Late Applications of Fungicide on Field Corn

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

This year has been a bad one for foliar diseases on corn, particularly Gray leaf spot. Growers may wonder if there is a need to apply a second, late application of fungicides for foliar disease control. A large body of research indicates that a single, well timed fungicide application between VT/R1 (tasseling/silking) is the most consistent in terms of disease control and economic return. In general, multiple applications of fungicide are not very beneficial. However, it is conceivable that a late season fungicide application may help in some situations, particularly if the hybrid has poor to low resistance to Gray leaf spot and disease pressure is high. Other factors, such as application cost, expected yield, etc. also will come into play.

The information in the table below provides general estimates for yield losses depending on the amount of Gray leaf spot on ear leaves at early dent stage (R5). Actual yield losses will vary depending on the specific scenario. If you decide to make a later season application, remember to check the harvest restriction time on the fungicide label. A link to the Corn Disease Working Group’s fungicide recommendations can be found at my Field Crops Disease Blog: http://extension.udel.edu/fieldcropdisease/2013/06/28/2013-corn-fungicide-list/

Table 1. Estimated corn yield loss based on the percent of infected leaf tissue.
Source: Pat Lipps, Professor (retired) The Ohio State University Department of Plant Pathology

% Ear Leaf Area Affected at Early Dent (R5)

Estimated Yield Loss

5% or less

0-2%

6-25%

2-10%

25-75%

5-20%

75-100%
(dead ear leaf)

15-50%

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