Within-field variability and spatial analysis of white mould and soybean crop attributes in southern Brazil

White mould (Sclerotinia sclerotiorum) is a damaging disease of soybean crops in Brazil. Within-field spatial analyses of white mould disease and inoculum, as well as yield components at the field level may provide insights into their relationship, but this information is lacking in the country. During three years, spatially explicit within-field data on white mould and soybean stand and yield were measured at three fields, with sizes ranging from 4 to 12 ha, located in the Campos Gerais region of Parana State, Brazil and all naturally infested with sclerotia. Crop stand, white mould incidence and severity, soybean yield and sclerotia collected at harvest were assessed in quadrats of 7.2 m2 distant from each other by 8 to 50 m. Soilborne sclerotia were counted in four quadrats (0.25 m2 and 0.05 m depth) at each sampling point. The semivariograms fitted the pure nugget effect, linear, spherical, and exponential models. The pure nugget model best fitted sclerotia data, suggesting a random distribution. Significant and positive associations were found between disease incidence and sclerotia amount at harvest, which were both negative associated with yield.