Fungicides Produce Minimal Corn Yield Response Under Drought Conditions

• Dry conditions across the study area during the latter portion of the 2020 growing season resulted in low foliar disease pressure.
• Foliar fungicide treatments had minimal effect on corn yield, averaging only 1.4 bu/acre more than the untreated check.
• Similar results have been observed in previous growing seasons that experienced abnormally dry conditions.

• Foliar fungicides have proven their value as a disease management tool in corn. In over 2,000 Pioneer on-farm trials conducted from 2007 to 2018, a fungicide application increased corn yield by an average of 7.5 bu/acre (Jeschke, 2020).
• The most important factor determining the value of a foliar fungicide application is disease pressure. When weather conditions are conducive for foliar diseases, a fungicide application can be beneficial. 
• Occasionally, conducive weather conditions can persist past the effective residual effect of the fungicide.
• Research was conducted in 2020 to evaluate the potential yield benefit of expanding the window of fungicide activity with a split foliar application at or near tasseling (VT/R1) and again at the milk stage of kernel development (R3).

Experimental Design:

• 17 locations across the U.S. Corn Belt.
• Strip plot design
• Two corn hybrids per location. Hybrid selection for each location varied.
• Fungicide treatments applied via ground application:
  1. Untreated check
  2. 6.8 oz/acre DuPont™ Aproach Prima fungicide applied at VT/R1
  3. 3.4 oz/acre DuPont™ Aproach^® Prima applied at VT/R1 followed by another 3.4 oz/acre at R3

Data Collected:

• Harvest yield
• Harvest moisture

• Foliar fungicide treatments had little effect on corn yield in 2020. Across the 13 trial locations that were harvested for yield, the average yield with fungicide treatment was only 1.4 bu/acre greater than the untreated check (Figure 1).
  • The 6.8 oz/acre treatment at VT/R1 averaged 0.5 bu/acre more than the untreated check. Grain moisture averaged 0.4 points wetter.
  • The 3.4 oz/acre at VT/R1 followed by 3.4 oz/acre at R3 treatment averaged 2.3 bu/acre more than the untreated check. Grain moisture averaged 0.8 points wetter.

Figure 1. Average yield of foliar fungicide treatments across 13 on-farm trial locations in 2020.

Figure 2. Differences in green foliar tissue among treatments late in the season at on on-farm trial location in Missouri (September 3, 2020).

Figure 3. U.S. Drought Monitor maps showing the onset of drought conditions across much of the Corn Belt in the latter part of the 2020 growing season, affecting the majority of on-farm trial locations.

• The most important factor determining the value of a foliar fungicide application is disease pressure.
• Due to the lack of disease pressure across on-farm trial locations in 2020, results of this study did not provide any insights into the potential value of split fungicide applications compared to a single application at VT/R1.
• When weather conditions are conducive for foliar diseases, a fungicide application can be beneficial; however, in 2020 the very dry weather conditions that occurred at most of the trial locations in August and September were not conducive for late season foliar disease progression.
• Results similar to those of this study have been observed in previous growing seasons that experienced drought conditions during the latter portion of the growing season.
  • In 2011 and 2012, which were both abnormally dry years in Iowa, the average yield response to foliar fungicide treatments in Pioneer on-farm trials in Iowa was 2.5 bu/acre (Jeschke, 2017).
  • In 2013 and 2014, which had normal to above-average precipitation, the average yield response to fungicide treatment was 7.5 bu/acre.

• Jeschke, M.R. 2017. Maximizing the Value of Foliar Fungicides in Corn. Crop Insights 27:3. Pioneer. Johnston, IA.
• Jeschke, M.R. 2020. Maximizing the Value of Foliar Fungicides in Corn. Crop Insights 30:7. Pioneer. Johnston, IA.