Fighting White Mold in Soybeans: What Farmers Need to Know

White mold, also known as Sclerotinia stem rot, has become an increasing concern for soybean growers across the Northern U.S. and Canada. Once a sporadic issue, it's now a frequent yield-limiting disease. Managing it requires foresight, an understanding of environmental triggers and a balanced agronomic strategy. Here's what you need to know to protect your fields.

Why White Mold Is a Bigger Problem Today

White mold thrives in high-yield soybean environments. Ironically, practices that push for better yields—like early planting, narrow rows and dense canopies—also create ideal conditions for the disease. These setups trap moisture and shade beneath the canopy, fostering mold development.

How It Develops: The White Mold Life Cycle

White mold is a one-cycle-per-season disease, starting from sclerotia—dark, seed-like structures that can survive in soil for years. These germinate in cool, wet conditions and produce mushroom-like apothecia, which release millions of spores.

However, spores can’t invade healthy tissue directly. Instead, they colonize senescing (dying) flowers, often lodged in leaf axils or pods. From there, the infection spreads, forming white, cottony growths on stems and eventually causing plants to wilt and die.

Conditions That Favor White Mold

White mold thrives when all the following align:

• Cool temperatures (40–60°F)
• Prolonged wetness (e.g. fog, humidity and leaf wetness)
• Dense canopies that retain moisture
• Flowering stage (early bloom to pod fill)

Early canopy closure—a yield-boosting goal—also increases the risk of mold outbreaks.

Risk Factors in Your Field

Some risk indicators to watch:

• Field history: Past mold presence or nearby infected areas
• Early canopy closure: Especially with high plant populations
• Crop rotation: Short rotations with other susceptible crops (e.g. edible beans or canola)
• Topography: Low spots or windbreaks that trap humidity
• Variety susceptibility: Some soybeans are more prone than others

Building an Integrated Management Plan

There's no silver bullet for white mold. The best approach layers multiple tactics.

1. Avoid Disease Spread

• Clean harvest equipment thoroughly—especially before moving to clean fields
• Avoid saving seed from infected fields
• Purchase clean, inspected seed

2. Pick the Right Variety

• Choose soybean varieties with high white mold tolerance (rated 7–9 on a 1–9 scale)
• Work with your local seed rep to find the best fit for your field and maturity zone

3. Adjust Agronomics

• No-till systems help break the mold cycle by leaving sclerotia on the surface, where they degrade
• Crop rotation with non-hosts like corn or small grains reduces pressure (avoid alfalfa, canola and sunflowers)
• Planting dates: Later planting may reduce mold risk but also limits yield—consider only for high-risk fields
• Row spacing/seeding rate: Wider rows and lower seeding rates can limit mold—but may reduce yields without disease presence

4. Control Broadleaf Weeds

Weeds like pigweed, ragweed and velvetleaf can also host white mold. Good weed control isn’t just for yield—it reduces mold pressure too.

What About Fungicides?

Chemical control is a tool—but not a cure. Fungicides must be applied before symptoms appear, ideally at the R1–R2 growth stage (first bloom). Later applications are less effective due to reduced canopy penetration.

Effective Fungicides (rated fair to very good):

• Endura® (boscalid) – very good
• Aproach® (picoxystrobin) – good
• Propulse®, Omega® and Proline® – good to fair

University and on-farm trials show sequential applications at R1 and R3 yield the best results—up to 13 bu/acre advantage over untreated soybeans.

Additional Tools

Cobra® Herbicide

• Active ingredient: Lactofen
• Triggers soybean defenses but can also cause leaf burn
• Yield results are inconsistent and depend on variety and pressure—use with caution

Contans® Biological Fungicide

• Targets sclerotia in the soil
• Needs to be applied 3+ months in advance and incorporated into soil
• Best used in fall

White mold is most damaging in your highest-yielding environments. That’s why it’s critical to balance practices that push yield with those that protect it. Evaluate your fields annually and adapt your strategy based on risk levels.

Need help selecting the right varieties or adjusting your management plan? Contact your local Hoegemeyer rep—we're Right Here to help.

Find the full agronomy bulletin and list of references here