Iowa Corn: 2021 Summary of Foliar Fungicide Applications

Corn foliar fungicide trials done at six locations in Iowa in 2021: ISU Northwest Research and Demonstration Farm (NWRF), Sutherland; Northeast Research and Demonstration Farm (NERF), Nashua; Northern Research and Demonstration Farm (NRF), Kanawha; Southwest Research and Demonstration Farm (SWRF), Lewis; Southeast Research and Demonstration Farm (SERF), Crawfordsville; and the Ag Engineering and Agronomy Farm (AEA) near Boone.

The goal of these trials was to help farmers determine best practices for foliar fungicides in corn production. Our objectives are to 1) assess the effect of fungicide application timing on foliar disease, 2) evaluate the yield response of hybrid corn to foliar fungicides and 3) discern differences between fungicide products.

Products used and application timings tested

Seven products, applied at growth stages V12 or R1, were evaluated at (Table 1). No surfactant was included in applications made at V12. A randomized complete block design with six replications was used at each site. Each plot was four rows wide (30-in. row spacing) and ranged from 30 to 73 ft long depending on the farm.

All plots were bordered by two rows on each side. Disease severity on the ear leaf, upper canopy and lower canopy on five plants in the middle two rows of each plot was assessed at R5 (last week of August).

All four rows of each plot were harvested using a plot combine. All data were subjected to analysis of variance and means were compared at the 0.1 significance level using Fisher’s protected least significant difference (LSD) test.

Table 1. Mean yields of corn (bu/ac) sprayed with foliar fungicides at either growth stage V12 or R1 in small plot trials done at six locations in Iowa in 2021.

Monthly precipitation at each of the research farms

In general, the growing season started off drier at all farms with April and June precipitation totals well below average, and May similar to, the mean monthly precipitation for 2014-2020 (Figure 1). The exception was SERF, which was very wet.

For the northern farms, August was as wet (NWRF and NRF) or excessively wet (NERF) while AEA, SWRF and SERF were very dry. The season ended with a drier September and similar or wetter October for all farms compared to 2014-2020.

Figure 1. Monthly precipitation total (in inches) in 2021 compared to mean monthly precipitation total from 2014 through 2020 for each ISU research farm where corn foliar fungicide trials were done. Data were compiled from Iowa Environmental Mesonet. Click Image to Enlarge

Effect of product and timing on foliar disease

Disease severity in the trials was less than 1% in the non-treated controls at NERF, while no disease was observed at all other locations. Disease data were not collected at SERF. The low disease severity was not surprising due to the drier than normal gorwing season that was not favorable for disease development.

Effect of product and timing on yield

Yields of the non-sprayed check ranged from 170.1 bu/A at NRF to 244.6 bu/A at SWRF (Table 1). We detected no effect of a fungicide application on yield (P>0.1) apart from at one location, NERF (P=0.016).  Mean yield of the plots treated with Miravis Neo at R1was greater than both non-sprayed checks.

Management recommendations

Data from these trials are consistent with previous work that indicates corn yields are rarely greater following a fungicide application in the absence of disease. Moreover, the extreme drought conditions that occurred in 2021 limited disease development, and as in previous years, fungicide applications did not benefit drought stressed corn.

For a list of fungicides effective against GLS, northern corn leaf blight, tar spot and other diseases on corn, the publication “Fungicide efficacy for corn diseases” is available from the Crop Protection Network. This publication is updated annually by corn pathologists across the U.S. and Ontario, Canada.

Acknowledgements

Thank you to the farm managers and staff at each location who managed the trial and applied the fungicides. Thanks to Jyotsna Acharya for analysis of the data and Daryl Herzmann for help accessing weather data.