White Mold in Soybean: Mid-Season Management

Key Takeaways

• White mold in soybeans can cause significant yield loss, especially in cool, wet conditions during flowering when infection risk is highest.
• Timely fungicide application is critical—apply at early flowering (R1) with follow-up through R3 for effective white mold control.
• Scouting and early identification matter—look for stem lesions, white cottony growth, wilting plants, and sclerotia to confirm white mold.
• Reduce white mold risk with integrated management, including lower seeding rates, wider rows, crop rotation, and selecting tolerant soybean varieties.

Impact of White Mold in Soybean

White mold, or Sclerotinia stem rot, is a soybean disease caused by the fungus Sclerotinia sclerotiorum that can cause considerable economic yield loss. In 2017, the yield loss across the United States and Ontario, Canada was estimated at 57.4 million bushels.¹ That same region reported estimated yield losses of 26.1 million bushels in 2024.² Disease incidence is the percentage of plants expressing symptoms divided by the number of plants assessed. An estimated two to five bu/acre yield reduction may occur for every 10% increase in disease incidence at the R7 growth stage (beginning maturity).³ Infected seeds can also have reduced germination and quality.

White Mold Symptoms and Identification

White mold often occurs in patches in the field. Initial symptoms appear as water-soaked lesions on the stem which eventually become bleached and stringy (Figure 1). You must look under the canopy to identify this symptom. As the disease progresses, you will see the characteristic production of white, fluffy, cottony mycelial growth on the outer stem layer and pods (Figure 1). This is also accompanied by wilting of the leaves, which develop a grayish-green cast (Figure 2), and plant death. Small, black, and hard structures (sclerotia) that resemble mouse or rat droppings can be found inside and/or outside infected tissues (Figure 3).

White Mold Disease Cycle

As with all crop diseases, the disease triangle is in play with white mold. The pathogen must be present to infect a susceptible host and the growing conditions must be favorable to sustain the pathogen’s development.⁴ The timing of these three components is also key since flowers—which are present from R1 to R3—are the primary tissue for infection. In infested fields, the hard sclerotia overwinter and germinate in the spring to form fruiting bodies (apothecia or mushrooms), which begin releasing spores when mature (Figure 4). The spores are forcibly ejected from the apothecia and land on flowers or other tissues, such as senesced lower stems. When wet, cool (53.6 to 75.2 °F) growing conditions are present within and below the canopy, spores can infect and initiate disease development. There are other fungal species that produce mushrooms that can be confused with white mold apothecia, especially bird’s nest fungus, which is a harmless organism that helps break down stubble and other organic residue.^5,6

Considerations for White Mold Management

Fields with a history of white mold should have priority for managing the disease. After infection occurs, little can be done to alleviate potential yield loss. When considering the disease triangle, high tolerance or resistance among soybean products is limited and environmental management is not possible except for managing irrigation, which may have to be reduced.

No-till environments leave sclerotia on the soil surface where they can germinate; however, sclerotia numbers generally decrease over time when on the soil surface. Since sclerotia can survive being buried with tillage, subsequent tillage can bring the sclerotia to the surface where they can germinate.^5,6,7

In areas with a high prevalence of white mold, especially Iowa, Wisconsin, Minnesota, northern Illinois and Indiana, Ohio, and Michigan, the planting of other white mold-susceptible crops should be avoided. Short intervals between rotations such as a corn-soybean rotation should also be avoided because the long-lived sclerotia can continue to increase in the soil.^5,6,7 Many weeds are susceptible to white mold; therefore, weed growth should be managed appropriately.

Other management factors that can be controlled include selecting soybean products with higher tolerance, reducing seeding rate, and employing an appropriate soybean row width.^5,7 Soybean products vary on tolerance to white mold; therefore, careful review of seed guides can help determine products that have higher tolerance ratings. An early canopy closure helps keep the soil moist, which is favorable for white mold development. Therefore, creating an environment where canopy closure is delayed by decreasing seeding rates and using wide rows can help reduce the potential for white mold development.

Manure and nitrogen applications should be avoided on soybean fields with a history of white mold. These practices can increase early plant growth, resulting in quicker canopy closer, which is favorable for white mold development.

A timely fungicide application of a product labeled for white mold can help prevent white mold. Since white mold infects through the flowers, it is imperative the application is applied during flowering. Applications should be made at the beginning of flowering (R1 growth stage) with a possible follow-up application a week or two later, up to the beginning of pod development (R3 growth stage). To be successful, the fungicide should have good penetration deep into the canopy.⁵

The Crop Risk Assessment Tool from the Crop Protection Network provides site-specific weather-based forecasting and risk assessment for diseases like White Mold.⁸

Additionally, you can check out Bayer’s Disease Risk Maps for more information on the spread of White Mold in your area:

Soybean Disease Risk Maps | Crop Science US

Delaro® 325 SC and Delaro® Complete Fungicides Provide an Option for Suppression of White Mold

Apply Delaro® 325 SC fungicide at 8.0 to 11.0 fl oz/acre at R1 when 80% of the field is flowering, prior to disease development for the suppression of white mold. Follow up with a second application at R3. Up to three applications can be made annually, with a maximum application rate of 33.0 fl oz/acre. When using sequential applications, it is recommended to alternate with a fungicide from another group to reduce the potential for resistance developing. Delaro® 325 SC fungicide contains prothioconzazole (Group 3) and trifloxystrobin (Group 11) and is labelled for control of Alternaria leaf spot, anthracnose, Asian soybean rust, brown spot, cercospora blight, frogeye leaf spot, pod and stem blight, powdery mildew and rhizoctonia aerial blight. Consult the label for more instructions, and to determine if this product is labeled in your state.

Delaro® Complete fungicide is labelled for control of the same diseases listed above and includes an additional mode of action, fluopyram, a Group 7 product. Delaro® Complete fungicide should be applied at 8.0 to 11.0 fl oz/acre at R1 when 80% of the field is flowering, then follow with a second application at R3. Delaro® Complete is labeled for suppression of white mold and target spot in addition to the diseases listed above. Up to three applications can be made annually, with a maximum application rate of 33.0 fl oz/acre. When using sequential applications, it is recommended to alternate with a fungicide from another group to reduce the potential for resistance developing. Consult the label for more instructions, and to determine if this product is labeled in your state.

To learn more about Delaro® 325 SC Fungicide, please visit https://www.cropscience.bayer.us/products/fungicides/delaro or contact your retailer.

For more information on Delaro® Complete Fungicide, please go to https://www.cropscience.bayer.us/crop-protection/fungicide/delaro-complete-fungicide or contact your retailer.

Delaro® 325 SC Fungicide and Delaro® Complete Fungicide are not registered for use in all states and may be subject to use restrictions.

The use of adjuvants depends on the fungicide and the timing of application. Fungicide labels should be read to determine if and when adjuvants can be used.

Sources

¹Bradley, C., Allen, T., Tenuta, A., Mehl, K., and Sisson, A. Soybean disease loss estimates from the United States and Ontario, Canada-2017. Soybean Disease Management. CPN-1018-17-W. Crop Protection Network. https://crop-protection-network.s3.amazonaws.com/publications/disease-loss-estimates-2017-filename-2019-07-26-165710.pdf.
² Sikora, E., Faske, T., Spurlock, T., et al. Soybean disease loss estimates from the United States and Ontario, Canada – 2024. 2025. Crop Protection Network. https://cropprotectionnetwork.org/publications/soybean-disease-loss-estimates-from-the-united-states-and-ontario-canada-2024
³Byamukama, E., Tande, C., and Mathew, F. 2020. White mold (Sclerotinia stem rot) of soybean. SDSU Extension. South Dakota State University. https://extension.sdstate.edu/sites/default/files/2020-08/P-00181.pdf.
⁴Staton, M. and Chilvers, M. 2021. Begin managing white mold in soybeans this spring. MSU Extension. Michigan State University. https://www.canr.msu.edu/news/begin_managing_white_mold_in_soybeans_this_spring
⁵Chilvers, M. 2025. Stay ahead of white mold: Mid-season management tactics. Michigan State University Extension. https://www.canr.msu.edu/news/fungicide-use-for-managing-white-mold-in-soybeans
⁶Mangel, D. 2025. Soybean white mold management season is here. Cropwatch. University of Nebraska Extension. https://cropwatch.unl.edu/soybean-white-mold-management-season-here/
⁷Crop Protection Network. 2015. Soybean disease management. CPN-1005. Originally published as White Mold in Soybean, Iowa State University Extension publication CSI 0040. https://crops.extension.iastate.edu/files/blog/files/cpn-1005-white-mold-2.0.pdf
⁸Crop Protection Network. 2025. Crop Risk Online Tool. Doi.org/10.31274/cpn-20250918-1. https://connect.doit.wisc.edu/cpn-risk-tool/k Tool
Web sources verified 4/15/2026 1311_143920