In 2020, corn foliar fungicide trials were conducted at six locations in Iowa to help farmers determine if a foliar fungicide was necessary. The objectives were to assess the effect of application timing on disease, evaluate the yield response of hybrid corn to foliar applications and discern differences, if any, between products.
The six locations were:
- 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
- Ag Engineering and Agronomy Farm (AEA) near Boone
Six products at various application timings were evaluated (Table 1). Fungicides were applied at growth stage V12 and/or R1 based on the company's suggestions. No surfactant was included in applications made at V12.
Below are results on the effect of product and timing on foliar disease:
- Percent disease in the canopy below the ear leaf, the ear leaf and the canopy above was estimated visually at R5 (Table 1).
- Disease severity was very low (less than 1% on ear leaf of control plots) at AEA, NRF, NERF, NWRF and SWRF due to drier conditions during grain fill across the state.
- No effect of fungicide on disease was detected at AEA, NRF, NERF, NWRF and SWRF.
- At SERF, gray leaf spot (GLS) severity in the lower canopy of the control plots was 5.5%.
- Fungicides reduced GLS at SERF.
- Applications at V12 reduced disease severity in the lower canopy more than applications made at R1.
- Other diseases observed included common and southern rusts (all locations), and tar spot (NERF and SERF). All were present at trace levels (less than 0.1% of the canopy affected).
- Below are the effects of product and timing on yield:
- Yields of the non-sprayed check ranged from 195.7 bushels per acre at AEA to 245.1 bushels per acre at NWRF.
- No effect of fungicide on yield was detected.
All fungicides in these trials were effective against gray leaf spot. For a list of fungicides effective against GLS and all diseases on corn, check out Fungicide efficacy for corn diseases at the Crop Protection Network. This publication is updated annually by corn pathologists across the U.S. and Canada.
Applications at V12 reduced GLS severity more than applications made at R1. These data are similar to what we reported in 2017,where V12 applications also reduced GLS more than applications at R1. Remember GLS always starts in the lower canopy. With applications at V12, fungicides are more likely to reach the lower canopy and protect the lower leaves.
More results include:
- Greater yields were not detected when a fungicide was applied.
- The extreme drought conditions that occurred limited disease development. In general, if GLS severity is greater than 5% on the ear leaf at R5, yield loss may be expected.
- There are other reports of no yield response of crops to fungicide applications in drought conditions from Pioneer and the University of Illinois.
To limit resistance developing to fungicide chemistries, reserve fungicide applications for fields that are more likely to have disease, such as those planted to susceptible hybrids, low-lying fields where morning fogs often occur, or fields with a history of disease.
Follow local Extension pathologists and agronomists on social media to stay informed on diseases prevalent in your area, the risk of disease, and the need for a fungicide application.
Robertson is an associate professor of plant pathology and microbiology at Iowa State University.Source: Integrated Crop Management News and Iowa State University Extension, which are responsible for the information provided and is wholly owned by the source. Informa Business Media and its subsidiaries aren't responsible for any of the content contained in this information asset.