Evaluation of Disease Management Systems in Soybean – White Mold

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Evaluation of Disease Management Systems in Soybean – White Mold - 2020

 

TRIAL OBJECTIVE 

  • White mold (WM, also called Sclerotinia stem rot) is a substantial 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.  

  • 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:
    • Untreated
    • 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. 
    • Resistant varieties were left out of most data analyses because they were unavailable or missing from 5 out of the 13 locations. 

  • Plots were randomized within the trial. 

  • WM disease ratings were taken at the R6 growth stage.

  • 50 trial locations from 2019 and 2020 were planted for this study, and the data shown below is the average of the 13 locations (26%) kept for this analysis because they had moderate to high white mold pressure.

 

UNDERSTANDING THE RESULTS

image Figure 1. Average WM disease index rating for each fungicide treatment of Delaro® 325 SC fungicide tank-mixed with Luna® Privilege fungicide. WM disease index: 1 = no disease, 9 = severe disease. Mean separation letters (a, b, c) denote statistically significant differences at an alpha = 0.1.
image Figure 2. Average WM disease index rating by fungicide spray treatment and WM disease classification of soybean products. Fungicides: Delaro® 325 SC fungicide tank-mixed with Luna® Privilege fungicide. WM disease index: 1 = no disease, 9 = severe disease. Mean separation letters (a through h) denote statistically significant differences at an alpha = 0.1.
image Figure 3. Average yield for each fungicide treatment across all soybean products and locations. Fungicides: Delaro® 325 SC fungicide tank-mixed with Luna® Privilege fungicide. Mean separation letters (a, b) denote statistically significant differences at an alpha = 0.1.
image Figure 4. Average yield of treatments for each WM disease classification of soybean products. Mean separation letters (a) denote statistically significant differences at an alpha = 0.1.
image Figure 5. Average yield by fungicide treatment and WM disease classification of soybean products. Fungicides: Delaro® 325 SC fungicide tank-mixed with Luna® Privilege fungicide.
image Figure 6. Aerial imagery showing visual differences of WM disease severity for each of the fungicide spray treatments and WM disease classification of products. Soybean products sprayed at R1 then followed by an R3 application yielded the highest and had the lowest WM disease index recorded in a location with relatively high WM incidence and severity (WM index numbers in yellow. WM disease index: 1 = no disease, 9 = severe disease). Fungicides: Delaro® 325 SC fungicide tank-mixed with Luna® Privilege fungicide.
image Figure 7. Side-by-side comparison of a soybean product susceptible to WM showcasing the effect of fungicide applications (R1 and R3) on WM disease control and plant health. Fungicides: Delaro® 325 SC fungicide tank-mixed with Luna® Privilege fungicide. WM disease index: 1 = no disease, 9 = severe disease.

KEY LEARNINGS

  • Within the data set, there was strong WM disease suppression in response to fungicide application, resulting in a significant advantage of more than 2 bu/acre over the unsprayed treatment. 
  • Within the data set, these interactions between disease classification and fungicide application at R1 growth stage were found ​-
    • Moderately Resistant soybean products and Moderately Resistant/Moderately Susceptible soybean products had a 1.45 bu/acre advantage with fungicide applied at the R1 growth stage compared to untreated check.​
    • Moderately Susceptible soybean products and Susceptible soybean products had a 2.85 bu/acre advantage when fungicide was applied at R1 growth stage compared to untreated check.​ 
  • Yield of Moderately Resistant soybean products with fungicide applied at R1 growth stage was not statistically different than yield from other disease classes with fungicide applied at R1 growth stage.
    • However, yield of Moderately Resistant soybean products with fungicide applied at R1 growth stage was numerically highest of all management systems that were untreated or had a fungicide applied at R1 growth stage.

 

 

 

 

Evaluation of Disease Management Systems in Soybean – White Mold - 2019

 

TRIAL OBJECTIVE

 

  • 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: 

    • Untreated
    • 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.

 

 

KEY LEARNINGS

 

 
  • 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.



 

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