Estimates of yield and economic losses associated with white mold of rain-fed dry bean in North Dakota

White mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary] of dry bean (Phaseolus vulgaris L.) is the most important disease affecting rain-fed dry bean yields in North Dakota. The economic impact of this disease in North Dakota was assessed through a survey of 250 fields during 2003 to 2005. Profitability of a single fungicide application for managing white mold also was examined. Yield loss was estimated by regressing the mean of white mold incidence per county and year with their respective estimated yields. The slope of the resulting equation was divided by its intercept and multiplied by 100 to express yield loss as percentage of potential yield. Results of these analyses indicated a loss of 14 kg/ha (R² 0.50; P = 0.03) for every unit of white mold incidence, which represents a loss of 0.8% of the potential yield. The economic impact of the disease was assessed using estimated hectarage with ≥20% white mold incidence in conjunction with yield and dry bean prices as reported by National Agricultural Statistics Service for North Dakota. Over the 3-yr period, economic losses were highest in 2004 and least in 2005; yield loss averaged 524 kg/ha (range 424-722 kg/ha) while production loss averaged 64331 (range 1,789-10,4381). These represent an average economic loss of U.S. $2.95 million (range U.S. $0.63-5.74 million) per year. Profitability of a fungicide application to manage white mold was heavily influenced by disease pressure and varied widely between years. In years with high disease pressure, like 2004, a fungicide application would have produced a positive return in 72% of the fields; but under moderate to low disease-pressure, applying fungicides would have been a profitable practice in <20% of fields.