7 Key White Mold Management Strategies Every Soybean Agronomist Should Know

White mold remains one of the most challenging diseases facing soybean production across the North Central U.S. and Canada. According to information from the Soybean Research & Information Network (SRIN), white mold has evolved from a sporadic disease issue into an annual threat that can significantly reduce soybean yields, impact seed quality, and complicate production decisions. For ag retailers and agronomists, understanding disease development and management is essential for helping growers minimize losses.

1. Recognize the Conditions That Favor White Mold

White mold, caused by the soilborne fungus Sclerotinia sclerotiorum, thrives under cool, moist conditions during soybean flowering. Temperatures in the 70s to mid-80s°F, frequent rainfall, extended dew periods, fog, and poor air movement create an ideal environment for infection.

Dense canopies are particularly favorable because they trap moisture and reduce airflow, creating the microclimate the pathogen needs to infect plants.

2. Understand the Disease Cycle

The pathogen survives in the soil as hard, black structures called sclerotia, which can remain viable for years. When conditions are favorable, sclerotia near the soil surface germinate and produce small, tan, cup-shaped mushrooms called apothecia.

These apothecia release airborne spores that colonize aging soybean flowers. Infection then spreads into stems at flowering stages R1 through R3. As the disease progresses, the fungus girdles stems, disrupting water and nutrient movement and causing wilting, lodging, and plant death.

A key diagnostic feature is the presence of white, cottony fungal growth and black sclerotia on stems and pods.

3. Scout at the Right Time

Scouting is most effective at two critical periods.

The first opportunity is at canopy closure, typically in late June and early July. Agronomists should inspect moist, shaded areas of fields for apothecia, especially where moisture accumulates due to fog, dew, or poor air drainage.

The second key scouting period occurs during pod set. White mold often appears in patches, particularly near tree lines, sheltered areas, and portions of fields with thick canopies. Infected plants may initially resemble drought-stressed soybeans, making stem inspection critical for accurate diagnosis.

4. Use Field History to Assess Risk

A field’s history remains one of the best predictors of future white mold pressure. Fields with previous outbreaks likely contain higher levels of sclerotia, increasing the risk of future infections.

Maintaining detailed records of disease severity, affected field areas, and variety performance can help agronomists make better recommendations regarding variety selection and management practices in future seasons.

5. Select Varieties Carefully

While no soybean variety is completely resistant to white mold, many offer partial resistance. These varieties typically experience lower disease incidence than susceptible varieties under the same conditions.

When working with growers who have a history of white mold, avoiding highly susceptible varieties should be a top priority. Agronomists should rely on resistance ratings generated across multiple locations and years when making recommendations.

6. Manage the Canopy

Many modern production practices that maximize yield potential can also increase white mold risk.

Early planting, narrow rows, high plant populations, and high fertility programs accelerate canopy closure and create favorable disease conditions. Plant populations above 175,000 plants per acre have been associated with greater disease incidence.

Where white mold risk is high, growers may benefit from adjusting seeding rates and considering wider row spacing while maintaining economic yield potential. Weed control is also important because many broadleaf weed species serve as hosts for the pathogen and contribute to canopy density.

7. Take an Integrated Management Approach

No single tactic provides complete white mold control. Effective management requires combining several strategies.

Crop rotation remains valuable, particularly when growers include two to three years of non-host crops such as corn or small grains. Rotations involving other susceptible crops — including edible beans, canola, sunflowers, peas, chickpeas, lentils, potatoes, and cole crops — can increase disease pressure.

Fungicides can help suppress white mold but should not be viewed as standalone solutions. University trials have shown disease reductions ranging from 0% to approximately 60%, depending on product selection, timing, and environmental conditions.

Biological control products containing Coniothyrium minitans may offer long-term suppression by degrading sclerotia in the soil before they can produce apothecia. Research has shown significant reductions in sclerotia populations and disease incidence, although additional soybean-specific studies are ongoing.

Bottom Line

White mold management begins with understanding risk factors and field history. For agronomists and ag retailers, the most successful programs combine resistant varieties, canopy management, crop rotation, diligent scouting, and targeted use of fungicides or biological controls. An integrated approach offers the best opportunity to reduce disease pressure and protect soybean yield potential season after season.

For additional white mold management resources, disease identification tools, and the latest soybean research, visit the Soybean Research & Information Network.