The fungus, Sclerotinia Sclerotiorum, can overwinter for several years in the soil as sclerotia. From these, mushroom like structures will emerge to produce ascospores which infect a soybean during R1 as flowers senesce. A white, fuzzy growth with embedded black sclerotia eventually colonizes the stems and nodes during R3-R6 stage.
Cool, wet & high relative humidity are ideal conditions for White Mold to thrive. Although poor airflow within the crop canopy could accelerate spread of the disease throughout.