Foliar Fungicide Considerations for Corn

The economic return from a fungicide application is usually greater when fungicide use is based on the presence of a foliar disease. The exact yield response to a fungicide treatment cannot be predicted with certainty due to different types of crop stress and crop genetics. In corn, fungicides applied from tasseling to early silking may have the best possibility for economic return.

A Corn Seed Product Yield Response to Fungicide Application study was conducted by Monsanto, at Camden Point, Missouri in 2017. Disease incidence at the site was as follows: gray leaf spot (GLS)—moderate; southern rust—low; crown rot—observed to be present. Six seed products had two treatments: fungicide applied at silking (R1) growth stage and no fungicide treatment. In this trial the yield increase from a fungicide application on five seed products ranged from 7.1 to 27.1 bu/acre and is likely the result of the inhibition of GLS and/or southern rust development. One seed product expressed no yield increase from a fungicide application as the product’s genetic GLS tolerance presumably provided adequate protection from GLS. This study suggests moderate to susceptible seed products are more likely to benefit from a fungicide treatment under high disease pressure environments.

According to research conducted by University of Illinois from 2008 to 2014, under low disease pressure plot environments, the average yield response to a foliar fungicide applied between tasselling (VT) and silking (R1) was 2.8 bu/acre. While under moderate to high disease pressure environments, the average yield response was 9.5 bu/acre.1

In most cases, fungicide applications should be applied at or soon after tasseling. University of Illinois research showed that fungicide applications during the mid-vegetative growth stages (V5-V6) did not significantly reduce foliar disease severity or increase yields when compared with either untreated controls or applications made at R1.1 Fungicides applied from VT to early R1 tend to have the best possibility for economic return.

Begin scouting fields for foliar disease symptoms just before tasseling and continue through the grain filling stages of growth. Since the majority of the plant's energy supply to fill the ear comes from the ear leaf and two or three leaves above and below the ear leaf, examine the ear leaf and leaves above and below the ear at several locations throughout a field. Consider a fungicide application if fungal disease is present on the third leaf below the ear leaf or higher on 50% of the plants at tasseling and the product is susceptible to the disease.

Also, since GLS has a long latent period, symptoms may not be abundant at VT to R2 (blister) growth stages even though considerable infection is occurring. Fungicide decisions for GLS need to consider previous history of the disease in that specific field as well as disease reaction of the product being grown and the occurrence of warm, humid weather that favors infection. Other environmental conditions, costs, and potential profit factors should also be considered when making these considerations. If fungal diseases are present and weather conditions are extremely wet and favorable during early grain fill from silking to R4 (dough), a fungicide application between R2 and R4 may be helpful if applications have not been made previously, but earlier applications have typically produced greater yield returns than later applications.


Sources: 1Bradley, C.A. 2015. Getting to know the foliar diseases of corn. The 2015 University of Illinois Corn & Soybean Classic. University of Illinois. 2Hershman, D.E., Vincelli, P., and Kaiser, C.A. 2011. Foliar fungicide use in corn and soybean. University of Kentucky. PPFS-GEN-12. 3Robertson, A. and Mueller, D. 2011. Foliar fungicides on corn. Integrated crop management. Iowa State University. 2017. Corn seed product yield response to fungicide application - DEKALB - CO KS MO. Research Summary. Technology Development & Agronomy by Monsanto. Web sources verified 06/07/18. 180607094806.