White mold (WM, also called Sclerotinia stem rot) is a significant problem in the U.S. North Central soybean production region and in Canada. Caused by the fungus Sclerotinia sclerotiorum that overwinters in the soil, WM is often recognized by fluffy, white growth on soybean stems. WM development is favored by cool, cloudy, wet, and humid weather at first flowering. The disease is more problematic in soybeans in high-yield environments where high plant populations, narrow row spacing, and an early-closing canopy are commonly used.
The objective of this study was to evaluate a system-based approach for WM disease management supported by genetic resistance of germplasm and foliar fungicide.
Select soybean products with varying levels of resistance to WM were evaluated under different fungicide management options.
RESEARCH SITE DETAILS
Fields with a history of WM were selected for this study.
Plots were planted in a split-plot design with fungicide treatment as the main plot and soybean product as the sub-plot.
Fungicide treatments included:
- Application of Delaro® 325 SC fungicide (Group 3 + Group 11) at 8 oz/acre tank-mixed with Luna® Privilege (Group 7) fungicide at 2 oz/acre at R1
- Application of Delaro 325 SC fungicide at 8 oz/acre tank-mixed with Luna Privilege fungicide at 2 oz/acre at R1 and R3
Soybean products used were classified as susceptible (S), moderately susceptible (MS), moderately resistant/moderately susceptible (MR/MS), moderately resistant (MR), or resistant (R) to WM.
Plots were randomized within the trial.
WM disease ratings were taken at the R6 growth stage.
- Nine trial locations from 2019 with WM symptoms were analyzed for this study, and the data shown below is the average of the 9 locations. Most locations had mild to moderate WM incidence and severity.
UNDERSTANDING THE RESULTS
Both fungicide treatments significantly contributed to WM disease suppression and an average yield advantage of 2 bu/acre over the unsprayed treatment.
For soybean products with below-average resistance to WM, the fungicide treatments resulted in a 4 bu/acre yield advantage compared to the unsprayed treatment.
Although not statistically significant, soybean products with enhanced resistance to WM provided an average yield advantage of 2 bu/acre over susceptible checks.
- In a year with mild to moderate WM incidence and severity, and below-average fungicide performance based on adverse weather conditions, the use of fungicide consistently provided a yield advantage over the unsprayed treatment across soybean products, with the largest yield response observed in soybean products with below-average resistance to WM.