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