Fungicide Effect on Corn Yield


  • Application of a fungicide has been shown to protect corn plants from foliar diseases and improve overall plant appearance, which may lead to increased grain yield.

  • Yield increases observed from the application of fungicide in the absence of foliar disease greatly depends on the corn product, as individual products respond differently to fungicide application. While fungicide is often used as a high-yield management strategy, it can also be used to protect the yield of products with poor plant and stalk strength ratings.

  • The objective of this study was to evaluate the impact fungicide application has on corn yield and good plant appearance.



  • Seven Lewis Hybrids™ brand blend corn products were tested including products that ranged from 109 to 116 RM. 

  • Plots were planted as strip trials at four of the locations, with Huxley being arranged as a small-plot trial. 

  • The locations served as replications. 

  • Each site was sprayed with USF0411 fungicide at 8 oz/acre with a ground sprayer at the R1 corn growth stage. 

  • Foliar disease and stalk quality ratings were taken at R4 growth stage and grain moisture and yield were collected at harvest.



  •  All research locations had some levels of corn disease incidence, with disease level averaging from low to moderate across locations. Gray leaf spot, Northern Corn Leaf Blight and Anthracnose stalk rot were the most predominant diseases across locations. Disease incidence was observed in both fungicide-treated and untreated plots, and there were no differences in disease incidence and severity between treatments.

  • Late season stay green and intactness scores were taken but there were no differences observed between the fungicide-treated and untreated plots.

  • Across all corn products, spraying fungicide resulted in an overall average of 15 bu/acre advantage vs. the unsprayed treatment (Figures 1). For this study, a 7 bu/acre response was considered a profitable response ($24/acre cost for fungicide application with $3.50 corn). 

  • Fungicide application little to no effect on grain moisture, with an overall average of 0.2% difference in moisture between the sprayed and unsprayed treatments. (Table 1).


  • The 2019 growing season saw a range of moisture and temperature extremes across the state of Iowa. Generally, the research sites experienced wet planting conditions, a hot and dry July, and a wet late summer/harvest season. This led to some levels of stalk strength and plant appearance issues due to excess moisture, nutrient shortages, and prolonged harvest conditions. 

  • Such conditions may explain why fungicide was profitable across nearly all products tested in 2019. While plant appearance was notably improved by fungicide use, we did not observe dramatic differences in stalk strength between sprayed and unsprayed products. This could be due, in part, to improvements in our corn germplasm to inherently tolerate some of these adverse growing conditions. 

  • The results of this study suggest that fungicide application could promote a healthier upper canopy that would lead to increased photosynthetic activity and better plant stress tolerance, which might result in increased corn yields. To gain the full benefits of a fungicide, the right corn product should be selected for the growing region.

  • Going forward, protecting yield and improving overall plant appearance with the use of a fungicide may be a management decision worth considering on your operation. 






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