White mold, caused by Sclerotinia sclerotiorum, remains one of the most economically damaging diseases of soybean, particularly in environments that favor cool temperatures, extended leaf wetness, and dense canopies (Figure 1). While white mold can occur in any field, past field history, row spacing, population density, and weather patterns during flowering help identify acres at greatest risk. Proactive planning is critical, because once symptoms are visible, yield loss has already occurred.
White mold disease cycle and symptomology
White mold infection begins when sclerotia in the soil germinate and form apothecia—small, mushroom-like structures that release spores into the soybean canopy (Figure 2). These spores do not infect healthy green tissue directly; instead, they colonize senescing flower petals. When infected petals lodge in leaf axils or on stems under humid conditions, the fungus gains entry into the plant. Infection can occur anytime during flowering (R1 through early R3) when moisture and temperature conditions are favorable.
As the disease progresses, stem tissue becomes bleached and brittle, reducing nutrient flow and ultimately decreasing seed number, seed size, and overall grain quality. White, cotton-like mycelium may also be found on stems (Figure 3). Sclerotia formed in infected plants return to the soil at harvest, allowing white mold pressure to persist for years. Because there is no “curative” option once infection has occurred, management must focus on prevention.
Why timing matters and how Zorina™ fungicide delivers
Fungicide timing is the single most important in-season management decision for white mold. Research and field experience consistently show that applications made during active flowering provide the greatest level of protection. Applying too early may leave flowers unprotected when spores are released, while applications made after canopy closure or after infection offer little benefit. The optimal window is typically late R1 to early R2, when flowers are present and canopy humidity begins to increase but spray coverage is still achievable.
Effective white mold management also depends on achieving good canopy penetration. Higher water volumes, appropriate droplet size, and applications made prior to full canopy closure help ensure fungicide reaches flowers where infection begins.
Zorina™ fungicide is the newest white mold fungicide on the market. Zorina is specifically designed to prevent white mold by protecting soybeans during the critical flowering window. It combines the proven performance of Endura® fungicide with the long-lasting, broad-spectrum activity of Revysol® fungicide. Applied at 18.5-20 fl oz/A in late R1 to early R2, Zorina delivers consistent protection of actively flowering tissue, helping reduce infection, limit sclerotia development, and protect soybean yield potential (Figure 4). When properly timed and applied, Zorina provides growers with a dependable tool to stay ahead of white mold and protect high-risk soybean acres.
