Field studies will be established at the NDSU Carrington Research Extension Center and at the NDSU Robert Titus Research Farm south of Oakes at sites with overhead irrigation capabilities and a previous history of Sclerotinia. Six 00-maturity varieties (Carrington only), six early 0-maturity (0.1 to 0.3) varieties (Carrington and Oakes), six mid 0-maturity (0.4 to 0.6) varieties (Carrington and Oakes), six late 0-maturity (0.7 to 0.9) varieties (Carrington and Oakes) and six early 1.0-maturity (1.0 to 1.2) varieties (Oakes only) will be evaluated. All studies will be established as completely randomized split-split plot designs with four replicates with soybean maturity grouping as the main factor, fungicide treatment as the sub-factor, and soybean variety as the sub-sub factor. Three fungicide treatments will be tested: Non-treated, 5.5 oz/ac Endura (70% boscalid by weight; BASF Corp.) applied at R2 growth stage, and 5.5 oz/ac Endura applied at R2 and R3.

An additional field study will be conducted in Carrington in which intensive irrigation favoring white mold will be applied for a 3-week period beginning at the V4, R2, or R4 growth stage. Experimental design will be a completely randomized split-split plot with four replicates and with irrigation timing as the main factor, soybean variety as the sub-factor, and fungicide treatment as the sub-sub factor. Three soybean varieties of 0.4 to 0.6 maturity will be evaluated, and three fungicide treatments (non-treated, 5.5 oz/ac Endura at R2, and 5.5 oz/ac Endura at R2 plus R3) will be tested.

In all studies, soybeans will be seeded to rows 14 inches apart at 165,000 pure live seeds/ac. Sclerotinia incidence, severity, and severity index will be assessed at the R5, R6, and R7 growth stages (irrigation study) or shortly before maturity (maturity group study); and soybean yield, test weight, and percent contamination with sclerotia (by weight) of harvested grain and mechanically cleaned grain will be quantified. Data will be analyzed in SAS 9.4 (SAS Institute, Cary, NC), with model assumptions evaluated prior to analysis. Yield-loss relationships will be determined for each soybean variety within each maturity group (first study) and within each irrigation timing (second study) using regression analysis. The calculated yield-loss relationships will be utilized to calculate expected thresholds for the profitability of one versus two fungicide applications at a representative range of soybean and fungicide input prices, and the observed responses to fungicide applications will be utilized to verify the accuracy of the calculated thresholds. The relationship between soybean maturity (first study) or irrigation timing (second study) and soybean performance (Sclerotinia disease levels, seed yield, test weight, and contamination of grain with sclerotia) across the various fungicide treatments will be analyzed with analysis of variance. The relationship between the impact of Sclerotinia on yield and soybean maturity will be evaluated with analysis of variance (for each group of soybean varieties) and with regression analysis (across all varieties). Agronomics will be conducted in accordance with best practices.