White Mold Management in Soybean Fields

By Scout Nelson

White mold is a serious soybean disease that spreads during cool and wet growing seasons. Recent weather patterns increase the risk of this disease in soybean fields and in crops such as dry beans and sunflowers. Research over many years provides useful guidance to help farmers protect yield and grain quality.

Row spacing plays an important role in disease control. Wide rows reduce white mold levels but only give the best yields when disease pressure is very high. Research shows that intermediate row spacing, around 21 to 22.5 inches, offers the best balance between yield and disease control in most fields.

Seeding rate also affects white mold levels. Lower seeding rates help reduce disease pressure. Planting about 100,000 viable seeds per acre works best when at least 15 percent of the crop canopy shows disease symptoms later in the season.

Variety choice is another key factor. Soybean varieties with longer maturity times show higher risk for white mold. Farmers should consider maturity groups and disease tolerance when selecting seeds. Fields planted in longer-maturing varieties are more likely to benefit from fungicide use.

Fungicide timing is critical. When weather favors disease as plants begin to bloom, a single fungicide spray works best when almost all plants reach the R2 growth stage or when the canopy closes. In higher-risk fields, two fungicide sprays provide better protection. The first spray should occur early in the bloom stage, and the second spray should follow based on the maturity group.

Spray droplet size also affects how well fungicides work. Smaller droplets work best when the canopy is still open. Medium or coarse droplets work better as the canopy closes. Farmers can estimate canopy closure visually or by using simple phone apps to guide spray settings.

These research-based steps help reduce disease losses and protect grain quality. By following proper planting, variety of selection, and spray practices, farmers can improve soybean health, lower disease risk, and support long-term farm profits.

Photo Credit: istock-ds70